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Polysiloxane Functionalized Carbon Dots and Their Crosslinked Flexible Silicone Rubbers for Color Conversion and Encapsulation of White LEDs Yunfeng Wang, Zhengmao Yin, Zheng Xie, Xinxin Zhao, Chuanjian Zhou, Shuyun Zhou, and Ping Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b01511 • Publication Date (Web): 01 Apr 2016 Downloaded from http://pubs.acs.org on April 4, 2016

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ACS Applied Materials & Interfaces

Polysiloxane Functionalized Carbon Dots and Their Crosslinked Flexible Silicone Rubbers for Color Conversion and Encapsulation of White LEDs Yunfeng Wang,a,b Zhengmao Yin,c Zheng Xie,*,b Xinxin Zhao,a Chuanjian Zhou,*,a,d Shuyun Zhou,b Ping Chenb a

School of Materials Science and Engineering, Shandong University, Jinan, 250061, China

b

Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190, China

c

College of Materials Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, China d

Key Laboratory of Special Functional Aggregated Materials, Ministry of Education, Jinan, 250061, China Abstract: In this work, aminopropylmethylpolysiloxane (AMS)-functionalized luminescent carbon dots (AMS-CDs) were prepared via one-step solvothermal method. AMS-CDs could be self- or co-crosslinking with AMS to form 3D flexible transparent silicone rubbers (SRs) where CDs acted as crosslinking points, so loading fraction of AMS-CDs could be adjusted from 10 to 100 wt%, thus modulating fluorescence properties and flexibility of silicone rubbers. Due to self-curing property and high thermal stability, AMS-CDs were also studied in white LEDs (WLEDs), serving as color conversion and encapsulation layer of GaN-based blue LEDs simultaneously which would avoid traditional problem of poor compatibility between emitting and packaging materials. And the color coordinate of AMS-CDs based WLEDs (0.33, 0.28) was very close to the pure white light. In addition, the obtained CDs crosslinked SRs had good transparency (T > 80%) at 510-1400 nm and high refractive index (1.33-1.54) which could meet the need of commercial packaging materials and optical application. AMS-CDs were also promising to be used in the UV LEDs based WLEDs according to their wide wavelength emission and flexible optoelectronic device. Keywords: AMS-CDs, self-curing, silicone rubbers, WLEDs, flexibility 1

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1. Introduction Light emitting diodes (LEDs) have already attracted significant interest in the field of display and lighting, 1 because of their superior properties of low-power consumption, long lifespan, and good durability. Currently, commercial white LEDs (WLEDs) are most based on blue LEDs with YAG:Ce yellow phosphors as color conversion layer (CCL) dispersing in the silicone or polymer matrix that are often used as packaging materials in the LED industry. However, there are certain disadvantages of phosphors like light blocking, leaking2,3 and even relatively low color quality4,5, and their poor compatibility with packaging resin6, which were crucial factors in the WLEDs application. On the other hand, these phosphors generally involve expensive rare earth ions that are resource-restricted and not environmentally friendly.7 These defects of phosphors listed above have limited their use in the application of WLEDs. Given these, it is urgent and necessary to develop a new CCL for the substitute of phosphors. Recently, several groups have reported the employ of photoluminescent (PL) organic polymers,8,9 quantum dots (QDs),10-16,17 and carbon dots (CDs)18-24 for WLEDs applications. In fact, poor compatibility between QDs and silicone or polymer matrix seriously influenced optical properties and stability of the device.12,25,26 In addition, organopolymers which showed broad absorption and emission were chosen as CCL. However, organopolymer-based technology presented poor thermal stability, especially for optoelectronic applications.27 Furthermore, organic polymers and QDs would have photo-bleaching28,29 or optical scintillation30 that had negative effects on WLEDs applications in the long run. Photoluminescent CDs have received wide attention on account of plenty of advantages such as good biocompatibility, high photo-stability and eco-friendliness.31-35 To date, CDs-based 3D macrostructure has been realized by simply embedding CDs in silica gel glass or organopolymer,22,36,37 for solid-state emitting, but doping concentration and performances of CDs were limited. In our previous work, we have prepared silane-functionalized CDs (SiCDs) which could completely bulk polymerize or co-polymerize with silica gel glass in which the concentration of SiCDs could be easily controlled from 0 to 100 wt%.38 However, SiCDs exhibited poor thermal stability in the optoelectronic devices even at room temperature. Since condensation reaction of large numbers of alkoxysilyl groups occurred by trace water and CO2 in the air or heating, resulting in continuous release of water and 2


