Shape Of Photoluminescence Spectra Research Articles

Investigation of the Characteristic of Solution‐Processed Tetraphenyldibenzoperiflanthene (DBP) Film and Its Application on Organic Photovoltaic Cells

Solution‐processed tetraphenyldibenzoperiflanthene (DBP) films are prepared with three popular solvents, including chroloform (CF), chrolobenzene (CB), and dichrolobenzene (ODCB). The absorption and photoluminescence (PL) spectra of the DBP solution and DBP film are investigated. The absorption spectra between the DBP film and DBP solution are similar, whereas the PL spectrum shape of the DBP film and DBP solution is completely different, originating from the DBP molecular aggregation in the film, causing conjugate expansion, which results in dimer luminescence. The DBP donor layer at 32 nm prepared from solvent of CF, CB, and ODCB achieves a power conversion efficiency (PCE) of 1.42%, 0.88%, and 0.48%, respectively. The annealing temperature and DBP thickness are optimized; the 32 nm‐thick active layer annealed at 50 °C achieves the highest performance. The CF‐DBP film represents an interpenetrating network morphology, slightly higher roughness and hole mobility, which may be the main contribution to the relatively higher photocurrent than the CB‐DBP and ODCB‐DBP devices. Herein, a simple guidance for preparing solution‐processed DBP films is provided and simultaneously its application on organic photovoltaic cells (OPVs) is expanded.

Annealing impact on emission and phase varying of Nd-doped Si-rich-HfO2 films prepared by RF magnetron sputtering

HfO2 films doped with Nd and Si atoms were produced by RF magnetron sputtering in argon plasma atmosphere. The effect of annealing treatment on the morphology, crystal structure and light emission of the films was investigated by means of the scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). The thermal treatment was performed in the temperature range of TA = 800–1100 °C in horizontal furnace with continuous nitrogen flow. For annealed Si–HfO2:Nd films, the SEM study revealed the formation of the grains with the mean size of about 20–60 nm that show the tendency to enlarge with the TA rise. Besides, the phase separation was observed and tetragonal HfO2 and SiO2 phases were detected by the XRD method for the films annealed at TA > 950 °C. The PL study revealed that both Nd3+ ions and host defects contribute to PL emission whereas their relative contribution depends on the TA and on the crystal phase of host matrix. The highest PL intensity of Nd3+ ions via 4f inner electronic shell levels was detected for TA = 950 °C. The variation of PL intensity of Nd3+ ions was correlated with the change of PL intensity of the band caused by the host defects. These latter participate in the energy transfer towards Nd3+ ions. This statement was confirmed by XPS data, as well as by the shape of PL spectra. It was shown that the bright emission via Nd3+ ions can be achieved for those located in the tetragonal HfO2 matrix.

Emission Dependent on composition of Si-rich-SiNX Films obtained by PECVD

Silicon-rich silicon nitride films with different stoichiometry were grown on silicon substrate using the plasma-enhanced chemical vapor deposition. The excess silicon content in the films was monitored via a variation of the NH3/SiH4 gas flow ratio from 0.45 up to 1.0. Morphology and luminescence properties of the films were studied by means of atomic force microscopy (AFM) and photoluminescence (PL) methods. High-temperature annealing was employed to produce the silicon nanocrystals in the films and to enhance the photoluminescence in the range of 1.6-3.0 eV. The PL spectrum was found to be complex due to the contribution of several radiative channels in emission process. It was determined that their competition leads to the non-monotonous variation of total PL peak position with the increase of the Si excess content. It was observed that the shape of PL spectra depends on an excitation wavelength. The ways to control the PL emission is proposed based on the discussion of the PL mechanism.

Light emitting mechanisms dependent on stoichiometry of Si-rich-SiNx films grown by PECVD

Light emission and morphology of silicon-rich silicon nitride films grown by plasma-enhanced chemical vapor deposition were investigated versus film’s stoichiometry. The excess silicon content in the films was controlled varying the NH3/SiH4 gas flow ratio from 0.45 up to 1.0. High-temperature annealing was employed to form the silicon quantum dots (QDs) and to enhance the photoluminescence (PL) in visible spectral range. The PL spectrum was found to be complex. The competition of five PL bands leads to the non-monotonous variation of total PL peak position in the range of 1.55–2.95 eV when the Si excess content increases. The shape of PL spectra depends also on an excitation light wavelength. It is shown that for the films fabricated with R ≤ 0.56 and R ≥ 0.67 the dominant contribution into PL spectra is given by native SiNx defects, whereas in the films obtained with R = 0.59–0.67 the Si-QDs form the main radiative channel. The highest PL intensity is detected in Si-rich SiNx films grown at R = 0.59–0.67 as well. PL mechanisms are discussed in terms of the contribution of different radiative channels in the light emission process that can show the ways for the optimization of SiNx light-emitting properties.

