Down- and up-converting dual-mode YPO4:Yb3+,Tb3+ nanocrystals: synthesis and spectroscopic properties

Abstract

Tetragonal YPO₄ nanocrystals doped with Yb³⁺ and Tb³⁺ ions were synthesized by 900 °C annealing of precursors obtained with a co-precipitation method in the presence of glycerine. These materials exhibited intense green luminescence under ultraviolet excitation and up-conversion emission from the ⁵D₃ and ⁵D₄ Tb³⁺ excited states after irradiation with near infrared light (λ = 980 nm). The structure and morphology of the products were analysed by recording X-ray diffraction patterns and transmission electron microscopy images. The obtained nanomaterials were single-phased with spherical shaped nanocrystals that had an average size of 18 ± 3 nm. The spectroscopic properties of YPO₄:Yb³⁺,Tb³⁺ nanocrystals were investigated based on their excitation and emission spectra. The time-resolved luminescence traces were measured, and the luminescence lifetimes of Tb³⁺ and Yb³⁺ ions were calculated. The most effective dopant concentrations were determined to be 5% Yb³⁺ and 15% Tb³⁺, which exhibited the most intense ultraviolet excited emission and up-conversion. Because the integral intensity was observed to be dependent on the power of the pumping laser, a cooperative energy transfer (CET) mechanism underlying the observed up-conversion was proposed.