A unified cohesive energy model for predicting size-dependent optical and thermal properties of CdSe and ZnSe nanoparticles

Abstract

Semiconductor nanoparticles exhibit remarkable deviations in thermal and optical properties compared to their bulk counterparts due to quantum confinement and enhanced surface effects. In this study, a unified cohesive energy-based theoretical model is developed to predict the size-dependent melting temperature and optical bandgap of cadmium selenide (CdSe) and zinc selenide (ZnSe) nanoparticles. The model is implemented through MATLAB® simulations, utilizing a geometric scaling approach based on the surface-to-volume atomic ratio. The results reveal that for CdSe, the optical bandgap increases from ~ 1.74 eV (bulk) to ~ 2.21 eV at 4 nm, while the melting temperature decreases from ~ 1510 to ~ 1316 K. Similarly, ZnSe nanoparticles show a bandgap increase from ~ 2.70 to ~ 3.39 eV and a melting temperature reduction from ~ 1795 to ~ 1568 K. These trends are attributed to the dominant role of under-coordinated surface atoms and the consequent reduction in cohesive energy. The model predictions demonstrate strong agreement with experimental measurements and theoretical frameworks, establishing a pronounced inverse correlation between thermal stability and optical bandgap energy. This computationally efficient and scalable approach provides critical insights into the design and optimization of nanostructured semiconductors for applications in optoelectronics, thermal imaging, and photovoltaics.