Optical studies of the growth ofCd1−xZnxS nanocrystals in borosilicate glass

Abstract

We analyze optical-absorption and Raman-scattering measurements of CdS- and Zn-doped borosilicate glass, heat treated at 600 \ifmmode^\circ\else\textdegree\fi{}C to 725 \ifmmode^\circ\else\textdegree\fi{}C, to study the nucleation and growth of II-VI nanoparticles. The energy of vibrational Raman modes indicates that ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$S crystallites form where x is initially zero and increases to 0.15 with time. In glass which is quenched from high temperature (>1000 \ifmmode^\circ\else\textdegree\fi{}C) there is a weak, monotonic optical absorption which increases with photon energy. Heat treatment at 600 \ifmmode^\circ\else\textdegree\fi{}C to 725 \ifmmode^\circ\else\textdegree\fi{}C causes the optical absorption to increase and to form a peak between 3.0 and 3.2 eV. After the peak reaches its maximum value, it begins to shift to lower energy. We interpret the optical data in terms of quantum confinement of electron and hole excited states. We conclude that nucleation of particles in this glass composition is homogeneous. Typical critical nuclei are in the range from 1.5 to 2 nm. The particle size distribution is narrowest (25% full width at half maximum) at the end of the homogeneous nucleation stage and broadens when coarsening begins.