PL quenching

Poly(l,l-silole)s, SCPs catenated through the ring silicon atom, can be regarded as a new class of polysilanes. It was found that PL intensities of the toluene solution of a poly(l,l-silole) 24 (Fig. 12) could be quenched by the addition of tiny amounts of 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenol (picric acid), 2,4-dinitrotoluene (DNT), and nitrobenzene, demonstrating that poly(l,l-silole)s are potential chemosensors for explosives.41 TNT could also be detected using the polymer film. In an air stream containing 4 ppb TNT, 8.2% decrease of the PL intensity was found from the film. PL quenching can also be detected when the film contacts a 50 ppb TNT-water solution. 

Such bilayers were studied by photoluminescence, with a view to extracting the degree of photoluminescence quenching induced by a thin acceptor layer on the polymer [18]. Studies of photoluminescence quenching in bilayers have corroborated the picture derived from studies of photoelectrical performance. The short exciton diffusion length in PEOPT is 5 nm, consistent with both PL quenching and photodiode performance. 

Another possibility to determine PGr, which is free of these drawbacks, is electric-field modulation (EFM) of photoluminescence (PL). Electric-field effect on the effective charge separation efficiency (rj0 l) shows up in the varying population of CT states, and consequently, in the varying concentration of the emitting states. It is expected that the field-induced increase in the charge separation efficiency would translate into PL quenching. The ratio (<5) of the PL efficiency in the presence (external electric field (F) would give directly Pgr... 

Figure 173 Electric field dependence of the PL quenching rates of two different devices ITO/Alq3(200nm)/Mg Ag ( ) and ITO/ Alq3(100nm)/Al (O) (with a solid line as a guide to eyes). The negative values of the electric field indicate the negative bias of the ITO electrode. After Ref. 233. Copyright 2001 Jpn. JAP, with permission.

Figure 12 The photoluminescence (PL) spectra of AZO-FO doped with different concentrations of a stilbene derivative (MAPS). The inset shows the PL quenching scheme.

The curves in Fig. 1 demonstrate the decrease of PL intensity (quenching) and the red shift of PL maximum with the voltage increased. At the values of electrical field strength E up to 10 V/cm the PL of nanorods is quenched more than PL of QDs. However, the wavelength shift of PL maximum with applied electric field for nanorods increases very weak. Evidently, due to the elongated shape of nanorods, the external electric field effect may differ for S- and P-polarized PL. This property is important for application of this material in optoelectronic nanodevices. To understand reasons of the electric field effect difference between QDs and nanorods, the mechanism of nanorods PL quenching has to be studied. The quantum-confined Stark effect is probably not the single factor in force. 

It is seen from Fig. 2 that at the same molar ratios x the PL quenching is more effective for smaller QDs. For the analysis of the PL quenching curves as a function ofx, we have modified Stem-Volmer formalism as follows... 

Table 1. PL quenching rate constants k, for QDs of various CdSe core diameters dCdSe upon titration by (m-Pyr)4-H2P (toluene, 295 K). Number of ZnS monolayers is for all QDs.

Figure 3. Scheme of the PL quenching model (A) and and the comparison (B) of experimental quenching rate A, constants (left axis) with calculated probability density functions i/(r) of a Is electron at the outer interface. 

PL quenching rate scales inversely with the QD diameter and can be understood in terms of a tunnelling of the electron (of the excited electron-hole pair) followed by a (self-) localization of the electron or formation of trap states. These observations are in line with the microscopic understanding of blinking phenomena of single QD. Our findings show also that single functionalized molecules can be considered as one of the probes for the complex interface physics and dynamics of colloidal semiconductor QD. 

For QDs with tCl-l,2-BQ at x=5, the observed variation of PL quenching efficiency on is explained by the dependence of the photoinduced electron transfer rate constant on the Gibbs free energy ACf for PET in the normal region ... 

The structures alumina xerogel/PAA doped with Tb demonstrated very low thermal PL quenching which is untypical for lanthanide-doped films [17]. The thermal quenching does not exceed a factor of two within a temperature range from 10 to 300 K. It is much lower in comparison with (i) Tb-doped titania xerogel, (ii)... 

In the highly ordered pristine PPV synthesized by Holmes and co-workers [80] the polaron resonance was PL-enhancing at 2 = 353 nin, and no PL-quenching was detectable. This is consistent with the rapid decay of free polarons to p, -pi pairs trapped at close... 

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