Size-dependent solvatochromism of CdS nanoparticles: Experimental absorption and fluorescence analyses

•Size controlled CdS nanoparticles were synthesized using precipitation method.•The as-synthesized nanoparticles were characterized.•Quantum confinement effect were evaluated.•Their solvatochromic response was investigated using Lippert–Mataga equation.•Large permanent dipole moment have been predicted for cubic CdS nanoparticles. Owing to the quantum confinement effect, a nanocrystal shows a unique blend of molecular and solid properties: discrete energy levels with large polarizabilities which could respond to solvent environments. In this paper, we used steady-state fluorescence and absorption spectroscopy to study the size-dependent solvatochromism of CdS nanoparticles. The dipolar character of the ground state and the first excited state of the nanoparticle were also investigated with in the framework of Onsager reaction field theory using Ooshika–Mataga–Lippert equation. The results of the present study revealed that the solvatochromic responses were size dependent. Additionally, the responses increased with the particle size up to a certain size beyond which the response started to fall again. Hence, fine-tuning the nanoparticle's solvatochromic response and band gap is possible by appropriate choice of size. Moreover, size-dependent dipole moment values of CdS nanoparticles were determined. Based on the findings of the present study it was noted that steady-state fluorescence and absorption spectroscopy methods can efficiently be used to study the size-dependent solvatochromism of CdS nanoparticles. [Display omitted]