Ultra-Wide band Near-Infrared (NIR) optical thermometry (12-673K) performance enhanced by Stark sublevel splitting in Er3+ ion near first biological window in PbZr0.53Ti0.47O3:Er3+/Yb3+ phosphor

The fluorescence intensity ratio (FIR) approach, which relies on thermally coupled levels (TCLs), is significantly important for optical thermometry at room tempertaures and above but found impractical for low temperature sensing due to limited population desnity (thermal) or lack of spectrum at extremely low temperatures. Herein we report a wide range temperature (12-673K) sensing capability of PbZr0.53Ti0.47O3:Er3+/Yb3+ (C1:PZT) phosphor utilising bandwidth of Stark sublevel spilt near infra red (NIR) emission bands as one sensing parameter and FIR as another. Motivated by our previous upconversion (UC) emission studies on C1:PZT phosphor and its promising thermometry performance for real time nanothermometer monitoring(using visible TCLs), an extended part of the work where upconverted NIR emission as TCLs have been investigated. The temperature dependent UC spectra were obtained in the 12–313 K and 313-673 K range under 980 nm excitations, and their sensing abilities were thoroughly examined. An enveloped single emission band consisted of several peaks in NIR region was observed and deconvoluted using Gaussian fitting. These multiple peaks were studied and explained considering the Stark sublevel splitting observed at 12 K and the variation of their full width at half maxima was compared up to 313 K. Based on the temperature dependent bandwidth, two peaks, ~11655 cm−1 (858 nm) and 11454 cm−1 (873 nm), were identified as TCL levels, and a sensitivity (Sr) of 0.68 ± 0.01% K− 1 at 673 K was observed, making it a suitable thermometer for reading low temperatures using NIR bands.