Photoluminescence decay time

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. 

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. 

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))... 

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. 

Very fast recombination process can be studied by photoluminescence transients [182,199]. In this experiment, very short laser pulses are used and ultra-fast recombination studied. For a mechanically polished but unetched sample of n-CdSe, luminescence decay times of 50 ps were found due to recombination in the damaged surface layer. On etching, the quantum yield for luminescence and the decay lifetime were both substantially increased [182]. 

In early studies of MEH-PPV/Cjq composites, it was found that the strong photoluminescence of MEH-PPV is quenched by a factor in excess of 10 and the luminescence decay time is reduced from t 550 ps to t,3, < 60 ps (the instrumental resolution) indicating that charge transfer has cut-off the radiative decay [149,177,178]. An estimate of the transfer rate, 1/t can be obtained from the quenching of the photoluminescence ... 

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. 2.47 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.

In display applications, fast (video rate) switching of the pixels is required. The intrinsic lifetime of the electroluminescence is the decay time of the photoluminescence i. e. less than a nanosecond. Thus, for pixilated polymer emissive displays, the switching rate is limited only by the RC time constant of the device. For the small pixels of a full-color display, C is sufficiently small that the devices can be switched in times in the nanosecond regime. This fast switching is demonstrated for a single pixel in Fig. 4.19. 

Time-Resolved Photoluminescence In time-resolved photoluminescence (TRL) spectroscopy, the sample is excited by a laser pulse and the sample luminescence is measured as a function of time and wavelength. This can give valuable information about the decay pathways (e.g., radiative versus nonradiative) available to photogenerated excitons, which can help identify the mechanisms... 

Energy-level gaps and both radiative and radiationless decay constants have been obtained for a series of Os complexes containing 7r-conjugated ligands. This has been done by computer analysis of the intensity and decay time of the photoluminescence. An ion-parent coupling model has been used to rationalize the empirical parameters and the emitting levels shown to have CT con-... 

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