I. S. Gorban

Multiserial Structure of Excitonic Energy Spectrum in Monoclinic ZnP2 Crystal

One-photon excitonic absorption spectra of the monoclinic ZnP 2 (β-ZnP 2 ) crystals are analysed. There exist four series characterized by the serial law E n = E g - Ry/n 2 + Δ/n 3 with the same value of energy gap Eg = 1.6026 meV. By variational calculations of the exciton energy dependence on the anisotropy parameter, we conclude an appearance of several hydrogen-like series caused by the splitting of excitonic states with different quantum numbers l and |m| due to the low symmetry of the crystal. Conclusions are made that two series with Δ = 0 can be attributed to the P-states of an exciton, and two others with Δ ¬= 0 to the S-states of an exciton. Calculations of e-h exchange interaction in an S-exciton are performed. Splitting of the series with Δ ¬= 0 is interpreted to have exchange origin (ortho-para-splitting). Its value is obtained to be 12.7 meV.

Radiative transitions in an excitonic molecule

Abstract The ratio of intensities of inverse hydrogenlike series (IHS) luminescence bands which are due to two-electron transitions in an excitonic molecule (EM) have been calculated. The rates of two-photon and two-electron spontaneous transitions in the excitonic molecule have been estimated. Their ratio has been obtained as 0.13. The correlation between theoretical estimations and experimental results obtained from the luminescence spectra of β - ZnP2 crystals has been analyzed.

BIEXCITONIC LIQUID IN MONOCLINIC ZINC DIPHOSPHIDE CRYSTALS

Abstract The dielectric gas-dielectric liquid phase transition in the system of excitonic molecules in β - ZnP2 crystals is considered. The influence of crystal anisotropy is under discussion. The features of β - ZnP2 photoluminescence (PL) spectra under intermediate excitation intensities (Iexc ∼ 103 - - 105 W/cm2) at liquid helium temperatures are considered. In previous works optical manifestations of the dielectric biexcitonic liquid have been observed. An experimental study of the phase diagram of this liquid is performed. Biexcitonic liquid critical parameters are estimated.

Ions of excitonic molecule in β - ZnP2 crystals

Abstract Broad T emission band appears in the low-temperature spectra of β - ZnP2 crystals between bands of the free excitons and biexcitons. This band is shown to be due to free ions of excitonic molecule (trions). The dependence of this band intensity IT on the excitation intensity Iexc ( I T ∝ I exc 3 2 ) proves trion origin of T band. The binding energy of trion has been determined as 4.1 meV. Correlation of experimental intensities of the bands of trions and excitons is shown to be in good agreement with theoretical estimations. The behaviour of emission spectrum in external electric field has been studied. The intensity of T band decreases with increase of the applied voltage, proving the destroying of trions in electric field.

Acoustically stimulated phase transition and low temperature optical spectra in PbI2 crystal

The influence of an intensive ultrasonic wave on the crystal structure of PbI2 was investigated. Acoustically stimulated phase transition have been observed for the first time.

Quantum biexcitonic liquid in monoclinic ZnP2 crystals

A phonon–roton dispersion relation is proposed for the elementary excitations of a quantum biexcitonic liquid in semiconductors. The proposed dispersion relation is used as a starting point for a calculation of the photoluminescence spectrum of the liquid and an analysis of its behavior under variation of temperature and density of the biexcitonic liquid. The parameters of the dispersion curve of elementary excitations of the quantum biexcitonic liquid are evaluated by fitting the calculated photoluminescence spectrum to the experimental spectrum of the biexcitonic liquid of semiconducting β-ZnP2 crystals. Experimental studies of how the photoluminescence spectrum of a biexcitonic liquid in β-ZnP2 depends on the temperature and the intensity of the laser excitation confirm the initial theoretical model. The dependence of the temperature of the crystals on the excitation intensity is measured, and for some of the samples an anomalous dependence is found: the temperature of the crystal decreases as the exci...

Fine structure of the emission spectrum of biexcitonic liquid in monoclinic ZnP2 crystal

A problem of the emission (photoluminescence or PL) spectrum of molecular type electron-hole (biexcitonic) Bose liquid in semiconductors is considered. A model of quantum Bose liquid with HeII-like phonon-roton dispersion law is used to calculate the theoretical emission spectrum of such a liquid. At excitation intensities higher than ∼1 kW/cm2 and temperatures lower than 5 K biexcitonic liquid exists in semiconductor β-ZnP2 crystal. The fine structure of PL spectrum of this liquid at various excitation intensities and temperatures is analyzed in the frame of the model of quantum Bose liquid with phonon-roton dispersion law.

Luminescence of ultracold excitons in cuprous oxide crystal

Abstract Two new bands were observed in luminescence spectrum of high-purity Cu 2 O crystal under resonant excitation. The detailed study of their shape and excitation spectra allowed us to interpret these bands as two-electron transitions in the non-equilibrium system of interacting ortho- and para-excitons. The schematics of energy spectrum and quantum transitions for this system are suggested. The influence of exciton–exciton scattering is under consideration.