Unique Color Converter Architecture Enabling Phosphor-in-Glass (PiG

Subscriber access provided by UNIV OF DURHAM

Functional Inorganic Materials and Devices

A unique color converter architecture enabling phosphor-in-glass (PiG) films suitable for high-power and high-luminance laser-driven white lighting Peng Zheng, Shuxing Li, Le Wang, Tianliang Zhou, Shihai You, Takashi Takeda, Naoto Hirosaki, and Rong-Jun Xie ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b03168 • Publication Date (Web): 11 Apr 2018 Downloaded from http://pubs.acs.org on April 11, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

A unique color converter architecture enabling phosphor-in-glass (PiG) films suitable for highpower and high-luminance laser-driven white lighting Peng Zheng, † Shuxing Li, *,† Le Wang, *,‡ Tian-Liang Zhou, † Shihai You, † Takashi Takeda, § Naoto Hirosaki, § and Rong-Jun Xie, *,† †

College of Materials, Xiamen University, Xiamen 361005, P. R. China. Email:

[email protected]; [email protected]

‡

College of Optical and Electronic Technology, China Jiliang University, Hangzhou 310018, P.

R. China. Email: [email protected]

§

Sialon Group, National Institute for Materials Science 1-1 Namiki, Tsukuba, Ibaraki 305-0044,

Japan KEYWORDS: solid-state lighting, high-luminance laser lighting, one-dimensional photonic crystals, sapphire, phosphor-in-glass (PiG) film

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 35

ABSTRACT:

As a next-generation high-power lighting technology, laser lighting has attracted great attention in high-luminance applications. However, thermally robust and highly efficient color converters suitable for high-quality laser lighting are scarce. Despite of its versatility, the phosphor-in-glass (PiG) has been seldomly applied in laser lighting due to its low thermal conductivity. In this work, we develop a unique architecture that a phosphor-in-glass (PiG) film was directly sintered on a high thermally conductive sapphire substrate coated by one-dimensional photonic crystals (1DPCs). The designed color converter with the composite architecture exhibits a high internal quantum efficiency close to that of the original phosphor powders and an excellent packaging efficiency up to 90%. Furthermore, the PiG film can even be survived under the 11.2 Wmm-2 blue laser excitation. Combining blue laser diodes with the YAG-PiG-on-sapphire plate, a uniform white light with a high luminance of 845 Mcdm-2 (luminous flux: 1839 lm), luminous efficacy of 210 lmW-1 and correlated color temperature (CCT) of 6504 K was obtained. A high color rendering index (CRI) of 74 was attained by adding a robust orange or red phosphor layer to the architecture. These outstanding properties meet the standards of vehicle regulations, enabling the PiG films with the composite architecture to be applied in automotive lighting or other high-power and high-luminance laser lighting.


2

Page 3 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. INTRODUCTION Since the invention of InGaN blue light emitting diode (LED) in early 1990s,1,2 white LED lighting has achieved spectacular success. However, blue LEDs suffer severe “efficiency droop” at high input current density.3 This leads to a low luminous flux per unit area of LED chips and a large étendue of the LED optical system, seriously hindering their applications in highluminance and low-étendue desired products, such as cinema projectors, automotive headlights, laser TVs, and etc. Compared with blue LEDs, blue laser diodes (LDs) have smaller emitting area, lower beam divergence and higher efficiency at high input current density.4 Therefore, a high-luminance white light source can be realized by combining the highly focused blue laser beam with the down-converting color converters. However, traditional color converters (phosphor powders + organic binders) used in white LEDs will be carbonized when irradiated statically under high density laser excitation due to the poor heat resistance and low thermal conductivity.5 To solve this problem, novel color converters such as single crystal phosphors,6-8 phosphor ceramics,9-15 and phosphor-in-glasses (PiGs),16-19 have been studied for laser lighting. Cantore et al. demonstrated that YAG:Ce single crystal is capable of emitting a peak luminous flux of 1100 lm with a CRI of 62 under blue laser excitation.6 Li et al. fabricated a high thermal conductivity Al2O3-YAG:Ce composite phosphor ceramic, which gives a luminous flux of 2000 lm under 45 W laser excitation.9 Zhu et al. investigated the reliability of β-Sialon:Eu PiG, and the luminescence saturation was observed at a power density of ~1.0 Wmm-2 with a maximum luminous flux of ~275 lm.16 Most recently, Park et al. developed a phosphor-aluminum composite consisting of a YAG-PiG as the luminescent layer and an aluminum-glass composite as the thermally graded layer, giving an output of 430 lm under a 4 W blue laser excitation.18 Despite these efforts, some problems still remain unsolved in


3


Page 4 of 35

laser lighting: such as (i) complex fabrication process of all-inorganic color converters (single crystals, phosphor ceramics); (ii) low CRI value (usually ~60); and (iii) low luminance with uneven white light. Therefore, the development of robust color converters that can be simply fabricated and show high quality white light is an urgent demand. Among the aforementioned color converters, PiGs possess competitive advantages over other counterparts, i.e., (i) ease fabrication; (ii) tunable refractive index of the glass matrix; (iii) controllable chromaticity coordinates just by mixing different phosphors.17,20-24 Till now, PiGs have already proved their excellent performance in high-power white LED applications.25-27 But there are very limited reports on the development and applications of PiGs in high luminance laser-driven white light sources due to the low thermal conductivity of the glass matrix (usually < 1 Wm-1K-1). As PiGs have a shortcoming of low thermal conductivity, how to solve it is thus a must for them to be used in laser lighting. Herein, we design a novel architecture in which the YAG-PiG film is directly sintered on a single crystal sapphire substrate. Sapphire is selected as the substrate because of its high thermal conductivity (~30 Wm-1K-1), excellent mechanical properties, and high in-line transmittance (~86%) suitable for the transmissive configuration.28 Importantly, one-dimensional photonic crystals (1DPCs) are coated on the sapphire substrate to utilize its potential to the fullest, i.e., one side of the sapphire substrate is coated by an antireflection (AR) layer to decrease the reflection loss of the incident blue light, and the other side is covered by a blue-pass (BP) filter to reflect the backward yellow emission from the phosphor particle in the sintered film. The merits of the blue-pass filter in LED applications were demonstrated by Oh et al.29 In that work, phosphors were deposited onto the substrate by a sedimentation method and might not be well-bonded to the substrate. Most recently, Yang et al.


