1：Experimental Design and Method Selection:

The study utilized an upconversion fluorescence nanosystem involving Gd2O3:Yb,Er nanospheres (UCNS) and TMB, leveraging the inner filter effect for detection. The detection mechanisms include oxidation reactions and complex formation.

2：Sample Selection and Data Sources:

Synthetic samples with varying concentrations of MnO4? and Cr2O72? ions were prepared. Real samples included tap water and pond water spiked with known concentrations of the ions.

3：List of Experimental Equipment and Materials:

Materials included Gd(NO3)3·6H2O, Yb(NO3)3·6H2O, Er(NO3)3·6H2O, urea, sodium acetate, KMnO4, Na2Cr2O7, TMB, ethanol, acetic acid, and various salts for interference tests. Equipment included XRD diffractometer, TEM, UV-Vis spectrophotometer, photoluminescence spectrometer, XPS, ICP spectrometer, elemental analyzer, and upconversion luminescence spectrometer.

4：Experimental Procedures and Operational Workflow:

Synthesis of UCNS via precipitation and annealing. Detection involved dispersing UCNS in buffer with TMB, adding analyte ions, and measuring UC fluorescence under 980 nm excitation. Optimization of pH, TMB concentration, and incubation time was performed. Selectivity tests with interfering ions and real sample analyses were conducted.

5：Data Analysis Methods:

Linear regression for calibration curves, limit of detection calculation based on signal-to-noise ratio, and statistical analysis for recovery and RSD in real samples.