1：Experimental Design and Method Selection:

The study uses ultrasonication-assisted synthesis without polar solvents to prepare CsPbBr3 and Cs4PbBr6 PNCs. The method involves tip-sonication of precursors in a mixture of liquid paraffin, oleic acid (OA), and oleylamine (OAm), with variations in ultrasound power, radiation time, and immersion height of the vibrating spear to control properties. Reversible transformation is achieved by adding OAm or water.

2：Sample Selection and Data Sources:

Precursors include Cs2CO3 and PbBr2 powders. Samples are synthesized under controlled conditions and characterized using spectroscopy and microscopy techniques.

3：List of Experimental Equipment and Materials:

Equipment includes tip-sonication apparatus, centrifuges, transmission electron microscope (TEM, JEM-2100F), high-resolution TEM (HRTEM, JEOL JEM-2100F), X-ray diffractometer (XRD, D8-Advance), field-emission scanning electron microscope (SEM, Merlin), UV–vis spectrometer (Shimadzu), and fluorescence spectrophotometer (RF-6000). Materials include Cs2CO3, PbBr2, liquid paraffin, OA, OAm, toluene, and methyl acetate.

4：0). Materials include Cs2CO3, PbBr2, liquid paraffin, OA, OAm, toluene, and methyl acetate. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: For CsPbBr3 PNCs, precursors are sonicated at specified power and time, then purified by centrifugation and redispersed in toluene. For Cs4PbBr6 PNCs, OAm amount is increased. Reversible transformation involves adding water to Cs4PbBr6 PNCs solution. Characterization steps include TEM, HRTEM, XRD, SEM, UV–vis, and PL measurements.

5：Data Analysis Methods:

Data analysis involves interpreting XRD patterns for crystal structure, TEM and HRTEM for morphology and lattice spacing, UV–vis and PL spectra for optical properties, and calculating PL QY using rhodamine 101 as reference.