Recently, optical technology progress in a wide range of applications, and still demands the further development. Since conventional crystal materials face some of the limitations, these issues require new optical single crystals. Here, novel single crystals, which have advantageous characteristics toward the above demands, will be introduced.

β-Ga₂O₃ exhibits the largest band gap (Eg = 4.8 eV) among the transparent conductive oxides (TCOs). 1 and 2 inch size β-Ga₂O₃ single crystals were grown by the FZ and EFG techniques, respectively. Epitaxial growth of c-plane wurtzite InGaN-MQW on a-plane β-Ga₂O₃ was realized by the MOCVD technique. Vertical structured blue LEDs on β-Ga₂O₃ with different packaging styles were demonstrated.

Tb₃(Sc_1-xLu_x)₂Al₃O₁₂ (TSLAG) single crystals with 1 inch in diameter have been designed and grown for high-power laser machinery. TSLAG showed a higher visible transparency and a larger Faraday rotation than Tb₃Ga₅O₁₂. TSLAG is therefore very promising material in particular for new magneto-optical isolator applications in the VIS-NIR wavelength.

High-brightness LEDs (HB-LEDs) are facing several difficulties such as temperature- and photo-degradation of Ce:YAG powder phosphor and epoxy dome containing them. A new concept of white LEDs based on Ce,Gd:YAG single crystal phosphor plates (SCPPs), which are able to overcome the above issues, is proposed. SCPPs demonstrated excellent thermal stability with no temperature quenching, high values of luminous efficacy and increased quantum efficiency.

Acknowledgements: Authors would like to thanks to Mr. K. Aoki of Koha Co., Ltd., Dr. D. Inomata of Tamura Corp., and Mr. T. Hatanaka, Mr. A. Funaki, Mr. T. Kizaki and Mr. K. Naoe of Fujikura Ltd., for the collaboration.

Fig.: 2-inch size β-Ga₂O₃ single crystal wafer grown by the EFG technique (left) and magneto-optical Tb₃(Sc_1-xLu_x)₂Al₃O₁₂ single crystal grown by the Czochralski technique (right).

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