1：Experimental Design and Method Selection:

The study involved preparing ZnO thin films with single Fe doping, co-doping Fe with Mg, and triple doping Fe with Mg and Cu using ultrasonic spray pyrolysis technique (USPT). Different solutions (nitrate and chlorate) were used for Fe doping. Structural, morphological, and spectroscopic analyses were conducted using XRD, SEM, XPS, and EPR measurements. Temperature-dependent EPR spectroscopy was also performed.

2：Sample Selection and Data Sources:

Samples were grown on glass substrates cleaned with piranha solution, methanol, acetone, and deionized water. Precursor solutions were prepared with zinc nitrate, hexamethylenetetramine, and specific amounts of iron nitrate or iron chlorate, magnesium nitrate, and copper nitrate to achieve Fe doping levels of 5%, 10%, and 20%.

3：0%. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included an ultrasonic spray pyrolysis system with a pneumatic nozzle and halogen lamps for heating, x-ray diffractometer (GNR APD 2000 PRO with Cu Kα radiation), field emission scanning electron microscope (Quanta 450 FEG), XPS system (Flex-Mod SPECS with Al Kα radiation), and EPR spectrometer (Varian E-104 X-band and Jeol ESDVT4 for variable temperature). Materials included zinc nitrate hexahydrate, hexamethylenetetramine, iron nitrate, iron chlorate, magnesium nitrate, copper nitrate, deionized water, glass substrates, piranha solution, methanol, acetone, and DPPH as a standard.

4：Experimental Procedures and Operational Workflow:

Substrates were cleaned and dried. Precursor solutions were sprayed at 450°C for 30 minutes. XRD measurements were performed to analyze crystallinity, grain size, and lattice parameters using Scherrer's equation. SEM was used for morphology and cross-section examination. XPS measurements were conducted after Ar+ ion etching to analyze chemical states. EPR spectra were recorded at room temperature and variable temperatures (140-380 K) with specific microwave power and magnetic field ranges.

5：Data Analysis Methods:

XRD data were analyzed using Scherrer's equation for grain size and equations for lattice parameters. XPS data were fitted using CASA program to determine elemental compositions and binding energies. EPR signal intensities, linewidths, and g-factors were analyzed with respect to temperature and doping concentrations.