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ethanol during the curing process. More methods can be used to modify thermal properties, for example, introducing heat-resistant siloxane-based macromolecule with long chains of Si-O-Si. So far, polysiloxane have captured the extensive concern due to their unique properties as both organic and inorganic materials.39 They also possess better performances like good transparency, weatherability,40-42 excellent low/high temperature resistance39,43 and designable molecular structure that can be beneficial for various applications. Therefore, polysiloxane matrix can be good host material for encapsulation. To our best knowledge, polysiloxane-functionalized CDs have not been reported before. In this work, we reported on the preparation of aminopropylmethylpolysiloxane (AMS, aminopropylmethyl silicone oil) functionalized luminescent CDs (AMS-CDs) and their application in WLEDs. AMS could be a good choice due to their excellent stability, and carboxyl (from carbon source) and aminopropyl (from AMS) groups on surface of the obtained AMS-CDs would react with each other to form a completely crosslinking network. Therefore, AMS-CDs could form CDs crosslinked silicone rubbers (SRs) by bulk self- or co-crosslinking with AMS where CDs acted as crosslinking points at 50-80 oC. AMS-CDs doped concentration in SRs was controlled from 10 to 100 wt% (100 wt% SR was referred to the self-crosslinking AMS-CDs without AMS). More importantly, this CDs-based SR coatings with high thermal stability could serve as CCL and encapsulation layer simultaneously, which would help to optimize the compatibility between luminescent materials and encapsulation matrix effectively, comparing to the commercial WLEDs with two-component system. The color coordinate of the as-fabricated WLEDs at (0.33, 0.28) was very close to that of the pure white light. The curing flexible 100 wt% SRs with the shore hardness at 13A were expected to have potential application in the flexible optoelectronic devices since a few groups have reported that kind of work based on CDs44-48, graphene49, and carbon nanotubes50-52.

2. Experimental section 2.1 Preparation of luminescent AMS-CDs Luminescent AMS-CDs were prepared by solvothermal method. In detail, 1 g of AMS53 (the designed molecular weight was 5 kD) and 1.5 g of citric acid were dissolved in 20 mL ethanol under continuous stirring at room temperature. Then the mixture was transferred into an autoclave with a PTFE inner vessel and placed in oven at 150 oC for 8 h. After cooling to ambient temperature naturally, the obtained products were collected and filtered through a 0.22 µm polyethersulfone (PES) membrane. The obtained 3



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brownish CDs were further purified by dialysis (MWCO: 100-500 D) for 48h in order to remove the unreacted materials.

2.2 Preparation of luminescent CDs crosslinked SRs AMS-CDs self or doped with AMS in the concentration ranging from 10 to 100 wt% was carried out by changing the weight ratio of AMS-CDs to AMS. Then after heat treatment at 50-80 oC for several days, a series of fluorescent CDs crosslinked SRs would be obtained.

2.3 Assembly of WLEDs The WLEDs device was assembled by combining blue-light LED chips with the wavelength centered at 460 nm with the self-crosslinking AMS-CDs. AMS-CDs solution was easily dropped onto the blue-light chips, then curing after heat treatment at elevated temperature.

