Protected-annealing regulated defects to improve optical properties and luminescence performance of Ce:YAG transparent ceramics for white LEDs

Sun, Bingheng; Zhang, Le; Zhou, Tianyuan; Shao, Cen; Zhang, Lei; Ma, Yuelong; Yao, Qing; Jiang, Zhigang; Selim, F. A.; Chen, Hao

doi:10.1039/c8tc06600k

Cited by 79 publications

(35 citation statements)

References 48 publications

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“…[ 1–7 ] The most widely used SSL is white light‐emitting diodes (WLEDs) structured by blue LED chips and yellow‐emitting Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce 3+ ) phosphors. [ 8–14 ] But the “efficiency droop” of blue LEDs limit the development in the field of high‐power lighting. [ 15,16 ] Laser diodes look like a perfect successor due to the merits of smaller size, higher brightness, faster switching, and especially a higher conversion efficiency even at an ultrahigh‐driven power density, which is much better than the performance of LEDs.…”

Section: Figurementioning

confidence: 99%

“…To obtain a high quality YAG:Ce 3+ TCP, TEOS is usually added as flux in the sintering process. [11,12,36] Inevitably, Si 4+ will enter the YAG TCP and introduce defects due to the charge mismatch between Si 4+ and Al 3+ . Thus the luminous efficiency (≈170 lm W −1 ) is not high enough.…”

Section: Doi: 101002/adma201907888mentioning

confidence: 99%

“…[1][2][3][4][5][6][7] The most widely used SSL is white light-emitting diodes (WLEDs) structured by blue LED chips and yellow-emitting Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce 3+ ) phosphors. [8][9][10][11][12][13][14] But the "efficiency droop" of blue LEDs limit the development in the field of high-power best value in TCPs reported now. These results demonstrate that YAG:Ce 3+ TCPs optimized in a fitting strategy will brighten once again in the next-generation LD lighting.…”

Section: Doi: 101002/adma201907888mentioning

confidence: 99%

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YAG:Ce³⁺ Transparent Ceramic Phosphors Brighten the Next‐Generation Laser‐Driven Lighting

et al. 2020

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Y3Al5O12:Ce3+ (YAG:Ce3+) transparent ceramic phosphors (TCPs) are regarded as the most promising luminescent converter for laser‐driven (LD) lighting. High‐quality YAG:Ce3+ TCPs are still urgent for high efficiency LD lighting devices. YAG:Ce3+ TCPs in a vacuum ambience by using nano‐sized raw materials are prepared. Controlling defects by adding nano‐sized MgO and SiO2 simultaneously enables a high transmittance nearly 80%. After annealing in air furthermore, the luminous efficiency is enhanced greatly from 106 to 223 lm W−1, which is the best result reported now for LD lighting. These results demonstrate that the optimizing YAG:Ce3+ TCPs in a fitting strategy will brighten once again in the next‐generation LD lighting. Based on scanning electron microscopy (SEM) coupled with a cathodoluminescence system, defects and Ce3+ distributions in grains are identified directly for the first time.

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Section: Figurementioning

confidence: 99%

Section: Doi: 101002/adma201907888mentioning

confidence: 99%

Section: Doi: 101002/adma201907888mentioning

confidence: 99%

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YAG:Ce³⁺ Transparent Ceramic Phosphors Brighten the Next‐Generation Laser‐Driven Lighting

et al. 2020

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“…[24,25] Great attentions focus on the yellow Y 3 Al 5 O 12 :Ce resulted from oxygen vacancies. [42] After annealing in air, color centers disappear and CPs change into bright yellow. Correspondingly, the emission changes from yellow-green to green for unannealed and annealed CPs under 365 nm UV light.…”

Section: Introductionmentioning

confidence: 99%

High Efficiency Green‐Emitting LuAG:Ce Ceramic Phosphors for Laser Diode Lighting

Liu

et al. 2021

Advanced Optical Materials

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CP because it can be achieved white light directly combined with blue LDs. [19][20][21][22][23] Recently, yellow/green/red CPs were discovered to rich spectral components and modify the color quality for white LD lighting. [24][25][26][27][28] Lu 3 Al 5 O 12 :Ce (LuAG:Ce) is a well-known green color converter due to its high thermal stability and high efficiency. [29][30][31] LuAG:Ce CPs are regarded as the best type that is robust irradiated by high-power LD light (15-25 W, up to 49 W mm −2 ). [32][33][34][35][36] The luminous efficacy (LE) of LuAG:Ce CPs in LD lighting has been greatly enhanced from about 54 to 205 lm W −1 by designing geometric structures and introducing scattering centers. [32][33][34][35][36][37] However, LuAG CPs are usually sintered higher than 1700 °C, SiO 2 or TEOS is commonly added as sintering aid. [32][33][34] SiO 2 begins to react with the garnets at about 1400 °C, [38] and defects are inevitable due to the size and charge mismatches between Si 4+ and Lu 3+ /Al 3+ . [39] The defects decline the thermal stability that is directly related with the performance of LuAG:Ce in LD lighting. [19] Thus, how to depress the defect and maintain the high thermal stability is the hardest challenge in fabricating LuAG CPs and achieving high LE value.As we know, heavy atom can depress lattice relaxation and improve thermal stability. [40,41] Considering valence state, in this work, we design the Ba 2+ -Si 4+ pair to substitute the Lu 3+ -Al 3+ pair to keep charge balance. SiO 2 powder are used as sintering aid and BaCO 3 provides the Ba 2+ to control defects and adjust thermal stability. Combining annealing process in air to eliminate oxygen vacancies, LuAG:Ce CPs manifest high LE of 213.7-216.9 lm W −1 in LD lighting, which is the best performance up to date. These results demonstrate that suitable strategies further improve LuAG:Ce CPs properties, thus in turn making great contributions to high-brightness and efficient white LD lighting. The tunable thermal stability by Ba 2+ -Si 4+ pairs and relationships with performance of LuAG:Ce CPs in LD lighting are detailed in present report. Results and DiscussionNominal compositions of Lu 2.995−x Ba x Al 5−x Si x O 12 :0.005Ce (LuAG:0.5%Ce+xBS, x = 0, 0.005, 0.01, 0.015, and 0.02) CPs sintered in vacuum are dark yellow (unannealed samples in Figure 1a), especial for x = 0, due to a lot of color centers Lu 3 Al 5 O 12 :Ce 3+ (LuAG:Ce 3+ ) ceramic phosphors (CPs) are regarded as the most promising green color converter and play a key role in high quality white light in the next-generation laser diode (LD) lighting. High efficient LuAG:Ce 3+ CPs are still urgent for high luminous efficacy (LE) LD lighting devices. By designing the Ba 2+ -Si 4+ pair to keep charge balance and annealing in air to remove oxygen vacancy defects, the luminescent properties of LuAG:Ce CPs are greatly enhanced. The LE is promoted to 216.9 lm W −1 , which is the best performance of LuAG:Ce in LD lighting so far. Strategies for optimizing LuAG:Ce 3+ CPs are detailed. It is believed ...

