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C: Plasmonics; Optical, Magnetic, and Hybrid Materials
Red-shifted Emission in Y3MgSiAl3O12: Ce3+ Garnet Phosphor for Blue Light Pumped White Light Emitting Diodes Can He, Haipeng Ji, Zhaohui Huang, Tiesheng Wang, Xiaoguang Zhang, Yangai Liu, Minghao Fang, Xiaowen Wu, Jiaqi Zhang, and Xin Min J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b03940 • Publication Date (Web): 13 Jun 2018 Downloaded from http://pubs.acs.org on June 14, 2018
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The Journal of Physical Chemistry
Red-shifted Emission in Y3MgSiAl3O12: Ce3+ Garnet Phosphor for Blue Light Pumped White Light Emitting Diodes Can He,1,† Haipeng Ji,1,† Zhaohui Huang,1,* Tiesheng Wang,2 Xiaoguang Zhang,1 Yangai Liu,1 Minghao Fang,1 Xiaowen Wu,1 Jiaqi Zhang,3 Xin Min1,2,* †
C. He and H.P. Ji contributed equally to this paper.
1
School of Materials Science and Technology, Beijing Key Laboratory of Materials
Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, China University of Geosciences, Beijing 100083, China 2
Department of Materials Science and Metallurgy, University of Cambridge, 27
Charles Babbage Road, Cambridge CB3 0FS, United Kingdom 3
College of Materials Science and Engineering, Jilin University, Changchun, 130012,
China
*Corresponding author Tel: +86-010-82322186, Fax: +86-010-82322186 E-mail:
[email protected],
[email protected] ACS Paragon Plus Environment
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Abstract It is highly desirable to red-shift the emission of Y3Al5O12:Ce3+ phosphor in order to obtain a warmer correlated color temperature (CCT) in applications for blue light pumped white light emitting diodes (w-LEDs) with high color rendering index (CRI). In this paper, we reported the red-shifted emission of Y3MgSiAl3O12:Ce3+ garnet phosphor for w-LEDs through a chemical unit co-substituting in solid solution design strategy. The fabrication temperature of the Y3MgSiAl3O12:Ce3+ powder was optimized
at
1600
ºC
and
its
structure,
photoluminescence
properties,
micromorphology, decay curves, quantum yield, as well as the thermal stability of the samples were investigated in details. The as-prepared Y3MgSiAl3O12:Ce3+ phosphors displayed a broad excitation band ranging from 300 to 520 nm (centered at 450 nm), and presented an intense Ce3+ 5d-4f emission band in the yellow light region (λem=564 nm, obviously red-shifted away from Y3Al5O12:Ce3+). This can be explained by the increase of the crystal field splitting in the Ce3+ 5d levels due to the chemical unit co-substitution of Al3+(I) and Al3+(II) ions by Mg2+ and Si4+ ions. The quantum yield of the Y2.92MgSiAl3O12:0.08Ce3+ phosphor was measured as 61.8%. Further investigation on the packaged w-LEDs lamp by combining Y2.92MgSiAl3O12:0.08Ce3+ phosphors on a blue InGaN chip exhibit a lower CCT and higher CRI compared to the commercial Y3Al5O12: Ce3+ based device, indicating their outstanding strengths for potential applications in w-LEDs.
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The Journal of Physical Chemistry
1 Introduction Phosphors converted white light emitting diodes (w-LEDs) have recently attracted a growing interest because of their high electrical energy to light energy conversion efficiency, long lifetime, compactness, environmental friendliness and designable features, replacing the conventional incandescent bulbs and fluorescent lamps
1-6
. In addition, because of their excellent performance, w-LEDs have been
gradually used in several new application fields such as backlighting of liquid-crystal displays and portable electronics, architectural lighting, car headlights, medical lighting and plant cultivation 7. Commercial w-LEDs are mainly obtained through the combination of a blue indium gallium nitride (InGaN) chip and yellow phosphors (e. g. Y3Al5O12:Ce (YAG:Ce)) which can be excited by the blue light.
8,9,10
However,
these w-LEDs are always limited because of their several disadvantages, such as poor color reproduction, low color rendering index (CRI), and high correlated color temperature (CCT), due to the absence of red light component. In order to improve the luminescence properties of YAG:Ce phosphors, several studies have been reported on the redshift of emission spectrum through element doping in YAG structure, including the cation-substitution
11-12
and the anion-group
-substitution 13. The results indicated that the emission wavelength mainly depended on changes in lattice parameter and strength of the crystal-field splitting of Ce3+ ions during elements substitution
14-15
. Recently, the chemical unit co-substituting solid
solution design strategy has been proposed to adjust the emission of YAG:Ce phosphors, such as (GdxY3-x)Al2Ga3O12:Ce3+ (x=1,2,3) (x=2,3,4)
17
, and Y2BaAl4SiO12:Ce3+
16
, YGd2Al5-xGaxO12:Ce3+
18
. This approach is considered to have more
effects on changing the local or long-range structures of crystal lattice resulting in greater redshift and better CRI value than the one-element substituted YAG:Ce phosphors 19 upon improving YAG’s luminescence properties.20 To further develop novel phosphors via chemical unit co-substitution with diverse compositions and better CRI, the Y3MgSiAl3O12:Ce3+ phosphors were designed and prepared here. The Al3+-Al3+ couples are supposed to be partly substituted by
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Mg2+-Si4+ pairs to form a novel Y3MgSiAl3O12: Ce3+ composition without significant changes in phase and crystal structure (different from the previous studies
21 22
). It is
known that all Ce3+ ions are surrounded by several AlO6 octahedral and AlO4 tetrahedral
23
. Thus, the co-substitution of Al3+-Al3+ couples by Mg2+-Si4+ pairs can
obtain new MgO6 and AlO4 coordination polyhedrons, obviously change the local crystal field of Ce3+ ion, theoretically enhance its 5d level splitting and finally red-shift the emission peak into long wavelength regime. Under the excitation at 450 nm, the co-substituted Y3MgSiAl3O12:Ce3+samples emit intense yellow light centered at 564 nm, further demonstrating the obvious redshift of the emission peaks in comparison to those of the YAG:Ce phosphors (λem= ~535nm). Meanwhile, a slight redshift of the emission spectrum was observed with the increasing doping concentration of Ce3+ ions. To further demonstrate the potential of Y2.92MgSiAl3O12 phosphors for w-LEDs application, the Y2.92MgSiAl3O12: 0.08Ce3+ phosphors were packaged with the blue LED chip to produce a w-LED lamp with excellent CCT and CRI.
2 Experimental 2.1 Preparation of the Y3MgSiAl3O12:Ce3+ phosphor The Y3MgSiAl3O12:Ce3+ phosphors were prepared through the conventional high-temperature solid-state reaction under a reducing atmosphere (10% H2，90% N2). The raw materials were Y2O3 (99.99%), MgCO3 (99.99%), SiO2 (99.99%), Al2O3 (99.99%) and CeO2 (99.99%). At first, the optimal synthesis temperature was studied. All the raw materials were mixed according to the stoichiometric ratio in their chemical formula. The powder was carefully mixed and ground in an agate mortar, loaded into a corundum crucible and calcined at different temperatures (1450 ºC, 1500 ºC, 1550 ºC, 1600 ºC) for 5 hours under the reducing atmosphere. The powder was melt when the temperature was over 1600 ºC. The heating rate was 8º C/min for T1400 º C. The cooling rate was 5ºC /min until T