2.4 Characterization The fluorescence spectra and the relative QY excited at 365 nm was measured by F-4500 (Hitachi, Japan), scan speed is 1200 nm/min, and the EM slit is 2.5 nm. U-3000 (Hitachi, Japan) was used for UV-Vis absorption spectra at room temperature, scan speed is 600 nm/min and wavelength accuracy is ± 0.3 nm. Quantaurus-QY (Hamamatsu Photonics, Japan) was used to measure the absolute QYs of solid samples. The high resolution transmission electron microscope (HRTEM) images were obtained using JEM-2100F (JEOL, Japan) with an acceleration voltage of 200 kV. The scanning electron microscope (SEM) images were recorded by S-4800 (Hitachi, Japan) with an acceleration voltage ranging from 0.5 to 30 kV. The Fourier transform infrared (FTIR) spectra was obtained by Excalibur HE 3100 (Varian, America), through dropping the solution sample onto the KBr pellets, the wavenumber accuracy is < 0.01 cm-1. In addition, solid samples (0.3-1mm) were measured by attenuated total reflection (ATR) accessory. The UV-Vis-NIR transmission spectra in the UV-Vis-NIR region were characterized by Cary 5000 (Varian, America). X-ray photoelectron spectroscopy (XPS) was carried out using Axis Ultra DLD (Kratos, UK) spectrometer with monochromatic Al Kα as the excitation source. The resolved fluorescent lifetimes of the samples were measured by LP920 (Edinburgh instruments, UK) with a laser at 375 nm excitation, the pulse length is ps, and the detected fluorescent lifetime is from 0.1ns to millisecond. The thermal analysis was recorded with SDT-Q600 (TA instruments, America) in the nitrogen gas atmosphere, with heating rate at 10 oC/min. Hardness was measured by HV-10Z (Lianer, China), load is 0.5kg. Shore hardness (HS) can be obtained by the following formula: HS=HV/10+12. 4


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Mechanical measurements were carried out by UMTM4204 (SUNS, China) at room temperature, with loading rate at 1mm/min. Test method for flexural properties is GB 1449-83, standard sample size is 80 mm×15 mm×4 mm, length of span is 40 mm. The HASS-1200 (Everfine, China) was utilized to characterize optical properties of WLEDs device based on the blue GaN LEDs under a forward current of 20 mA. The refractive index of the samples were measured at 600 nm by Model 2010 (Metricon, America), accuracy is ± 0.0005.

3. Results and discussion The illustration for the synthesis of AMS-CDs and CDs crosslinked SRs is shown in Figure 1. AMS and citric acid were heated based on solvothermal method, in which the formation of CDs and polysiloxane functionalization process would be simultaneous. In this solvothermal process, amino group of AMS side chain would react with carboxyl group (from citric acid) to form amido bond, thus CDs were linked with AMS by covalent bond. However, carboxyl group could not be completely reacted (see Figure 3a) mainly due to its excessive molar ratio compared with that of amino group. Further, AMS has long chains that will entangle with each other, which will induce some steric hindrance to block reaction between carboxyl group and amino group. Hence, we got AMS-CDs with residual carboxyl groups which would continue to react with the amino group of AMS-CDs (or AMS) to form crosslinking structure at elevated temperature. As a result, AMS-CDs could realize curing process by self- or co-crosslinking with AMS for the construction of CDs crosslinked SRs at 50-80 oC.

3.1 Characterization and optical properties of luminescent AMS-CDs The HRTEM image (Figure 2a) shows AMS-CDs are nearly spherical and well dispersed with a lattice spacing of ca. 0.23 nm which indicated the (001) facet of graphite. Figure 2b plots the histogram of size distribution of CDs, telling CDs have small diameter ranging from 2.0 to 3.8 nm with an average size of 2.9 nm. It should be noted that AMS-CDs were functionalized by polysiloxane macromolecule which made it hard to find the legible particles. The FTIR spectra of AMS-CDs and different SRs is shown in Figure 3a. The successful chemical functionalization and formation of amide groups on CDs surface can be confirmed by the typical peak at ca. 1020 cm-1 and 1080 cm-1 (ν Si-O-Si ) and 1645 cm-1 (ν CONH).38 The vibration of C=O group from carboxyl group is also found on surface of CDs at 1710 cm-1.54 The intensity of this C=O peak occurs to decrease, relative to that of CONH, with the decrease of AMS-CDs doping concentration in SRs. 5



