Positive effect of codoping Yb3+ on the super-long persistent luminescence of Cr3+-doped zinc aluminum germanate

A series of novel near-infrared (NIR) long persistent phosphors of Zn1.2Al1.6Ge0.2O4: Cr3+, Yb3+ was synthesized by a solid state method. The crystal structure of Zn1.2Al1.6Ge0.2O4 was identified. Yb3+ ions were effective codopants for improving the NIR persistent luminescence intensity even after 100 h of decay. The persistent luminescence decay curves and the thermo-luminescence spectra were analyzed. Results indicated that the increase in efficient electron trap concentration induced by doping Yb3+ ions was a major factor in the improvement of the NIR persistent luminescence. Moreover, short-wave infrared (SWIR = 900–1700 nm) emission of Yb3+ was be excited by UV and visible light through charge transfer transition of O2-–Yb3+ and energy transfer from Cr3+ to Yb3+, respectively.