Next Article in Journal
A Robust Tracking Method for Multiple Moving Targets Based on Equivalent Magnetic Force
Next Article in Special Issue
Effects of Voids on Thermal Fatigue Reliability of Solder Joints on Inner Rings in Ball Grid Array Packaging by Finite Element Analysis
Previous Article in Journal
A Heterogeneity-Aware Replacement Policy for the Partitioned Cache on Asymmetric Multi-Core Architectures
Previous Article in Special Issue
Automatic Illumination Control Method for Indoor Luminaires Based on Multichromatic Quantum Dot Light-Emitting Diodes
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:

Fabrication of LuAG:Ce3+ Ceramic Phosphors Prepared with Nanophosphors Synthesized by a Sol-Gel-Combustion Method

School of Advanced Materials Science and Engineering, SungKyunKwan University, Suwon 16419, Republic of Korea
Lighting Materials & Components Research Center, Korea Photonics Technology Institute, Gwangju 61007, Republic of Korea
Department of Electronic Materials and Devices Engineering, Soonchunhyang University, Asan City 31538, Republic of Korea
Department of Display Materials Engineering, Soonchunhyang University, Asan City 31538, Republic of Korea
Authors to whom correspondence should be addressed.
These authors contributed equally to this work.
Micromachines 2022, 13(11), 2017;
Submission received: 24 October 2022 / Revised: 10 November 2022 / Accepted: 17 November 2022 / Published: 18 November 2022
(This article belongs to the Special Issue Advanced Technologies in Electronic Packaging)


The aim of this study was to investigate properties of ceramic phosphors fabricated using nano Lu3Al5O12:Ce3+ phosphors produced with a sol-gel-combustion method. These nano Lu3Al5O12:Ce3+ phosphors had a size of about 200 nm, leading to high density when fabricated as a ceramic phosphor. We manufactured ceramic phosphors through vacuum sintering. Alumina powder was added to improve properties. We mounted the manufactured ceramic phosphor in a high-power laser beam projector and drove it to determine its optical performance. Ceramic phosphor manufactured according to our route will have a significant impact on the laser-driven lighting industry.

1. Introduction

Light emitting diodes (LEDs) have fascinated the lighting market for a long time due to their advantages, such as low power consumption, high efficiency, and long reliability [1,2,3,4,5]. However, the constantly developing and evolving technology market demands brighter and more efficient products for better performance. LEDs cannot escape the “efficiency droop” phenomenon that occurs in high-current driving [6,7,8]. For this reason, the current trend in the lighting market is selecting laser diodes as strong candidates for the next generation of light sources. Laser diodes (LDs) are high-power light sources that can achieve excellent performance, where output power increases linearly with rising driving current. They have characteristics such as fast conversion, long throw distance, and high brightness [6,9,10,11]. The combination of laser diodes and converters is driven by a remote type that is unlike the general in-chip LED package, because heat generation is inevitable due to a high output. Types of remote phosphors typically include phosphor in glass, single-crystal phosphor, and ceramic phosphor [12,13,14,15]. Among these types, ceramic phosphors have been studied a great deal in the laser lighting field due to their excellent properties, such as a high light extraction effect, conversion efficiency, thermal conductivity, and thermal shock resistance [16,17].
Garnet-structured oxide phosphors are well known as light converters because of their high thermal properties and their high light efficiency [18]. In addition, their optical properties are not destroyed by high-temperature impact in the process of manufacturing powder into ceramics. A typical example of such a garnet-structured oxide phosphor is a cerium-doped yttrium aluminum garnet phosphor that is used as a material for realizing white light in laser-lighting applications [19]. Lu3Al5O12:Ce3+ (LuAG: Ce3+) phosphor, which has the same garnet structure in which lutetium is substituted for yttrium, is a well-known type of green phosphor [20,21]. This green LuAG:Ce3+ phosphor is manufactured as a ceramic phosphor. It has been widely applied to blue laser-based projection technology. As projection technology is accompanied by high output and long operation time, it is necessary to improve thermal characteristics and light-extraction efficiency of the optical converter used [22,23]. To improve these two properties, the size of the phosphor particle for densification and the addition of functional materials for improving thermal properties can play important roles [24,25].
In this study, nano-sized phosphors were prepared using the sol-gel-combustion method to improve properties of LuAG:Ce3+ ceramic phosphor. The sol-gel-combustion synthesis method has the advantage that it can not only manufacture the phosphor in nanosize, but also enable mass production. Furthermore, we prepared a ceramic phosphor by adding alumina to improve thermal properties. It exhibited an excellent value of 2475 lumens with electroluminescence intensity improved by 6.5%, compared with a commercial sample.

