Abstract The power dependence up to the destruction limit and the coefficient of two photon absorption in Xe and Kr crystals are derived from transmission and luminescence experiments. A temperature dependent reduction of the quantum efficiency for luminescence at high power densities due to exciton—exciton annihilation is observed.
To understand the optical properties of atoms in solid state matrices, the absorption, excitation, and emission spectra of rubidium doped thin-films of argon, krypton, and xenon were investigated in detail. A two-dimensional spectral analysis extends earlier reports on the excitation and emission properties of rubidium in rare-gas hosts. We found that the doped crystals of krypton and xenon exhibit a simple absorption-emission relation, whereas rubidium in argon showed more complicated spectral structures. Our sample preparation employed in the present work yielded different results for the Ar crystal, but our peak positions were consistent with the prediction based on the linear extrapolation of Xe and Kr data. We also observed a bleaching behavior in rubidium excitation spectra, which suggests a population transfer from one to another spectral feature due to hole-burning. The observed optical response implies that rubidium in rare-gas thin-films is detectable with extremely high sensitivity, possibly down to a single atom level, in low concentration samples.
This paper presents the first results on a correlation between the luminescence of excitons self-trapped at the surface of solid argon and desorption. Recently, Jennison and Emin showed that localisation of electronic excitation at the surface of the crystal is an essential condition, and that especially self-trapping of excitons can lead to desorption of neutral atoms1. In the case of solid argon, self-trapping of excitons at the surface has been proved to exist2. It leads to characteristic luninescence bands which were also measured with electron excitation techniques3. Two of them exactly coincide with the 3P1 and 1P1 emission of isolated argon atoms and were not understood up to now. In the course of this work it turned out that they are emitted by desorbing neutral atoms.
We review the nonlinear-optical effects observed at room temperature in semiconductor quantum-well structures photoexcited near the band gap. A comprehensive discussion of optical transitions in these microstructures is given, including excitonic effects and the specific features of room-temperature exciton resonances. Experimental investigations using continuous-wave, picosecond-, and femtosecond-laser sources are presented. They show extremely efficient nonlinear processes. In the case of excitations that are long compared with the exciton-ionization time, the induced changes in absorption and refraction do not depend on the wavelength or on the duration of excitation. These changes depend only on the density of absorbed photons and are interpreted in terms of electron–hole plasma screening and band filling. In contrast, for ultrashort excitation, nonlinear processes depend critically on the excitation wavelength. The selective generation of excitons is found to produce effects larger than a plasma of the same density. This unexpected result is shown to arise from the low temperature of the exciton gas before it interacts with the lattice and from the decrease of screening that is the reduced dimensionality of quantum-well structures.
To understand the optical properties of atoms in solid state matrices, the absorption, excitation and emis-sion spectra of rubidium doped thin-films of argon, krypton and xenon were investigated in detail. A two-dimensional spectral analysis extends earlier reports on the excitation and emission properties of rubidium in rare-gas hosts. We found that the doped crystals of krypton and xenon exhibit a simple absorption-emission relation, whereas rubidium in argon showed more complicated spectral structures. Our sample preparation employed in the present work yielded different results for the Ar crystal, but our peak positions were consis-tent with the prediction based on the linear extrapolation of Xe and Kr data. We also observed a bleaching behavior in rubidium excitation spectra, which suggests a population transfer from one to another spectral feature due to hole-burning. The observed optical response implies that rubidium in rare-gas thin-films is detectable with extremely high sensitivity, possibly down to a single atom level, in low concentration samples. I.
This paper proposes for consideration an additional mechanism for influencing the exciton absorption spectra and observing temperature redistribution peculiarities of the crystal absorptive power. They are caused by nonlinear phonon-exciton interactions, which are due to anharmonic effects in the exciton-phonon system. The arising of the borderline frequency, which possesses the smallest region of optical bistability realization, is caused by a break in the direction of the absorption curve. At low temperatures the basic role is played by the exciton-exciton interaction, and at high temperatures nonlinear exciton-exciton-phonon processes play the most important role the value of the borderline frequency is defined by the size and sign of the nonlinear exciton-exciton-phonon function as well as by the crystal temperature and the exciton density, which is created by the external powerful laser wave.
An exciton-phonon mechanism for producing cavityless optical bistability is suggested. We consider the influence of the oscillating subsystem of a crystal on the absorption process of a laser wave in the region of exciton frequencies. It is shown that exciton-phonon interaction leads to nonlinear dependence of the absorption coefficient on the density of the exciton gas. The increase of absorption with increasing exciton density, however, is possible only in the frequency region on the long-wavelength tail of the exiton band. As a result, the exciton density of the crystal becomes a hysteresis function of external parameters (intensity of the incident wave, temperature, etc.). We calculate the absorption coefficient of excitons and define the frequency and temperature regions where optical bistability may exist. We analyze different relaxation mechanisms of excitons and explain the experimental results of observing optical bistability in different semiconductor crystals.