Two different mechanisms of formation of quantum dots in borosilicate glass

The nucleation and growth of Cd_1-xZn_xS and CdS_xSe_1-x nanocrystals in borosilicate glass are investigated through optical absorption and resonant Raman scattering measurements. The optical absorption spectra are interpreted with the help of a quantized-state effective-mass model applied for heterogeneous and homogeneous nucleation of nanocrystals. Stoichiometry changes of the particles during the growth stage are monitored by resonant Raman measurements. The findings indicate that the formation of Cd_1-xZn_xS particles involves a stage of homogeneous nucleation and then a rapid transition to ripening. No growth is observed. CdS_xSe_1-x particles undergo heterogeneous nucleation and growth simultaneously with a gradual transition into the ripening stage.