Structural and optical properties of Zn2.95Ga2−xSnO8:xCr3+: An excellent X-ray charging-based persistent phosphor

This study investigates structural and luminescence properties of Cr³⁺ doped Zn<inf>2.95</inf>Ga<inf>2</inf>SnO<inf>8</inf> phosphor. XRD analysis determines the phase purity and lattice parameters, while SEM and TEM analysis were utilized to study the particle size and surface morphology of the sample. UV–visible absorption and PL excitation spectra provided information on the excitation bands and the band-gap of both the undoped and Cr³⁺ doped Zn<inf>2.95</inf>Ga<inf>2</inf>SnO<inf>8</inf>. The optical band-gap of the material decreases upon doping with Cr³⁺ ions. Analysis of the Racah parameter and Tanabe Sugano diagram highlights a robust crystal field within Cr³⁺: Zn<inf>2.95</inf>Ga<inf>2</inf>SnO<inf>8</inf>, causing ²E<inf>g</inf> level to become the lowest excited state with sharp emission at 699 nm. Concentration quenching at higher Cr³⁺ concentrations (> 0.6 mol%) is primarily attributed to the quadrupole-quadrupole interactions. Two distinct traps with trap depths at 0.51 eV and 0.73 eV were identified by using thermoluminescence measurement. The material gives persistent luminescence with a decay time of more than 30 min when charged with blue light (420 nm) and an excellent decay time of more than 16 h when charged with X-rays. Notably, this is the first report on X-ray charging-based persistent luminescence in Zn<inf>2.95</inf>Ga<inf>2</inf>SnO<inf>8</inf>. The outstanding persistent luminescence makes this material highly promising for various applications.