4

Page 5 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


also proposed to use the blue-pass filter coated sapphire substrate for laser lighting.30 However, they used the potassium silicate as the phosphor binder, so the aging behavior of the color converter would be a problem since the potassium silicate is soluble in water. Therefore, it is quite important to select appropriate glass compositions with high resistance to moisture attacks. In this study, a borosilicate glass with the composition of B2O3-SiO2-Al2O3-BaO-ZnO is selected because of its excellent moisture resistance and high inertness for the YAG phosphor.17,24 The current YAG-based laser-driven white light usually has a low color rendering index of ~60 due to the sharper emission spectrum of laser diodes (compared to LEDs) and the deficiency of sufficient red component in YAG phosphors.6,30,31 To enhance the luminous efficacy and color rendition of white laser lighting, Bicanic et al. developed a model using a phosphor blend of YAG and KTF:Mn4+ (red phosphor), but the KTF:Mn4+ is not suitable for laser lighting due to its long decay time and instability.32 To overcome this problem, we selected either the robust orange-emitting Ca-α-SiAlON:Eu2+ or red-emitting CaAlSiN3:Eu2+ to supplement the red spectral component in YAG-PiG films. In this work, we attempt to apply the YAG-PiG film to the high-luminance laser lighting by co-firing it with a 1DPCs coated sapphire substrate and improve the color rendering index of laser lighting by using the red-enhanced YAG-PiG film containing additional orange or red phosphors. The interface between the PiG film and the sapphire substrate, optical properties of both the luminescent PiG film and the entire architecture, and the structure-property relationship will be systematically investigated. Owing to the unique structure, the YAG-PiG film can be survived from a high blue laser density of 11.2 Wmm-2, and a uniform white light with a high luminance of 845 Mcdm-2 can be achieved. Moreover, a high color rendering index of 74 can


5


Page 6 of 35

also be attained by using an additional orange or red phosphor layer. The designed PiG films will find great potentials for use in automotive or other high-power and high-luminance laser lighting. 2. EXPERIMENTAL SECTION 2.1. Materials The phosphor materials, such as Y3Al5O12:Ce3+ (YAG, LANGDA, China), (Sr,Ca)AlSiN3:Eu2+ (SCASN, Grirem, China), and Ca-α-SiAlON:Eu2+ (α-SiAlON, Denka, Japan), are commercially available. A borosilicate glass powder (B2O3-SiO2-Al2O3-BaO-ZnO) used as the binder has the glass transition point of 585 °C, softening point of 730 °C, refractive index of 1.62, and density of 3.1 gcm-3. The sapphire and 1DPCs coated sapphire substrates with a size of 10 × 10 × 0.3 mm3 were bought from Crystal-optech (China). Terpineol (Aladdin, China, 95%), 2-(2Butoxyethoxy)ethyl acetate (Aladdin, China, 98%), and ethyl cellulose (Aladdin, China, 1822mPa·s) were used as solvents of the organic vehicles. The silicone resin (OE-6630A, B) was obtained from Dow Corning (USA). Magic Tape with a thickness of 55 µm (3M, USA) was used to control the thicknesses of the phosphor films. 2.2. Fabrication of PiG films The viscous YAG or α-SiAlON ink pastes were prepared by admixing YAG or α-SiAlON phosphors, glass powders, and organic vehicles in an agate mortar. The weight ratio of the YAG phosphor to the glass powder (abbreviated as YtG ratio) was chosen to be 5:1, 4:1, 3:1, 2:1, and 1:1, and the ratio of the α-SiAlON phosphor to the glass powder was fixed at 1:10. The organic vehicle was made by fully mixing terpineol, 2-(2-Butoxyethoxy) ethyl acetate, and ethyl cellulose at 80 °C for 10 h at 600 rpm. The viscous SCASN ink paste was prepared by admixing SCASN with OE-6630A and B silicone resin in a mass ratio of 1:3:3. Then the ink paste was vacuumed at 0.01 MPa for 20 min to release the air bubbles. The resultant phosphor pastes were


6

Page 7 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


printed on the sapphire or 1DPCs coated sapphire substrate (these two substrates are abbreviated as SA and CSA, respectively) using the blade-coating technique.33 The film thickness was controlled by the viscosity of the ink paste or the stack number of the tapes. A single phosphor layer was prepared by coating the ink paste on the SA or CSA substrate (the as-prepared PiG plates are abbreviated as PiG-on-SA or PiG-on-CSA). The double layer structures of YAG+αSiAlON and YAG+SCASN were prepared by re-coating of the α-SiAlON or SCASN layer on the sintered YAG-PiG film. The printed phosphor glass films were sintered at 800 °C for 10 min, and the silicone films were dried at 150 °C for 12 h in an oven. 2.3. Characterizations The microstructure and elemental mappings were observed by a field-emission scanning microscope (SU70, Hitachi) equipped with an energy dispersive X-ray spectroscope (EDS) system. The X-ray powder diffraction (XRD) patterns were acquired by a Bruker D8 ADVANCE powder diffractometer operating with Cu Kα radiation at 40 kV and 40 mA. The photoluminescence excitation (PLE) and emission spectra (PL) were recorded on a steady state fluorescence spectrometers (FLS980, Edinburgh Instruments) equipped with a 450 W Xe lamp and the thermoelectric cooled red-sensitive PMT. The transmittance spectra were measured with a

UV-Vis

spectrophotometer

(UV-3600Plus,

Shimadzu).

The

temperature-dependent

luminescence was measured using a home-made measurement system, which composes of a 450 nm LED light source, a cooling/heating stage (THMS600E, Linkam Scientific Instruments) and a charge-coupled device (CCD) spectrometer (USB2000+, Ocean optics). The samples were heated from 25 to 300 °C with a step size of 25 °C at a heating rate of 50 °Cmin-1, and soaked at each temperature for 1 min. Photographs of the samples and illumination images were taken by a


7


Page 8 of 35

digital camera (EOS 700D, Canon). The surface temperature of the YAG-PiG-on-Sapphire plate was measured by an infrared (IR) thermal imager (TIX580, Fluke). The quantum efficiency (QE) was measured with a custom-built sphere-spectroradiometer system. This system consists of an excitation light source (50 mW single-mode blue laser diode, λem = 450 nm) and an integrating sphere (diameter of 15 cm) which is connected to a CCD spectrometer (USB2000+, Ocean Optics). The standard tungsten halogen lamp (SCL-600, Labsphere) is used to calibrate this sphere-spectroradiometer system. The high diffuse reflective BaSO4 was used as the reference sample and all the samples were placed on the diffuse reflective BaSO4-coated sample holder. The emission spectra, i.e., spectral power distribution (SPD) or the total spectral radiant flux (TSRF) Φ(λ) (unit: µW/nm), ranging from 400 to 800 nm were measured in this system. All the photometric and colorimetric values were calculated from TSRF. The detailed calculation methods are given in the Supporting Information. The optical properties of the PiG-on-CSA plates under high power density laser irradiation were measured by another sphere-spectroradiometer system. This system consists of a high power blue laser light source and an integrating sphere (diameter of 30 cm, Labsphere) which is connected to a CCD spectrometer (HR4000, Ocean Optics). The high power blue laser (LSR445CP-FC-48W, LASEVER) consists of twelve blue laser diodes (λem = 450 nm) which were coupled into a 1 mm core diameter silica fiber (the coupled emission has several peaks due to the manufacturing tolerance of the laser diodes). Two plano-convex lens were used to collimate and focus the laser beam, and the irradiated spot size was nearly a circular area with diameter of 1 mm (0.785 mm2). The optical power of the laser diodes was stabilized by a thermoelectric cooler (TEC) module setting at 25 °C. The optical power of the blue laser, as


