CAO Wangsheng ^{1, 2}, WANG Guilu ^{2, 4}, ZHANG Zhiyong ^{2, 4}, ZHENG Xigui ^{2, 5}, LU Yanna ^{2, 4},

KONG Yuqiang ^{2, 4}, MA Yuelong ^{3, 6}, HAO Yongxing ^{2, 4}

(1. School of Mechanical and Electrical Engineering, Henan Institute of Science and Technology, Xinxiang 453003, Henan, China;

2. School of Mechanical Engineering, Zhengzhou University of Science and Technology, Zhengzhou 450064, Henan, China; 3. School of Mechanical and Electrical Engineering, Henan University of Technology, Zhengzhou 450001, Henan, China; 4. Zhengzhou Advanced Manufacturing Engineering Research Center of Key Parts for Dental Implant, Zhengzhou 450064, Henan, China; 5. Henan Digital Intelligent Equipment Engineering Research Center, Zhengzhou University of Science and Technology, Zhengzhou 450064,

Henan, China; 6. SongShan Laboratory, Zhengzhou 450046, Henan, China)

Extended abstract:

[Background and purposes] Laser lighting, as a new generation of solid-state lighting technology, has demonstrated extensive application prospects in fields, such as special lighting and high-end displays, due to its advantages of small size, high brightness and good directionality. However, this advancement also imposes higher requirements on the comprehensive performance of phosphor conversion materials. The traditional encapsulation materials composed of “organic resin+phosphor” are prone to aging and failure under high laser power due to excessive temperature. Luminescent glass, with its simple preparation process, low cost and easily tunable spectrum, is regarded as one of the most promising fluorescent conversion materials. Nevertheless, the current white light laser lighting based on luminescent glass still faces challenges, including low Color Rendering Index (CRI) and high Correlated Color Temperature (CCT), failing to meet the stringent color quality requirements for high-quality lighting applications. To address these issues, this study was aimed to develop a luminescent glass material system with high CRI, suitable CCT and excellent thermal stability, through optimizing material design and preparation processes. Specifically, based on GdYAG:Ce³⁺ phosphor, CASN:Eu²⁺ phosphor was introduced for mixing, with the expectation of effectively improving the white light quality through spectral complementarity, while their microstructure, luminescence properties and thermal stability were systematically studied. In this study, experimental evidence and theoretical reference were provided for the design and preparation of highperformance phosphor conversion materials for laser lighting applications.

[Methods] A series of luminescent glass samples, consisting of GdYAG:Ce³⁺ and its mixture with CASN:Eu²⁺, were fabricated via a one-step sintering approach. Firstly, commercial GdYAG:Ce³⁺ phosphor and low-melting-point glass powder were mixed and ground uniformly in various mass ratios (6 wt.% to 14 wt.%), followed by sintering at 430 ℃ in nitrogen atmosphere to fabricate the luminescent glass. While maintaining a total phosphor content of 10 wt.%, the mass ratio of GdYAG:Ce³⁺ to CASN:Eu²⁺ was adjusted from 98 wt.%+2 wt.% to 90 wt.%+10 wt.%, leading to a series of mixed samples. The phase composition, micromorphology and elemental distribution of the samples were systematically characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Photoluminescence spectrum, excitation spectrum and variable temperature emission spectrum were measured by using a fluorescence spectrometer. Finally, the CRI, CCT and luminous flux (LF) were measured under 450 nm blue laser excitation by means of a home-built integrating sphere spectral testing system.

[Results] The GdYAG:Ce³⁺ phosphor was uniformly dispersed within the glass matrix, with its crystal structure remaining intact, while no significant interfacial reaction or impurity phase formation was observed. In the mixed samples, GdYAG:Ce³⁺ and CASN:Eu²⁺ coexisted in two distinct phases with clear elemental distribution, confirming their stable combination in the matrix. Under 450 nm laser excitation, the luminescence intensity of the GdYAG:Ce³⁺ sample increased with increasing content of GdYAG:Ce³⁺, while the CCT gradually decreased and the CRI first increased and then decreased. When the GdYAG:Ce³⁺ content was 10 wt.%, the sample achieved the optimal color rendering performance, with a CRI of 78.1 and a CCT of 5282 K. After introducing the CASN:Eu²⁺ red phosphor, the spectral coverage of the mixed sample was effectively broadened, while the addition of the red component significantly improved the white-light color quality. When the mass ratio of GdYAG:Ce³⁺ to CASN:Eu²⁺ was 94 wt.%+6 wt.%, the sample exhibited the highest comprehensive performance under 2.4 W laser excitation. The CRI was increased to 83, the CCT was decreased to 3983 K and the CIE chromaticity coordinates were shifted toward the warm-white region, resulting in a softer and more natural white-light visual appearance. The mixed sample can maintain 62.87% of its room-temperature luminescence intensity at a high temperature of 423 K, providing a material foundation for long-term stable operation under high-power laser lighting.

[Conclusions] A series of luminescent glass samples, GdYAG:Ce³⁺ and its mixture with CASN:Eu²⁺, were prepared by using a one-step sintering method. The effects of phosphor ratio on microstructure, luminescence properties and thermal stability were systematically studied. By optimizing the mixing ratio, the spectral balance between blue light conversion and red light compensation can be effectively reconciled, achieving a synergistic improvement in CRI and CCT. Under the optimal ratio, the sample exhibits a high CRI of 83, a favorable CCT of 3983 K and excellent luminescence retention at elevated temperatures, significantly improving the light color quality and practical reliability of luminescent glass for laser lighting. This work is expected to not only provide a feasible material design and processing strategy for developing high-performance luminescent glass converters suitable for high-quality laser lighting, but also further expand the application prospects of luminescent glass in the field of solid-state lighting. It holds positive reference value for advancing the development of next-generation white laser lighting devices featuring high power and high light quality.

Key words: laser lighting; luminescent glass; color rendering index; correlated color temperature; luminescent properties