C. Benoit à la Guillaume

Spin-lattice relaxation in paramagnetic CdMnTe

Abstract Paramagnetic Relaxation has been used to determine the interaction time between Mn 2+ spins and phonons in Cd 1− x Mn x Te for x ≤ 0.02 in the temperature range 2–30 K. We measure the frequency dependance of the differential susceptibility, as a function of a DC magnetic field applied parallel to the modulated field (∼1 gauss , 100 Hz ≤ v ≤ 1 MHz ), in a Faraday experiment. As shown by Casimir and Du Pre, the basic physics is contained into the relation between isothermal and adiabatic magnetic susceptibility. The interaction time τ SL is found to decrease roughly as T −2 and decreases also when x increases. We discuss these results in the context of other experiments, in the field of Semimagnetic Semiconductors, concerned with localized spins relaxation.

Time of flight of excitonic polaritons in CdSe

Abstract Time of flight of polaritons is studied in the forbidden, mixed and allowed modes of propagation. With only one adjustable parameter, we obtain a very good agreement between all the experimental data and the usual oscillator model. In the calculation, the excited states of the A exciton and the n = 1 state of the B exciton are taken into account. The longitudinal-transverse splitting energy ħω LT is found to be equal to 1.3 meV. We show that very close to resonances, it is not possible to describe the temporal evolution of the pulse by the group velocity of the wave packet. We give an example which shows we have to use the Fourier transform method.

Spectral analysis of the fatigue of the photoluminescence and of the creation of paramagnetic centres in amorphous Ge x Se1–x

Abstract We report an extensive experimental study of the fatigue of the photo-luminescence and the photocreation of paramagnetic centres in a series of amorphous Ge x Se1 – x glasses. For each composition of this series, from pure selenium to Ge0·4Se0·6, we have studied the effect of the energy of the excitation light on these two photoinduced metastable phenomena. The experimental results are analysed by means of a model of progressive saturation across the sample from the illuminated area. This analysis allows us to define cross-sections for the fatigue of a luminescence centre and for the photocreation of a paramagnetic centre, respectively F and FS. The energy spectra for F and FS are quite different. This fact is inconsistent with the model of Street and Mott (1975) which predicts a single process for the photoluminescence fatigue and for the creation of paramagnetic centres. Therefore we discuss our results within the framework of several other models: variations on point-defect models and a model ...

Variation of Raman spectrum after optical excitation in amorphous As2Se3 at 1.6°K

Abstract Several experiments, involving electronic states have shown that amorphous As 2 Se 3 is modified at low temperature by the action of not very strongly absorbed light (α∼10 2 cm −1 ). This paper presents Raman scattering results before and after illumination. The shape of the Raman spectrum is changed by illumination: its high energy side has grown near 260 cm −1 . This light induced modification of the vibrational states is discussed within the framework of a previous qualitative model involving changes in local atomic configuration.

Excitation spectra of photoluminescence fatigue and creation of paramagnetic centers in amorphous GexSe1−x

Abstract We have studied the fatigue of the photoluminescence and the creation of metastable paramagnetic centers in a complete amorphous serie Ge x Se 1−x as a function of the illumination energy. We propose a model of progressive saturation along the sample which leads to the conclusion that those photoinduced metastable phenomena are two distinct processes.

Nucleation studies of electron-hole drops in pure Ge

SummaryWe investigate at different temperatures the excitation dependence of the size and relative number of electron-hole drops in pure Ge slightly above their threshold of formation. Our results allow a study of the kinetics of formation for the condensed phase, which can be compared with the predictions of some recent theories.RiassuntoSi analizza a diverse temperature la dipendenza dall’eccitazione dalla grandezza e dal numero relativo delle goccie del complesso elettrone-buca nel Ge puro leggermente al di sopra della loro soglia di formazione. I nostri risultati permettono lo studio della cinetica di formazione della fase condensata che può essere confrontato con le predizioni di alcune recenti teorie.РезюмеМы исследуем при различных температурах зависимость возбуждения от размера и относительного числа электрон-дырочных капель в чистом германии, в области немного выше порога образования. Наши результаты позволяют исследовать кинетику образования конденсированной фазы, которую можно сравнить с предсказаниями некоторых недавно предложенных теорий.

Study of exciton luminescence in Cu2O

Abstract The exciton photoluminescence of Cu 2 O is studied at different excitation regimes. The experimental features are well reproduced by a set of coupled rate equations. Several parameters such as the ortho-para transfer rate, Auger cross section are extracted. Extrapolation of the model to very high excitation rates confirms the previously reported Bose Einstein quantum degeneracy.

Optical orientation of excitonic polaritons and resonant faraday effect in CdSe

SummaryThe optical orientation of «Raman-like» peaks in CdSe is studied in the polariton bottleneck region, by including the effect of a longitudinal magnetic field. The interpretation of the data is based on the assumption of possible quasi-elastic scattering of polaritons, to be added to the 2 LO-phonon «Raman-like» scattering.RiassuntoSi studia l’orientamento ottico dei picchi tipo Raman in CdSe nella regione «bottleneck» del polaritone, comprendendo l’effetto di un campo magnetico longitudinale. L’interpretazione dei dati è basata sull’ipotesi di un possibile scattering quasi elastico di polaritoni da addizionare allo scattering tipo Raman a due fononi LO.РезюмеИсследуется оптическая ориентация пиков «рамановского типа» в CdSe в поляритонной области, включая эффект продольного магнитного поля. Интерпретация полученных данных основана на предположении возможного квази-упругого рассеяния поляритонов в дополнение к 2-LO-фононному рассеянию «рамановского типа».

Splitting of acceptor ground state in zincblende semiconductor alloys

Abstract We have evaluated the splitting of the acceptor ground state induced by compositional disorder in zincblende semiconductor alloys, by a perturbation method. We show that the splitting is proportional to the quadrupolar moment of the impurity distribution around the acceptor, weighted by the hole probability distribution. We discuss applications of this calculation to exciton bound to N in III–V alloys, and possible consequences for magnetic polarons bound to acceptors in II–VI semimagnetic alloys.

Comments on the paper “anti-stokes luminescence in europium monochalcogenides”

Abstract We have reported earlier magnon assisted transition in the ferromagnetic semiconductor EuO. Recently, Merlin et al. have published similar experiments, but due to an error in line assignments, they disagree with our interpretation. We recall briefly the experimental features and develop the arguments supporting our point of view.