Tuning the crystal structure, optical band gap and persistent luminescence performance of a Cr3+-doped LiGa5O8 spinel by adding aluminium and indium.

The possibility of tuning the optical band gap, crystal structure and persistent luminescence performance of a Cr3+-doped LiGa5O8 spinel by partially replacing Ga with Al and/or In has been studied extensively. For this purpose, a series of Cr3+-doped Li(Ga1-x-yAlxIny)5O8 (x = 0…0.5; y = 0…0.1) microcrystalline phosphors were synthesised using a conventional solid-state reaction method and characterised using powder X-ray diffraction, SEM-EDX and luminescence techniques. DFT-based electronic structure calculations were carried out for the same Li(Ga1-x-yAlxIny)5O8 compositions, and the results were compared with the experimental ones. Based on the studies performed, the mechanism of Al and In incorporation into the LiGa5O8 spinel structure as well as the tuning of the crystal lattice parameters, the local structure of M3+ (M = Ga, Al, and In) cations and the optical band gap of the material have been established. The multicentre structure and the broadening of the local structural disorder of the octahedrally coordinated Cr3+ centres observed in this case have been confirmed by high-resolution, low-temperature photoluminescence measurements. Band gap engineering through alterations in the chemical composition of the LiGa5O8 spinel, as well as the depth of the native point defects responsible for charge trapping, allows for the efficient tuning of the thermoluminescence and persistent luminescence properties of Li(Ga1-x-yAlxIny)5O8:Cr3+ phosphors. Thus, the room-temperature persistent luminescence performance of the phosphors modified by the addition of Al and annealing under an oxygen-free atmosphere was increased threefold compared to the pristine LiGa5O8:Cr3+ phosphor synthesised under the same conditions.