Frequency upconversion and fluorescence intensity ratio method in Yb-ion-sensitized GdO:Er-Eu phosphors for display and temperature sensing.

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.