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A multiphoton spectroscopic approach is implemented to study the photoluminescence (PL) emission from excitonic traps and optical nonlinear properties of wide-bandgap semiconductor cadmium iodide single crystals. As a multiphoton approach, we use two-photon and three-photon schemes to excite the crystals for PL spectroscopic diagnosis. The PL spectra are observed and studied. The results show that PL emissions are from the defect-induced self-trapped excitons in the visible region. It is found that due to much longer absorption depth, the three-photon excitation enhances the PL yield and that the order of nonlinearity depends on the kind of the photon excitation scheme. The PL is also found to depend on the thickness of the crystals. Power-dependent activation energy of the excitonic traps is determined for both the bi-photonic and tri-photonic excitation schemes. The values range from 2.62 to 2.43 meV (2.64 to 2.45 meV) for three-photon (two-photon) excitation with pump energy within 5–40 MW/cm2. This power dependence might be related to the excitation depth.

The input–output power response of the glycerol solution with different glycerin concentrations is studied. It is found that there is an optical power limiting activity for glycerol. The transmission of the optical power is found to decrease with increasing the concentration. The decrease in optical power follows the well-known Beer–Lambert law at lower powers. However, at higher powers we observe an optical limiting property with saturated output powers. The saturated output power of the solution for various concentrations is estimated and is found to decrease with an increase in the concentration of the solution. The limiting mechanism is found to be reverse-saturable absorption and is discussed on the basis of the five level energy diagram of the molecular system.

Fluorescence spectroscopy was used to study the protoporphyrin IX (PpIX) metabolism level in chick embryos during the cell proliferation process. The emission spectra were measured for PpIX bound to albumin from nonincubated and incubated eggs. The relative characteristic emission intensity of PpIX was used to determine the level of PpIX metabolism as a function of the embryonic development time. This technique might be used to estimate tumor development time. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 237–240, 2001