The optical properties of the chromium doped spinel type semiconductor $\alpha$-$\rm ZnAl\sb2S\sb4$ have been examined over the temperature range 2-540K. From extrinsic absorption and photoluminescence spectra the transitions between the ground state $\rm\sp4A\sb{2g}$ and the excited levels $\rm\sp2E\sb{g}\ (R\sb1$ and R$\rm\sb2),\ \sp2T\sb{2g},\ \sp4T\sb{2g}$ and $\rm\sp4T\sb{1g}$ of the Cr$\sp{3+}$ ions were observed. A fit of the measured temperature dependence of the PL decay, using a four level model, yielded the lifetimes of the $\rm\sp2E\sb{g}\ (R\sb1$ and R$\sb2)$ and $\rm\sp4T\sb{2g}$ levels and the energy gaps between the $\rm\sp2E\sb{g}\sp{(1)}$-$\rm\sp2E\sb{g}\sp{(2)}$ and $\rm\sp2E\sb{g}\sp{(1)}$-$\rm\sp4T\sb{2g}$ states which were found to be very close to the values obtained from steady-state measurements. A configurational coordinate diagram for Cr$\sp{3+}$ ions in a $\alpha$-$\rm ZnAl\sb2S\sb4$:Cr spinel host has been constructed. Optical gain measurements at 198 K, 298 K and 380 K displayed two separate spectral regions associated to the Cr$\sp{3+}$ ions and possibly to Cr$\sp{4+}$ impurity centers. Gain values of up to 25 cm$\sp{-1}$ (730 nm) at 198 K were obtained. Finally the intrinsic photoluminescence measurements revealed an intense UV peak around 380 nm from 20 K to 296 K which corresponds to the indirect band gap of the host crystal, $\alpha$-$\rm ZnAl\sb2S\sb4.$
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/4514 |
| Date | January 1998 |
| Creators | Broussell, Isabelle. |
| Contributors | Fortin, E., |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Detected Language | English |
| Type | Thesis |
| Format | 63 p. |
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