NIR light guided enhanced photoluminescence and temperature sensing in Ho³⁺/Yb³⁺/Bi³⁺ co-doped ZnGa₂O₄ phosphor

The conversion of NIR light into visible light has been studied in Ho³⁺/Yb³⁺/Bi³⁺ co-doped ZnGa₂O₄ phosphor for the first time. The crystallinity and particles size of the phosphor increase through Bi³⁺ doping. The absorption characteristics of Ho³⁺, Yb³⁺ and Bi³⁺ ions are identified by the UV-vis-NIR measurements. The Ho³⁺ doped phosphor produces intense green upconversion (UC) emission under 980 nm excitations. The emission intensity ~ excitation power density plots show contribution of two photons for the UC emissions. The UC intensity of green emission is weak in the Ho³⁺ doped phosphor, which enhances upto 128 and 228 times through co-doping of Yb³⁺ and Yb³⁺/Bi³⁺ ions, respectively. The relative and absolute temperature sensing sensitivities of Ho³⁺/Yb³⁺/5Bi³⁺ co-doped ZnGa₂O₄ phosphor are calculated to be 13.6 × 10^-4 and 14.3 × 10^-4 K^-1, respectively. The variation in concentration of Bi³⁺ ion and power density produces excellent color tunability from green to red via yellow regions. The CCT also varies with concentration of Bi³⁺ ion and power density from cool to warm light. The color purity of phosphor is achieved to 98.6% through Bi³⁺ doping. Therefore, the Ho³⁺/Yb³⁺/Bi³⁺:ZnGa₂O₄ phosphors can be suitable for UC-based color tunable devices, green light emitting diodes and temperature sensing.