Photoluminescence excitation PLE

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).

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. 

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. 

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. 

Uniform 1.5 pm thick PS layers were formed by anodization of p-type Si wafers of 0.3 Ohm em resistivity in 48% HE. After anodization, the HE electrolyte was replaced by a O.IM FeS04+0.001M EifNOals solution and a Fe Er film was electrochemically deposited into PS. As SIMS analysis showed, both Er and Fe can be introduced deeply into PS by this electrochemical technique [5], The maximum Er and Fe concentrations were estimated to be 0.1 and 10 at. %. The samples were oxidized at 500°C for 360 min and then at 1100°C for 15 min in O2 atmosphere. This treatment has been shown to form 5-50 nm iron/erbium oxide clusters inside OPS [5]. As comparison reference, Er-doped OPS containing Si clusters (without Fe) samples were fabricated in a similar way by polarization of PS in an Er(N03)3 solution. Photoluminescence excitation (PLE) spectra were recorded at 77 K by a grating spectrometer MDR-23 equipped with a Ge Cu detector. A Xe lamp was used as the excitation source. 

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... 

Figure 5.14 Photoluminescence excitation (PLE) spectra (solid lines) and photoluminescence (PL) spectra (dotted lines) of [Cu26Sei3(PEt2Ph)i4] (1), [Cu44Se22(PEt2Ph)ig] (3), and [Cu7oSe35(PEt2Ph)23] (4) measured at different temperatures.

In D-A energy-transfer systems, pronounced photoluminescence (PL) of A can be observed as only D is excited. As a result, the photoluminescence excitation (PLE) spectrum of A contains the characteristic excitation spectrum of D. This is strong spectroscopic evidence for the occurrence of D-A energy transfer. The other spectroscopic effect of energy transfer is an intensity decrease of D luminescence followed by an intensity increase of A luminescence. 

As seen in Fig. 9.8, ultraviolet-visible diffuse reflection (UV-Vis) spectra shows a strong absorption band from 275 to 500 nm, which is derived from the 4/ 5d transition of Eu " ions [39]. In addition. Fig. 9.8 shows the photoluminescence excitation (PLE) and photoluminescence emission (PL) of NaBaScSi2O7 0.1Eu phosphor. The PLE spectmm indicates the typically broad... 

Fig.5.3-ft (a) Low-temperature (10 K) absorption spectra of CdSe dots dispersed in a polymer matrix, for various mean diameters. (b) Nanosecond saturated-absorption spectra for 67 A dots. The pump beam had a 7 ns FWHM. The excitation photon energy, 1.984 eV, is prolonged as a dashed vertical line from (a) for easier comparison. The horizontal dashed line corresponds to AOD = 0. (c),(d) Photoluminescence(PL) and photoluminescence-excitation(PLE, observed at 2.022 eV) spectra for 67 A dots (c) and for 62 A dots (d). (After [3.29])... 

The basic instnimentation required for acquiring photoluminescence excitation (PLE) spectrum ofa given PL band is nearly the same as that for a PLsetup. However, the excitation source must be a tunable source such as a tunable laser or a broadband lamp dispersed by a monochromator. The wavelength of the excitation source is varied, and the PL spectrum or simply the intensity of a particular transition (such as the peak PL intensity) is recorded at various excitation wavelengths to obtain the excitation spectrum. The PLE spectrum is similar to the absorption spectrum with the only difference that in the case of absorption spectrum several different transitions may contribute and complicate the spectral analysis. Photoionization of a defect is an inverse process to the luminescence, and in n-type ZnO such a process involves the transition of an electron from an acceptor-like level to the conduction band or to the excited state of the defect. Note that the photoionization spectra measured by PLE, absorption, photocapacitance, and photoconductivity methods should have more or less similar features because the mechanism of the photoexcitation is the same for all these approaches. 

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