1：Experimental Design and Method Selection:

A sol–gel synthesis method was chosen for its ability to produce pure oxides at relatively low annealing temperatures. The process involved dissolving stoichiometric amounts of precursors in distilled water, drying, sintering, and annealing to obtain the final powder.

2：Sample Selection and Data Sources:

A series of Na3Y1-xSi2O7:Gdx samples with x ranging from

3：01 to 11 were prepared using high-purity chemicals as listed in Table I. List of Experimental Equipment and Materials:

Equipment included a Rigaku Miniflex-II diffractometer for XRD, Hitachi S-3400 SEM for morphology, Perkin Elmer FTIR spectrometer, Shimadzu RF-5301PC spectrofluorophotometer for PL, and JEOL FES-FA200 ESR spectrometer for EPR. Materials included NaNO3, Y(NO3)3·6H2O, SiO2, citric acid, Gd(NO3)3·6H2O, KBr, and DPPH.

4：Experimental Procedures and Operational Workflow:

Precursors were dissolved and stirred to form a homogeneous solution, dried at 383 K for 12 h, sintered at 673 K for 2 h, ground, and annealed at 1073 K for 3 h. Characterization involved XRD with Cu-Kα radiation, SEM imaging, FTIR with KBr pellets, PL measurements with a xenon lamp, and EPR at room temperature.

5：Data Analysis Methods:

XRD data were analyzed using the Debye–Scherrer equation for crystallite size. PL and EPR spectra were interpreted based on known transitions and g-values, with statistical consistency ensured by using the same amount of sample for each measurement.