Design of need-based phosphors and scintillators by compositional modulation in the ZnGa 2- x Al x O 4 :Cr 3+ spinel: pure compound versus solid solutions.

Materials that can depict persistent deep red light under both ultraviolet (UV) and X-ray illumination can be a boon to sustainable economy, particularly for optical imaging, solid state lighting, and anticounterfeiting applications. Herein, we have made a series of compounds starting from ZnGa 2 O 4 :Cr 3+ to ZnAl 2 O 4 :Cr 3+ (individual spinel) by substituting the varied concentration of Al 3+ in place of Ga 3+ in ZnGa 2- x Al x O 4 :Cr 3+ (solid solution). By virtue of the structural and defect engineering doping strategy, the photo and radioluminescence are expected to be improved. Both Cr and Al doping was found to be energetically favorable in ZnGa 2 O 4 , where the same does not hold true for Ga doping in ZnAl 2 O 4 , as indicated by the DFT-calculated defect formation energies. There seems to be ordering around the dopant ion in the solid solutions compared to either ZnGa 2 O 4 or ZnAl 2 O 4 and is also reflected to as lower persistent luminescence (PerL) lifetimes. PerL under UV, in general. was found to be lower with the enhancement in the Al 3+ content endowed by the formation of Cr-Cr ion pair, lower probability of antisite formation, and widening band gap. On the other hand, X-ray excited emission enhances in the solid solution due to the decrease in cation inversion and associated defects. Confocal Microscopy showed that larger particles depicted much brighter deep red emission but failed to percolate to the human cells to a detectable limit; hence, future work is needed for the functionalization of the ZnGa 2- x Al x O 4 :Cr 3+ spinel. This work could be of great implication in designing need-based materials, where UV and X-ray excitation is required, for deep red emission with persistent characteristics from chromium-doped spinels.