Mn ions‐activated Gd3(Al,Ga)5O12 garnet solid‐solution ceramics: Cation substitution for dual wavelength red‐emission.

Red‐emitting color‐convertors have attracted considerable attention for promising applications in solid‐state lighting (SSL) to improve color rendition. However, the current nitride and fluoride phosphor powders have encountered several challenges, such as high cost, narrow emission bands, and insufficient stability during operation, which limit the development of high‐power full‐spectrum SSL. In this study, thermally robust Gd3(Al,Ga)5O12:Mn (GAGG:Mn) solid‐solution ceramics (SSCs) with dual wavelength red‐emission bands were prepared via an oxygen solid‐state sintering reaction. The doped Mn ions occupied octahedral Al3+ and Ga3+ sites to generate Mn4+ luminescent centers with pronounced deep‐red emissions peaking at 698 nm (2E → 4A2), and Mn2+ luminescent centers with broad red emissions at 628 nm (4T1 → 6A1). Because the cationic radius matching effect induced the regulation of valence state of Mn, the photoluminescence of the GAGG:Mn SSCs can be tailored by the substitution of Al3+ with Ga3+. Moreover, the Mn3+ also existed in the GAGG lattice host, and their concentration decreased with increasing Ga3+ contents owing to the mismatch of ionic radius between Mn3+ and Ga3+ ions. With the optimization of Al/Ga ratio and concentration of Mn ions, a broad emission band ranging from 550 to 800 nm (bandwidth = 250 nm) was achieved from Gd3Al3Ga2O12:0.3%Mn SSCs upon 465‐nm excitation. Moreover, the GAGG:Mn SSC has over 17‐fold enhanced thermal conductivity compared with the corresponding phosphor powder. This paper opens a door of regulating the valence state of luminescence centers with cation substitution and the application of oxide red‐emitting color‐convertors. [ABSTRACT FROM AUTHOR]