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