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Near infrared (NIR) to visible frequency upconversion emission studies in Er-Eu/Er-Eu-Yb co-doped/tri-doped GdO phosphors prepared by the co-precipitation technique have been explored under 980 nm laser diode radiation. The developed phosphors were characterized with the help of XRD, FE-SEM and FTIR analysis. No upconversion (UC) emission was found in the Eu-doped GdO phosphor. UC emission from Eu ions along with Er ions was observed in Er-Eu and Er-Eu-Yb co-doped/tri-doped phosphors. The UC emission arising from the Er and Eu ions was enhanced several times due to the incorporation of Yb ions. The processes involved in the UC emission were obtained on the basis of the effect of energy transfer/sensitization through the Yb → Er → Eu process. The red/green intensity ratio was improved from 0.16 to 1.50 and 1.01 to 1.50 for Er-Eu-Yb tri-doped phosphors as compared to the Er-doped and Er-Yb co-doped phosphors, respectively, at a fixed pump power density. A UC fluorescence intensity ratio (FIR)-based temperature sensing study was performed in the prepared Er-Eu-Yb tri-doped GdO phosphors for green upconversion emission bands in the 300 K-443 K temperature range. A maximum sensor sensitivity of about ∼0.0043 K at 300 K was achieved for the synthesized tri-doped phosphors upon excitation with a 980 nm laser diode. The colour coordinates lying in the green-yellow region are invariant, with variation in pump power density and temperature. The observed results support the utility of the prepared tri-doped phosphors in optical temperature sensing, display devices and NIR to visible upconverters.

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Frequency up-conversion (UC) emission from the Nd -Yb /Nd -Yb -Li co-doped gadolinium oxide (Gd O ) phosphors prepared by the solution combustion technique in the visible range have been studied by using 980 nm near infrared (NIR) laser diode excitation. The crystalline structure and formation of the cubic phase has been confirmed with the help of X-ray diffraction (XRD) studies. XRD peak shifts have been found towards the lower diffraction angle side in the case of the Nd -Yb -Li co-doped phosphors. Surface morphology and particle size information have been observed by using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis. Down-conversion emission study under 351 nm excitation in the visible region for the Nd -Yb /Nd -Yb -Li co-doped phosphors has been performed. The UC emission bands lying in the green and red region arising from the Nd ions have been enhanced by ~260 times, ~113 times due to incorporation of Li ions in the Nd -Yb co-doped phosphors. Photometric characterization has been done for the Nd -Yb /Nd -Yb -Li co-doped phosphors. The present study suggests the capability of the synthesized phosphors in near-infrared (NIR) to visible upconverter and luminescent device applications.