Tb3+ photoluminescence in mesoporous glasses, terbium nitrate and terbium chloride hexahydrates, and coordination compounds

We have compared the intensity and shape of photoluminescence spectra of Tb3+ ions in mesoporous glasses, inorganic phosphors (terbium nitrate and terbium chloride hexahydrates), and coordination compounds (terbium benzoate, terbium o-phenoxybenzoate, and terbium terephthalate). The excitation sources used were a repetitively pulsed nitrogen laser with an emission wavelength of 337 nm and cw semiconductor light-emitting diodes with wavelengths of 369 and 385 nm. It has been shown that the highest photoluminescence intensity normalized by the percentage of terbium is offered by terbium terephthalate and terbium- doped mesoporous glass. We are thus led to conclude that introducing terbium terephthalate into the pores of mesoporous photonic glass and mesoporous photonic crystals is a promising approach for obtaining efficient laser operation in the green spectral region on the 5 D 4–7 F 5 transition of the terbium ion.

Impact of Carrier Profile and Rear-Side Reflection on Photoluminescence Spectra in Planar Crystalline Silicon Wafers at Different Temperatures

The increasing use of spectral photoluminescence as an advanced and accurate diagnostic tool motivates a comprehensive assessment of the effects of some important optical and electrical properties on the photoluminescence spectra from crystalline silicon wafers. In this paper, we present both modeling results and measurements to elucidate the effects of the internal reflectance at the planar wafer surfaces, as well as the carrier profile varying across the sample thickness due to an increased rear-surface recombination velocity, as a function of temperature. These results suggest that the accuracy of existing spectral PL techniques may be improved by using higher temperatures due to the increased effect of the carrier profile at higher temperatures. They also show that changes in the photoluminescence spectrum shape caused by the addition of a rear-side specular reflector offset those caused by changes in the carrier profile due to increased rear surface recombination, and therefore, considerable care needs to be taken when changing the rear-side optics. Finally, the possible impact of variations in the rear-side reflectance on the band-band absorption coefficient and radiative recombination coefficient, which have previously been determined using the spectral photoluminescence technique, is assessed and demonstrated to be insignificant in practice.

Determination of CdTe bulk carrier lifetime and interface recombination velocity of CdTe/MgCdTe double heterostructures grown by molecular beam epitaxy

The bulk Shockley-Read-Hall carrier lifetime of CdTe and interface recombination velocity at the CdTe/Mg0.24Cd0.76Te heterointerface are estimated to be around 0.5 μs and (4.7 ± 0.4) × 102 cm/s, respectively, using time-resolved photoluminescence (PL) measurements. Four CdTe/MgCdTe double heterostructures (DHs) with varying CdTe layer thicknesses were grown on nearly lattice-matched InSb (001) substrates using molecular beam epitaxy. The longest lifetime of 179 ns is observed in the DH with a 2 μm thick CdTe layer. It is also shown that the photon recycling effect has a strong influence on the bulk radiative lifetime, and the reabsorption process affects the measured PL spectrum shape and intensity.

The influence of annealing on structural and photoluminescence properties of silicon-rich Al2O3 films prepared by co-sputtering

Si-rich Al2O3 films were produced by RF magnetron co-sputtering of pure silicon and alumina targets onto a long silicon oxide substrate. The effect of an annealing treatment on structure and light emission property of the films with different Si content was investigated by means of X-ray diffraction, Raman scattering and photoluminescence (PL) methods. The formation of amorphous Si clusters upon deposition process was observed for the films with Si volume content exceeded 70%. The annealing treatment of the films with Si content exceeded 80% results in the formation of Si crystallites with the mean size of about ∼14nm. Three overlapped PL bands were detected in the 500–950nm spectral range. The analysis of PL spectrum shape revealed that the near-infrared PL component, peaked at 850nm, is caused by the exciton recombination inside Si crystallites. Another, the most intense PL band with maximum at 560–580nm can be ascribed to defects in matrix located near nanocrystal/matrix interface, while the origin of the third PL band with the peak position at 700–750nm is supposed to be also due to host defects whose nature requires more investigation.

