Multifunctional Er(III)‐Activated Ca ₂ SrWO ₆ Double Perovskite for Ratiometric Thermometry and Lighting Devices

Owing to thermally coupled energy levels (TCLs), Er 3+ ‐activated phosphors have garnered notable attention for their use in optical thermometry. Herein, Er 3+ ‐activated Ca 2 SrWO 6 was examined for the optical thermometry within 298–523 K. A series of Er 3+ ‐doped Ca 2 SrWO 6 phosphors with varying Er 3+ concentration were prepared using solid‐state reaction with calcine temperature of 1200°C. Under 380 nm excitation, the Ca 2 SrWO 6 :Er 3+ displayed strong green photoluminescence (PL) at 527 nm ( 2 H 11/2 ‐ 4 I 15/2 ) and 560 nm ( 4 S 3/2 ‐ 4 I 15/2 ). To investigate the thermometric performance, the temperature‐dependent PL (TDPL) spectra of the Ca 2 SrWO 6 :Er 3+ phosphor were recorded within 298–523 K. Upon 380 nm excitation, the Er 3+ prominent transitions, 2 H 11/2 ‐ 4 I 15/2 and 4 S 3/2 ‐ 4 I 15/2 , displayed different responses to thermal variation. Taking this into account, the principle of fluorescence intensity ratio (FIR) of the TCLs, the thermometry investigation has conducted. The maximum relative sensitivity ( S R ) attained to be 0.69% K −1 at 298 K, indicating the suitability of the phosphor for thermometry. Additionally, repeatability experiments carried out to check the reliability of the FIR confirm the excellent performance in thermometry. Moreover, the decay lifetime of the 4 S 3/2 state of the Er 3+ was evaluated from the luminescence decay, and the photometric analysis confirms the green emission of the phosphors with the highest color purity of 92.67%.