Picosecond time-resolved luminescence of hydrogenated amorphous silicon-carbon

Photoluminescence decay curves and time-resolved luminescence spectra of amorphous Si_0.15C_0.85 : H films are measure. The decay curves are nearly exponential with a time-constant of about 200 psec at room temperature. The peak of the emission spectrum is shifted from 440 nm immediately after the excitation to 490 nm at 400 psec after the excitation.     

Picosecond time-resolved luminescence of localized excitons in CdS1-xSex

We present time-resolved luminescence results on CdS_0.36Se_0.64 which give a new insight on the kinetics of excitons localized by alloy potential fluctuations. By exciting in the localized exciton band with detection close to the exciting wavelength we obtain the lifetime across the band. Below the exciting laser energy two processes contribute to luminescence: transfer of localized excitons by tunnel effect assisted by acoustical phonons, and luminescence (assisted by acoustical phonons) of all the states excited at time t = 0 either directly or through their acoustical absorption wing. The time behavior of luminescence with respect to the detuning from the exciting energy helps to discriminate between those two contributions. Furthermore it shows that intermediate long-living states are involved in the exciton relaxation process.     

Picosecond luminescence studies of vertical transport in short-period superlattices

Photoluminescence studies with ps-time resolution are reported for three different types of GaAs-AlGaAs microstructures: (i) a short-period superlattice, (ii) a superlattice, where an enlarged well is introduced into the center, and, (iii) a superlattice, where this well is separated from the superlattice by enlarged barriers. Exciting the samples by a mode-locked Ar⁺ laser very high sensitivity is achieved by an electro-optical cross-correlation technique using a gain modulated Si avalanche photodiode as a detector. From the data obtained we are able to determine the relevant parameters of vertical transport and nonradiative recombination in the respective structures.     

Photostimulated luminescence and its capabilities in studies of recombination in phosphors

An analysis is made of the effects of various factors on the temperature dependence of the brightness of photostimulated luminescence. A detailed study is made of the thermal dissociation of hole centers, the thermal ionization of one type of electron center, and repeated localization of electrons. It is shown that the brightness changes observed in photostimulated luminescence as a sample is heated reflect not only the mechanism of photostimulated electron liberation, but also several fundamental processes governing the mechanism for the thermal deexcitation of phosphors.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 2, pp. 50–56, February, 1971.     

Coherent detection of THz waves based on THz-induced time-resolved luminescence quenching in bulk gallium arsenide

A kind of photoluminescence quenching, in which the time-resolved photoluminescence is modulated by a THz pulse, has been theoretically investigated by performing the ensemble Monte Carlo method in bulk gallium arsenide (GaAs) at room temperature. The quenching ratio could reach up to 50% under a strong THz field (100 kV/cm). The range in which luminescence quenching is linearly proportional to the THz field could be over 60 kV/cm. On the basis of these results, a principle for THz modulation and coherent detection is proposed.     

Photoluminescence studies of surface damage states in InP

We have observed a radiative transition (1.306 eV) in the photoluminescence spectra of InP which we show is due to near surface states created by surface damage.     

Phonon satellites and time-resolved studies of carrier recombination dynamics in InGaN quantum wells

We have studied the photoluminescence and time-resolved photoluminescence of a set of InGaN quantum wells with well thickness from 1 to 7.5 nm. An analysis of the phonon satellites at 5 K shows Huang–Rhys factors from 0.32 to 0.44. The increase of this factor is caused by the electron–hole separation induced by the piezoelectric field. The time-resolved photoluminescence at room temperature shows that the decay time of the 1 and 2 nm wells does not depend on the wavelength. The maximum decay time is around 600 ps for the 2, 3 and 4 nm wells. However, for the 3 and 4 nm wells a decrease of the photoluminescence decay time is observed at the highest wavelengths. This suggest the onset of a non-radiative process in these samples. The optimum well width for efficient emission for these single quantum wells was found to be 2 nm.     

Characteristics of time-resolved luminescence in quartz

Time-resolved luminescence measurements were performed with samples of synthetic quartz (Sawyer Premium Q) and granular quartz extracted from ceramics and sediment samples under pulsed (5 ns) laser stimulation (OPO). The luminescence was detected in the UV region using colour glass filters (FWHM 280–380 nm). The time-resolved spectrum is dominated by a single exponential decay that remains substantially unaltered when the stimulation wavelength is changed from 600 to 450 nm indicating that the same recombination process is being observed. The lifetime measured at room temperature was 40±0.6 μs for the synthetic quartz; at elevated temperatures the measured lifetime is reduced in a manner that is consistent with a competitive non-radiative recombination process (thermal quenching). An average lifetime of 33±0.3 μs was obtained for seven samples of granular quartz, indicating a common recombination process in these natural samples that differs from the value for synthetic quartz.     

