Green Synthesis of ZnSe Nanoparticles via Laser Fragmentation: Effect of Laser Pulse Energy on Nanoparticle Size and Surface Phonon Modes

ZnSe nanoparticles were synthesized via the sustainable laser fragmentation in liquids (LFL) technique using a Nd:YAG laser at 1064 nm. The pulse energy was varied to study its effect on the particle size and vibrational properties. UV-Vis absorption spectra show a blue shift in the absorption edge with a decreasing pulse energy. The sample processed at the lowest pulse energy has the smallest nanoparticles (10.3 nm average), reaches an optical band gap of 2.83 eV, and exhibits a high-energy shoulder attributed to spin-orbit-related transitions. Raman spectra reveal a strong enhancement of the surface phonon mode (231-234 cm^-1), where its intensity surpasses that of the longitudinal optical mode, demonstrating the dominant role of surface atoms in the vibrational response. TEM confirms a wide size distribution, i.e., centered at 10.3 ± 6.4 nm, which can account for the simultaneous observation of bulk-like and quantum-confined optical and Raman features. These results show that the pulse energy effectively tunes the nanoparticle size and phonon behavior, positioning LFL as a clean and versatile method for producing ZnSe nanostructures with relevant properties for optoelectronic applications.