Ce:GAGG and Al₂O₃−Ce:GAGG phosphor ceramics for laser-driven lighting: Effects of Ga³⁺ substitution

Monophase Ce:Gd₃Al_5−xGa_xO₁₂ (Ce:GAGG) with x = 0.5–3.0 and 50 vol% Al₂O₃−containing 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, and 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, and the transformation of (Al,Ga)₂O₃ from the α- to κ-phase (x ≥ 2.0) with the formation of elongated grains and their partial melting (x = 3) is 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 series: 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 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 high application potential in solid-state laser lighting.