Ca4(PO4)2O:Eu2+, Eu3+ phosphor enabled sundry spectral range sub-K optical thermometry

•Ca4(PO4)2O:Eu2+, Eu3+ phosphor demonstrated sub-K temperature sensitivity.•This material allowed temperature sensitivity from LIR and lifetime methods.•LIR method realized an average sensitivity of 1.76%/°C (20–60 °C).•Lifetime method realized an average sensitivity of 1.96%/°C (20–60 °C).•This material could have potential application in low-temperature thermal imaging. Herein, we report on the luminescence and thermometric properties of Ca4(PO4)2O:Eu. The photoluminescence emission exhibited blue and red bands from Eu2+ and yellow and red lines from Eu3+. The multiple-emission features allowed a study of the thermometric properties in the different spectral ranges, namely, blue-green, yellow, red and near-infrared, using the luminescence intensity ratio method. The average temperature sensitivities of 1.76, 0.1, 0.11 and 0.11%/°C (in the temperature range of 30–60 °C) were obtained from the 425 to 525 nm, 560 to 580 nm, 615 to 635 nm, and 635 to 900 nm spectral ranges, respectively. The lifetime method produced high-temperature sensitivities of 1.96%/°C and 1.77%/°C in the 20–60 °C from the 700 to 455 nm bands, respectively. This suggests that this material could be applied in low-temperature thermal imaging applications such as thermal convection and biological processes. [Display omitted]