Upconversion luminescence of KGd(MoO4)2:Er3+,Yb3+ powder prepared by Pechini method

Er3+ doped potassium gadolinium molybdate (KGM) phosphor with sensitizer Yb3+ ion was synthesized by the Pechini method using citric acid and ethylene glycol. The crystallization processes of the phosphor precursors were characterized by X-ray diffraction (XRD) and thermogravimetry-differential scanning calorimetry (TG-DSC), which indicated that ultrafine uniform crystallites of KGM:Er,Yb were obtained by sintering the precursors at above 650 degrees C for 5 h. Upconversion luminescence (UL) spectra of the samples were studied by a 976 nm semiconductor laser diode (LD) excitation. The UL spectra exhibited the green and red emission bands that were attributed to the H-2(11/2), S-4(3/2)-> I-4(15/2) and F-4(9/2)-> I-4(15/2) transitions of Er3+, respectively. The possible UL mechanisms of Er3+ were explained by means of an energy level diagram. The maximum luminescent intensity was achieved when the concentration of Er3+, Yb3+ arrived at 1 mol.% and 20 mol.%, respectively.