Up- and Down-Conversion Luminescence of LuNbO4:Yb3+, Er3+ Phosphors

Up-conversion (UC) and down-conversion (DC) luminescence of LuNbO 4 :0.18Yb 3+ , xEr 3+ (x = 0.01-0.07) powders were investigated. Post-annealed powders were composed of a single LuNbO 4 phase with a monoclinic fergusonite structure, whereas as-calcined powders contained a small amount of the Li 3 NbO 4 impurity phase. Under near infrared radiation, the UC spectra of the post-annealed powders exhibited the strong green and weak red emission peaks assigned to the transition of 2 H 11/2 / 4 S 3/2 and 4 F 9/2 to the ground state ( 4 I 15/2 ) of Er 3+ ions, respectively; the green and red emission intensities were approximately 330 and 270% stronger, respectively, than those of the as-calcined powders. A two-photon UC process was involved in the emission as a result of an energy transfer from Yb 3+ to Er 3+ . Under ultraviolet radiation, the DC spectra exhibited broad blue and sharp green emission bands. The DC mechanism was explained using self-activated [NbO 4 ] 3-niobates and an energy transfer from [NbO 4 ] 3-to Er 3+ .