Investigations on upconversion luminescence of K3Y(PO4)2:Yb3+-Er3+/Ho3+/Tm3+ phosphors for optical temperature sensing

Abstract

A series of Yb3+-Er3+/Ho3+/Tm3+ doped K3Y(PO4)2 (KYP) phosphors were synthesized by solid-state reaction method. Several effective strategies for temperature sensing were introduced based on their upconversion (UC) luminescence properties. For Yb3+-Er3+ codoped KYP, it was found the relative intensities of different emissions of Er3+ change with temperature, and the repeatability of measurement was evaluated. The sensor sensitivities were calculated and compared based on the thermally coupled and non-thermally coupled levels of Er3+. For Yb3+-Ho3+ codoped KYP, red emission was obtained due to the strong 5F5-5I8 transition of Ho3+. With increasing temperature, the 5F5-5I8 and (5F4,5S2)-5I8 emissions show different decrease rates in intensity. The high absolute sensitivity of 0.078 K−1 was obtained from the dependence of the fluorescence intensity ratio (FIR) on temperature, but the relative sensitivity is low compared with that of Er3+ activated KYP. For Yb3+-Tm3+ codoped KYP, various emission peaks of Tm3+ have been found from the near-ultraviolet to near-infrared range. The temperature dependence of the FIR for (3F2,3F3)-3H6 and 3H4-3H6 transitions of Tm3+ reveals the relative sensitivity is more than twice as much as that of the Yb3+-Er3+ codoped KYP, but it shows a much lower absolute sensitivity due to the low FIR value.