Upconversion Properties of Nanocrystalline ZrO₂:Yb³⁺, Er³⁺Phosphors

Abstract

Combustion and sol-gel methods were used to prepare the upconverting nanocrystallineZrO2:Yb3+,Er3+phosphors. The crystal structure was studied by X-ray powder diffraction and the crystallite sizes were estimated with the Scherrer formula. Impurities and nanomaterials' thermal degradation were analyzed with FT-IR spectroscopy and thermal analysis, respectively. Upconversion luminescence and luminescence decays were studied with IR-laser excitation at 977 nm. All nanomaterials possessed the cubicZrO2fluorite-type structure except for a small monoclinic impurity obtained with the sol-gel method. The conventionalNO3−andOH−impurities were observed for the combustion synthesis products. TheZrO2:Yb3,Er3+nanomaterials showed red (630–710 nm) and green (510–570 nm) upconversion luminescence due to the4F9/2→4I15/2and(2H11/2,4S3/2)→4I15/2transitions ofEr3+, respectively. The products of the combustion synthesis exhibited the most intense luminescence intensity and showed considerable afterglow. It was concluded that excitation energy is partially trapped in the system and subsequently bleached thermally to the luminescentEr3+center to yield “persistent upconversion”.