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“…More importantly, various composite and complex structures can be actualized by combining a plurality of existing ceramic forming technologies . Obviously, compared with traditional dry pressing, the colloidal processing, which is represented by gelcasting, has the advantages of simple processing, high green body density and easy to form a large or complex shape . It can offer the great feasibility and flexibility for the design of laser gain media in various applications, especially for the “ultimate‐dimension” (such as ultra‐long) laser ceramics that have the problems of weak strength, susceptible cracking, and easy fracture.…”

Section: Introductionmentioning

confidence: 99%

Viscoelastic behaviors and drying kinetics of different aqueous gelcasting systems for large Nd: YAG laser ceramics rods

Yao

Gao

et al. 2020

J Am Ceram Soc

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Large and nondeforming Nd: YAG ceramic prepared by wet forming is of great importance as gain medium to obtain high‐power solid‐state lasers. However, it is difficult to achieve high‐quality laser ceramics due to insufficiency of the in‐depth understanding of transformation mechanism of gels viscoelasticity and effective control means during drying process. In this work, the rheological behaviors, viscoelastic characteristics, and mechanical strengths in classical acrylamide (AM) and novel Isobam (PIBM) gelcastings were systematically compared to explore the suitable route for the large‐sized 2% Nd: YAG transparent ceramics with high aspect ratio (>10). AM system exhibited a higher complex viscosity (1.82 × 105 Pa s), a shorter gel time (92.9 seconds), and a higher flexural strength (about 24.46 MPa) than PIBM system, and especially its ability to quickly gel was beneficial to the homogeneity of green body. In addition, the order of drying rates of wet gels in four drying media was observed as follows: 55℃ hot air> ethanol> solid desiccant> PEG‐11000 and the moisture diffusion coefficients were calculated and simulated to offer the deep consideration of drying kinetics. The “ethanol + 55℃ hot air” was regarded as an effective composite drying method to eliminate defect and to achieve φ8 mm × 160 mm Nd: YAG ceramic with the in‐line transmittance of 83% @1064 nm. Therefore, not only the cognition of gel process, but also the defects control strategy is proposed. More importantly, this work greatly promotes the application of wet forming and laser ceramics in high‐power lasers.

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Protected-annealing regulated defects to improve optical properties and luminescence performance of Ce:YAG transparent ceramics for white LEDs

Abstract: The redox state of cerium and elimination of defects were synergistically regulated by a protected-annealing treatment in Ce:YAG transparent ceramics.

Cited by 79 publications

References 48 publications

YAG:Ce³⁺ Transparent Ceramic Phosphors Brighten the Next‐Generation Laser‐Driven Lighting

YAG:Ce³⁺ Transparent Ceramic Phosphors Brighten the Next‐Generation Laser‐Driven Lighting

High Efficiency Green‐Emitting LuAG:Ce Ceramic Phosphors for Laser Diode Lighting

Viscoelastic behaviors and drying kinetics of different aqueous gelcasting systems for large Nd: YAG laser ceramics rods

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Protected-annealing regulated defects to improve optical properties and luminescence performance of Ce:YAG transparent ceramics for white LEDs

Abstract: The redox state of cerium and elimination of defects were synergistically regulated by a protected-annealing treatment in Ce:YAG transparent ceramics.

Cited by 79 publications

References 48 publications

YAG:Ce3+ Transparent Ceramic Phosphors Brighten the Next‐Generation Laser‐Driven Lighting

YAG:Ce3+ Transparent Ceramic Phosphors Brighten the Next‐Generation Laser‐Driven Lighting

High Efficiency Green‐Emitting LuAG:Ce Ceramic Phosphors for Laser Diode Lighting

Viscoelastic behaviors and drying kinetics of different aqueous gelcasting systems for large Nd: YAG laser ceramics rods

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Product

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YAG:Ce³⁺ Transparent Ceramic Phosphors Brighten the Next‐Generation Laser‐Driven Lighting

YAG:Ce³⁺ Transparent Ceramic Phosphors Brighten the Next‐Generation Laser‐Driven Lighting