Up-conversion luminescence and photo-thermal effect of KY₃F₁₀:Yb³⁺,Ho³⁺ nanocrystals

The cubic phase KY₃F₁₀:15%Yb³⁺,1%Ho³⁺ up-converting nanocrystals are prepared by a simple hydrothermal method. Under 980 nm excitation, strong green and red emissions are produced at the same time. According to a set of steady state rate equations and the power dependence of up-conversion luminescence, it is confirmed that two-step energy transfer from Yb³⁺ to Ho³⁺dominates the population of green emission level, while the multi-phonon decay of ⁵S₂/⁵F₄ to ⁵F₅ and promotion from ⁵I₇ to ⁵F₅ are responsible for the red emission. Long-term laser irradiation leads to significant thermal effects. Based on the ratiometric luminescence temperature sensing behavior, the light to heat conversion ability is evaluated. This multi-functional nanocrystal is potentially applicable as the nano-heater for photo-thermal therapy of tumors. (paper)