2. Materials and Methods

Nano LuAG:Ce3+ phosphor was prepared via the sol-gel-combustion method. First, 20 g of lutetium oxide was completely dissolved in 200 mL of 70% nitric acid. The remaining raw materials, such as citric acid, aluminum nitrate, cerium nitrate, and propylene glycol, were also dissolved in nitric acid. The completely dissolved solution was adjusted to pH 6.0 with aqueous ammonia. The prepared solution was evaporated while boiling on a hot plate and heat treated at 300 °C to prepare ash. Finally, the ash was put in a mortar, ground, and pulverized. It was then placed in an alumina crucible and calcined at 1400 °C to prepare a nano LuAG:Ce3+ phosphor. The alumina (Al2O3) used in the manufacture of ceramics was purchased from Sigma-Aldrich. The synthesis method is described in Figure 1.
Ceramic phosphor was manufactured through conventional pellet-forming and vacuum-sintering processes. Nano LuAG:Ce3+ phosphor and alumina powder were mixed with acetone in a mortar at a 1:1 ratio. The mixed powder was filled in a mold to make pellets using a uniaxial pressure. Pellets were packed in a silicone wrapper and isotropically pressed under 2000 bar with a cold isostatic press. Densified pellets were put into a BN crucible and sintered at 1800 °C in a vacuum atmosphere. After grinding and dicing the sintered body, it was finally oxidized in an atmospheric atmosphere at 1400 °C to remove carburization on the surface and inside. Commercial ceramic phosphors used in laser beam projectors were used as a comparison group.
Electroluminescence spectra were measured by double integrating spheres (PSI Co., Ltd./Korea) under blue laser at 450 nm. The surface morphology of samples was measured by field emission scanning electron microscopy (FE-SEM, JEOL, JSM-7600F). XRD patterns of the LuAG:Ce3+ powder and ceramic phosphor were performed over the range of 20° ≤ 2θ ≤ 80° using a diffractometer (XRD, D8 Advance, Bruker) operated at 40 kV and 40 mA with the CuKα target. A ceramic phosphor was attached to the copper plate for laser projection. Illuminance (lx) was measured by attaching a ceramic phosphor to a handmade beam projector.

3. Results

The SEM images of nano LuAG:Ce3+ phosphor particles prepared by the sol-gel-combustion method are shown in Figure 2. The SEM results confirmed that a single particle included in the aggregated particle was about 200 nm in size. The combination of the instantaneous high temperature during combustion and the release of large amounts of volatiles from the mixture was prone to particle aggregation. However, because the final application of the material was a ceramic aimed at high densification, aggregation between nanoparticles was not disturbed at all.
The SEM and EDS results of the top view of the ceramic phosphor shown in Figure 3a–c were performed for elemental analysis of Al2O3 and LuAG:Ce3+. In Figure 3a, clear contrast and interface were observed between Al2O3 and LuAG:Ce3+ phosphor, indicating that further interaction between particles did not occur. The EDS results in Figure 3b,c showed bright and dark particles confirmed to be LuAG:Ce3+ and Al2O3 particles, respectively. The SEM images also suggested that the ceramic phosphor was highly densified. Thus, the intrinsic characteristics of each composition were well maintained after coarsening and densification. Therefore, high-quality ceramic phosphor was successfully fabricated.
The results of the analysis of photoluminescence (PL) and PL excitation of nano LuAG:Ce3+ phosphors prepared by the method depicted in Figure 1 are displayed in Figure 4a. The XRD pattern shown in Figure 4b suggested that LuAG:Ce3+ ceramic phosphor fabricated by mixing with Al2O3 powder coexisted without collapsing. The reason that the phases could be maintained without collapsing the grains, even after sintering at a high temperature of 1700 °C, was that the thermal expansion coefficients of LuAG:Ce3+ and Al2O3 particles were similar [26]. Alumina with a hexagonal structure is well known for its high thermal stability and internal light-scattering-inducing properties. Therefore, if alumina is located in the manufactured ceramic phosphor, an improvement in optical properties and robust thermal properties can be expected during laser irradiation. As shown in Figure 4c, the specimen immediately after vacuum sintering was carburized with a blackish color. This carburizing phenomenon is inevitable, because the main component inside the vacuum sintering furnace is carbon. A carburized specimen can be easily removed through oxidation treatment at 1400 °C. It has an excellent color and an improved PL intensity. To confirm the performance of the manufactured ceramic phosphor, we analyzed the EL spectrum with a comparative specimen. The results are shown in Figure 4d. The prepared ceramic phosphor obtained a maximum emission intensity that was 6.5% higher than that of the comparative group. The nano LuAG:Ce3+ phosphor fabricated by our combustion synthesis method was proven to be very effective in ceramic applications.
To evaluate the optical performance of the LuAG:Ce3+ ceramic phosphor applied to a laser-driven projection system, a prototype was fabricated, as shown in Figure 5a. It was confirmed that the blue light from the laser light source was successfully converted into green light. Subsequently, in order to measure the projection uniformity according to the location, five points were designated in the projected screen and the illuminance was measured. The measured illuminance values for each part are shown in the inset table on the left of Figure 5b. The mean value and the standard error of the mean were 2414 and 18.76 lx, respectively, indicating uniform illumination. The right inset of Figure 5b plots the spectrum of green-converted light by LuAG:Ce3+ ceramic phosphor on the CIE chromaticity diagram. The calculated chromaticity coordinate was (0.3218, 0.6389), which was located in the green region. This suggests that LuAG:Ce3+ ceramic phosphor is a significant potential candidate as a green color conversion material for the laser-driven projection system.

