Investigation of dopant concentration and excitation power on sensitivities of Y4.67(SiO4)3O:Yb3+,Er3+ upconversion phosphors for optical thermometer

In this work, a series of Y4.67(0.99-x)(SiO4)(3)O:xYb(3+),1%Er3+(5% <= x <= 20%) phosphors were prepared by solid-state reaction, and their upconversion luminescence properties under 980 nm excitation were studied for optical temperature sensing. Single-phase samples were checked by XRD patterns. Upon 980 nm excitation, three emission peaks of Er3+ appeared, and the relative intensities of the green and red emissions were found to change with Yb3+ concentration. The temperature dependences of both fluorescence intensity ratio and decay lifetime of Er3+ were evaluated. By using I-522/I-547, the absolute sensitivity (S-A) shows a continuous increase with rising temperature and the maximal value for x = 10% reached 5.17 x 10(-3) K-1 at 550 K. The relative sensitivity is decreased at higher Yb3+ concentration. By using I-661/I-522, it has been found that the absolute sensitivity decreases with rising temperature, and the sample for x = 10% shows the largest S-A. The relative sensitivities for all the samples decrease gradually when the temperature is increased. For different pump powers, the sample excited at 62 mW/mm(2) shows the largest absolute sensitivity at high temperature, but high relative sensitivity is achieved at low temperature. The above results indicate the present phosphors could have potential applications in optical thermometers.