Abstract

Multi-photon-excited thermal-correlated green and red upconversion (UC) emissions have been quantified in ${{\rm Ho}^{3 +}}/{{\rm Yb}^{3 +}}$ co-doped fluotellurite (BZLFT) glass phosphor under the 978 nm laser excitation. The temperature dependence of the fluorescence intensity ratio (FIR) originated from UC emissions bands centered at 550 nm and 661 nm has been verified in the range of 303−543 K. The net emission photon numbers of ${ ^5{\rm F}_4}{+ ^5}{{\rm S}_2}\to{^5}{{\rm I}_8}$ and $^5{{\rm F}_5}\to{ ^5}{{\rm I}_8}$ transition emissions are up to ${40.08} \times {{10}^{12}}$ and ${68.51} \times {{10}^{12}}\;{\rm cps}$ in the ${0.4}\;{\rm wt}.\;\% \;{{\rm Ho}_2}{{\rm O}_3} {-} {0.4}\;{\rm wt}.\;\% \;{{\rm Yb}_2}{{\rm O}_3}$ co-doped BZLFT case under the ${6.95}\;{{\rm W/mm}^2}$ laser power density. Furthermore, the quantum yield (QY) and luminous flux are determined to be dependent on pumping power. When the excitation power increases 874 mW, the QY values for 550 nm and 661 nm emissions are as high as ${0.94} \times {{10}^{- 5}}$ and ${1.60} \times {{10}^{- 5}}.$ In addition, the high photon producing efficiency is conducive to ensuring high feedback to thermosensitive performance. The temperature thermal sensor can be manipulated steadily in medium temperature range, and the relative sensitivity reaches ${0.4}\% {{\rm K}^{- 1}}$ at 303 K, which is 1 order of magnitude larger than those in several rare-earth-doped materials. Efficient photon conversion ability and high temperature sensitivity indicate that the rare-earth-ion-doped fluotellurite material has a prospective application in the construction of optical temperature sensors based on the FIR technique allowing for self-referenced temperature determination.

© 2020 Optical Society of America

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