Formation of microstructure and optical characteristics of Al₂O₃/YAG:Ce eutectic obtained by HDC method

DOI: 10.62564/M4-YS1033

Yurii Siryk, Oleh Vovk, Leonid Gryn, Viacheslav Baranov, Sergii Nizhankovskyi

State Scientific Institution “Institute for Single Crystals” of National Academy of Sciences of Ukraine


Ce³⁺ doped directionally crystallized Al₂O₃/YAG eutectic composites show promise as fluorescent converters for powerful LED and LD white light sources [1]. The mechanical and optical characteristics of these composites depend on the dimensional and morphological parameters of the eutectic microstructure, which are influenced by the crystallization conditions and Ce impurity concentration. This work investigates the effect of crystallization rate and Ce concentration on the microstructure parameters of the Al₂O₃/YAG:Ce³⁺ eutectic obtained through the horizontal directional crystallization (HDC) method. The results indicate that Al₂O₃/YAG:Ce³⁺ eutectic is a proficient optical medium for light scattering. The shape of the elastic light scattering indicator depends on the sample thickness, the characteristic eutectic distance λₑᵤₜ, and the angle of incidence of the primary beam. The presence of Al₂O₃/YAG:Ce³⁺ eutectic texture with a cellular morphology obtained by directional crystallization causes these effects. It is important to consider these factors during converter manufacturing. The emission spectra of Al₂O₃/YAG:Ce³⁺ eutectic samples exhibit a broad emission band resulting from 5d¹ - 4f electronic transitions of the Ce³⁺ ion in the YAG matrix. The radiation intensity of the samples varies along the ingot due to an increase in Ce concentration from the beginning to the end of the ingot. Analysis of the emission peaks revealed that the eutectic morphology can increase the reabsorption of Ce³⁺ ion radiation, resulting in a shift of the luminescence maximum towards the red part of the spectrum. The Al₂O₃/YAG:Ce³⁺ eutectic samples obtained exhibit excellent lighting characteristics, with a luminous efficacy of 142 lm/W, a color rendering index of 72%, a correlated color temperature of 5120 K, and chromatic coordinates of x-0.3500 and y-0.400. Therefore, we recommend this eutectic as a phosphor for high-power white LEDs.

Keywords
eutectic, crystallization, microstructure, luminescence, phosphor

Acknowledgments
This study was supported by the Ministry of Education and Science of Ukraine, project No. 0123U102743 "Ensuring the development and the investigation of properties of eutectic composites from refractory oxides".

References
[1] Shakhno A, Zorenko T, Witkiewicz-Łukaszek S, Cieszko M, Szczepański Z, Vovk O, Nizhankovskyi S, Siryk Y, Zorenko Y. Ce³⁺ Doped Al₂O₃-YAG Eutectic as an Efficient Light Converter for White LEDs. Materials. 2023; 16(7)