Time integration, photoluminescence

Figure 7.5 Ultrafast spectrally resolved dynamics of two CdS tSei x nanobelts. The fluorescence image is shown in the upper left corner. Note that the broad, time-integrated photoluminescence spectrum shown on the left consists of two distinct features centered at 628 and 636 nm with vastly different dynamics that is clearly discernible in the 2D map.

Fig. 2.48 Time-resolved photoluminescence spectra of PFB F8BT blends of different weight ratios, (a), (b) and (c), and of films of pure PFB and F8BT (d). The spectrum with the highest intensity represents the PL emission integrated over the first 10 ns. The less-intense spectra are the delayed PL integrated over subsequent 10-ns time windows, i.e. over 10-20 ns, 20-30 ns,..., 80-90 ns.

Figures 2.27(b) shows the spectral dependence of the long-time photoluminescence integrated over 30-90 ns after excitation as a function of temperature. At these times the initial exciton population has completely decayed and all the remaining emission originates from the long-lived exciplex states. At low temperatures, we see the red-shifted emission characteristic of the exciplex. For higher temperatures, however, the emission spectrum increasingly acquires excitonic...

Time-resolved PL measurements were also performed using time-correlated single-photon counting (TCSPC) and photoluminescence upconversion (PLUC) spectroscopies. Descriptions of the setups can be found in refs. [14, 65], respectively. All measurements were taken in continuous-flow He cryostats (Oxford Instruments OptistatCF) under inert conditions. Finally, PL efficiency measurements were performed on simple polymer thin films spin coated on Spectrosil substrates using an integrating sphere coupled to an Oriel InstaSpec IV spectrograph and excitation with the same Ar+ laser as above. 

Photoluminescence spectra of the ceramics are shown in Fig. 10.10 [123]. According to Fig. 10.10a, the undoped and Yb-doped Ba(ZrMgTa)03 had emission peaks at about 440 and 470 nm under the 286 nm excitation, with very similar profiles. The emission spectra of pure and Yb-doped (LaSr)(AlTa)03, shown in Fig. 10.10b, were recorded under 324 nm excitation. This group of ceramics had longer integration times than the Ba(ZrMgTa)03-based ceramics, due to low emission intensities. The shapes of the spectra of the two samples were quite similar. In these ceramics, only one intense peak at 500 nm was observed. 

In addition to the radiative processes, there are nonradiative processes in semiconductors because of imperfections that act as nonradiative centers. We should mention some defects as radiative recombination centers, which in a photoluminescence experiment can shed light on the energy levels of defect states. For a semiconductor containing nonradiative traps or recombination centers, in an experiment such as time-dependent PL, the decay in the integrated PL intensity versus temperature is related to the low-temperature integrated PL intensity as... 

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