Synthesis and photophysical properties of $\mathrm{CdS}$ nanocomposites

We synthesized nanocomposites composed of polymethylmethacrylate with $\mathrm{CdS}$ nanoparticles distributed in it and prepared samples – films with a thickness of 0.3 mm. The sizes of the nanoparticles were determined by X-ray phase analysis. The photophysical properties of the $\mathrm{CdS}$ nanocomposites were investigated by luminescence spectroscopy. It was found that the luminescence at the domains of 430 nm and 529 nm was caused by the radiative recombination of electron-hole pairs in the nanoparticles with sizes of approximately 3 nm and more than 100 nm, respectively. The luminescence at the domain of 640 nm was associated with the radiative recombination of excitons on the defect states of the nanocomposites. These results indicate that the dependence of the luminescence intensity $I$ at the excitation by femtosecond laser pulses on the excitation energy density $P$ is described by the function $I\sim P^3$, which corresponds to the three-photon absorption.