Polariton effects in luminescence from ZnTe crystals: surface and bulk polaritons

The exciton-polariton luminescence spectra of the ZnTe cystals are investigated in the region of the ground (n= 1) exciton state. In addition to emission of the both branches of bulk polaritons, luminescence of surface polaritons is first revealed. The temperature dependence of luminescence of the bulk and surface polaritons is considered.     

四苯基卟啉—锌化合物的微微秒瞬态吸收和荧光动力学研究

用微微秒瞬态吸收和荧光动力学测量方法,研究了四苯基卟啉-锌的三重态建立过程和单重态的衰减过德;测量了样品的系际交叉速率、单重态的寿命及其对532nm波长的吸收截面.     

Picosecond excitonic luminescence in ZnO and other wide-gap semiconductors

Radiative lifetimes of free-atom transitions, scaled by ω³ for comparison at 368 nm, are not faster than about 6.9 ns. BaF₂ core-valence luminescence, scaled in the same way from 220 to 368 nm, corresponds to 4.1 ns. In contrast, excitonic transitions in wide-gap semiconductors display subnanosecond radiative lifetimes, and in particular ZnO has radiative lifetimes measured at 50–300 ps for D^o,X and 400–900 ps for free excitons. The “giant oscillator strength” corresponding to these lifetimes can be explained by theories developed initially for defect-bound excitons, then quantum wells, and nanoparticles. An exciton is a coherent array of N dipoles, where N is the number of sites covered by coherent translational motion of the exciton. This is not essentially a phenomenon of multiple excitons, but applies as well to single-exciton decay. It differs in that regard from the more familiar Dicke giant dipole of N coherently excited atoms lacking translational periodicity. The phenomenon suggests possibilities for achieving ultrafast scintillators and high light yield.     

Picosecond luminescence spectroscopy of highly excited GaAs

Time resolved luminescence of highly excited GaAs is studied using a streak camera. We observe the Mott transition from the electron-hole plasma to the excitonic state. This transition is smooth and does not show a phase separation. The plasmon sideband of the electron-hole plasma emission is identified.     

Temperature dependence of the InP(001) bulk and surface dielectric function

Received: 14 July 1997/Accepted: 14 July 1997     

Magnetooptical studies of defects and recombination luminescence in LiBaF3

Optically detected EPR investigations have been performed on the recombination luminescence (RL-EPR) of LiBaF₃ crystal, X-irradiated at T=4.2 K. RL-EPR lines of V_K- centres were found, as well as further lines of a defect with and an axial g-tensor with its main axis along a [1 0 0] direction of the crystal.

Measurements of the magnetic circular dichroism of the absorption (MCDA) have been performed on LiBaF₃ crystals X-irradiated at two temperatures (4.2 K and RT). After irradiation at T=4.2 K, the main MCDA bands peak at 453 and 500 nm, but after irradiation at T=300 K, the main bands peak at 444 and 390 nm, there is a change of the sign between the peaks in both cases. The MCDA-detected EPR (MCDA-EPR) consists of one broad EPR line in both cases and belong to electron trap centres. Analysis of half-widths of MCDA-EPR lines showed that both defects should have g-tensors with their axes along the [1 0 0] direction. This symmetry has to be expected for F-type centres in LiBaF₃ crystals. The low-temperature electron centre has a more perturbed ground state as the RT centre.     

Picosecond time-resolved photoluminescence studies of exciton-magnetic polaron complexes in Cd1−xMnxSe

The evolution of magnetic polarons in Cd_1?xMn_xSe was examined using time-resolved photoluminescence spectra of excitons at cryogenic temperatures. Sample with manganese concentration x = 0.05, 0.10 and 0.20 were studied using a streak camera, with a system resolution of 80 psec. The formation of magnetic polarons was observed to have a large effect on the exciton lifetime, and to be strongly dependent on temperature and manganese concentration.     

Picosecond time-resolved X-ray absorption spectroscopy of ultrafast aluminum plasmas

We have used point-projection K-shell absorption spectroscopy to infer the ionization and recombination dynamics of transient aluminum plasmas. Two femtosecond beams of the 100 TW laser at the LULI facility were used to produce an aluminum plasma on a thin aluminum foil (83 or 50 nm), and a picosecond x-ray backlighter source. The short-pulse backlighter probed the aluminum plasma at different times by adjusting the delay between the two femtosecond driving beams. Absorption x-ray spectra at early times are characteristic of a dense and rather homogeneous plasma. Collisional-radiative atomic physics coupled with hydrodynamic simulations reproduce fairly well the measured average ionization as a function of time.