Down- and up-converting dual-mode YPO 4 :Yb 3+ ,Tb 3+ nanocrystals: synthesis and spectroscopic properties

Tetragonal YPO4 nanocrystals doped with Yb(3+) and Tb(3+) 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 (5)D3 and (5)D4 Tb(3+) 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:Yb(3+),Tb(3+) nanocrystals were investigated based on their excitation and emission spectra. The time-resolved luminescence traces were measured, and the luminescence lifetimes of Tb(3+) and Yb(3+) ions were calculated. The most effective dopant concentrations were determined to be 5% Yb(3+) and 15% Tb(3+), 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.