Cool white light emitting Dy3+ activated KNaCa2(PO4)2 phosphor for outdoor lighting and optical thermometric applications

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Dy3+ incorporated KNaCa2(PO4)2 phosphor (KNCP) with doping concentrations ranging from 0.005 to 0.7 mol were synthesised via high-temperature solid state reaction route. The morphological characteristics were examined using FESEM images and found agglomerated structure in micrometers with an average particle size of 4.037 µm. Photoluminescence emission spectra under 350 nm excitation reveal nearly equal intense blue and yellow emission bands owing to 4F9/2→6H15/2 and 4F9/2→6H13/2 Dy3+ transitions, respectively. The concentration-dependent emission properties were examined and the optimum concentration was found to be 0.03 mol. The synthesized phosphor exhibits a quantum yield of 69.06 % at the optimal Dy³⁺ doping concentration. The time-correlated emission characteristics were analysed from the TRES plot. Furthermore, the emission bands at 479 nm (4F9/2→6H15/2) and 572 nm (4F9/2→6H13/2) under 350 nm excitation follow bi-exponential decay having an average lifetime in the range of 0.90–0.37 ms. The prepared phosphors exhibit an intense cool white light regardless of doping concentration and delay time. Optical thermometric properties of KNCP Dy phosphor were investigated by fluorescence intensity ratio (FIR) technique and exhibit relative thermal sensitivity of 2.57 and 0.7 %K−1 in the temperature range of 90 −230 K and 250–500 K respectively. The excellent quantum yield, sub-millisecond lifetime, cool colour temperature, and higher temperature sensitivities make them ideal for outdoor lighting and optical thermometric applications.