Photoluminescence decay

Transient UV-vis absorption spectra showed that theTi02/Ru(II) films yield prompt electron injection upon photolysis ( >108s 1) These same films displayed photoluminescence decays with parallel first- and second-order components, the first-order component having a rate constant of about lxl06s-1. These two sets of results provide further support for the existence of at least two populations of adsorbed Ru(II), one of which injects electrons rapidly and another which does not inject electrons and is thus capable of luminescing on a longer time scale. The second-order component of the luminescence decay is attributed to bimolecular triplet-triplet annihilation of surface-bound Ru(II). (Note that the second-order rate constants reported for luminescence decay have units of s-1 because they are actually values for k2(Asi))... 

L.M. Herz and R.T. Phillips, Effects of interchain interactions, polarization anisotropy, and photo-oxidation on the ultrafast photoluminescence decay from a polyfluorene, Phys. Rev. B, 61 13691-13697, 2000. 

M. Sun, Fiberoptic thermometry based on photoluminescent decay times, Temperature—Its Measurement and Control in Science and Industry, Vol. 6, Part 2, pp. 715-719, American Institute of Physics, New York (1992). 

Fig. 4. Energy below the conduction band of levels reported in the literature for GaP. States are arranged from top to bottom chronologically, then by author. At the left is an indication of the method of sample growth or preparation liquid phase epitaxy (LPE), liquid encapsulated Czochralski (LEC), irradiated with 1-MeV electrons (1-MeV e), and vapor phase epitaxy (VPE). Next to this the experimental method is listed photoluminescence (PL), photoluminescence decay time (PLD), junction photocurrent (PCUR), photocapacitance (PCAP), transient capacitance (TCAP), thermally stimulated current (TSC), transient junction dark current (TC), deep level transient spectroscopy (DLTS), photoconductivity (PC), and optical absorption (OA).

In addition to these three kinds of spectra, the photoluminescence decay time can be measured after pulsed or step illumination. 

A long time ago, Hong, Noolandi, and Street [16] investigated geminate electron-hole recombination in amorphous semiconductors. In their model they included the effects of tunneling, Coulomb interaction, and diffusion. Combination of tunneling and diffusion leads to an S(t) oc t 1/2 behavior. However, when the Coulomb interactions are included in the theory, deviations from the universal t /2 law are observed—for example, in the analysis of photoluminescence decay in amorphous Si H, as a function of temperature. 

Rate constants for electron transfer were recently also determined at thin As-capped GaAs quantum wells (thickness 50 A) by measuring the photoluminescence decay in the presence of ferrocenium ions as electron acceptors [34]. In this case, rate constants were obtained which are about one order of magnitude smaller than those reported by Meier et al. and no adsorption was found. These results indicate that the composition of the GaAs surface plays an important role. 

Fig. 7.60 Photoluminescence decay characteristics for p-GaAs passivated with Na2S measured under the following conditions a) in air b) in acetonitrile c) upon addition of 1 mM cobaltoce-nium as an electron acceptor d) the same as c) but with 1 mM ferrocinium as an electron acceptor. (After ref. [82])...

It is clear that the surface recombination velocity. sy can also be determined by photoluminescence decay measurements. One nice example (n-lnP) is given in Fig. 7.61. InP is a semiconductor which exhibits in contact with H2O a rather low surface recombination (i r < 500 cm s" , curve a). After the electrode had been dipped into a solution of CuSOy, Rosenwaks et al. found a considerably steeper decay (curves b-d) [83]. An excellent agreement between theoretical and experimental curves was obtained. Values of up to = 3.5 X 10 cm s were reported for the surface recombination velocity. The same authors showed by capacity measurements that an additional capacity due to surface states occurs simultaneously, as already discussed in Section 5.2.4. 

Castellano et al.221 reported the formation of a luminescence lifetime-based sensor for cyanide and other counterions using Ru11 diimines possessing MLCT excited states with the anion recognition capabilities of 2,3-di(l//-2-pyrrolyl)quinoxaline (DPQ). Using time-resolved photoluminescence decay, its viability as a lifetime-based sensor for anions has been tested. There were significant changes to the UV-vis and steady-state emission properties after the addition of several ions (e.g., fluoride, cyanide, and phosphate). 