8

Page 9 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


determined by the input current, was measured with a laser power meter (LP-3C, Physoe). The PiG-on-CSA plates were excited by varied blue laser powers in a transmissive configuration. 3. RESULTS AND DISCUSSION 3.1. Microstructures and optical properties of the PiG-on-SA plates Normalized photoluminescence excitation (PLE) and emission spectra (PL) of the commercial YAG, α-SiAlON, SCASN phosphors (denoted as Y, O, R, respectively) are shown in Figure S1. The YAG phosphor exhibits a broad emission band peaking at ~545 nm, while the α-SiAlON and SCASN phosphors give emissions peaking at 600 and 628 nm, respectively. The α-SiAlON and SCASN phosphors are selected to compensate for the red spectral component, and also to reduce the trade-off between CRI and luminous efficacy without deep red component in their emission simultaneously.34 All phosphors have a strong excitation peak around 450 nm, enabling them to absorb the 450 nm incident laser. The morphologies of the phosphors and glass powder are shown in Figure S2. The commercial phosphors show a good crystalline morphology, while the glass powder exhibits an irregular particle shape. The XRD patterns (Figure S3) of the phosphors are in a good agreement with their respective standard cards. Figure 1a shows the fabrication schematic of the PiG-on-SA plates (see Experimental Section for details). The YAG and α-SiAlON phosphors were fabricated as PiG films while SCASN was encapsulated in the silicone (PiS) due to the severe deterioration in quantum efficiency of SCASN-PiG.35,36 The SEM images shown in Figure 1c and e indicate that the YAG and α-SiAlON phosphor particles are uniformly dispersed in the glass matrix, and the insets present the photographs of the corresponding translucent PiG-on-SA plates. The cross-sectional images demonstrate that the PiG films are bonded tightly to the SA substrates (Figure 1b and d).


9


Page 10 of 35

Figure 1. (a) Fabrication schematic of the PiG-on-SA plate; Cross-sections of (b) YAG-PiG-onSA and (d) α-SiAlON-PiG-on-SA plates; Surface SEM images of (c) YAG-PiG-on-SA and (e) α-SiAlON-PiG-on-SA plates. The insets in (c) and (e) are the corresponding photographs; SEMEDS mapping images of (f) YAG-PiG and (g) α-SiAlON-PiG films. The weight ratio of YAG to glass and α-SiAlON to glass is 1:1 and 1:10, respectively.

The optical properties of the original powders and PiG/PiS-on-SA plates under the 450 nm excitation are listed in Table 1. Since the phosphor powders are tightly compacted (i.e., high phosphor particle density) whereas the PiG/PiS-on-SA plates are in the state of film and the phosphor particles are uniformly distributed in the glass matrix (i.e., low phosphor particle density), it is reasonable to find that the emission spectra of PiG/PiS-on-SA plates are blueshifted (Figure S5) due to the reduced self-absorption effect when compared to those of the phosphor powders.37,38 This is also affirmed by the overlap area between the excitation and emission spectra, as shown in Figure S1. The internal quantum efficiencies (IQEs) of YAG-onSA and α-SiAlON-on-SA are only ~1 or 2% lower than those of the phosphors, indicating no


10

Page 11 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


erosive reactions between phosphors and the glass that would deteriorate the luminescence efficiency of phosphor particles. This is also verified by the fact that the characteristic elements of Y (YAG) and Ca (α-SiAlON) in the phosphor powders do not diffuse into the glass matrix (Figure 1f and g). The quantified elemental compositions by EDS are shown in Figure S4. Based on these results, it is corroborated that the as-prepared PiG-on-SA plates possess fine interfaces and microstructures, and therefore the excellent optical properties are attained. Table 1. Internal and external quantum efficiencies (IQE and EQE), absorption efficiency (AE), and the emission peak (λem) of the original phosphor powders and the as-prepared PiG/PiS-onSA plates under the 450 nm excitation. Sample YAG YAG-on-SA α-SiAlON α-SiAlON-on-SA SCASN SCASN-on-SA

IQE (%) 87 86 77 75 77 78

EQE (%) 70 77 66 56 65 62

AE (%) 80 89 86 74 84 80

λem (nm) 545 536 600 595 628 621

To investigate the effect of the composition on the transmittance and scattering properties of YAG-on-SA plates, PiG films with different weight ratios of YAG to glass (YtG = 1:1, 2:1, 3:1, 4:1, 5:1) were sintered on the sapphire plate. The top views of SEM images for samples with YtG ratios of 1:1, 3:1, and 5:1 are shown in Figure 2a-c, and the insets give the corresponding cross-sections. With the increase of the YtG ratio, the roughness of the surface increases obviously. As seen, pores start to generate in the glass matrix with increasing the YtG ratio since the lower glass content tends to produce more trapped air in the microstructure during the sintering process. It is also seen that the phosphor particles protrude from the glass matrix, implying the glass has a relative low viscosity at the firing temperature of 800 °C. The low


11


Page 12 of 35

viscosity is beneficial for the formation of a highly dense glass matrix, as shown in the inset of Figure 2d (SEM picture).

Figure 2. Top view SEM images of the YAG-PiG films with YtG ratio of (a) 1:1, (b) 3:1, (c) 5:1. Insets are the corresponding cross-section images; (d) In-line transmittance spectra of sapphire, glass-on-SA, and YAG-PiG-on-SA (YtG ratio of 1:1) plates. Insets in the left are the photograph and cross-section of the glass-on-SA plate while inset in the right is the in-line transmittance spectrum of YAG-PiG-on-SA (YtG ratio of 1:1) plate; (e) Ratio dependence of total transmittance spectra. Insets show the white light photographs with YtG ratio of 1:1, 3:1, and 5:1, respectively.

