Photoluminescence excitation

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. 

Figure 9-12. Absorption (Abs), photoluminescence excitation spectrum (PLCX), pholo-lumincscence (PL), and electroluminescence (EL) emission of mLPPP.

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... 

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).

Fig 18. Comparision between the spectral dependence of the photoneutralization cross section (dashed line, taken in a junction by photocapacitance). [After Monemar and Samuel-son (1978, Fig. 3), with the photocapacitance data provided by . H. Henry, and data taken at 190°K.]... 

Figure 5. Triboluminescence Spectrum of Uranyl Nitrate Hexa-hydrate. The photoluminescence excitation spectrum is shown for comparison the photoluminescence emission has been...

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... 

The action spectrum of the photocatalytic isomerization reactions on MgO, defined as the plot of the reaction rate vs the wavelength of the light used, shows a good agreement with the absorption spectrum, i.e., the photoluminescence excitation spectrum of the MgO (96-98, 248). The addition of O2 or CO to MgO led to the quenching of the photoluminescence. Similarly, the rates of the photocatalytic isomerization reactions on MgO were easily inhibited by the addition of CO. its extent increasing with an increase in CO pressure. 

For the PL measurements performed at room temperature a xenon lamp (Xex = 285 nm) was used. The photoluminescence excitation (PLE) measurements were carried out using a 0.3 m diffraction monochromator with grating of 1200 lines/mm. 

Monemar, B. Fundamental energy gap of GaN from photoluminescence excitation spectra. Phys. Rev. 1974, BIO, 676. 

Mitkova Dushkina, N., Ullrich. B. Intensity dependence of two-photon absorption in CdS measured by photoluminescence excited by femtosecond laser pulses. Opt. Eng. 41, 2365-2368 (2002)... 

Fig. 9.8 Photoluminescence excitation spectrum of a quantum well structure with parabolic potential barriers. (After ref. [85])...

Depending on the excitation method used, luminescence techniques are divided into photoluminescence excited by photons, cathodoluminescence generated under the action of cathode rays, X-ray luminescence excited by X-rays, candoluminescence generated under the action of heat, and sonoluminescence excited by ultrasound. Emission generated under the action of a stream of ions from alkali metals in vaccum is called ionoluminescence radiation which atoms emit on optical excitation in plasma is known as atomic fluorescence chemiluminescence is the emission of radiation generated by the energy of chemical reactions, it does not require an external excitation source. The excitation source needed in each particular case is chosen on the basis of this classification. 

The absence of an absorption cross section for the exciplex means that it cannot be excited optically. Instead, an exciplex is formed by complexation of a ground-state molecule with an excited-state molecule, i.e. by Dexter-type energy transfer from a bulk exciton. Figure 2.10 plots the photoluminescence excitation spectra of the PFB, the F8BT, and the exciplex emission, all measured from the same 50 50 PFB F8BT blend. The PLE signature of the exciplex is a superposition of those of the two excitons. Hence, the exciplex is excited via energy transfer from the two bulk excitons. 

Fig. 2.10 Photoluminescence excitation spectra of a PFB F8BT blend. The detection wavelengths are 465 nm (black), 540 nm (red), and 600 nm (green), corresponding to the PFB and F8BT exciton emissions and the exciplex emission, respectively. The exciplex spectrum resembles a superposition ofthe two exciton spectra, pointing towards indirect excitation of the exciplex via transfer from the excitons. The spectra were taken using a SpexNova spectrofluorimeter and are not corrected for the spectral response.

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]. 

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. 

The absorption edge shifts to the blue (Fig. 1). The photoluminescence has a broad band peaking at 640 nm. The luminescence line shape is not Lorentzian and has a strong Stokes shift. Photoluminescence excitation (PLE) spectra have revealed a fine substructure of the band at its short-wave wing whose origin is attributed to the intrinsic luminescence contribution and to radiative recombination on defects. 

Figure 1. Photoluminescence emission spectra (PL) and photoluminescence excitation spectra (PLE) of CdSiMn nanocrystals embedded in a polymer film.

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

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. 

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