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Furthermore, vibration peaks for N-H and -OH in SRs weaken, compared with that in CDs. This data indicates carboxyl and aminopropyl groups were consumed to react with each other, forming the cured SRs. The surface composition and elemental analysis of AMS-CDs were further characterized by XPS. Due to their self-crosslinking property, liquid CDs would make changes after heat treatment. In that case, we had to choose the 100 wt% CDs crosslinked SR (self-crosslinking AMS-CDs) to take XPS test. Figure S1a indicates main XPS peaks of the surveyed 100 wt% SR. The C 1s XPS spectra (Figure S1b) reveals the following peaks can be assigned to C-C (284.7 eV), C-N (285.4 eV), C-OH (286.8 eV), C=O (288.4 eV, 289 eV, belonging to CONH and COOH respectively)55. The obtained results are consistent with that measured by FTIR in terms of surface groups of AMS-CDs. The peak of Si 2p is located at 102.2 eV in Figure S1c.56 Figure 3b presents that AMS-CDs with shoulder absorption peaks at ca. 280 nm, 300 nm and 360 nm in the UV-Vis spectra, which can be assigned to π-π* transition of C=C (280 nm) and n-π* transition of C=O (300 nm, 360 nm). In the PL spectra, AMS-CDs exhibit strong blue emission when excited from 360 to 400 nm and emission wavelengths appear to red shift with decreasing PL intensity, which is similar to that reported in the previous literature.57-59 When excitation wavelength is at 460 nm, PL emission wavelength reaches to 558 nm, which exhibits AMS-CDs have potential application in GaN-based WLEDs. We have made a series of experiments by adjusting the ratio of AMS to citric acid, reacting temperature and time, and changing some other factors like molecule weight. The results are shown in Table S1, S2. Citric acid contributes to increase QYs to 16% when ratio of AMS to citric acid was 1:3, however, QYs come to decrease when more citric acid was added from 1:3 to 1:10 (AMS to citric acid). In addition, raising temperature and extending reaction time are favorable to increase QYs. Interestingly, molecule weight of AMS do not affect QYs. Eventually, we got the highest QYs at around 16 % (360 nm excited).

3.2 Properties of CDs crosslinked SRs CDs crosslinked SRs varied with different concentration of AMS-CDs were prepared successfully. Photographs (Figure 4a) show these SRs are transparent with good optical quality, and their color under visible light get darker when loading fraction of AMS-CDs increases from 10 to 100 wt%. Any macroscopic separation from fractured sections of the samples (25 and 100 wt% SRs) is not found, as 6


