J.Y. Zhang

HIGH-TEMPERATURE STABILITY OF A SPECTRAL HOLE BURNT IN SM-DOPED SRFCL CRYSTALS

A long-lived spectral hole at high temperature is observed in SrFCl:Sm. The measured hole lifetimes at 292 and 315 K are approximately 14 days and 16 h, respectively. Thermally induced hole filling is studied by using the time-decay experimental data of the hole area at different temperatures and by assuming a thermally activated process. An average thermal activation energy of 1.2 eV needed for hole filling is deduced.

Process of persistent spectral hole burning in SrFCl:Sm2+

Abstract Persistent spectral hole burning in SrFCl:Sm2+ at 77 K is reported. Spectral distributions before and after burning a hole are compared. It is pointed out that Sm3+ ions act as principal electron traps in the hole-burning process. It was observed in our experiments that the total hole area reaches a maximum with increasing number of holes. We consider that the number of Sm3+ ions limit the area of the holes burnt in the inhomogeneous line. By studying the hole-burning process, a theoretical relationship between total hole area and hole numbers is obtained, which is in good agreement with the experimental data. The behavior of thermal hole filling and laser induced hole filling is also discussed.

Dispersive optical bistability in ZnSe-ZnS/GaAs multiple quantum wells

Abstract Optical bistabilities with different directions of hysteresis loops in the ZnSe-ZnS multiple quantum wells (MQWs) grown by the metal-organic chemical vapour deposition (MOCVD) on GaAs substrates have been observed in transmission at 77 K with nanosecond switching time, for the first time. On the basis of the shape of the measured hysteresis loops, photoluminescence (PL) and absorption spectra measured, the optical bistability in ZnSe-ZnS/GaAs MQWs obtained here are attributed to the dispersive nonlinearity due to the effect of excitonic saturating absorption.

The 5D2 → 7F0 transition probability and its effect on hole-burning quantum efficiency in BaFClxBr1 − x: Sm2+

Abstract In this paper, The 5 D 2 → 7 F 0 emission transition probability in BaFClxBr1 − x:Sm2+ system was studied. The experimental studies show that, with the increase of Br concentration in the BaFClxBr1 − x:Sm2+ system, the 4f5d bands of Sm2+ are nearer to the 5D2 level and the 5 D 2 → 7 F 0 transition probabilities increase. The effect of the 5 D 2 → 7 F 0 transition probability on the hole-burning quantum efficiency is analyzed. The increase of 5 D 2 → 7 F 0 transition probability favours the increase of the hole-burning quantum efficiency.

Multiphonon Raman scattering in ZnSe/Zn0.80Cd0.20Se superlattices

Abstract A study of the multiphonon (MP) Raman scattering in ZnSe Zn 0.80 Cd 0.20 Se superlattices has been performed for the first time. Two kinds of longitudinal optical phonon modes were observed under the excitation of the 457.9 nm (2.71 eV) and 488.0 nm (2.54 eV) lines of an Ar+ ion laser at room temperature. A systematic discussion to distinguish the MP Raman scattering from hot luminescence is presented.

Optical bistability in ZnSe-ZnS superlattices with a Fabry-Pérot cavity

A Fabry-Perot (FP) cavity is prepared by the vacuum deposition method on ZnSe-ZnS superlattices grown on CaF2. Optical bistability (OB) of excitonic origin is observed at a wavelength of 440 nm in ZnSe-ZnS superlattices on CaF2 with FP cavity for the first time.

EXCITONIC EMISSION IN ZNCDSE-ZNSE MULTIPLE-QUANTUM WELLS

Abstract Zn 1− x Cd x Se - ZnSe multiple quantum wells (MQWs) are grown on GaAs (100) substrate by MOCVD. Their photoluminescence (PL) is studied at temperatures between 77 and 300 K. We have observed five emission bands in Zn 0.68 Cd 0.32 Se - ZnSe MQWs under the 457.9 nm line of an Ar ion laser excitation at 77 K for the first time. Three of these bands are attributed to different exciton emission: the n = 1 heavy-hole (HH) exciton transition, the n = 1 light-hole (LH) exciton transiton and the n = 1 HH exciton transiton with the emission of two LO phonons. The two exciton emission bands P 2 and P 3 of n = 1 HH and n = 1 HH with two LO phonons emission can be observed up to 230 K.

STARK LOCALIZATION IN ZNSE-ZNCDSE SUPERLATTICES UNDER AN ELECTRIC-FIELD

Photoluminescence measurements have been carried out in ZnSe-ZnCdSe Strained-layer superlattices subjucted to an electric field. It is observed that luminescence quenching and the peak shift toward the lower energy side due to the excitonic Stark effect for small electric fields. Subsequently, we find reversal to a blue shift and the luminescence peak enhancement for higher electric field, which is explained by a field-induced localization of carriers to isolated quantum wells.

Donor–acceptor pair luminescence in Zn0.8Cd0.2Se–ZnSe strained-layer superlattice

Abstract The optical property of a Zn 0.8 Cd 0.2 Se–ZnSe strained-layer superlattice (SLS) has been investigated by making use of photoluminescence and time-resolved spectra. It is found that the donor–acceptor pair (DAP) band shifts towards lower energy with decreasing excitation density and increasing delay time. The luminescence lifetime of the DAP band is slower than that of the exciton luminescence. On the basis of these results the DAP band originates from the radiative recombination of the donor–acceptor pair in Zn 0.8 Cd 0.2 Se–ZnSe SLS.

Picosecond optical bistability in ZnSeCdZnSe multiple quantum wells with a Fabry-Pérot cavity

Abstract Excitonic optical bistability with picosecond switching time in ZnSeCdZnSe multiple quantum wells (MQWs) with a Fabry-Perot (FP) cavity is investigated at room temperature. The result indicates that the threshold and switching time for the optical bistability in ZnSeCdZnSe MQWs with a FP cavity are about 210 kW/cm 2 and 50 ps, respectively. On the basis of the excitonic nonlinear theories, excitonic absorption spectra in the ZnSeCdZnSe MQWs under different excitation intensities obtained here, we attribute the major nonlinear mechanism for the optical bistability in ZnSeCdZnSe MQWs with a FP cavity to the phase space filling of excitonic states and excitonic band broadening due to exciton-exciton interactions.