Persistent luminescence of ZnGa2O4:Cr3+ transparent glass‐ceramics : Effect of excitation wavelength and excitation power

Highly transparent glass-ceramics were prepared by glass crystallization. This method enables the synthesis of up to 50 wt% of size-controllable Cr3+-doped ZnGa2O4 nanocrystals embedded in a SiO2-rich glass matrix after crystallization for 10 min at 900°C-1000°C, respectively. Rietveld refinements and transmission electron microscopy imaging show that the nanoparticles size are about 16 nm and 33 nm for the glass-ceramics annealed at 900 °C and 1000 °C. Photoluminescence measurements of these glass-ceramics revealed intense deep red (695 nm) persistent emission detectable up to 10 h, similar to that previously observed in ZnGa2O4 powders. Thermoluminescence measurements showed the presence of wide distribution of trap depths, centered at about 325 K. The traps can be charged not only under UV light, but also under visible light excitation from 365 nm up to 625 nm. Electron paramagnetic resonance measurements of Cr3+ clearly showed that ZnGa2O4 nanocrystals in glass-ceramics exhibit the same types of defects and disorder as microcrystalline ZnGa2O4 powders, which point to antisite defects as the dominant traps responsible for the persistent luminescence. It is proposed that the ability of charging ZnGa2O4 particles by visible light is the combination of a two-photon absorption and the presence of a local electric field due to antisite defects in the vicinity of some Cr3+ ions.