The in-line transmittance spectra show that the sapphire substrate has the theoretical maximum transmittance of ~86% while the glass-on-SA plate has a value of ~65% (Figure 2d). By contrast,


12

Page 13 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the in-line transmittance of the YAG-PiG-on-SA plate with the YtG ratio of 1:1 is as low as 0.25%-0.35% (the right inset in Figure 2d). The in-line transmittance spectrum shows two absorption bands around 340 and 450 nm, which correspond to the electronic transitions of 2

F5/2→2D5/2 and 2F5/2→2D3/2 of Ce3+, respectively. Since the in-line transmittance of YAG-PiG-on-SA plate is too low to distinguish, the total

transmittance spectra were measured to characterize the transmittance properties. As shown in Figure 2e, the total transmittance varies from ~30 to ~50%, and monotonously decreases with increasing the YtG ratio. The decline is attributable to the increased phosphor and pore content. Interestingly, the light quality is directly related to the total transmittance. As seen from insets in Figure 2e, when the YtG ratio is 1:1, the low absorption and scattering coefficients lead to a high blue transmittance. The blue laser spot directly penetrates through the YAG-PiG-on-SA plate, and lies in the center of the illumination photograph. This is disastrous to the illumination uniformity, and a blue tinge center is observed as marked with a circle. This phenomenon that the light beam has a bluish-white center and a yellow ring around the outside is called “yellow ring” effect in LED. With the increase of the YtG ratio, the “yellow ring” effect is notably alleviated, and the white light is uniform when the YtG ratio is 3:1 and 5:1. That is to say, owing to the increased amount of phosphor particles and pores, the PiG functions as a diffuser film to homogenize the incident laser, the highly oriented blue laser beam is thus scattered into a widely divergent distribution. This finally leads to the uniform white light. 3.2. Microstructures and optical properties of PiG-on-CSA plates The theoretical maximum transmittance of sapphire is ~86%, which is a little bit lower than that of the high transparent glass or silicone. The main transmittance loss of sapphire is attributed to the Fresnel reflection loss which occurs at the interface between sapphire and air. To improve


13


Page 14 of 35

the transmittance of sapphire, an anti-reflection (AR) layer was coated on the surface of sapphire in this work. At the same time, a blue-pass filter (BP) was covered on the other surface to enhance the forward yellow emission. The cross-section images of AR layer and BP filter coated sapphire are shown in Figure 3a and b. Both the AR layer and the BP filter consist of transparent thin film structures with alternating layers of the high refractive index TiO2 and the low refractive index SiO2.

Figure 3. Cross-sections of (a) the AR coating and (b) the BP filter (the inset is the photograph of the AR and BP coated sapphire plate, i.e., CSA plate); (c) In-line transmittance spectra of sapphire, AR coated sapphire, BP coated sapphire, AR-BP coated sapphire, and the AR-BP coated sapphire after treated at 800 oC; (d) Visualized comparison between YAG-PiG-on-SA and YAG-PiG-on-CSA plates under the blue laser excitation (the laser beam direction toward the left).


14

Page 15 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The AR layer with a thickness of ~700 nm was firstly deposited on the laser entry facet of the sapphire substrate, and the transmittance of sapphire is increased to ~92%, as shown in Figure 3c. Then, the BP filter with a thickness of ~2.5 µm was coated on the laser exit facet, and the transmittance is further enhanced up to ~97% in the blue spectral band. Moreover, the reflectance of the yellow spectral band is increased to ~99% (shown in Figure 3c as ~1% transmittance). It is also found that the heat treatment at 800 °C has little impact on the in-line transmittance properties of both the AR layer and the BP filter (see Figure S7 and Figure 3c). Therefore, the photonic multilayers (i.e., AR and BP), which are usually called as onedimensional photonic crystals (1DPCs), enables to improve the transmittance of the blue laser and simultaneously hold back the backward emission of the phosphor.29 It is also evidenced by comparing the visualized views of both YAG-PiG-on-SA and YAG-PiG-on-CSA under the blue laser excitation. Due to the spontaneous emission characteristics of phosphor particles, both forward and backward emissions of YAG can be observed for YAG-PiG-on-SA. In contrast, only the forward emission can be seen in the YAG-PiG-on-CSA plate due to the mirror effect of the BP filter. Therefore, both of the transmittance and the forward extraction efficiencies can be enhanced by introducing the AR layer and BP filter to the architecture. The emission spectra of YAG-PiG-on-SA and YAG-PiG-on-CSA under 1.2 W laser excitation are shown in Figure S6 (The PiG film thickness is fixed at 44 µm with the YtG ratio of 4:1), the emission intensity of the YAG-PiG-on-CSA is nearly doubled when compared to that of the YAG-PiG-on-SA, so the forward extraction efficiency is greatly enhanced by the 1DPCs.


15


Page 16 of 35

Figure 4. Cross-sections YAG-PiG-on-CSA plates with different YtG ratios (a) 1:1, (b) 3:1, (c) 4:1; (d) The transmitted blue laser power, the converted yellow light power, and the conversion efficiency as a function of the YtG ratio; CIE color coordinates with (e) different YtG ratios (film thickness fixed at ~33 µm) and (f) different film thicknesses (YtG ratio fixed at 4:1).

To determine the optimal phosphor content, YAG-PiG-on-CSA plates with different YtG ratios (i.e., 1:1, 2:1, 3:1, 4:1, 5:1) were fabricated at a fixed PiG film thickness of ~33 µm. The cross-sections of these YAG-PiG-on-CSA plates with different YtG ratios are shown in Figure 4a-c. For the YtG ratio of 1:1, many pores are formed at the interface between the glass film and the blue-pass filter, which may be ascribed to the poor wettability of glass on the blue-pass filter. With increasing the YtG ratio, the number of pores at the interface is reduced while that of pores in the glass matrix increases. The microstructures of the interface and the PiG film have a great impact on the optical properties of YAG-PiG-on-CSA plate. The conversion efficiency, defined


16

Page 17 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


as the ratio of the converted yellow light to the absorbed blue light (i.e., total blue laser power subtracts the transmitted blue light), was calculated at an incident laser power of 1.2 W, as shown in Figure 4d. As the YtG ratio increases, the converted yellow light increases whereas the transmitted blue light exhibits an opposite trend due to the enhanced blue absorption by the YAG phosphor particles. Interestingly, the conversion efficiency reaches its maximum (60%) at the YtG ratio of 4:1, because a lower or higher glass content will lead to a larger number of pores at the PiG film/BP filter interface or in the glass matrix which in turn increases the scattering loss. Based on the aforementioned light quality results and the conversion efficiency, the optimal YtG ratio was determined at 4:1. Figure 4e gives the corresponding Commission Internationale de l’Eclairage (CIE) 1931 color coordinates with different YtG ratios. As seen in Figure 4e, the color coordinates of YAG-PiG-on-CSA plates shift from the blue to the yellow region, and cross the black body locus at ~8000 K with the increase of the YtG ratio. In addition, when the YtG ratio is fixed at the optimal ratio of 4:1 and the samples are excited under the 1.2 W blue laser, the color coordinates shift from green white to yellow with increasing the thickness of the PiG film, and further move away from the black body locus due to the increased blue absorption of the YAG phosphor (Figure 4f). This is an interesting merit of the transmissive configuration, i.e., the color coordinates of laser lighting can be easily controlled by changing the thickness of the PiG film. Moreover, it is again confirmed that the PiG film has a high scattering coefficient (i.e., the low in-line transmittance is obtained) as a slight change in thickness leads to a significant variation in color coordinates.


