Sextuple ratiometric thermometry based on 980-nm-upconverted green fluorescence of Er3+ ions in submicron crystals.

980-nm-upconverted 530 and 550 nm Er3+ green fluorescence spectra of Er3+/Yb3+-codoped NaGd(WO 4) 2 submicron crystals were measured in the temperature range of 298–383 K. A sextuple ratiometric thermometry is proposed. It is established on the basis of six schemes of fluorescence intensity ratio (FIR) that considers three component peaks of the 530 nm emission band and two component peaks of the 550 nm emission band, which involve electronic transitions between two Stark sublevels of Er3+. The study shows that the phosphor shows strong green fluorescence, which is verified by measured quantum yield, and thermally stable spectral structure desired for the sextuple ratiometric thermometry. All of the six FIR schemes display highly efficient sensing performances with slightly different thermal sensitivities. Each scheme gives a temperature value and the six schemes give an averaged result. In parallel, we have also carried out an ex vivo experimental study on the temperature characteristics of the green fluorescence of the phosphor. Almost same results have been obtained, verifying biological applicability of the phosphor. The ex vivo experimental results also show that the sextuple thermometry increases considerably the accuracy and reliability of temperature measurement in comparison with the conventional intensity integration method. We have demonstrated a sextuple ratiometric thermometry based on six schemes of fluorescence intensity ratio (FIR) that considers three component peaks of 530 nm emission band and two component peaks of 550 nm emission band of Er3+/Yb3+-codoped NaGd(WO 4) 2 (NGW) submicron crystals. Our study shows that the NGW phosphor shows strong fluorescence and thermally stable spectral structure, all of the six FIR schemes display highly efficient sensing performances, and the temperature can be overall determined by the six FIR schemes. Further ex vivo experimental results show that the NGW-dispersed suspension aqueous solution which was hypodermically injection into fresh chicken breast does not affect the spectral structure, strong fluorescence intensity, as well as highly efficient sensing performance, confirming the biological applicability of the NGW phosphor. The ex-vivo experimental results also show that the sextuple ratiometric thermometry considerably increases the accuracy and reliability of temperature detection in comparison with the conventional intensity-integration method. It is concluded that sextuple thermometry is promising for more accurate temperature detection of biological tissue. Unlabelled Image • A sextuple thermometry based on FIR of green emissions of Er3+ is proposed. • It considers electronic transitions between Stark sublevels of Er3+ ion. • Temperature is determined by six FIR schemes with efficient sensing performance. • The sextuple method is more accurate than the usual intensity-integration method. • Ex vivo experiments verify biological applicability of Er3+/Yb3+:NGW phosphor. [ABSTRACT FROM AUTHOR]