Abstract
A series of Zn1·8Al1.6Ge0.2O4: Cr3+ x mol% (x = 0.5, 1, 1.5, 2, 2.5, 3) phosphors were synthesized via a high temperature solid state reaction. It was shown in the previous study that suitable germanium substitution in the original ZnAl2O4: Cr3+ infrared long persistent phosphors can enhance the afterglow time. In this paper, powder X-ray diffraction, afterglow decay curves, photoluminescence and isometric thermoluminescence spectra were collected to identify the influence of the Cr ions on the luminescence in the spinel structure. With the increase of doping, the diffraction peaks shift to the shorter angles which confirm a swelling of the crystal cell. Meanwhile, according to the photoluminescence, the excitation emissions of Cr3+ shift which respond to the structural changes. The Stoke and anti-Stoke lines of Cr3+ infrared emission are noticeable for these samples and the dependence of these lines with temperature is demonstrated. Both thermoluminescence (TL) and afterglow results prove that 1.5 mol% Cr is the optimized doping concentration. All the results indicate that with a suitable concentration, Zn1·8Al1.6Ge0.2O4: Cr3+ could be prepared as an excellent infrared long afterglow phosphor and the emission lines of Cr ions are excellent probe ions that record structural changes.
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