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The Y3(Al,Ga)5O12:Ce3+,Cr3+,Nd3+(YAGG) nano-phosphors with homogeneous particle-size distribution, low aggregation and average crystalline size of about 65 nm were obtained using a modified Pechini method. Only slight aggregation of the crystallites occurs after post-annealing at 1100 °C. The intense Ce3+bands in the excitation spectra of the Ce3+,Cr3+,Nd3+co-doped materials monitoring the Cr3+emission at 690 nm indicate energy transfer from Ce3+to Cr3+. Weak Nd3+lines are observed, as well. In addition, the emission of Nd3+at 1060 nm with excitation of Ce3+and Cr3+confirms the Ce3+/Cr3+to Nd3+energy transfer. The short average luminescence decay times for the Ce3+emission indicate the Ce3+/Cr3+to Nd3+energy transfer. Eventually, the Y3(Al,Ga)5O12:Ce3+,Cr3+,Nd3+nano-phosphors exhibit persistent luminescence originating from the 4f3→ 4f3transitions of Nd3+which matches well to the first biological window to be used in bioimaging applications.

The persistent luminescence (PersL) dependence on the dopants and derived mechanism of trapping and de-trapping processes were investigated in Y3Al2Ga3O12(YAGG) based nanophosphor, doped with Ce3+and/or Cr3+. It is found that the presence of Cr3+ions produce electron and hole traps and capture suitable charge after X-ray irradiation. The effect of irradiation on the carriers trapping and their pathways after excitation was studied by means of thermo luminescence technique. On the other hand, for blue light irradiation the mechanism seems to be different. In the latter case, the Ce3+ions, having the position of energy levels in the conduction band, become sensitizers for the electrons and main emission centres for the PersL (de-trapping process goes through Ce3+).