Multiphoton excitation and thermal activation in indirect bandgap semiconductors

The single crystals of wide- and indirect-bandgap semiconductor CdI₂ were grown and their optical properties as well as the defect-induced excitonic photoluminescence (PL) spectra were studied. The multiphoton excited PL spectra, charactering the emissions from excitons in the visible region, were taken. The PL intensity (I_PL) was found to vary nonlinearly with pumping power (P). The I_PL was also found to decrease with increasing temperature. The temperature dependence of I_PL for each P followed a fashionable relationship, from which the activation energy (∆E) of the defect-induced excitonic trapping was calculated. The ∆E was found to slightly decrease with increasing P, with an average value of 2.5 meV. The results, however, demonstrates the existence of the self-trapped excitons responsible for the characteristics broad-band emission in the visible range. This study shows that the single crystals of CdI₂ might have potential in applications as thermo-luminescent dosimeters in radiation measurements.