Photochemistry of semiconductor colloids. 17. Strong luminescing CdS and CdS‐Ag₂S particles

Abstract

Abstract The luminescence of colloidal CdS in solutions containing sodium polyphosphate as stabilizer is activated by the addition of either Ag(ClO 4 ) or colloidal Ag 2 S. The degree of activation depends on how strongly the CdS and Ag2S particles are attached to each other, and this attachment is controlled by the concentration of polyphosphate and added divalent metal ions which bind to polyphosphate. The CdS fluorescence in these solutions can be excited by light of wavelengths longer than the wavelength of the absorption edge of CdS. The results are explained in terms of an interfacial region in which anion vacancies and incorporated silver centers, which deliver electrons into the conduction band of CdS upon illumination with photon energies less than the bandgap energy of CdS, are present. The preparation of Q‐CdS sols which fluoresce with quantum yields close to 100% is also described. Strong fluorescence occurs when defect sites, at which radiationless recombination takes place, are blocked.