Photoluminescence excitation spectroscopy

Band gaps in semiconductors can be investigated by other optical methods, such as photoluminescence, cathodoluminescence, photoluminescence excitation spectroscopy, absorption, spectral ellipsometry, photocurrent spectroscopy, and resonant Raman spectroscopy. Photoluminescence and cathodoluminescence involve an emission process and hence can be used to evaluate only features near the fundamental band gap. The other methods are related to the absorption process or its derivative (resonant Raman scattering). Most of these methods require cryogenic temperatures. 

NHE OCP ONO OPS PCD PDS PL PLE PMMA PP PP PS PSG PSL PTFE PVC PVDF normal hydrogen electrode (= SHE) open circuit potential oxide-nitride-oxide dielectric oxidized porous silicon photoconductive decay photothermal displacement spectroscopy photoluminescence photoluminescence excitation spectroscopy polymethyl methacrylate passivation potential polypropylene porous silicon phosphosilicate glass porous silicon layer polytetrafluoroethylene polyvinyl chloride polyvinylidene fluoride... 

TABLE 2 Summary of free exciton binding energies in GaN. PLE, PL, PR, R, TPS mean photoluminescence excitation spectroscopy, photoluminescence, photoreflectance, reflectance and two-photon spectroscopy respectively. 

Photoluminescence excitation spectroscopy (PLE) was performed on GaN Er by several groups [15-17], FIGURE 2 shows typical PLE spectra probing the second and third excited Er states while monitoring the 1.539 pm PL line. The Stark splitting caused by the crystal field is clearly shown. The excitation source was 250 mW from a tunable Ti sapphire laser. 

Photoluminescence excitation spectroscopy (PLE) is generally used to identify the excited-state structure in quantum wells. For GalnN/GaN quantum wells, Im et al [14] used PLE to study single wells of various widths. Similarly to the results from absorption, electro-absorption, and electroreflectance measurements, a large Stokes shift of the onset of the PLE spectrum with respect to the dominating photoluminescence peak was observed at low temperature [14]. 

Low-excitation, low-temperature experiments like photoluminescence or photoluminescence excitation spectroscopy tend to indicate a considerable influence of localisation effects on the optical properties of GakiN/GaN quantum wells. Under high-excitation conditions typical for lasing, however, it is clearly seen that lasing from GalnN/GaN quantum well structures is due to a free-carrier plasma. 

P PAE PD PDS PEC PL PLE PMBE PPC PPPW PR PV PWP PWPP pi-MODFET precipitate power added efficiency photodetector photothermal deflection spectroscopy photoelectrochemical photoluminescence photoluminescence excitation spectroscopy plasma-assisted molecular beam epitaxy persistent photoconductivity pseudo-potential plane-wave photoreflectance photovoltage plane-wave pseudo-potential plane-wave pseudo-potential piezoelectric modulation doped field effect transistor... 

When investigating the PFB F8BT system above we also used photoluminescence excitation spectroscopy to directly show the energy transfer to the exciplex. This is not possible here because of the very similar emission spectra of the F8BT exciton and the long-lived exciplex emission. The reasons for this similarity will be discussed in Section 2.2. We therefore conclude that the heterojunction between TFB and F8BT also supports exciplex formation. 

PHOTOLUMINESCENCE EXCITATION SPECTROSCOPY OF ERBIUM INCORPORATED WITH IRON IN OXIDIZED POROUS SILICON... 

Thin films of CdSe/ZnS QDs under study were prepared using moderate-temperature organometallic reactions. QDs of appropriate radius (3.4 0.4 nm) were choosed for resonant excitation of the first electron excited state (lP3/2(h)-lP(e), lP i/2(h)-lP(e) transitions) by picosecond pulses of the second harmonic (hro =2.353 eV) of Nd3+ -phosphate mode-locked laser. Owing to size dispersion, only the lowest transition (lS3/2(h)-lS(e)) was clearly observed in the absorption spectra. For observation of resonant excited transitions the method of photoluminescence excitation spectroscopy (PLE) was used (Fig. 1). 

