Abstract

Recently, the vibrational states of quantum dots have been intensively studied as well as the optical properties due to carrier confinement. Tanaka et al. repotted that phonon energies of CdSe microscystals in a GeO₂ glass decrease with decreasing microcrystal size. To the contrary, Scamarcio et al. demonstrated that CdS_xSe_1−x nanocrystals in a B₂O₃-SiO₂ glass experience lattice contraction leading the blueshift of observed Raman peaks.² In addition to those experiments, Roca et al. obtained theoretically the phonon frequency for a microcrystal.³ However, the phonon frequency decreases with decreasing size for negative phonon dispersion and does not depend on host material. In this report, a modified expression is proposed, which can explain the observed size- and glass-dependent phonon energies of CdSe quantum dots in B₂O₃-SiO₂ and SiO₂ glasses and the previously reported ones in a GeO₂ glass.¹

© 1996 Optical Society of America