The EPR measurements are carried out at room temperature using a Bruker ELEXYS E500 spectrometer operating at X-band frequencies (9.5 GHz) and a Bruker ER4119HS resonator. The spin trap solution (25 mM) was prepared by first dissolving 50 mg of BMPO (MW = 199.25, Dojindo Molecular Technologies, Inc.) in 2.5 mL of absolute EtOH (99.5 %, Baker HPLC Analyzed, J.T.Baker). Then, 7.5 mL of toluene (99.5 %) was added. For the particle's solution, the HPs powder was first dispersed in toluene by sonication for 3 min. For the measurements, 40 μL of HPs particle solution was mixed with 40 μL of the spin trap solution (solution 1 or Sol. 1), 12.5 % ethanol) using a vortex. For the samples with 42 % ethanol, 40 μL of EtOH was added to solution 1 (solution 2 or Sol. 2). Samples were loaded into Vitrocom quartz capillaries, CV1012-Q-100, with a 1 mm inner diameter. The experimental conditions of the EPR spectral analysis were as follows: microwave power of 20 mW, 0.1 mT modulation amplitude, and 100 kHz modulation frequency. The sweep range was 10 mT, and the spectra consisted of 512 points. The samples were irradiated under white light using a SCHOTT KL 2500 LED light source with a maximum light intensity of 1,100 lm. The tested samples were continuously illuminated during the experiment, and the EPR spectra were taken every 3 min. The fitting of the EPR spectra was done with winsim2002 software. The plots with the fitting parameters were done with the assistance of MATLAB R2021a and easy spin-5.2.