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shown in Figure S2. The transmission spectra in Figure S3 clearly reveals SRs has T > 80% at 510-1400 nm while they own lower transparency with increasing doping concentration of AMS-CDs in the visible region. Refractive index of these SRs (1.33-1.54) are listed in Table S4, which can satisfy the commercial need of WLEDs. 100 wt% SR was flexible as Figure 4b demonstrates, with the shore hardness at 13 A, and it could bear for many bend cycles. Besides, 10 and 25 wt% SRs were resilient while 50 and 75 wt% SRs were hard and brittle. The results predicted that SRs would keep flexible when doping concentration of AMS-CDs was below 25 or above 75 wt%. 10-25 wt% SRs had good elasticity which was attributed to 3D network with low crosslinking density. And crosslinking structure of 75-100 wt% SRs were not impact because only part of carboxyl groups were reacted, resulting in certain flexibility. In this case, flexibility of SRs could be adjusted by changing concentration of AMS-CDs. Figure S4 gives some mechanical properties of 25 wt% SR related to flexibility. At room temperature, the maximum bending deflection and radius of standard samples can reach to 9.58 mm and 26 mm respectively before fracture, and flexural modulus is as low as 5.2 MPa. The shore hardness of 25 wt% SR is 20 which is similar to that of the reported silicone elastomer.60,61 These data all indicate certain flexibility of 25 wt% SR. We also investigate optical property of 10 and 25 wt% SRs before bending and after bending for 100 times, as shown in Figure S5. There is no obvious change in the absorption, emission wavelength and transmission. As we know, flexible optoelectronic devices like organic LEDs (OLEDs) looking thinner, durable and ductile have demonstrated potential and innovative applications of display technology currently.62,63 The fluorescent AMS-CDs glass or films will be hopeful to be used in the flexible device for solid-state lighting, display, especially for conversion layer of backlight display and other large-area flexible devices. Figure 4c demonstrates there are no obvious absorption peaks in the UV-Vis spectra of different SRs. In Figure 4d, these SRs show emission wavelength at 450 nm when excited at 360 nm and broad emission at ca. 500-550 nm will appear with increasing ratios from 25 to 100 wt%. Figure 4e shows fluorescence emission peaks are located at 504 nm, 503 nm, 526 nm, 533 nm, 544 nm for 10 to 100 wt% SRs at 460 nm excitation, which means fluorescence properties of CDs crosslinked SRs can be easily modulated. When doping concentration increases, red shift can be also observed at 460 nm excitation. Figure S6 illustrates PL emission spectra of 100 wt% SR excited from 340 nm to 500 nm, indicating 100 wt% SR shows best emission at 500 nm-550 nm when excited at 460 nm, which is important for 7



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GaN-based WLEDs. This emission spectra of 100 wt% SR is totally different from that of AMS-CDs solution. Further, these broadband fluorescence properties of SRs will be beneficial to WLEDs applications based on UV LEDs. PL lifetimes and QYs of AMS-CDs and SRs are shown in Table S3, Figure 5a. A two-component decay-time model originated a good fit with the average lifetimes (τavg=3.17-6.91 ns). The lifetime of AMS-CDs (6.91 ns) is particularly longer than SRs (3.17-6 ns). When AMS-CDs concentration increases in SRs, lifetime will increase firstly to 6.01 ns at 50 wt% and then decrease to 3.17 ns at 100 wt%. Those SRs with high doping concentration show lower QYs (360 nm and 460 nm excited), thus indicating it can promote solid-state luminescence quenching to some extent. QYs (460 nm excited) maintain and even become higher at 10-25 wt% in the solid matrix, compared to that of AMS-CDs solution. Thermal gravimetric analysis (TGA) was employed to investigate the effects of different ratios of AMS-CDs in SRs under nitrogen gas atmosphere. The data is shown in Figure 5b in which the weight loss of diverse SRs (10-100 wt%) come to 8 %, 5.3 %, 4.5 %, 3.6 %, 1.5 % in sequence from room temperature to 200 oC. 100 wt% SR exhibited highest thermal stability under 200 oC, thus this self-curing material served as LED encapsulation is hopeful. When the temperature reached to 200 oC below 300 oC, the weight loss might be caused by the breakage of the partial -Si-O-Si-, as side chain contained amino group would accelerate this procedure, and decomposition of residual carboxy group. When the temperature was more than 300 oC, the decomposition would mainly come from -Si-O-Sigroup, bringing in ring and small molecules. Figure S7 compares PL intensity of 100 wt% SR and commercial phosphor after 120 oC aging treatment under air atmosphere to verify the thermal stability. Commercial phosphor maintained its emission intensity after 300 h and showed good thermal stability. PL intensity of 100 wt% SR would keep 85% from the initial intensity after 330 h aging time which makes AMS-CDs potential to be used in WLEDs.