17


Page 18 of 35

Figure 5. Schematic of the transmissive configuration for laser-driven white light.

The transmissive configuration for the generation of the laser lighting source is schematically illustrated in Figure 5. The YAG-PiG film in our study differs from the PiG plate used in white LEDs in the following aspects: (i) mismatched refractive index (refractive index of the YAG phosphor and the host glass is 1.84 and 1.62, respectively); (ii) high phosphor content (the YtG ratio can be up to 4:1); (iii) the presence of pores in the film. Based on the Mie theory, these characteristics will result in high scattering and absorption coefficients, so the blue laser will be absorbed adequately and scattered uniformly by PiG films with a relatively small thickness, which is beneficial to the heat dissipation. Besides, the scattering can homogenize the incident laser light and even reduce the speckle contrast that is notorious in laser lighting applications.39,40 On the other hand, the scattering also slightly decreases the conversion efficiency,41 and the packaging efficiency can maintain ~90%. The packaging efficiency is defined as the ratio of the conversion efficiency of the YAG-PiG-on-CSA plate to that of the YAG phosphor (i.e., 67%). The packaging efficiency loss can be attributed to the transmittance loss of the CSA substrate


18

Page 19 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(i.e., transmittance < 100%) and the Mie scattering loss due to the mismatched refractive index and a similar size of the pore comparable to the visible light wavelength. Nevertheless, the appropriate scattering of the PiG film can lead to a good balance between the high quality white laser light and a high conversion efficiency. 3.3. White light under high-power blue laser excitations Three samples were prepared to create laser-driven white light, including YAG-PiG-on-CSA (one-layer film), (α-SiAlON-PiG+YAG-PiG)-on-CSA (two-layer film) and (SCASN-PiS+YAGPiG)-on-CSA (two-layer film) plates (the YtG ratio is 4:1). The latter two aim to improve the red spectral component and thus to enhance the color rendering index.

Figure 6. Cross-sections of (a) YAG+α-SiAlON and (b) YAG+SCASN layer structures.


19


Page 20 of 35

As shown in Figure 6, both the α-SiAlON-PiG layer and the SCASN-PiS layer are bonded tightly to the YAG-PiG layer, and a clear interface between them is formed. The layer structure has already been used for facile tuning of the chromaticity.42,43 The emission spectra of the three PiG-on-CSA plates, i.e., YAG (Y), YAG+α-SiAlON (Y+O), YAG+SCASN (Y+R), and the corresponding photometric and colorimetric properties under 1.1 W laser excitation are shown in Figure 7a and Table 2, respectively. The YAG-PiG-on-CSA plate gives a luminous flux of 282 lm, a luminous efficacy (light-light conversion efficiency) of 256 lmW-1 and CRI of 63. The color rendering index is further increased to 66 or 72 by adding the α-SiAlON or SCASN layer. Table 2. Photometric and colorimetric properties of the three typical plates under 1.1 W laser excitation. Sample Incident laser power (W) Optical power density (Wmm-2) Luminous Flux (lm) Luminous Efficacy (lmW-1) CRI CIE_x CIE_y CCT (K)

YAG 1.10

YAG+α-SiAlON 1.10

YAG+SCASN 1.10

1.40

1.40

1.40

282 256 63 0.3303 0.3940 5585

268 244 66 0.3570 0.3816 4773

259 235 72 0.3504 0.3621 4905


20

Page 21 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. (a) Emission spectra of the three typical plates under 1.1 W laser excitation. The insets show the corresponding photographs; Emission spectra of (b) YAG-PiG-on-CSA, (c) (YAGPiG+α-SiAlON-PiG)-on-CSA, (d) (YAG-PiG+SCASN-PiS)-on-CSA plates with the incident laser power increasing from 1.1 W to the respective maximum value. The insets are the magnified spectra of blue laser bands.

Further, the emission spectra and optical properties of the three typical plates were investigated by changing the blue laser power, and the results are given in Figure 7b-d and Tables S1-S3. The emission intensity of the three typical plates increases monotonously as the incident laser power increases from 1.1 W to the respective maximum value i.e., 8.77 W for YAG-PiG-on-CSA, 6.84 W for (YAG-PiG+α-SiAlON-PiG)-on-CSA, and 6.15 W for (YAG-PiG+SCASN-PiS)-on-CSA. On the other hand, the conversion efficiency (see Tables S1-S3) decreases with increasing the


21


Page 22 of 35

incident laser power, indicating that the temperature of the phosphor increases upon high power laser irradiation. The increased temperature will reduce the quantum efficiency of the phosphor, which in turn further increases the temperature. When the heat cannot be efficiently dissipated but accumulated (i.e., when the laser powers are beyond the respective maximum value), the temperature of the color converter will rise continuously, producing a thermal “run-away” effect.44 This uncontrollable feedback will lead to a catastrophic result if the laser continues to irradiate the phosphor, and it will even leave a black spot in the laser irradiation area. Consequently, the luminous flux for all the three samples initially increases linearly with increasing the incident laser power, and then abruptly decreases beyond the respective threshold value (Figure 8a). The luminous efficacy, however, decreases steadily as the incident laser power increases. The resultant luminous efficacies of the YAG-PiG-on-CSA, (YAG-PiG+α-SiAlONPiG)-on-CSA, and (YAG-PiG+SCASN-PiS)-on-CSA under the respective maximum incident laser excitation are 210 lmW-1, 194 lmW-1, 205 lmW-1, respectively (Table 3). Considering the current blue laser diode has a wall plug efficiency of ~38.5%,45 the final wall-plug efficiency of the three plates are about 81 lmW-1, 75 lmW-1, 79 lmW-1, respectively.


22

Page 23 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. (a) Luminous flux (LF) and luminous efficacy (LE) of the three typical plates (YAG (Y), YAG+α-SiAlON (Y+O), YAG+SCASN (Y+R)) as a function of the incident blue laser power; (b) Infrared thermal image of the YAG-PiG-on-CSA plate under 8.77 W laser excitation; (c) CIE color coordinate variations with increasing the blue laser power. The hexagon white light areas specified by ECE R48 standard are also shown in the picture. The insets show illumination images of the three plates under the maximum excitation power; (d) Temperature dependence of the spectral emission of YAG-PiG-on-SA plate (YtG ratio of 1:1) with temperature increasing from 25 to 300 oC.