4. Conclusions

We prepared a ceramic phosphor that can be applied to laser-driven projection and lighting using nano LuAG:Ce3+ phosphors synthesized by a sol-gel-combustion method. We added alumina as a functional material to improve thermal and optical properties. We built a blue laser-based beam projector and installed the manufactured ceramic phosphor as an optical converter and drove it. Its optical properties were detected with a measuring instrument at a distance of 1.5 m in a dark room. As a result, the average value of illuminance measured at five designated locations was 2414 lx. This is an impressive result for a high-power, high-brightness laser-based projection technology.

Author Contributions

Writing—draft, S.B.K., S.H.C., and J.H.Y.; conceptualization, S.B.K., S.H.C., and S.Y.L.; visualization, S.B.K. and J.H.Y.; theoretical interpretation, B.Y.K., H.J.J., W.H.K., and J.P.K.; review and editing: B.K.K., D.H.Y., and Y.H.S. All authors have read and agreed to the published version of the manuscript.


This research was financially supported by the Ministry of Trade, Industry and Energy (MOTIE) and by the Korea Institute for Advancement of Technology (KIAT) through the International Cooperative R&D program. (Project No. P0022394). This work was also supported by the Technology Development Program (S2958896) funded by the Ministry of SMEs and Startups (MSS, Korea). This research was further supported by the “Leaders in Industry-university cooperation 3.0 project” through the National Research Foundation of Korea (NRF) funded by the Ministry of Education. Finally, this research was supported by the “Regional Innovation Strategy (RIS)” through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE) (2022RIS-004).

Conflicts of Interest

The authors declare no conflict of interest.


