Electronic structure engineering of Gd2.97Tb0.03Ga5−xAlxO12 persistent luminescence phosphors

Gd2.97Tb0.03Ga5−xAlxO12 powders with different Ga:Al ratio were prepared using modified Pechini method. Changing Ga:Al ratio opens the way to modulate the energy gap, and so, to modify the spectroscopic properties of the phosphors. Al3+ ions stabilize the metastable Gd3Ga5O12 garnet structure widening the energy gap. With increasing Ga content in the garnet structure, the energy gap between an excited 5d level of Tb3+ ions and the conduction band (CB) decreases, which leads to an overlap of the conduction band with the 5d band suppressing the energy transfer between the 5d band and the 4f levels of Tb3+ ions. The band gap changes lead to the blue shift of charge transfer band due to an expansion of the unit cell and decreased interaction between oxygen ligands and luminescent ions. The collected spectroscopic data show significant effect of crystal field strength of the host matrix on both conventional and persistent luminescence. From the resultant data the influence of Ga:Al ratio on the luminescence properties and trapping/releasing of electrons is discussed. The mechanism of Tb3+ persistent luminescence in Gd2.97Tb0.03Ga5−xAlxO12 is proposed.