Allotrope-dependent physicochemical and optical properties of red and grey selenium nanoparticles

Abstract

Selenium nanoparticles (SeNPs) are increasingly being investigated as safer and more bioavailable alternatives to conventional selenium compounds; however, the influence of selenium allotropy on their physicochemical and optical properties remains poorly understood. In this study, red and grey SeNPs were synthesized and comparatively characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, and fluorescence spectroscopy. Red SeNPs exhibited predominantly spherical morphology with an average diameter of 218 ± 24 nm and an amorphous structure, whereas grey SeNPs formed needle-like nanostructures with a mean length of 575 ± 202 nm and a trigonal crystalline structure. Raman spectra showed a broad band at 250–255 cm⁻¹ for red SeNPs and a sharp peak at 233 cm⁻¹ for grey SeNPs, corresponding to amorphous and trigonal selenium, respectively. Grey SeNPs displayed significantly stronger fluorescence emission at 430–450 nm than red SeNPs, indicating that increased crystallinity and structural ordering enhance fluorescence activity. These findings demonstrate that selenium allotropy governs morphology, crystallinity, and photophysical behavior and provide a physicochemical basis for understanding the different functional performances of selenium nanomaterials.