Stimulated photoluminescence and optical limiting in CdI2

High quality single crystal of cadmium iodide (CdI2) grown from the melt by the refining method was studied under ruby laser excitation. The low temperature (LNT) emission spectrum of the crystal was recorded by using a spectrofluorometer. The spectrum appeared a structureless emission with its peak in the green spectral region. Analysis of photoluminescence (PL) measurements in the crystal showed a quadratic dependence of the PL peak intensity on incident laser power. This might be explained with the existence of self-trapped excitons in the crystal. In the desired energy ranges of interest, the emission intensity of CdI2 was found to depend on the square of the laser power, indicating the biphotonic process of two-photon excitation, i.e., the nonlinear response is due to a second-order process, or two-photon absorption (2PA) process. The optical limiting properties of CdI2 were studied using 7 ns pulses from the laser. This investigation leads to the conclusion that apart from the 2PA reverse saturable absorption (RSA) is another mechanism for optical limiting in CdI2.