Time-resolved photoluminescence

Zinc sulfide, with its wide band gap of 3.66 eV, has been considered as an excellent electroluminescent (EL) material. The electroluminescence of ZnS has been used as a probe for unraveling the energetics at the ZnS/electrolyte interface and for possible application to display devices. Fan and Bard [127] examined the effect of temperature on EL of Al-doped self-activated ZnS single crystals in a persulfate-butyronitrile solution, as well as the time-resolved photoluminescence (PL) of the compound. Further [128], they investigated the PL and EL from single-crystal Mn-doped ZnS (ZnS Mn) centered at 580 nm. The PL was quenched by surface modification with U-treated poly(vinylferrocene). The effect of pH and temperature on the EL of ZnS Mn in aqueous and butyronitrile solutions upon reduction of per-oxydisulfate ion was also studied. EL of polycrystalline chemical vapor deposited (CVD) ZnS doped with Al, Cu-Al, and Mn was also observed with peaks at 430, 475, and 565 nm, respectively. High EL efficiency, comparable to that of singlecrystal ZnS, was found for the doped CVD polycrystalline ZnS. In all cases, the EL efficiency was about 0.2-0.3%. 

Varnavski, O., Ispasoiu, R.G., Balogh, L., Tomalia, D., and Goodson, T. (2001) Ultrafast time-resolved photoluminescence from novel metal-dendrimer nanocomposites./. Chem. Phys. 114, 1962-1965. 

J. Tauc, Time-Resolved Spectroscopy of Electronic Relaxation Processes P.E. Vanier, IR-Induced Quenching and Enhancement of Photoconductivity and Photoluminescence... 

L Smilowitz, A Hays, AJ Heeger, G Wang, and JE Bowers, Time-resolved photoluminescence from poly[2-methoxy, 5-(2-ethyl-hexyloxy)-p-phenylene-vinylene] solutions, gels, films, and blends, J. Chem. Phys., 98 6504-6509, 1993. 

Time-resolved measurements of photogenerated (very intense illumination, up to 0.56 GW/cm ) electron/hole recombination on CD (selenosulphate/NTA bath) CdSe of different crystal sizes has shown that the trapping of electrons, probably in surface states, occurs in ca. 0.5 ps, and a combination of (intensity-dependent) Auger recombination and shallow-trapped recombination occurs in a time frame of ca. 50 ps. A much slower (not measured) decay due to deeply trapped charges also occurred [102]. A different time-resolved photoluminescence study on similar films attributed emission to recombination from localized states [103]. In particular, the large difference in luminescence efficiency and lifetime between samples annealed in air and in vacuum evidenced the surface nature of these states. 

A3.5 Time-resolved photoluminescence studies of GaN A3.6 Persistent photoconductivity in GaN A3.7 Electrical transport in wurtzite and zincblende GaN A3.8 Characterisation of III-V nitrides by capacitance transient spectroscopy... 

Time-resolved photoluminescence was also used to show that the spatial separation of the electron and hole wavefunctions due to the piezoelectric fields in GalnN/GaN QWs leads to a dramatic reduction in oscillator strength, particularly for thick quantum wells [6]. Due to the reduced oscillator strength for the lowest energy state, the optical absorption spectrum of the quantum wells is expected to be dominated by highly excited states close to the strained bulk bandgap. 

Time-resolved fluorescence using 9-methylanthracene (9MAn) as a photoluminescent probe was used to detect residual stresses on polymer products. The fluorescence lifetimes of 9MAn in this nondestructive measurement were correlated with the stresses, not the strains, of the PVC samples containing carbon black and 9MAn. The test enabled the estimation of residual tensile stresses on... 

The determination of the photoluminescence parameters (excitation frequency, emission frequency, Stokes shift, fine structure parameter, and lifetime) can lead to information which, at the simplest level, indicates the presence of an electronically excited state of a species, but which can be sufficiently detailed so as to lead to a clear identification and characterization of the photoluminescent sites(J6-44). Moreover, measurements of the variations in the intensity and positions of the bands as a function of time (time-resolved photoluminescence) provide valuable kinetic data representing the reactions occurring at the surface. Although most of the photoluminescence measurements have been carried out at low temperatures for specific reasons (see Section III.C.2), there is much evidence that some of the excited states involved are present even at higher temperatures and that they play an important role in catalytic and photocatalytic reactions. Therefore, it is clear that the information obtained by photoluminescence techniques is useful and important lor the design of new catalysts and photocatalysts. 

The parameters that are measured run a wide gamut from the routine (current, potential or some electrical parameter) to the exotic (e.g., beam deflection due to refractive index changes). A hierarchical approach to discussing these variant methods has been described [52]. Thus, the methods in Table 2 fall under the categories of purely electrical (entries 1-3, 8 and 9), purely optical (entry titled photoluminescence spectroscopy and entries 12 and 13), electro-optic (electroluminescence spectroscopy) or opto-electric (entries 4-7). We can also distinguish between frequency-resolved (entries 3-7) and time-resolved (entries 10 and 14) measurements, although it must be noted that in many instances (e.g., entries 8 and 11) both steady-state and time-resolved approaches are feasible. 

TA-transient absorption TRANIP = time-resolved anisotropy TRPL = time-resolved photoluminescence TRIR = time-resolved IR TR = EPR-time-resolved electron paramagnetic resonance spectroscopy. 

Polarised fluorescence has been used to study the orientation of non-crystalline polymer chains and a fluorescence technique has been developed to quantify the amount of microgel in polyacryl-amide. Time resolved photoluminescence analysis of poly( -phenyl-... 

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