  An effect of alloying of the monoclinic beta- Ga2O3 with Al2O3 and In2O3 on
the photoluminescent, thermoluminescent and persistent luminescent properties
of Cr3+ ions has been comprehensively investigated. For this purpose, various
series of Cr3+ and Ca2+ co-doped microcrystalline phosphors were synthesized by
the solution combustion method, including pseudobinary compounds like
(Ga-Al)2O3 with up to 20% Al and (Ga-In)2O3 with up to 50% In as well as
pseudoternary compounds (Ga Al In)2O3 with balanced proportion of Al, Ga and
In. The phase composition and crystal structure of the obtained materials were
examined by X-ray powder diffraction technique. Detailed luminescence studies
were conducted for the (Ga-Al)2O3 and (Ga-In)2O3 compounds which exhibited a
single-phase monoclinic structure. Low-temperature and time-resolved
photoluminescence investigations of the Cr-doped pseudobinary compounds
unveiled several types of Cr3+ centres, attributed to the Al-, Ga- and
In-centred octahedra in the studied alloys. The obtained results underscore the
benefit of bandgap engineering through alteration in the host lattice chemical
composition for efficient tuning of the thermoluminescent and persistent
luminescent properties of the near-infrared-emitting beta Ga2O3:Cr based
phosphors. Furthermore, it was demonstrated that modification of the chemical
composition of the host lattice also adjusts the thermometric performance of
the studied phosphors. Indeed, the specific sensitivity of the beta- Ga2O3:Cr3+
decay time luminescence thermometer showed nearly twofold enhancement when the
host lattice was alloyed with 30% of In2O3.
