The concentration dependent up-conversion luminescence of Ho3+ and Yb3+ co-doped β-NaYF4

The concentration dependent up-conversion luminescence of 0.1; 0.2; 0.5; 1; 1.5; 2; 3; 4 and 5% Ho3+ and 20% Yb3+ co-doped β-NaYF4 colloidal nanocrystals have been studied. The obtained nanocrystals were homogenous in size and shape, as well as the crystallographic structure was pure. The absorption spectra, upconversion lifetimes, up-conversion emission and Quantum Yield power dependence have been measured to estimate the optimum doping concentration of Ho3+ ions. The experimental results were supported by the calculations based on Judd-Ofelt theory, in order to quantify the oscillator strengths in absorption and luminescence, excited-state radiative lifetimes, energy-transfer probabilities, and to estimate the quantum efficiencies of this interesting material. We have observed evident trend in rise- and luminescence decay profiles with rising Ho3+ activator concentration, and the 1-2% Ho3+ ions doping was found to be the most efficient nanophosphors.