Retracted Article: Effect of Ca2+ doping on the upconversion luminescence properties of NaYF4:Yb3+/Tm3+ nanoparticles and study of its temperature measurement performance

Abstract

A solvothermal method was used to prepare a series of Yb³⁺/Tm³⁺/Ca²⁺ co-doped NaYF₄ nanoparticles with different Ca²⁺ contents. Strong upconversion blue fluorescence could be observed under 980 nm laser excitation of the samples. The effect of different Ca²⁺ contents on the luminescence intensity was investigated, and it was found that the UV-vis upconversion luminescence increased and then decreased with an increasing Ca²⁺ concentration during the increase of the Ca²⁺ content from 0 mol% to 25 mol%, reaching the strongest fluorescence at 15 mol%, which was up to about 28 times stronger than that without Ca²⁺ doping. Furthermore, the mechanism was investigated, and it was found that the doping of Ca²⁺ disrupted the symmetry of the crystal field, resulting in a significant enhancement of the overall fluorescence. Applied to fluorescence intensity ratio thermometry, the absolute and relative sensitivities are as high as 0.0418 K⁻¹ and 2.31% K⁻¹, respectively, with a minimum temperature resolution of 0.0129 K.