A parallel investigation of un-doped and manganese ion-doped zinc selenide quantum dots at cryogenic temperature and application as an optical temperature sensor

Abstract

In this work, un-doped and manganese ion (Mn2+)-doped zinc selenide (ZnSe) quantum dots (QDs) were investigated by measuring photoluminescence (PL) and photoluminescence excitation (PLE) spectra in the temperature range from 300 to 77 K. Intense blue and orange PL were observed for ZnSe and Mn@ZnSe QDs, respectively. The intensity of PL spectra is found to be exceedingly dependent on temperature. The highest PL intensity is obtained at 77 K and then reduced with rising temperature up to 300 K. To understood the temperature-dependent PL origin and mechanism, the PL spectra with different excitation and PLE spectra at different PL wavelengths were investigated at decreasing temperature (300 - 77 K) and vis-a-vis. The calculated activation energy values come out to be 42.2 and 66.4 meV for ZnSe and Mn@ZnSe QDs, respectively. Furthermore, the lifetimes of Mn@ZnSe QDs were discussed at different temperatures. The absolute sensitivity (S) for the temperature sensor is calculated, and the maximum S values come out to be 0.58% K−1 at 225 K and 0.44% K−1 at 250 K for ZnSe and Mn@ZnSe QDs, respectively. The wide range linearity in temperature-dependent PL and moderate activation energy values suggest that the prepared QDs can be cast for a PL-intensity-based optical temperature sensor.