23


Page 24 of 35

Table 3. Photometric and colorimetric properties of the three typical plates under the respective maximum excitation powers. Sample Incident laser power (W) Optical power density (Wmm-2) Luminous Flux (lm) Luminous Efficacy (lmW-1) CRI CIE_x CIE_y CCT (K)

YAG 8.77

YAG+α-SiAlON 6.84

YAG+SCASN 6.15

11.20

8.70

7.80

1839 210 68 0.3095 0.3433 6504

1330 194 70 0.3333 0.3342 5478

1259 205 74 0.3294 0.3287 5649

The surface temperature of the color converter (YAG-PiG-on-CSA plate) was measured by an infrared (IR) thermal imager. As seen in Figure 8b, the laser spot on the YAG-PiG-on-CSA plate has a temperature as high as 187 oC (equilibrium temperature) under 8.77 W laser excitation. Besides, the red-shifted emission spectra of the YAG-PiG-on-CSA plate with increasing the blue laser also validate the increase of the surface temperature (Figure S8). As shown in Table 3, the YAG-PiG-on-CSA sample exhibits a highest luminous flux of 1839 lm but a lowest CRI of 68. For the (YAG-PiG+SCASN-PiS)-on-CSA sample, it shows a highest CRI of 74 but a lowest luminous flux of 1259 lm. A good balance between the luminous flux and CRI can be found in the (YAG-PiG+α-SiAlON-PiG)-on-CSA sample. In addition, the slight lower threshold of the laser power for two-layer films can be ascribed to (i) the larger thickness of the two-layer films, (ii) the longer emission wavelength (i.e., the larger Stokes shift), and (iii) the lower thermal conductivity of silicone compared to the glass. The estimated maximum luminance of the YAG-PiG-on-CSA, (YAG-PiG+α-SiAlON-PiG)-on-CSA and (YAGPiG+SCASN-PiS)-on-CSA is respectively 845 Mcdm-2, 610 Mcdm-2 and 580 Mcdm-2, which is 5.8-8.4 times higher than that of the high-intensity discharge (HID) lamp (approximately 100


24

Page 25 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Mcdm-2). Moreover, the white laser light using these PiG-on-CSA plates is 9.6-14 times brighter than the current high-power LEDs that only have the luminance in the range of ~60 Mcdm-2.46 One can find that the corresponding CIE color coordinates shift towards the blue region with the increase of the incident laser power (Figure 8c). The chromaticity areas of white light specified by the ECE R48 standard (usually for applications in vehicles defined by six boundaries) are also plotted. The blue-shift is mainly attributed to the decreased absorption of blue light at elevated temperatures caused by the high incident laser power,47,48 as shown in Figure 8d. Furthermore, the chromaticity coordinates of (YAG-PiG+α-SiAlON-PiG)-on-CSA and (YAG-PiG+SCASN-PiS)-on-CSA plates are located within the aforementioned standard range, and those of YAG-PiG-on-CSA are positioned around the blue boundary line of the ECE R48 standard. This implies that the chromaticity coordinates of white light using the as-prepared PiG-on-CSA plates can meet the color standards of the automotive lighting. It is worth noting that the color coordinates of white light using (YAG-PiG+α-SiAlON-PiG)-on-CSA (0.3333, 0.3342) and (YAG-PiG+SCASN-PiS)-on-CSA (0.3294, 0.3287) are very close to the equalenergy white point (0.3333, 0.3333). Figure 8c shows the illumination images taken by projecting the light sources to a white screen. Thanks to the unique structure of the designed PiG-on-CSA architecture, highly bright and uniform laser-driven white light can be achieved eventually by using PiG films as the color converter.

4. Conclusion In summary, the robust and efficient color converter with a unique architecture was constructed by sintering a phosphor-in-glass (PiG) film on a 1DPCs coated sapphire substrate to realize the high-luminance laser-driven white lighting. The white laser light could be attained by controlling


25


Page 26 of 35

the thickness of the PiG film and the phosphor-to-glass ratio. By introducing appropriate scattering factors in the PiG film, a balance between excellent packaging efficiency (90%) and high light uniformity was achieved. The PiG color converter having the special architecture (i.e., YAG-PiG-on-CSA plate) could withstand a high power density of 11.2 Wmm-2 blue laser excitation and give a high luminance of 845 Mcdm-2. Furthermore, a high CRI of 74 was obtained by adding a robust orange or red phosphor layer to the YAG-PiG film. With the designed composite architecture, the PiG film enables to be used as a promising robust and highly efficient candidate for the next-generation high-power and high-luminance laser lighting technologies.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. The method to calculate the quantum efficiency and absorption efficiency. PL and PLE spectra of the commercial phosphors. Morphologies, XRD patterns and elemental compositions of the commercial phosphors and glass powders. Emission spectra of the original phosphors and PiG/PiS-on-SA plates. Temperature dependence of in-line transmittance spectra of the AR and BP. Photometric and colorimetric properties of the three plates with increasing incident laser power. Normalized emission spectra of YAG-PiG-on-CSA plate with increasing incident laser power. AUTHOR INFORMATION


26

Page 27 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Corresponding Author E-mail: [email protected] E-mail: [email protected] Email: [email protected]

Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We are grateful to the financial supports from National Natural Science Foundation of China (no. 5157223, no. 51561135015, and no. 51472087), the National Key Research and Development Program (MOST, 2017YFB0404301), National Postdoctoral Program for Innovative Talents (no. BX201700138), China Postdoctoral Science Foundation Grant (no. 2017M622073). REFERENCES (1) Amano, H.; Sawaki, N.; Akasaki, I.; Toyoda, Y., Metalorganic vapor phase epitaxial growth of a high quality GaN film using an AlN buffer layer. Appl. Phys. Lett. 1986, 48 (5), 353-355. (2) Nakamura, S.; Mukai, T.; Senoh, M., Candela-Class High-Brightness Ingan/Algan DoubleHeterostructure Blue-Light-Emitting Diodes. Appl. Phys. Lett. 1994, 64 (13), 1687-1689. (3) Kim, M.-H.; Schubert, M. F.; Dai, Q.; Kim, J. K.; Schubert, E. F.; Piprek, J.; Park, Y., Origin of efficiency droop in GaN-based light-emitting diodes. Appl. Phys. Lett. 2007, 91 (18), 183507.