3.3 Application of WLEDs Due to unique properties of fluorescence and self-curing of the as-obtained AMS-CDs, they could be used to generate WLEDs as shown in Figure 6. Figure 6a demonstrate the preparation of WLEDs, by only dripping AMS-CDs onto the GaN blue LED chip, then drying at 50-80 oC for several days. After this process, the blue chip would be encapsulated by the self-curing AMS-CDs. The 8


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electroluminescence emission spectra of the made WLEDs was measured. Two emission peaks centered at 460 nm and 590 nm are observed in Figure 6b. The first one comes from the blue GaN LED and the other is from the prepared CDs. When the two emission bands are combined together, white light will produce (Figure 6a). Figure 6c exhibits the CIE 1931 chromaticity coordinate of AMS-CDs based WLEDs is at (0.33, 0.28), which is very close to the pure white light at (0.33, 0.33). CRI of this prepared WLEDs is 66.6 and near to that of the commercial WLEDs (65-80). Furthermore, the refractive index that is a crucial factor to the light extraction efficiency in the WLEDs of 100 wt% SR (1.5107) is close to that of commercial silicone-based encapsulating materials. However, emission intensity of AMS-CDs is about ten times lower than that of commercial phosphor based WLEDs, as shown in Figure S8. The luminous efficiency of AMS-CDs based WLEDs can reach to 14 lm/W, it is similarly ten times lower than that of commercial WLEDs. Although we have made a series of experiments by adjusting the ratio of AMS to citric acid, reacting temperature and time, and changing some other factors like molecule weight of AMS to increase this performance (see Table S1, S2). More efforts such as adjusting carbon sources, structures or functional groups of polysiloxane are needed to improve emission intensity of polysiloxane functionalized CDs to increase their feasibility. Recently, several groups have reported the best efficacy for organopolymers, QDs, and CDs-based WLEDs were 23.727, 4725 and 58.118 lm/w, respectively. Despite a few CD-based WLEDs have been reported, most of them employed QDs or CDs powders dispersing in encapsulation resin or gel glasses18. When doping concentration of QDs or CDs is increasingly high, leading to agglomeration and reduction of optical properties due to the poor compatibility between the two materials. Here, we first reported the self-curing AMS-CDs, which could act as dual role of luminescence and encapsulation layer for WLEDs application without any addition of encapsulation resin. This strategy was beneficial to avert traditional problem of compatibility between luminescent materials such as phosphors, QDs or CDs, and packaging materials and help to keep optical properties in 3D matrix. And the procedure of dripping AMS-CDs onto blue LEDs chips was quite simple, which indicated AMS-CDs could be expected as encapsulation layer on a large scale. Also, polysiloxane as the solid matrix has lots of superiorities like thermal stability, weatherability and high-temperature resistance, which is most suitable for the device encapsulation.

4. Conclusions 9



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In summary, we have demonstrated the preparation of AMS-CDs by one-step solvothermal method which could form CDs crosslinked SRs by self- or co-crosslinking with AMS. Loading fraction of AMS-CDs in SRs was controlled from 10 to 100 wt%, and properties like fluorescence and flexibility of these SRs could be modulated accordingly. All of the obtained SRs had high transmission (> 80 % at 510-1400 nm) and high refractive index (1.33-1.54) which were crucial factors in the optical device. Furthermore, AMS-CDs coating with high thermal stability as the substitute of phosphors were applied as CCL and encapsulation layer at one time in WLEDs device based on blue LEDs which helped to avoid compatibility problem between luminescent materials and packaging materials. AMS-CDs based WLEDs showed good CIE coordinates located at (0.33, 0.28) that was very close to the pure white light at (0.33, 0.33). Other than the application of blue LEDs based WLEDs, AMS-CDs could probably be applied in the UV LEDs based WLEDs due to their broadband luminescence properties. More importantly, soft SRs based on AMS-CDs could be bent, as well as their high transparency and controlled performances, thus they were expected to apply in the flexible solid-state lighting, display and other optoelectronic devices in the future.