Photoluminescence of aromatic compounds in photon traps under resonant pulse-periodic excitation

The photoluminescence spectra of aromatic compounds in a photon trap under ultraviolet pulse-periodic excitation are recorded. It is shown that the photoluminescence spectrum shape depends on the material layer thickness in a cell, physical state of the sample, and exciting radiation characteristics: as the layer thicknesses decreases, the intensity is significantly redistributed, which is explained by the transition from spontaneous luminescence to superluminescence.

Study of photophysical properties of composite materials based on polystyrene, polymethyl methacrylate, and Eu(III) complex with 1-(1,5-dimethyl-1h-pyrazole-4-yl)-4,4,4-trifluorobutane-1,3-dion and 1,10-phenanthroline

The effect of the polymer matrix on luminescence properties of the europium complex we synthesized is studied. It is shown that the interaction of complex molecules with the matrix has practically no effect on the photoluminescence spectrum shape. The excited state lifetime decreases no more than twice.

Localized surface plasmon resonance enhanced photoluminescence from SiNx with different N/Si ratios

Silver (Ag) nanostructures with different sizes and densities were deposited onto the luminescence matrixes to improve the photoluminescence (PL) intensity of silicon nitride (SiNx) films via localized surface plasmon resonance (LSPR) coupling. The shape of PL spectra from the SiNx matrixes is mainly determined by their stoichiometric ratio. Moreover, both the surface coverage and the size of Ag nanostructures should be considered for the improvement of PL intensity. The optimal PL intensity of SiNx films might be achieved by the addition of Ag nanostructures with proper surface coverage and size due to the enhanced photo-excitation by LSPR. The dipolar resonance absorption of Ag nanostructures has an insignificant contribution on this improvement.

Photoluminescence inhomogeneity and InAs QD laser structure parameters

Abstract The photoluminescence (PL) and its power dependences have been studied in InAs quantum dots (QDs) embedded in the symmetric In 0.15 Ga 0.85 As/GaAs quantum wells (QWs) with different PL intensities and different shapes of PL spectra. It was shown that two reasons are responsible for the PL intensity inhomogeneity and different shapes of PL spectra in the studied structure. The first reason deals with the variation of QD concentrations and the second one related to the bimodal QD size distribution in DWELL. At the same time both types of QD ensembles are characterized by high QD quality.

Formation and evolution of oxygen vacancies in ZnO white paint during proton exposure

The formation and evolution of oxygen vacancies in ZnO white paint during <200 keV protons exposure was investigated using photoluminescence spectroscopy. After irradiation, the shape of photoluminescence spectra changes little, but the peak height decreases. With increasing fluence, the amount of doubly ionized oxygen vacancies decreases, while that for the singly ionized oxygen vacancies increases. The former can trap electrons in the conduction bands to become the singly ionized oxygen vacancies, leading to that the latter gradually becoming the major defects induced by irradiation. The increase in content of singly ionized oxygen vacancies due to the irradiation can also promote an increase in the amount of absorbed oxygen in the paint, enhancing the quenching effect of photoluminescence and thus decreasing the photoluminescence peak.

Preparation and Optical Properties of Erbium Doped Chalcogenide Glass Films by Magnetron Sputtering

Erbium doped Ge-Ga-Se thin films were deposited by RF magnetron sputtering of powder and sintered composite targets. The dependence of the photoluminescence (PL) intensity of the films on the deposition conditions has been investigated. It is found that the intensity of PL depends on the RF power, whereas the composition of the films does not depend on that of the targets. Although the shape of PL spectrum in the films is similar to that of bulk glasses, the value of the PL life times in the films is shorter than that of bulk glasses. The reason would be the difference of composition of matrix glasses between bulk and the films.

Excitation diffusion due to photon trapping in GeGaSe glasses heavily doped with Er3+

The photoluminescence (PL) in erbium doped GeGaSe glasses with stoichiometric composition Ge28Ga6.2Se64.5S0.8:Er0.5 has been investigated in bulk samples and coarse and fine powders with varying average particle size 〈L〉. The shape of PL spectra and PL decay time are found to depend strongly on 〈L〉 at large 〈L〉 ≥ 500 μm. In fine powders with 〈L〉 ≤ 200 μm the PL decay time does not depend on 〈L〉 and is very close to the theoretical calculation of the lifetime using the Judd–Ofelt theory. In addition, the PL spectra do not depend on 〈L〉 ≤ 200 μm, and the shape of spectra closely follows the predictions of McCumber theory. The 〈L〉-independent decay time values and PL spectra are observed only in fine powders with 〈L〉 ≤ 200 μm.

