From the up-converting multimodal luminescent thermometer to ratiometric visual power density meter based on Er3+,Yb3+ emission.

This study demonstrates that thermally induced variations in the spectroscopic properties of Na3Sc2(PO4)3:Er3+,Yb3+ can be effectively harnessed for multimodal remote temperature sensing. As shown, Na3Sc2(PO4)3:Er3+,Yb3+ supports multiple ratiometric sensing modes based on the intensity ratios of (i) 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2; (ii) 2H9/2 → 4I13/2 and 4S3/2 → 4I15/2; and (iii) green-to-red emission intensity ratio, achieving maximum relative sensitivities of 2.8% K-1, 3% K-1, and 1.8% K-1, respectively. The synergy between thermal changes observed in the green-to-red emission intensity ratio of Er3+ ions, combined with the efficient optical heating of Na3Sc2(PO4)3:Er3+,Yb3+ at elevated Yb3+ concentrations enables the development of a visual optical power density sensor, exhibiting relative sensitivities of SRx = 1.0% W-1 cm2 and SRy = 0.9% W-1 cm2 at 15 W cm-2 when quantified using CIE 1931 chromaticity coordinates. To the best of our knowledge, this is the first report of a visual luminescent optical power density sensor. Furthermore, it was demonstrated that Na3Sc2(PO4)3:Er3+,Yb3+ can be successfully applied for two-dimensional imaging of optical power density, thereby enabling spatial visualization of power distribution within an illuminated field.