Abstract

Numerous attempts to use nanocrystaline doped media in non-linear optics were performed. As this application needs high optical quality bulky samples the only media to use were commercial semiconductor doped silicate glasses (SDG) [1]. Low concentration of nanocrystals restricts upper value of non-linearity of the SDG. As nonlinearity of the glasses at least in spectral region close to optical resonance is higher for media with narrower size distribution of the nanocrystals [2] commercial SDG are not optimal for the application. We present a novel P₂O₅ – Na₂O – ZnO – AlF₃ – Ga₂O₃ SDG doped with CdS, CdSe, PbSe and Cd – S – Se nanocrystals of different composition. The synthesis of well-crystallised nanoparticles of different semiconductors with average radii from 20 to 60 angstroms was achieved due to high flexibility of the glass matrix. Special regimes of the glass thermal treatment to form low- size-dispersed nanocrystals have been used. Contrary to conventional silicate SDG the phosphate glass can contain up to 1.2 wtsemiconductor, and temperature of the treatment is as low as 380-430 C. Characterization of the glass with material science techniques (transmission electron microscopy, electron probe microanalysis and X ray diffractometry) and optical absorption spectroscopy gives evidence of higher concentration and narrower dimensional distribution of nanocrystals comparatively to conventional SDG. The nanoparticles show wurtzit crystalline structure. Measured spectra demonstrate ”quasi-linear" structure of optical absorption of the glasses (CdS, CdSe, Cd – S – Se nanocrystals) with the absorption edge laying within the range 0.3 (CdS) −1.5 (PbSe) microns in dependence on composition and size of nanocrystals. The rich structure of the absorption is probably related to the change of selection roles for electron-hole transitions within the crystallites due to non-spherical shape of the grains. This can be treated as transitions from confined valence band with spin-orbit splitting for pure CdS and with crystal and spin-orbit splitting for Cd – S – Se, and is consistent with the splitting observed for CdSe [3,4]. Possibilities for non-linear optics applications [1,5] are discussed.

© 1996 IEEE