[Luminescence and quantum electronics].

Xinye Fan, Shijie Xu

Localized electron states induced by various disorders, including defects and impurities, usually exist in solids. Their electrical properties have been extensively investigated and well documented, while their optical properties such as localized-state ensemble (LSE) luminescence remain poorly understood. In particular, a microscopic quantum many-body (MB) theory has not yet been established for LSE luminescence so far. In this Letter, we attempt to fill this void via developing a quantum MB luminescence theory taking into account both electron-phonon (e-p) and electron-electron (e-e) interactions. Abnormal thermal behaviors such as redshift and subsequent blueshift of peak position, narrowing and succeeding broadening of linewidth, decline in intensity, and variation in lifetime can be quantitatively interpreted. Within the framework of the MB-LSE theory, moreover, Varshni's empirical formula for bandgap temperature dependence and Huang-Rhys factor for e-p coupling, and other key formulas are further derived and discussed.

B. Ullrich, Takayoshi Kobayashi

Recently, we have discovered that the excitation of thin CdS films with the 514.5 nm line causes an all-optical bistable luminescent emission in the near infrared part of the spectrum. A first insight in mechanism and origin of all-optical bistability in luminescence of semiconductors is presented. We show that the initial and final states of the bistable luminescence are determined by the thermal properties of the luminescence intensity of the thin CdS film. However, during the bistable switch of the luminescence thermal effects and electronic ones take place. Thus, all-optical bistability in luminescence is a thermally induced electronic bistability.

S. Abraham-Ibrahim, B. Caroli, C. Caroli +1 more

We study the competition, in the light scattering spectrum, between electronic resonant Raman scattering and luminescence, on a simple three-level model due to Takagahara et al., where electrons are assumed to couple, in the intermediate state, with a field of localized « phonons ». The model can be solved exactly. We show that the relative weight of Raman versus luminescence peaks is controlled by a single memory parameter γb /Γ — where γb and Γ are the damping rates of the intermediate electronic state and of the phonons. If γb/Γ >> 1, memory is quasi-perfect, and the spectrum is purely Raman; in the opposite limit luminescence predominates. For γb/Γ ∼ 1, both structures are present, as well as anomalous satellites characteristic of « hot » luminescence.

O.S. Heavens