Room temperature spectral hole burning and elimination of photodarkening in sol-gel derived CdS quantum dots

Spectral hole burning at room temperature is used as a technique to compare optical nonlinearities of semiconductor quantum dot materials prepared by the sol-gel and glass fusion techniques. In an effort to understand the mechanism of photodarkening in quantum dots and assess its effect on optical nonlinearities, we prepared and characterized three representative samples with similar dot sizes. We found that photodarkening can be reduced substantially by controlling the media surrounding the dots. The sol-gel derived samples with 80 wt % SiO₂ do not exhibit appreciable photodarkening while the melt-quenched glasses with 56 wt % SiO₂ exhibit strong photodarkening effects at room temperature which results in reduction of their optical nonlinearity by a factor of ≅20 compared with the sol-gel derived samples.