27


Page 28 of 35

(4) Wierer, J. J.; Tsao, J. Y.; Sizov, D. S., Comparison between blue lasers and light-emitting diodes for future solid-state lighting. Laser Photonics Rev. 2013, 7 (6), 963-993. (5) Ma, Y.; Lan, W.; Xie, B.; Hu, R.; Luo, X., An optical-thermal model for laser-excited remote phosphor with thermal quenching. Int. J. Heat Mass Transfer 2018, 116, 694-702. (6) Cantore, M.; Pfaff, N.; Farrell, R. M.; Speck, J. S.; Nakamura, S.; DenBaars, S. P., High luminous flux from single crystal phosphor-converted laser-based white lighting system. Opt. Express 2016, 24 (2), A215-A221. (7) Arjoca, S.; Víllora, E. G.; Inomata, D.; Aoki, K.; Sugahara, Y.; Shimamura, K., Ce:(Y1−xLux)3Al5O12 single-crystal phosphor plates for high-brightness white LEDs/LDs with high-color rendering (Ra > 90) and temperature stability. Mater. Res. Express 2014, 1 (2), 025041. (8) Kang, T. W.; Park, K. W.; Ryu, J. H.; Lim, S. G.; Yu, Y. M.; Kim, J. S., Strong thermal stability of Lu3Al5O12:Ce3+ single crystal phosphor for laser lighting. J. Lumin. 2017, 191, 35-39. (9) Li, S.; Zhu, Q.; Tang, D.; Liu, X.; Ouyang, G.; Cao, L.; Hirosaki, N.; Nishimura, T.; Huang, Z.; Xie, R.-J., Al2O3–YAG:Ce composite phosphor ceramic: a thermally robust and efficient color converter for solid state laser lighting. J. Mater. Chem. C 2016, 4 (37), 8648-8654. (10) Li, S.; Zhu, Q.; Wang, L.; Tang, D.; Cho, Y.; Liu, X.; Hirosaki, N.; Nishimura, T.; Sekiguchi, T.; Huang, Z.; Xie, R.-J., CaAlSiN3:Eu2+ translucent ceramic: a promising robust and efficient red color converter for solid state laser displays and lighting. J. Mater. Chem. C 2016, 4 (35), 8197-8205.


28

Page 29 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(11) Song, Y. H.; Ji, E. K.; Jeong, B. W.; Jung, M. K.; Kim, E. Y.; Lee, C. W.; Yoon, D. H., Design of laser-driven high-efficiency Al2O3/YAG:Ce3+ ceramic converter for automotive lighting: Fabrication, luminous emittance, and tunable color space. Dyes Pigm. 2017, 139, 688692. (12) Song, Y. H.; Ji, E. K.; Jeong, B. W.; Jung, M. K.; Kim, E. Y.; Yoon, D. H., High power laser-driven ceramic phosphor plate for outstanding efficient white light conversion in application of automotive lighting. Sci. Rep. 2016, 6, 31206. (13) Song, Y. H.; Kwon, S. B.; Jung, M. K.; Park, W. K.; Yoo, J. H.; Lee, C. W.; Kang, B. K.; Yang, W. S.; Yoon, D. H., Fabrication design for a high-quality laser diode-based ceramic converter for a laser headlamp application. Ceram. Int. 2018, 44 (1), 1182-1186. (14) Cozzan, C.; Brady, M. J.; O’Dea, N.; Levin, E. E.; Nakamura, S.; DenBaars, S. P.; Seshadri, R., Monolithic translucent BaMgAl10O17:Eu2+ phosphors for laser-driven solid state lighting. AIP Adv. 2016, 6 (10), 105005. (15) Xu, J.; Wang, J.; Gong, Y.; Ruan, X.; Liu, Z.; Hu, B.; Liu, B.; Li, H.; Wang, X.; Du, B., Investigation of an LuAG:Ce translucent ceramic synthesized via spark plasma sintering: Towards a facile synthetic route, robust thermal performance, and high-power solid state laser lighting. J. Eur. Ceram. Soc. 2018, 38 (1), 343-347. (16) Zhu, Q.-Q.; Wang, X.-J.; Wang, L.; Hirosaki, N.; Nishimura, T.; Tian, Z.-F.; Li, Q.; Xu, Y.Z.; Xu, X.; Xie, R.-J., β-Sialon:Eu phosphor-in-glass: a robust green color converter for high power blue laser lighting. J. Mater. Chem. C 2015, 3 (41), 10761-10766.


29


Page 30 of 35

(17) Zhang, X.; Yu, J.; Wang, J.; Lei, B.; Liu, Y.; Cho, Y.; Xie, R.-J.; Zhang, H.-W.; Li, Y.; Tian, Z.; Li, Y.; Su, Q., All-Inorganic Light Convertor Based on Phosphor-in-Glass Engineering for Next-Generation Modular High-Brightness White LEDs/LDs. ACS Photonics 2017, 4 (4), 986-995. (18) Park, J.; Kim, J.; Kwon, H., Phosphor-Aluminum Composite for Energy Recycling with High-Power White Lighting. Adv. Opt. Mater. 2017, 1700347. (19) Yoshimura, K.; Annen, K.; Fukunaga, H.; Harada, M.; Izumi, M.; Takahashi, K.; Uchikoshi, T.; Xie, R.-J.; Hirosaki, N., Optical properties of solid-state laser lighting devices using SiAlON phosphor–glass composite films as wavelength converters. Jpn. J. Appl. Phys. 2016, 55 (4), 042102. (20) Zhang, R.; Lin, H.; Yu, Y.; Chen, D.; Xu, J.; Wang, Y., A new-generation color converter for high-power white LED: transparent Ce3+:YAG phosphor-in-glass. Laser Photonics Rev. 2014, 8 (1), 158-164. (21) Chen, D. Q.; Xiang, W. D.; Liang, X. J.; Zhong, J. S.; Yu, H.; Ding, M. Y.; Lu, H. W.; Ji, Z. G., Advances in transparent glass-ceramic phosphors for white light-emitting diodes-A review. J. Eur. Ceram. Soc. 2015, 35 (3), 859-869. (22) Lee, Y. K.; Kim, Y. H.; Heo, J.; Im, W. B.; Chung, W. J., Control of chromaticity by phosphor in glasses with low temperature sintered silicate glasses for LED applications. Opt. Lett. 2014, 39 (14), 4084-4087.


