Photoluminescence, persistent luminescence and thermoluminescence studies of Cr-doped zinc gallogermanate (ZGGO:Cr)†

This paper reports a comprehensive study of single-phase polycrystalline chromium-doped zinc gallogermanate (ZGGO:Cr) synthesised by a high-temperature solid-state reaction, employing photoluminescence (PL), persistent luminescence (PersL) and thermoluminescence (TL) measurements. A bandgap energy of ∼4.77 eV (260 nm) was estimated by optical reflectance. The ZGGO:Cr luminescence was dominated by a red/near-infrared emission due to Cr³⁺ optical centres, which displayed well-resolved R1, R2, N1 and N2 lines, and a broad vibronic progression. PL excitation (PLE) data revealed that those centres were preferentially populated via intraionic absorption, being also excited via band-to-band absorption and by a defect excitation band at ∼0.9 eV below the conduction band, whose origin remains unknown. PersL of more than 10 h was identified and attributed to the N2 Cr³⁺-related defect. The TL results suggest a continuous distribution of electronic states with activation energies ranging from about 0.7 eV to 1.2 eV. An effective density of states was obtained for different delay times between irradiation and heating, revealing a rapid depopulation for activation energies below ∼1 eV. In short, this research contributes to a better understanding of traps in ZGGO:Cr and highlights the potential of the Cr³⁺-related emission in this material for dosimetric purposes, paving the way for developing novel ZGGO:Cr-based devices.