Peng Wenji

Time-Resolved Fluorescence Study of C60 Solution

Using a picosecond excitation source and a time-resolved streak camera detection system, the time-resolved fluorescence spectra of purified C60 have been recorded from toluene solution at room temperature. A fluorescence peak at about 730 nm was detected and its lifetime was directly determined to be 1.1±0.1 ns. Two fluorescence peaks obtained from the mixture of C60 and C70 at 676 and 696 nm were mainly related to C70 content.

Photoluminescence Study of C70 Film Manufactured by Physical Jet Deposition

We have fabricated C70 film by physical jet deposition (PJD) technique and measured the absorption and photoluminescence (PL) spectra of this kind C70 film. In comparison with the deposited C70 film in high vacuum, the absorption and integrated PL spectra are similar, but there is a big difference in the time-resolved PL. The C70 film made by PJD shows a very fast PL decay of less than 20 ps which should result from the fast relaxation process of C70 molecule in the excited state S1 of this new kind film.

Studies on the dynamics of optical bistability switching in the internal Fabry-Perot cavity with a CdSxSe1-x-doped glass channel waveguide

We report the optical bistability in CdSxSe1-x-doped glass channel waveguide with rise and fall times of about 24 and 30 ps, respectively, in bistable switching by means of fiber coupling input with a power of about 3 mW. The third-order nonlinear susceptibility (χ(3)) of CdSxSe1-x-doped glass is estimated experimentally to be 1.8 × 10-9 esu. The high speed switching and the value of χ(3) show that the optical bistability is caused by an optical nonlinearity which can be attributed to the band-filling effect.

Dynamics of carrier capture in AlGaAs / GaAs multiple quantum wells

Dynamics of carrier relaxation and capture in AlGaAs/GaAs multiple quantum wells (MQW) at 80 K is studied using picosecond luminescence and femtosecond absorption saturation measurements. Carriers generated in the wells and in the barriers scatter initially out of the excited states to a quasi-equilibrium state in 35 and 400 femtoseconds, respectively, before they are captured into the bound states of the quantum wells. Carrier capture occurs during carrier cooling and recombination. A carrier capture time of 25 ps has been deduced from time-resolved luminescence.

Ultrafast Exciton Trapping Dynamics in ZnSe/(CdSe) m (ZnSe)) n Short Period Superlattice Quantum Wells

The ultrafast exciton trapping dynamics in ZnSe/ZnCdSe short period superlattice quantum wells has been studied by using transient photoluminescence spectroscopy. A rapid exciton trapping time of less than 7 ps from the barriers to the wells is measured. In Te doped samples self-trapped excitons give rise to Stokes shifted broad band luminescence and exhibit much longer lifetime.

Time decay behavior of fullerene-C60 studied by time-resolved photoluminescence

The time-resoved photoluminescence spectra of C60 have been studied from toluence solution at room temperature and from thin film at both room temperature and 77 K. A photoluminescence peak at about 730 nm was detected from solution at room temperature and film at 77 K, in which lifetimes was determined to be 1.1 and 0.9 ns, respectively. At room temperature, the photoluminescence peak of thin film shifted to 740 nm with fast decay behavior which was fitted well to a double-exponential lifetimes with τ1 = 0.087 ns, τ2 = 0.68 ns. Two relaxation mechanisms are given tentatively in explaining this phenomenon.

Power Dependence of the Recombination Processes in the lnxGa1-xAs/GaAs Single Quantum Well

We have measured the power dependence of the photoluminesence spectra from a set of strained InxGa1-xAs/GaAs single quantum wells. The result shows that the excitation power has important effect on the carrier recombination processes. When the power increases from 0.5 to 14 mW, the photoluminescence from the barrier becomes more intense than that from the well and the trapping efficiency decreases. At high excitation level, the ratio of the radiative recombination rate to the nonradiative recombination rate of the barrier increases ten times than that at lower excitation level, while it only doubles for the well.

TIME-RESOLVED PHOTOLUMINESCENCE FROM INXGA1-XAS/GAAS SINGLE QUANTUM WELL

We have measured the time-resolved photoluminescence spectra of several InxGa1-xAs/GaAs single quantum well samples at 77K. The different temporal behaviors of the photoluminescence (PL) from the GaAs layer and the excitonic emission from the InxGa1-xAs well were obtained. The lifetime for the exciton in the InxGa1-xAs well were determined to be 110-170ps. The trapping efficiency of the well to the carriers was about 80%.