Afterglow enhancement of AlMgGaO4:Cr3+, Ln3+ (Ln=Eu, Sm, Yb) guiding by VRBE diagram

Abstract

The afterglow intensity of AlMgGaO4: Cr3+ has been enhanced by co-doping rare earth ions. The HRBE and VRBE diagram of the rare earth ions are constructed to determine the ground state energy level position of 4f in the forbidden band. The activation energy Ex is calculated to be 6.41 eV according to the diffuse reflection spectrum of AlMgGaO4, and the 4f level position of Eu2+ is obtained by the charge transfer band of Eu3+, whereby the ground state energy level position of all the divalent rare earth ions are determined. The energy difference between the ground state energy level of Eu3+ ion and Eu2+ ion are obtained by the centroids shift of the 5d energy level of Ce3+, and the ground state energy level position of all the trivalent rare earth ions are determined. The 4f energy levels of Eu2+, Sm2+ and Yb2+ are calculated to be 1.65, 0.4 and 1.21 eV below the conduction band, respectively, which can be used as energy storage levels of Cr3+. Then the near-infrared afterglow phosphors AlMgGaO4:0.03Cr3+, Ln3+ (Ln = Eu, Sm, Yb) are synthesized, and the afterglow properties are studied carefully. With Eu3+/Sm3+/Yb3+ concentrations increasing, the afterglow intensity is enhanced, and the intensity of thermoluminescence increases gradually and shifts to the high temperature, which indicates that the trap energy level of the phosphor is enriched with the increase of rare earth ion concentration. The results prove that constructing VRBE diagram is an effective way to select rare earth ions to enhance the afterglow intensity.