Associated content Supporting information Partial characterization data, including XPS spectra, SEM images tables for QYs and different reaction condition, transmission, PL and absorption spectra and so on.

Author information Corresponding author: *E-mail: [email protected] (Zheng Xie) *E-mail: [email protected] (Chuanjian Zhou) Notes The authors declare no competing financial interest.

Acknowledgements This work was supported by the joint program of National Natural Science Foundation of China and Israel Science Foundation (Grant 51561145004) and promotive research fund for excellent young and middle-aged scientists of Shandong Province (Grant BS2010CL026). 10


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Figure 1. Schematic for the preparation of AMS-CDs and their self- and co-crosslinking silicone rubbers. Figure 2. (a) HRTEM image of AMS-CDs; (b) histogram of their diameter distribution. Figure 3. (a) FTIR spectra of AMS-CDs and CDs crosslinked SRs at doping concentration of 25, 50 and 100 wt%; (b) UV-Vis absorption and PL emission spectra of AMS-CDs excited from 360 nm to 460 nm in 20 nm increments; the inset shows photographs of AMS-CDs under visible light (left) and 365 nm UV illumination (right). Figure 4. (a) Optical photographs of CDs crosslinked SRs with different ratios from 10 to 100 wt%, upon visible light (top) and 365 nm UV illumination (below); (b) the bended 100 wt% SR; (c) absorption and PL emission spectra of the luminescent SRs at different AMS-CDs concentrations excited at (d) 360 nm and (e) 460 nm. Figure 5. (a) Fluorescence decay curves for AMS-CDs solution and CDs crosslinked SRs with different fractions of AMS-CDs at the excitation of 375 nm; (b) TGA of 10-100 wt% SRs from room temperature to 800 oC under N2 atmosphere. Figure 6. (a) Schematic for the fabrication of 100 wt% SR based WLEDs based on blue GaN LED; (b) electroluminescence emission spectra; (c) CIE chromaticity diagram of AMS-CDs based WLEDs.

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oC

50

-80

O O

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50 -8

0 oC

AM S

Figure 1. Schematic for the preparation of AMS-CDs and their self- and co-crosslinking silicone rubbers.

(a)

(b) d=0.23 nm

Figure 2. (a) HRTEM image of AMS-CDs; (b) histogram of their diameter distribution.

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(a)

(b)

Figure 3. (a) FTIR spectra of AMS-CDs and CDs crosslinked SRs at doping concentration of 25, 50 and 100 wt%; (b) UV-Vis absorption and PL emission spectra of AMS-CDs excited from 360 nm to 460 nm in 20 nm increments; the inset shows photographs of AMS-CDs under visible light (left) and 365 nm UV illumination (right).

(a)

(c)

(b)

(d)

(e)

Figure 4. (a) Optical photographs of CDs crosslinked SRs with different ratios from 10 to 100 wt%, upon visible light (top) and 365 nm UV illumination (below); (b) the bended 100 wt% SR; (c) absorption and PL emission spectra of the luminescent SRs at different AMS-CDs concentrations excited at (d) 360 nm and (e) 460 nm.

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(a)

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(b)

Figure 5. (a) Fluorescence decay curves for AMS-CDs solution and CDs crosslinked SRs with different fractions of AMS-CDs at the excitation of 375 nm; (b) TGA of 10-100 wt% SRs from room temperature to 800 oC under N2 atmosphere.

(a)

(b)

(c)

Figure 6. (a) Schematic for the fabrication of 100 wt% SR based WLEDs based on blue GaN LED; (b) electroluminescence emission spectra; (c) CIE chromaticity diagram of AMS-CDs based WLEDs.

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Table of Contents The silicone oil functionalized carbon dots can be self- or co-crosslinking to form 3D luminescent flexible CDs-bulk glasses and 2D CDs-coatings for color conversion and encapsulation layers of white LEDs at one time.

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Polysiloxane Functionalized Carbon Dots and ... - ACS Publications

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