NIR grating harmonic excitation of Dy-doped CaWO4 phosphors for a new ratiometric thermometry strategy

The harmonic generation effect, a distinct nonlinear optical phenomenon , exhibits unique properties and has critical applications across multiple fields. However, harmonic generation during optical measurements can introduce significant interference or experimental errors. Here, we investigated the photoluminescence (PL) characteristics of Dy 3+ doped CaWO 4 phosphors under near-infrared (NIR) irradiation. Both characteristic yellow and blue emissions of Dy 3+ and a series of NIR-induced harmonic generation were observed. The study demonstrated that Dy 3+ emissions were excited by harmonic generation originating from the dual-grating configuration of a spectrophotometer. Leveraging the divergent temperature-dependent intensity evolution between Dy 3+ emissions and 1.5th harmonic generation, we proposed a novel ratiometric thermometric strategy based on the luminescence intensity ratio (LIR). This new thermometry achieved optimal temperature sensitivity, with a maximum absolute sensitivity of 74.57 × 10 −4 K −1 and relative sensitivity of 2.21 % K −1 , surpassing conventional ratiometric thermometry relying on thermally coupled energy levels. These findings not only clarified the origin of multiplex harmonic generation and its impact on spectral measurement but also harness harmonic generation for innovative applications in optical thermometry.