Study On The Upconversion Luminescence And Temperature Sensing Properties Of Rare-Earth Doped CaMoO₄

Recently,due to the excellent luminescent performance,the rare-earth doped up-conversion materials pride itself for the great potential in the field of bioimaging,solar cell,optical temperature sensing and photodynamic therapy and so on.The molybdates have advantages of low phonon energy,simple synthesis procedure and excellent stability under high temperature.Therefore,the rare-earth doped molybdates are regarded as a good upconversion material that can be used to measure temperature accurately over a wide range of temperature.In this work,the upconversion luminescence and temperature sensing properties of Yb³⁺/Er³⁺co-doped CaMoO₄ were investigated.The main content is divided into the following sections:The Yb³⁺/Er³⁺co-doped CaMoO₄ phosphors and sandwich structure were synthesized via sol-gel method.Under the 980 nm excitation,the effect of Yb³⁺concentration on upconversion luminescence was investigated,finding that the emission intensity of samples increased and reached the maximum value when the Yb³⁺concentration is 16%.Then,the emission intensity decreased as the concentration of Yb³⁺exceeds 16%,which was due to the enhancement of non-radiative relaxation.In addition,the effect of excitation power on the upconversion luminescence of sandwich structure and phosphors were investigated,indicating that the temperature of phosphors enhanced quickly with the increment of the excitation,which can be used as optical heater.On the contrary,the temperature of sandwich structure is almost constant due the small thickness and superior heat dispersion property.The temperature sensing properties of the phosphors and sandwich structure were investigated.The absolute sensitivity and relative sensitivity of the sandwich structure and phosphors are almost same.The effect of Yb³⁺on the temperature measurement uncertainty was investigated.Compared with the Er³⁺doped Phosphors,the temperature measurement uncertainty of 16%Yb³⁺doped phosphors decreased from 0.8 K to 0.1 K.The CaMoO₄:0.5%Ho³⁺/16%Yb³⁺/5%Eu³⁺phosphors were synthesized through sol-gel method.The upconversion luminescence of the sample were studied under the 405 nm and 980 nm excitation respectively.The result showed that the down conversion of the sample originated from the Eu³⁺under the 405 nm excitation,the appearance of the Ho³⁺and Eu³⁺luminescence under 980 nm excitation was because of the energy transfer upconversion?ETU?between the Ho³⁺and Yb³⁺and the non-resonant energy transfer between the Ho³⁺and Eu³⁺.What's more,on the co-excitation with 405 and 980 nm lasers,the color-tunable property of the phosphors was achieved through changing the excitation power of one of the lasers.Finally,the optical temperature sensing property of the sample was discussed upon the co-excitation with 405 and 980 nm lasers,indicating that the relative sensitivity of the phosphors could be improved through increasing the excitation power of 980nm laser.