Ce:GAGG and Al ₂ O ₃ −Ce:GAGG phosphor ceramics for laser-driven lighting: Effects of Ga ³⁺ substitution

Monophase Ce:Gd₃Al_5-xGa_xO₁₂ (Ce:GAGG) with x=0.5-3.0 and 50 vol% Al₂O₃−contained composite phosphor ceramics (PCs) were prepared in a pure oxygen atmosphere. The effects of Ga³⁺ substitution on their phase formation, microstructure, and luminescence properties were systematically investigated. For Ce:GAGG series samples, no additional phases were identified, the distribution of Ga between the octahedral (Al/Ga)₂ (0, 0, 0) and tetrahedral (Al/Ga)₃ (0.375, 0, 0.25) sites of the garnet phase was clarified; for Al₂O₃−Ce:GAGG composites, the exchange of Al and Ga elements between the phases of garnet Ga(Al,Ga)G and oxide (Al,Ga)₂O₃ was revealed, the transformation of (Al,Ga)₂O₃ from α- to κ-phase (x≥2.0) with the formation of elongated grains and their partial melting (x=3) was shown. This was also reflected in a less pronounced shift of the photoluminescence peak (PL) toward shorter wavelengths for the composite series in comparison with the monophase one: with an increase in x to 3.0, the shift in the position of the PL peak of intensity by 18 nm for Al₂O₃−Ce:GAGG was equivalent to that for Ce:GAGG at x=1.5. A phosphorescence phenomenon was found at x=2.5 and 3.0 for monophasic Ce:GAGG compositions. Under the excitation of 1 W 450 nm LDs in a reflection mode, 0.4 mm-thick Al₂O₃−Ce:GAGG with x=0.5-1.5 had an optimum correlated color temperature of 5400-6300 K, a luminous efficiency of 123-145 lm⋅W^-1, and a color rendering index Ra 69-64. The obtained PCs showed a high application potential in solid-state laser lighting.