30

Page 31 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Seo, J.; Kim, S.; Kim, Y.; lqbal, F.; Kim, H.; Setlur, A., Effect of Glass Refractive Index on Light Extraction Efficiency of Light-Emitting Diodes. J. Am. Ceram. Soc. 2014, 97 (9), 27892793. (24) Zhang, X.; Yu, J.; Wang, J.; Zhu, C.; Zhang, J.; Zou, R.; Lei, B.; Liu, Y.; Wu, M., Facile Preparation and Ultrastable Performance of Single-Component White-Light-Emitting Phosphorin-Glass used for High-Power Warm White LEDs. ACS Appl. Mater. Inter. 2015, 7 (51), 2812228127. (25) Ma, C.; Cao, Y.; Shen, X.; Wen, Z.; Ma, R.; Long, J.; Yuan, X., High reliable and chromaticity-tunable flip-chip w-LEDs with Ce:YAG glass-ceramics phosphor for long-lifetime automotive headlights applications. Opt. Mater. 2017, 69, 105-114. (26) Yoon, C. B.; Kim, S.; Choi, S. W.; Yoon, C.; Ahn, S. H.; Chung, W. J., Highly improved reliability of amber light emitting diode with Ca-α-SiAlON phosphor in glass formed by gas pressure sintering for automotive applications. Opt. Lett. 2016, 41 (7), 1590-1593. (27) Zhang, X.; Huang, L.; Pan, F.; Wu, M.; Wang, J.; Chen, Y.; Su, Q., Highly thermally stable single-component white-emitting silicate glass for organic-resin-free white-light-emitting diodes. ACS Appl. Mater. Inter. 2014, 6 (4), 2709-2717. (28) Apetz, R.; van Bruggen, M. P. B., Transparent alumina: A light-scattering model. J. Am. Ceram. Soc. 2003, 86 (3), 480-486. (29) Oh, J. R.; Cho, S.-H.; Lee, Y.-H.; Do, Y. R., Enhanced forward efficiency of Y3Al5O12:Ce3+ phosphor from white light-emitting diodes using blue-pass yellow-reflection filter. Opt. Express 2009, 17 (9), 7450.


31


Page 32 of 35

(30) Yang, Y.; Zhuang, S.; Kai, B., High brightness laser-driven white emitter for Etenduelimited applications. Appl. Opt. 2017, 56 (30), 8321-8325. (31) Denault, K. A.; Cantore, M.; Nakamura, S.; DenBaars, S. P.; Seshadri, R., Efficient and stable laser-driven white lighting. AIP Adv. 2013, 3 (7), 072107. (32) Bicanic, K. T.; Li, X.; Sabatini, R. P.; Hossain, N.; Wang, C.-F.; Fan, F.; Liang, H.; Hoogland, S.; Sargent, E. H., Design of Phosphor White Light Systems for High-Power Applications. ACS Photonics 2016, 3 (12), 2243-2248. (33) Kim, J. H.; Williams, S. T.; Cho, N.; Chueh, C.-C.; Jen, A. K. Y., Enhanced Environmental Stability of Planar Heterojunction Perovskite Solar Cells Based on Blade-Coating. Adv. Energy. Mater. 2015, 5 (4), 1401229. (34) Wang, L.; Xie, R. J.; Li, Y. Q.; Wang, X. J.; Ma, C. G.; Luo, D.; Takeda, T.; Tsai, Y. T.; Liu, R. S.; Hirosaki, N., Ca1-xLixAl1-xSi1+xN3:Eu2+ solid solutions as broadband, color-tunable and thermally robust red phosphors for superior color rendition white light-emitting diodes. Light-Sci. Appl. 2016, 5 (10), e16155. (35) Liu, G.; Tian, Z. F.; Chen, Z. H.; Wang, H. Z.; Zhang, Q. H.; Li, Y. G., CaAlSiN3:Eu2+ phosphors bonding with bismuth borate glass for high power light excitation. Opt. Mater. 2015, 40, 63-67. (36) Zhu, Q.-Q.; Xu, X.; Wang, L.; Tian, Z.-F.; Xu, Y.-Z.; Hirosaki, N.; Xie, R.-J., A robust redemitting phosphor-in-glass (PiG) for use in white lighting sources pumped by blue laser diodes. J. Alloys Compd. 2017, 702, 193-198.


32

Page 33 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(37) Jeon, S. W.; Noh, J. H.; Kim, K. H.; Kim, W. H.; Yun, C.; Song, S. B.; Kim, J. P., Improvement of phosphor modeling based on the absorption of Stokes shifted light by a phosphor. Opt. Express 2014, 22 Suppl 5, A1237-A1242. (38) Sakuma, K.; Hirosaki, N.; Xie, R.-J., Red-shift of emission wavelength caused by reabsorption mechanism of europium activated Ca-α-SiAlON ceramic phosphors. J. Lumin. 2007, 126 (2), 843-852. (39) Aquino, F.; Jadwisienczak, W. M.; Rahman, F., Effect of laser speckle on light from laser diode-pumped phosphor-converted light sources. Appl. Opt. 2017, 56 (2), 278-283. (40) Kinoshita, J.; Ikeda, Y.; Takeda, Y., Speckle-Free Phosphor-Scattered Blue Light Emitted out of InGaN/GaN Laser Diode with Broadened Spectral Behavior for High Luminance White Lamp Applications. IEICE T. Electron. 2013, E96.C (11), 1391-1398. (41) Fujita, S.; Umayahara, Y.; Tanabe, S., Influence of light scattering on luminous efficacy in Ce:YAG glass-ceramic phosphor. J. Ceram. Soc. Jpn. 2010, 118 (1374), 128-131. (42) Xiang, R.; Liang, X.; Xi, Q.; Yuan, Z.; Chen, C.; Xiang, W., A chromaticity-tunable white LED by screen-printing red phosphor coating on PiG plates. Ceram. Int. 2016, 42 (16), 1927619282. (43) Lin, Z.; Lin, H.; Xu, J.; Huang, F.; Chen, H.; Wang, B.; Wang, Y., Highly thermal-stable warm w-LED based on Ce:YAG PiG stacked with a red phosphor layer. J. Alloys Compd. 2015, 649, 661-665.


33


Page 34 of 35

(44) Lenef, A.; Kelso, J.; Tchoul, M.; Mehl, O.; Sorg, J.; Zheng, Y., Laser-activated remote phosphor conversion with ceramic phosphors. Proc. SPIE 2014, 9190, 91900C. (45) Nanishi, Y.; Schwarz, U. T.; Shim, J.-I.; Masui, S.; Nakatsu, Y.; Kasahara, D.; Nagahama, S.-i., Recent improvement in nitride lasers. Proc. SPIE 2017, 10104, 101041H. (46) Bhardwaj, J.; Cesaratto, J. M.; Wildeson, I. H.; Choy, H.; Tandon, A.; Soer, W. A.; Schmidt, P. J.; Spinger, B.; Deb, P.; Shchekin, O. B.; Götz, W., Progress in high-luminance LED technology for solid-state lighting. physica status solidi (a) 2017, 214 (8), 1600826. (47) Rejman, M.; Babin, V.; Kucerková, R.; Nikl, M., Temperature dependence of CIE-x,y color coordinates in YAG:Ce single crystal phosphor. J. Lumin. 2017, 187, 20-25. (48) Arjoca, S.; Víllora, E. G.; Inomata, D.; Aoki, K.; Sugahara, Y.; Shimamura, K., Temperature dependence of Ce:YAG single-crystal phosphors for high-brightness white LEDs/LDs. Mater. Res. Express 2015, 2 (5), 055503.


34

Page 35 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC figure:


35

Unique Color Converter Architecture Enabling Phosphor-in-Glass (PiG

Recommend Documents