1：Experimental Design and Method Selection:

Crystals were grown using a high-temperature solution method to study micromorphology, phase structure, and upconversion photoluminescence. The fluorescence intensity ratio (FIR) technique was employed for temperature sensing analysis.

2：Sample Selection and Data Sources:

Er3+/Yb3+-doped PZN-9PT crystals were synthesized from high-purity oxides (ZnO, Nb2O5, TiO2, PbO, Er2O3, Yb2O3 >99.99%). Data were collected from SEM, XRD, and spectrometer measurements.

3：99%). Data were collected from SEM, XRD, and spectrometer measurements. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Scanning electron microscope (SEM, Vega 3 SBH, TESCAN), X-ray diffractometer (XRD-6000, SHIMADZU), Lifetime and steady-state spectrometer (FLS980, Edinburgh) with a 980 nm laser, low temperature/dynamic-heating device (OptistatDN2, Oxford), platinum crucible, corundum crucible, Al2O3 powders, nitric acid, ultrasonic cleaner.

4：Experimental Procedures and Operational Workflow:

Precursor ZnNb2O6 was synthesized; mixed powders were ball-milled, dried, pressed into a platinum crucible, and heated in an electric furnace. Crystals were separated using nitric acid, cleaned, and analyzed for morphology (SEM), phase structure (XRD), UC PL under various powers and temperatures, and energy level lifetime.

5：Data Analysis Methods:

Luminescence intensity vs. power and temperature was plotted; FIR values and absolute sensitivity SA were calculated using equations; decay curves were fitted with biexponential functions.