UC/DC luminescence of Ho3+ doped pyrochlore structured La2(1–x)Yb2xTiO5 phosphor synthesized by sol-gel method

Abstract

AbstractHo3+ doped La2(1–x)Yb2xTiO5 samples were prepared by sol-gel method. Pyrochlore structured powders were obtained under the annealing of the as-prepared samples at 1100 °C for 3 h in the air. All the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescent spectroscopy. When x=0, we obtained La2TiO5 phosphors. Monitored at 546 nm, the excitation spectrum of Ho3+ activated La2TiO5 phosphors consisted of a broad band originating from the charge-transfer band (CTB) between Ho3+ ions and the nearest neighboring O2– ions at 250–280 nm and four sharp bands associated to f-f transitions of Ho3+ ions at 350–500 nm. Under the blue light excitation at 461 nm, Ho3+ ion in La2TiO5 emitted an intense green emission band at 546 nm due to the transition of 5S2, 5F4→5I8. Two intense bands were observed at 490 nm (blue, 5F3→I8) and 663 nm (red, 5F5→5I8) in the up-conversion (UC) spectrum under 980 nm NIR laser excitation in La2TiO5 phosphors activated with Ho3+ alone, whereas they were much different from the down-conversion (DC) luminescent samples. When x=7.5 mol.%–17.5 mol.%, the UC emission spectra of them dominated at 546 nm (green, 5S2,5F4→5I8) and enhanced significantly with the dose of Yb3+ ion. The decay curve also confirmed that the transitions of 5F4→5I8 and 5S2→5I8 were merged into one emission band at 546 nm.