Fig. 2.11 Photoluminescence decays of PFB (black curve, detection wavelength 450 nm)), F8BT (red and gray curves, detection at 540 nm and 620 nm, respectively), and a PFB F8BT blend (green curve, detection at 620nm).

Fig. 2.17 Photoluminescence decays of F8, PFB and a F8 PFB blend (weight ratio 90 10, spun from Chloroform) detected at 475 nm.

Fig. 2.30 Photoluminescence decays at 650 nm of the PFB/F8BT bilayer LED and the F8BT-only LED from Fig. 2.29 as well as the PFB F8BT blend LED from Fig. 2.31. The long-lived exciplex emission is clearly visible in both the blend and the bilayer data but its relative intensity is much lower in the bilayer device. An exponential fit of the delayed emission between 30-90 ns yields 51.5 and 38.7 ns for the blend and the bilayer device, respectively.

Fig. 2.47 Photoluminescence decays (measured at 620 nm) of pure F8BTand of PFB F8BT blends for different weight ratios as indicated in the figure. Fitting the delayed emission from the blends between 30-90 ns yields the time constants Tdeiayed given in Table 2.2. The decays have been normalized to their peak intensity.

Experimental evidence suggests that photoluminescence decay fluctuation occurs on time scales up to several seconds. Apparently, the photoluminescence decay rates of quantum dots are correlated to single time-averaged emission intensities. 

Jones, M., Lo, S. S. and Scholes, G. D. (2009) Quantitative Modeling of the Role of Surface Traps in CdSe/CdS/ZnS Nanocrystal Photoluminescence Decay Dynamic. Proc. Natl. Acad. Sci. USA., 106,3011-16. 

Figure 16 shows the minority carrier lifetime derived from the time resolved photoluminescence decay curve. The minority carrier lifetime increases from 1.66 ns (as-grown) to 4.66 ns after the plasma treatment, and gradually decreases with increasing annealing temperature. It is difficult to judge the crystal quality only by the... 

However, it was observed that, as new scintillators, these complex perovskite ceramics have a dilFerent thermal quenching effect, as compared to the conventional scintillator materials, which deserves further investigation in the future. Figure 10.8 shows a photograph of the perovskite transparent ceramic samples, with a thickness of 2 mm [123]. Optical properties, including transmittance, photoluminescence, and photoluminescence decay time, have been characterized. Scintillation properties, such as radioluminescence and pulse height spectra, were studied in details. 

Wadayama T, Arigane T, Hayamizu K, Hatta A (2002) Unusual photoluminescence decay of porous silicon prepared by rapid thermal oxidation and quenching in liquid nitrogen. Mater Trans... 

Figure 18 Time-resolved photoluminescence decays monitored at 620 nm for [Ru(deeb)3] + in acetonitrile (a) and dichloromethane (b) as a function of increased [TBAI]. (Inset a) A Stern-Volmer plot for lifetime quenching from which Ksw = 1.0 0.1 x 10 was abstracted. (Inset b) A Stern-Volmer plot for both lifetime (black) and amplitude (red) quenching components where quenching constants, Ksy = 4.1 0.2 x 10 M and = 2.30 0.03 x 10 M , were abstracted. (Adapted with pamission from Ref. 55. Royal Society of Chemistry, 2011.)...

Sharma, R. and Bhatti, H. S. (2007). Photoluminescence decay kinetics of doped ZnS nanophosphors. Nanotechnology, 18,465703. 

A second area of disagreement centers around photoluminescence quenching at high excitation densities in thin films. The formation of nonradiative interchain polarons [1237, 1238] and interchain exciton formation [1239] have been proposed as sources responsible for the quenching mechanism. At moderately high excitation densities, bimolecular decay, resulting from interchain interactions between the excited species, is considered to be responsible for the fast photoluminescence decay [1240-1243]. At high excitation conditions, the formation of biexcitons becomes favored [1244,1245]. 

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