By means of two-photon excited photoluminescence, we demonstrate the influence of self-absorption on the emission properties of thin (1.5 µm) film CdS formed by laser ablation. The excitation of the sample is performed with 200 fs pulses at 804 nm (1.54 eV). The photoluminescence spectrum takes the form of a single peak centered at 510 nm (2.43 eV) at 300 K. The spectrum is shifted about 45 meV to lower energies with respect to the photoluminescence excited by one photon absorption. By fitting the photoluminescence spectra with the Roosbroeck-Shockley relation and Urbach’s rule, it is shown by Beer’s law that the shift is caused by self-absorption. The results further provide evidence of low impurity concentration and excellent surface quality. They also confirm the outstanding optical properties of thin film CdS formed by pulsed-laser deposition and suggest the application of the films for effective up-conversation materials in ultra-fast experiments.

We studied the emission properties of colloidal PbS quantum dots (QDs) (5.3 nm) dispersed on semi-insulating GaAs in the temperature range of 5–300 K by employing Fourier transform infrared photoluminescence spectroscopy. The results reveal that the PbS QDs alter and notably enhance the emission features of the GaAs substrate itself. The dependence of the QD emission peak position on temperature is modeled equivalently well with the well-known empirical Varshni equation and with a relation based on thermodynamics. The work reveals that emission properties of PbS QDs do not follow predictably general rules but are determined sensitively by the preparation method and substrate used.

We are reporting an esoteric method to determine the optical bandgap of direct gap materials by employing Urbach’s rule. The latter, which describes the slope of the band tail absorption in semiconductors, in its original version, cannot be employed to pinpoint the optical bandgap. Herein, however, we show that a modified form of Urbach’s rule defines the optical bandgap, and therefore, enables the accurate determination of the optical bandgap energy, which turns out to be identical with the threshold energy for the band tail absorption. The model further produces an explicit expression for the absorption coefficient at the optical bandgap energy.

The work addresses an unresolved topic in solid-state physics, i.e., the dependence of the Debye temperature (T_D) on the energy band gap (E_g) of semiconducting materials. The systematic calculation of T_D by using the ratio of sound velocity and lattice constant from the literature resulted in the relation T_D∝exp(E_g). The exponential relationship is confirmed by a theoretical model based on the microscopic analysis of the electrical conductivity in metals and semiconductors.