Effect of Li doping on photoluminescence from Er, O-codoped GaAs

We investigated the effect of Li doping into Er-doped GaAs and Er, O-codoped GaAs on the enhancement of photoluminescence (PL) intensity. The Li doping into Er-doped GaAs increases the integrated intensity by 50 times higher than that from the Er-doped layer without Li doping. Main peak position of the Er, Li-codoped layer was slightly smaller than that of the Er-doped layer. This difference of peak position means that Li doping induced Er-related active centers different from those in Er-doped layer are formed. In the previous study, we have revealed that oxygen doping into Er-doped GaAs produced sharp and strong PL peak intensity due to Er-2O center. The Li doping into Er, O-codoped GaAs increases the integrated intensity twice higher than that from the Er, O-codoped layer without Li doping. However, the peak intensity decreased and the PL spectrum shape becomes broader. These results indicated that Li doping partly modified the Er-2O center and introduced many kinds of luminescent Er centers.

Spectroscopic studies of molecular-beam epitaxially grown Cr2+-doped ZnSe thin films

Cr:ZnSe thin films were grown by molecular-beam epitaxy with the long-term goal of demonstrating a route for the development of transitional-metal-doped semiconductor lasers. Photoluminescence (PL) and PL lifetime measurements of doped thin films and bulk crystals indicate that Cr is incorporated in the optically active Cr2+ state up to levels of 5×1019cm−3. The shape of PL spectra and lifetime measurements of doped thin films compares favorably with that reported for bulk samples. A microcavity formed by film interfaces is responsible for differences in spontaneous emission observed between films and bulk crystals.

Influence of annealing temperature on the luminescence of Er/Yb co-doped Al2O3 films

The influence of annealing temperature on the photo-luminescence (PL) of high co ncentration Er/Yb co-doped Al２O３ films was studied. The relationship betwe en PL spectra and microstructure of the films at various annealing temperatures was revealed by analyzing the dependence of the intensity and the full width at half-maximum of the PL spectra on the annealing temperature. The PL measurement shows that the annealing behavior may be split into three different regimes. Bel ow 750℃, the intensity increases with the increase of annealing temperature wit h a small slope, which corresponds to the amorphous Al２O３ films. Between 800℃ and 900℃, the PL intensity increases considerably, where the microstructure of the films was identified to be composed of γ-Al２O３ grains in nano-meter scale; At the temperature of 1000℃, the intensity of PL spectrum decre ases to a very low level, γ-Al２O３ grains and the segreg ation of Er2O ３ and Yb2O３ phases were observed by using transmis sion electron microscopy . Furthermore, the dependence of PL spectrum shape on the PL intensity of sub-le vel transition was analyzed and discussed by fitting the PL spectra at various t emperatures．

Enhanced yellow–green photoluminescence fromZnO–SiO2 composite opal

A remarkably enhanced yellow–green photoluminescence (PL) was observed from ZnO nanocrystals infiltratedinto SiO2 opal photonic crystals. It was clearly visible to the naked eye underthe excitation of an Xe lamp and had substantially improved thermalstability over pure ZnO nanocrystals. The PL spectrum shape of aZnO–SiO2 composite opal can be modified by annealing anSiO2 opal orchoosing an SiO2 opal with different lattice parameters. The enhancement of PL intensityis interpreted based on the dependence of the PL intensity on the size ofSiO2 microspheres as well as the anisotropy of the photoluminescence excitation (PLE) spectra.Our results may be interesting for further application.

Analysis of the Shape of PL Spectra and Its Temperature Dependence in Self-Supporting Porous Silicon

In this paper, the systematic change in the shape of the photoluminescence (PL) spectra with the change in the growth parameters for self-supporting porous silicon (PS) has been reported and mathematically analyzed. The confinement energy was found to be less than that in the case of non-self-supporting PS. The PL behavior is attributed to the quantum size effect. Also, a study of the temperature variation of PL for two of these samples was performed. The luminescence data can be explained in terms of a competition between an activated radiative process and a Berthlot-type hopping process.