Abstract
The low-temperature (T = 2 K) exciton-polariton luminescence (EPL) spectra in the vicinity of the exciton-resonance frequency An=1 for CdS-type crystals have been theoretically and experimentally investigated with allowance for the mechanical exciton decay . The results of the numerical calculations of the partial and interference contributions of the bulk and radiative surface spectral modes to the EPL in the geometry of additional s- and p-polarized waves emitted into vacuum are analyzed. It is shown that the contributions of purely longitudinal excitons and their interference with polaritons of the upper dispersion branch near the longitudinal frequency ÏL to the EPL are small (âŒ10% - 30%); nevertheless, they must be taken into account to obtain quantitative agreement with experimental data. Specifically these contributions are responsible for the formation of an additional line (along with the fundamental AT line) in the case of oblique incidence of radiation.
Highlights
It is shown that the contributions of purely longitudinal excitons and their interference with polaritons of the upper dispersion branch near the longitudinal frequency ÏL to the exciton-polariton luminescence (EPL) are small (~10% - 30%); they must be taken into account to obtain quantitative agreement with experimental data
Due to the transformation of the normal-wave spectrum with allowance for the real exciton decay, radiative surface modes are involved in the energy transfer through the crystal boundary, and the presence of spatial dispersion (SD) leads to their interference interaction
The contributions of 23 p to sharply decrease with an increase in Î, which can be explained by the SD suppression due to mechanical-exciton decay for longitudinal waves
Summary
In the frequency range Ï < ÏΞ , where condition (1) is always violated for waves 2 and 3, a real additive to wave vector kÎČ arises at finite Đ (curves 2 and 3); this additive indicates that radiative surface modes 2 and 3 cease to be purely decaying and are involved in the transfer of exciton excitation energy in the crystal The latter circumstances are undoubtedly of great importance for the formation of the EPL spectrum of crystals in the emission geometry of purely longitudinal excitons, whose analysis is the object of our study. In expression (8), IN is the normal component of the energy fluence to the surface and nÎČ wÎČ is the coupling coefficient between the energy fluence and the squared modulus of the electric field amplitude for the normal wave ÎČ: w=o c, 8Ï w=ÎČ c 8Ï ÎŽ ÎČ
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