Formation of Small‐Sized CdS x Se 1‐x Crystals in Sol‐Gel‐Derived SiO ₂ Glasses

Silica glasses doped with small‐sized CdS x ‐Se 1‐x crystals were prepared by the sol‐gel method. Gels synthesized by the hydrolysis of Si(OC 2 H 5 ) 4 , in the presence of CdSeO 4 with NH 4 SCN dissolved in HNO 3 or NH 4 OH, were heated in H 2 ‐N 2 atmosphere. The pH value of solutions for CdSeO 4 and NH 4 SCN primarily determined the fraction of anions in CdS x Se 1‐x crystals. The anion content in crystals was dependent on the pH value of the solvent and/or heat‐treatment temperature, and the sulfur fraction changed from 0.1 to 0.6. The optical absorption spectra were red‐shifted as the selenium content and the crystal size increased, and the emission spectra showed a sharp band near the absorption edge position and a broad tail extending into the long wavelength. The optical band gap energies increased reciprocally proportional to the square of the crystal size.