  1. Pimputkar, S.; Speck, J.S.; DenBaars, S.P.; Nakamura, S. Prospects for LED lighting. Nat. Photonics 2009, 3, 180–182. [Google Scholar] [CrossRef]
  2. Schubert, E.F.; Kim, J.K. Solid-State Light Sources Getting Smart. Science 2005, 308, 1274–1278. [Google Scholar] [CrossRef] [PubMed]
  3. Liu, Y.; Silver, J.; Xie, R.-J.; Zhang, J.; Xu, H.; Shao, H.; Jiang, J.; Jiang, H. An excellent cyan-emitting orthosilicate phosphor for NUV-pumped white LED application. J. Mater. Chem. C 2017, 5, 12365–12377. [Google Scholar] [CrossRef]
  4. Tsao, J.Y.; Crawford, M.H.; Coltrin, M.E.; Fischer, A.J.; Koleske, D.D.; Subramania, G.S.; Wang, G.T.; Wierer, J.J.; Karlicek, R.F. Toward Smart and Ultra-efficient Solid-State Lighting. Adv. Opt. Mater. 2014, 2, 809–836. [Google Scholar] [CrossRef]
  5. Wang, L.; Xie, R.J.; Suehiro, T.; Takeda, T.; Hirosaki, N. Down-Conversion Nitride Materials for Solid State Lighting: Recent Advances and Perspectives. Chem. Rev. 2018, 118, 1951–2009. [Google Scholar] [CrossRef]
  6. 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, 963–993. [Google Scholar] [CrossRef]
  7. Liu, Z.; Wei, T.; Guo, E.; Yi, X.; Wang, L.; Wang, J.; Wang, G.; Shi, Y.; Ferguson, I.; Li, J. Efficiency droop in InGaN/GaN multiple-quantum-well blue light-emitting diodes grown on free-standing GaN substrate. Appl. Phys. Lett. 2011, 99, 091104. [Google Scholar] [CrossRef]
  8. 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, 183507. [Google Scholar] [CrossRef] [Green Version]
  9. Chi, Y.C.; Hsieh, D.H.; Lin, C.Y.; Chen, H.Y.; Huang, C.Y.; He, J.H.; Ooi, B.; DenBaars, S.P.; Nakamura, S.; Kuo, H.C.; et al. Phosphorous Diffuser Diverged Blue Laser Diode for Indoor Lighting and Communication. Sci. Rep. 2015, 5, 18690. [Google Scholar] [CrossRef] [Green Version]
  10. KDenault, A.; Cantore, M.; Nakamura, S.; DenBaars, S.P.; Seshadri, R. Efficient and stable laser-driven white lighting. AIP Adv. 2013, 3, 072107. [Google Scholar] [CrossRef]
  11. George, A.F.; Al-waisawy, S.; Wright, J.T.; Jadwisienczak, W.M.; Rahman, F. Laser-driven phosphor-converted white light source for solid-state illumination. Appl. Opt. 2016, 55, 1899–1905. [Google Scholar] [CrossRef]
  12. 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, A215–A221. [Google Scholar] [CrossRef]
  13. Krasnoshchoka, A.; Thorseth, A.; Dam-Hansen, C.; Corell, D.D.; Petersen, P.M.; Jensen, O.B. Investigation of Saturation Effects in Ceramic Phosphors for Laser Lighting. Materials 2017, 10, 1407. [Google Scholar] [CrossRef] [Green Version]
  14. Lin, H.; Wang, B.; Xu, J.; Zhang, R.; Chen, H.; Yu, Y.; Wang, Y. Phosphor-in-glass for high-powered remote-type white AC-LED. ACS Appl. Mater. Interfaces 2014, 6, 21264–21269. [Google Scholar] [CrossRef]
  15. 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, 1182–1186. [Google Scholar] [CrossRef]
  16. 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, 8648–8654. [Google Scholar] [CrossRef]
  17. Liu, S.; Sun, P.; Liu, Y.; Zhou, T.; Li, S.; Xie, R.J.; Xu, X.; Dong, R.; Jiang, J.; Jiang, H. Warm White Light with a High Color-Rendering Index from a Single Gd3Al4GaO12:Ce3+ Transparent Ceramic for High-Power LEDs and LDs. ACS Appl. Mater. Interfaces 2019, 11, 2130–2139. [Google Scholar] [CrossRef]
  18. Xiao, Y.; Xiao, W.; Zhang, L.; Hao, Z.; Pan, G.-H.; Yang, Y.; Zhang, X.; Zhang, J. A highly efficient and thermally stable green phosphor (Lu2SrAl4SiO12:Ce3+) for full-spectrum white LEDs. J. Mater. Chem. C 2018, 6, 12159–12163. [Google Scholar] [CrossRef]
  19. Yao, Q.; Hu, P.; Sun, P.; Liu, M.; Dong, R.; Chao, K.; Liu, Y.; Jiang, J.; Jiang, H. YAG:Ce3+ Transparent Ceramic Phosphors Brighten the Next-Generation Laser-Driven Lighting. Adv. Mater. 2020, 32, e1907888. [Google Scholar] [CrossRef]
  20. 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. [Google Scholar] [CrossRef]
  21. Park, K.; Kim, T.; Yu, Y.; Seo, K.; Kim, J. Y/Gd-free yellow Lu3Al5O12:Ce3+ phosphor for white LEDs. J. Lumin. 2016, 173, 159–164. [Google Scholar] [CrossRef]
