1：Experimental Design and Method Selection:

The study used a citric acid-assisted sol-gel method to synthesize ZnGa2O4 nano-powders with varying Cr3+ doping concentrations (0-2.5 mol%). The rationale was to explore cost-effective synthesis and its impact on material properties for bio-imaging. Theoretical models included Scherer's equation for crystallite size and Williamson-Hall formula for strain analysis.

2：5 mol%). The rationale was to explore cost-effective synthesis and its impact on material properties for bio-imaging. Theoretical models included Scherer's equation for crystallite size and Williamson-Hall formula for strain analysis. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Samples were prepared with specific molar percentages of Cr3+ (0, 0.5, 1.0, 1.5, 2.0, 2.5 mol%) using zinc nitrate, gallium nitrate, chromium nitrate, and citric acid as raw materials. Data were acquired through various characterization techniques.

3：5, 0, 5, 0, 5 mol%) using zinc nitrate, gallium nitrate, chromium nitrate, and citric acid as raw materials. Data were acquired through various characterization techniques. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included an advance bruker diffractometer (XRD), Varian Cary Eclipse spectrofluorimeter (PL), Varian Cary UV–vis-NIR-spectrophotometer 6000i model (UV-Vis), Shimadzu Super scan ZU SSX-550 electron microscope (SEM), energy dispersive x-ray spectroscopy (EDS), high-resolution transmission electron microscope (HR-TEM), and Thermoluminescence reader (TL1009I). Materials were zinc nitrate hexahydrate (99.9%), gallium nitrate monohydrate (99.99%), chromium(III) nitrate nonahydrate (>99.99%), citric acid monohydrate (99.5%), and deionized water.

4：9%), gallium nitrate monohydrate (99%), chromium(III) nitrate nonahydrate (>99%), citric acid monohydrate (5%), and deionized water. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Stoichiometric quantities of precursors were dissolved in deionized water, stirred at 80°C to form a gel, dried at 110°C, annealed at 700°C for 2 hours, and crushed into powders. Characterization involved XRD for phase analysis, SEM and HR-TEM for morphology, EDS for composition, UV-Vis for optical properties, PL for emission, and TL for thermoluminescence.

5：Data Analysis Methods:

Data were analyzed using Scherer's equation for crystallite size, Williamson-Hall plot for strain, Kubelka-Munk function for band gap estimation, Gaussian fitting for particle size distribution, and multipole-multipole interaction models for concentration quenching.