NIR-to-NIR ratiometric and lifetime based luminescence thermometer on a structural phase transition in Na3Sc2(PO4)3:Yb3+†

The ratiometric approach is the most commonly employed readout technique in luminescence thermometry. To address the trade-off between the risk of measurement disturbance in thermometers with high spectral separation of emission bands (due to dispersion in the surrounding medium) and the low sensitivity observed in ratiometric thermometers based on Stark level thermalization, we propose a thermometer based on the structural phase transition in Na₃Sc₂(PO₄)₃:Yb³⁺. The use of Yb³⁺ ions as dopants and the changes in Stark level energies associated with the thermally induced monoclinic-to-trigonal phase transition enable the development of a thermometer with high relative sensitivity, achieving S_R max = 1.5% K⁻¹ at 340 K for Na₃Sc₂(PO₄)₃:0.1%Yb³⁺. Additionally, as demonstrated, the structural transition alters the probability of radiative depopulation of the ²F_5/2 state of Yb³⁺, allowing the development of a lifetime-based luminescence thermometer on Na₃Sc₂(PO₄)₃:Yb³⁺ with S_R max= 1.2% K⁻¹ at 355 K for Na₃Sc₂(PO₄)₃:1%Yb³⁺. Furthermore, the phase transition temperature and consequently the thermometric performance of Na₃Sc₂(PO₄)₃:Yb³⁺ can be modulated by varying the Yb³⁺ ion concentration, offering additional tunability for specific applications.