Optical properties of Ag2S quantum dots

Colloidal solutions of silver sulfide quantum dots of various sizes were synthesized from low-concentration water solutions of silver nitrate, sodium sulfide and sodium citrate as stabilizer. The size of Ag2S quantum dots in colloidal solutions was determined by dynamic light scattering. The produced Ag2S quantum dots were dispersed in a polyvinyl alcohol (PVA) film matrix. The transmission and absorption spectra of PVA films containing Ag2S were measured in the wavelength interval 190–900 nm. A comparative study of the optical properties of PVA films with Ag2S quantum dots showed that a decrease of quantum dots to ∼ 6 nm leads to an increase in the band gap Eg of silver sulfide to ∼ 1.6 eV, which is almost twice larger than the band gap of bulk Ag2S. The optical properties of PVA films with Ag2S quantum dots smaller than 5 nm exhibit specific features associated with exciton transitions.