Fig. 8. Energy below the conduction band of levels reported in the literature for GaAs. Arrangement and notations are the same as for Figs. 4 and 5. Notations not defined there are epitaxial layer on semi-insulating substrate (EPI/SI), boat-grown (BG), vapor phase epitaxial layer on semi-insulating substrate (VPE/SI), melt-grown (M), molecular beam epitaxy (MBE), horizontal Bridgman (HB), irradiated with 1-MeV electrons or rays (1-MeV e, y), thermally stimulated capacitance (TSCAP), photoluminescence excitation (PLE), and deep level optical spectroscopy (DLOS).

We have shown via absorption, PL, morphology-dependent PL, PDS, photoluminescence excitation, and time-resolved photoluminescence spectroscopy that exciplexes form at the PFB F8BT heterojunction. We note that exciplexes of poly-fluorenes with triphenylamine monomers have been observed recently [34]. 

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... 

Photoluminescence excitation (PLE) spectroscopy was carried out at 77K on oxidized porous silicon containing iron/erbium oxide clusters. The novel PLE spectrum of the 1535 nm Er PL band comprises a broad band extending from 350 to 570 nm and very week bands located at 640, 840, and 895 nm. The excitation at wavelengths of 400 - 560 nm was shown to be the most effective. No resonant PLE peaks related to the direct optical excitation of Er by absorption of pump photons were observed. The lack of the direct optical excitation indicates conclusively that Er is in the bound state and may be excited by the energy transfer within the clusters. 

In this paper, a photoluminescence excitation (PLE) spectroscopy is carried out to reveal the mechanism of luminescence from Er incorporated inside the iron oxide clusters in OPS. 

The electrical characterization was performed by means of DC measurements. The optical characterization included temperature-dependent (10-100 K) photoluminescence (PL) spectroscopy at low excitation (325 nm, 2 W/cm2), and low-temperature (10 K) reflection spectroscopy. Photoreflectance (PR) spectra were measured using the same HeCd laser beam with a power density of 0.1 mW/cm2 for modulation of internal electric fields. 

Together with the Banin group, the authors of Refs [10-12] carried out optical spectroscopy investigations on some of the cluster molecules obtained ] 14-16]. These materials were treated as the molecular limit of the bulk semiconductor CdSe, and issues such as oscillator strength, steady-state and time-resolved photoluminescence and photoluminescence excitation were addressed. In addition, emission-mediating vibrational modes were detected, and photobleaching effects observed. 

Figure 5.1 (a) Optical spectroscopy of InAs nanocrystals, with mean radius of 2.5 nm. The top frame shows the absorption (solid line), and the photoluminescence (dotted line) for the sample. The lower frame shows a size-selected photoluminescence excitation (PLE) spectrum, where eight transitions are resolved, measured... 

Because of the high sensitivity of Ti-containing luminescence centers to their local environments, photoluminescence spectroscopy can be applied to discriminate between various kinds of tetrahedral or near-tetrahedral titanium sites, such as perfectly closed Ti(OSi)4 and defective open Ti(OSi)3(OH) units. Lamberti et al. (49) reported an emission spectrum of TS-1 with a dominant band at 495 nm, with a shoulder at 430 nm when the sample was excited at 250 nm. When the excitation wavelength was 300 nm, the emission spectrum was characterized by a dominant band at 430 nm with a shoulder at 495 nm. These spectra and their dependence on the excitation wavelength clearly indicate the presence of two slightly different families of luminescent Ti species, which differ in their local environments, in agreement with EXAFS measurements carried out on the same samples. 

Luminescence is a well-established class of analytical spectroscopic techniques where a species emits light after excitation. Emission is an elecnonic nansition from an excited state as opposed to the ground state as is the case in most other spectroscopies. Photoluminescence, or light-induced fluorescence (LIE), is the most common route to induce emission where sufficient incident photons of a particular energy excite the target species via absorption. Although less common, nomadiative excitation can also occur via a chemical reaction termed chemiluminescence. Unless otherwise stated, the terms luminescence and fluorescence within this review infers excitation by light induction. 

The most common application of photoluminescence is found in fluorescence spectroscopy. Fluorescence is the immediate release of electromagnetic energy from an excited molecule or release of the energy from the singlet state. If the emitted energy arises from the triplet state or is delayed, the process is referred to as phosphorescence. 

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