  22. Johnson, R.B.; Mahajan, V.N.; Thibault, S.; Daniels, M.; Mehl, O.; Hartwig, U. Laser-activated remote phosphor light engine for projection applications. In Proceedings of the Current Developments in Lens Design and Optical Engineering XVI, San Diego, CA, USA, 9–13 August 2015. [Google Scholar]
  23. Yue, X.; Xu, J.; Lin, H.; Lin, S.; Li, R.; Wang, B.; Huang, Q.; Wang, P.; Sui, P.; Cheng, Y.; et al. β-SiAlON:Eu2+ Phosphor-in-Glass Film: An Efficient Laser-Driven Color Converter for High-Brightness Wide-Color-Gamut Projection Displays. Laser Photonics Rev. 2021, 15, 2100317. [Google Scholar] [CrossRef]
  24. Liu, Z.; Li, S.; Huang, Y.; Wang, L.; Zhang, H.; Jiang, R.; Huang, F.; Yao, X.; Liu, X.; Huang, Z. The effect of the porosity on the Al2O3-YAG:Ce phosphor ceramic: Microstructure, luminescent efficiency, and luminous stability in laser-driven lighting. J. Alloys Compd. 2019, 785, 125–130. [Google Scholar] [CrossRef]
  25. Zhao, H.; Li, Z.; Zhang, M.; Li, J.; Wu, M.; Li, X.; Chen, J.; Xie, M.; Li, J.; Sun, X. High-performance Al2O3–YAG:Ce composite ceramic phosphors for miniaturization of high-brightness white light-emitting diodes. Ceram. Int. 2020, 46, 653–662. [Google Scholar] [CrossRef]
  26. Aggarwal, R.L.; Ripin, D.J.; Ochoa, J.R.; Fan, T.Y. Measurement of thermo-optic properties of Y3Al5O12, Lu3Al5O12, YAlO3, LiYF4, LiLuF4, BaY2F8, KGd(WO4)2, and KY(WO4)2 laser crystals in the 80–300K temperature range. J. Appl. Phys. 2005, 98, 103514.1–103514.14. [Google Scholar] [CrossRef]
Figure 1. Schematic of the manufacturing process of nano phosphors through sol-gel combustion.
Figure 1. Schematic of the manufacturing process of nano phosphors through sol-gel combustion.
Micromachines 13 02017 g001
Figure 2. SEM images of LuAG:Ce3+ nanophosphor prepared by sol-gel combustion method.
Figure 2. SEM images of LuAG:Ce3+ nanophosphor prepared by sol-gel combustion method.
Micromachines 13 02017 g002
Figure 3. (a) Cross-sectional SEM image of the prepared ceramic phosphor; (b) and (c): point EDS spectra of LuAG:Ce3+ and Al2O3, respectively.
Figure 3. (a) Cross-sectional SEM image of the prepared ceramic phosphor; (b) and (c): point EDS spectra of LuAG:Ce3+ and Al2O3, respectively.
Micromachines 13 02017 g003
Figure 4. (a) PL and PLE of phosphor powder; (b) XRD patterns of LuAG:Ce3+ phosphor powder and LuAG-Al2O3 ceramic phosphor; (c) PL and PLE before and after carburization removal of specimen; (d) EL spectra with comparative specimens.
Figure 4. (a) PL and PLE of phosphor powder; (b) XRD patterns of LuAG:Ce3+ phosphor powder and LuAG-Al2O3 ceramic phosphor; (c) PL and PLE before and after carburization removal of specimen; (d) EL spectra with comparative specimens.
Micromachines 13 02017 g004
Figure 5. (a) Image of a beam projector in operation with the manufactured ceramic phosphor mounted; (b) illumination measured at five designated locations at a distance of 1.5 m.
Figure 5. (a) Image of a beam projector in operation with the manufactured ceramic phosphor mounted; (b) illumination measured at five designated locations at a distance of 1.5 m.
Micromachines 13 02017 g005
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Kwon, S.B.; Choi, S.H.; Yoo, J.H.; Lee, S.Y.; Kim, B.Y.; Jeong, H.J.; Kim, W.H.; Kim, J.P.; Kang, B.K.; Yoon, D.H.; et al. Fabrication of LuAG:Ce3+ Ceramic Phosphors Prepared with Nanophosphors Synthesized by a Sol-Gel-Combustion Method. Micromachines 2022, 13, 2017.

AMA Style

Kwon SB, Choi SH, Yoo JH, Lee SY, Kim BY, Jeong HJ, Kim WH, Kim JP, Kang BK, Yoon DH, et al. Fabrication of LuAG:Ce3+ Ceramic Phosphors Prepared with Nanophosphors Synthesized by a Sol-Gel-Combustion Method. Micromachines. 2022; 13(11):2017.

Chicago/Turabian Style

Kwon, Seok Bin, Seung Hee Choi, Jung Hyeon Yoo, Seon Yeong Lee, Bo Young Kim, Ho Jung Jeong, Wan Ho Kim, Jae Pil Kim, Bong Kyun Kang, Dae Ho Yoon, and et al. 2022. "Fabrication of LuAG:Ce3+ Ceramic Phosphors Prepared with Nanophosphors Synthesized by a Sol-Gel-Combustion Method" Micromachines 13, no. 11: 2017.

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop