1：Experimental Design and Method Selection:

The study uses combustion-assisted synthesis to prepare polycrystalline powder samples of Sr9-x-yMg

2：5(PO4)

xEu2+, yCe3+ (SMPO:xEu2+,yCe3+). The rationale is to investigate the effect of Ce3+ codoping on luminescence properties and Eu valence state reduction. Theoretical models include charge compensation for explaining the reduction mechanism.

3：Sample Selection and Data Sources:

Samples are synthesized with varying Eu2+ and Ce3+ concentrations (e.g., x=0.01-0.06, y=0-0.3). Starting materials include Sr(NO3)2, Mg(NO3)2·6H2O, NH4H2PO4, Eu2O3, Ce(NO3)3·6H2O, and CO(NH2)2 as fuel. Data sources are experimental measurements from XRD, PL, PLE spectra, and quantum yield measurements.

4：01-06, y=0-3). Starting materials include Sr(NO3)2, Mg(NO3)2·6H2O, NH4H2PO4, Eu2O3, Ce(NO3)3·6H2O, and CO(NH2)2 as fuel. Data sources are experimental measurements from XRD, PL, PLE spectra, and quantum yield measurements. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment includes a box furnace for sintering at 600°C, a horizontal tubular furnace for sintering at 1250°C under H2 atmosphere, a hydrogen generator (RX-H300, Analysis of Scientific Instrument Co., Ltd. Shanghai Rui, China), X-ray diffraction instrument (Bruker AXS D8, Cu Kα radiation), spectrofluorometer (Hitachi F-7000 with 150 W xenon light source), and fluorescence spectrophotometer (FLSP920, Edinburgh Instruments Ltd., UK) with integrating sphere for quantum yield measurements. Materials are analytical reagents and high-purity chemicals as specified.

5：Experimental Procedures and Operational Workflow:

Steps involve dissolving starting materials in water with urea fuel, sintering at 600°C for 10 min in self-generating atmosphere, regrinding, sintering at 1250°C for 4 h under H2 flow (40 mL/min), then characterizing with XRD, PL, PLE spectra, and quantum yield measurements under specified excitation wavelengths.

6：Data Analysis Methods:

Data analysis includes comparing XRD patterns with simulated patterns, analyzing PL and PLE spectra for emission and excitation peaks, calculating chromaticity coordinates, and measuring quantum yields. Statistical techniques are not explicitly mentioned, but spectral comparisons and intensity measurements are used.