The influence of germanium ions on the infrared long persistent phosphor Zn1+xAl2-2xGexO4: Cr

Germanium substitution in the original ZnAl2O4:Cr3+ infrared long persistent phosphors Zn1+xAl2-2xGexO4: Cr (x = 0.1, … 1) were synthesized via a high temperature solid state reaction. X-ray diffraction (XRD), afterglow decay curves, photoluminescence, and isometric thermoluminescence spectra were collected to characterize these samples. With the increase of substitution of germanium, the diffraction peaks shift to the shorter angles and the phase of Zn2GeO4 appears (x ≥ 0.5) as indicated by the X-ray diffraction results. Photoluminescence shows the infrared emissions of Cr3+ response, and consistently confirms that Cr3+ is very sensitive to the host crystal field in this material. A spinel structure is indicated for the Cr3+ infrared emission. However, the substitution of germanium can not only modify the host structure, but also provide defects which improve the afterglow of the materials as indicated by the thermoluminescence (TL) results. With a suitable substitution of germanium, TL peaks move to lower temperatures and become broader, which are both good factors for the room temperature afterglow phosphors. All the results indicate that non-gallate material ZnAl2O4 Cr3+, with a suitable concentration of germanium substitution, could be an excellent infrared long afterglow phosphor.