Regulation of phase structure, upconversion luminescence and thermal property of NaYF4:Yb3+,Ho3+,Ce3+ through doping concentration of Ce3+ and Yb3+

Abstract

NaYF4:Yb3+/Ho3+/Ce3+ upconversion phosphors were synthesized by using a citric acid assisted hydrothermal method. Both increasing the concentration of Ce3+ and decreasing the Yb3+ content are beneficial to the formation of cubic NaYF4. When the concentration of Yb3+/Ho3+/Ce3+ were 20/1/20 and 5/1/10, respectively, a pure cubic phase was obtained. The spectral conversion from green to red was achieved by first increasing Ce3+ concentration to 10% and then decreasing the Yb3+ concentration to 5%. In the first half, the two cross relaxation processes between Ho3+ and Ce3+ were responsible for the modulation of the luminescence, while in the latter half, the enhanced intensity ratio of red to green emission was related to the decreased energy transfer from Ho3+ to Yb3+. Except for the sample doped with 5% Yb3+, 1% Ho3+ and 10% Ce3+, the total emission intensity of other samples decreased linearly with increasing sample temperature. The maximum responsibility was obtained in the case of 20% Yb3+, 1% Ho3+ and 5% Ce3+ doping. Compared to the Er3+ based luminescent temperature sensing, this novel temperature sensing not only shown little impact from pump power, but also had the identical sensitivity at various temperatures, and thus being a promising candidate for temperature sensing.