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Mixtures of luminescence downshifting (LDS) materials has been used to increase the efficiency of poly(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) bulk heterojunction solar cell. This layers convert more energetic photons to lower energies that are better matched with wavelength peak of the external quantum efficiency (EQE) of a P3HT:PC61BM solar cell. Experimental studies were used to optimise the optical properties of LDS layers including the maximum of absorbance and the photoluminescence quantum yield (PLQY). To provide the significant improvements, combinations of LDS mixtures were prepared to provide the greatest absorption and PLQY. The approach is shown to simultaneously improve the photocurrent and increase the lifetime of the device by absorbing UV light. By optimising the optical properties of the LDS mixture, a relative increase of about 20% in the photocurrent density produced by the P3HT:PCBM cell could be achieved, which to our knowledge is one of the most significant reported for OPVs.

Segregation is an effect observed when CH3NH3Pb(I1-xBrx)3 mixed perovskites are illuminated with photon energy greater than their band gap. It is concerned to the formation of low band-gap I-rich domains that constitute attractive centers for the recombination of photogenerated electron-hole pairs, causing a significant red-shift of photoluminescence of the material with consequences for the operation of optoelectronic devices, such as light emitting diodes and photovoltaic cells. This effect is commonly observed as reversible, with a spontaneous remixing of the halogens occurring when the material is left in the dark. While the segregation process is already relatively well documented in the literature, much less attention has been paid to the causes and understanding of the remixing process. In this work are presented results that demonstrate the strong dependence of the remixing with the pressure to which the material is submitted. When the perovskite film is subjected to low pressure, it is noticed that the maximum displacement of PL during the dark time is significantly lower than in the case of the film at ambient pressure, indicating that under low pressure the remixing process is hampered. The dependence of the remixing process with the pressure can be used in new hybrid perovskite applications, such as in photoinscription to memory storage.

Organic photovoltaic devices (OPVs) have a shorter working lifespan and lower power conversion efficiency if compared to traditional silicon-based solar cells. Intending to increase the lifespan and improve the performance of OPVs, in this work we have applied a layer of Cadmium Sulfide (CdS) Quantum Dots (QDs) encapsulated in Zinc Sulfide (CdS/ZnS) to act as a luminescence down-shifting (LDS) layer in poly(3-hexylthiophene-2,5-diyl) (P3HT):phenyl-C61-butyric-acid-methyl ester (PCBM) organic solar cell. The QDs were synthesized by the hot injection route and deposited by casting on a device with ITO/PEDOT:PSS/P3HT:PCBM/Al structure. OPVs with and without the LDS layer of QDs were tested over time of exposure to the illumination of an AM1.5 solar simulator. The results showed that in the cells with the QDs layer, there was an increase in Open Circuit Voltage (Voc), Short Circuit Current Density (Jsc), Fill Factor (FF), and Power Conversion Efficiency (η), after 70 min of exposure, reaching a peak of these parameter values around 120 min of light exposure, while in the cells without the LDS layer, these parameters have decreased over the entire exposure time. This behavior was explained taking into account the improvement of the photoluminescence (PL) yield by the QDs film and the illumination process.

Luminescent poly p-phenylene vinylene (PPV) thin films were produced by the layer-by-layer technique, using organic dyes as the counter ion. It was observed that, when dyes with azo groups are incorporated in the PPV polymeric chains, the fluorescence intensity can be substantially increased by the photo-irradiation of the film with a linearly polarized laser beam. The data show that such emission enhancement is due to the alignment of the dye molecules caused by the photo-isomerization of the azo groups. This process leads to an absorbance of the dyes that is dependent both of the photo-irradiation dose and the polarization direction of the irradiation source, which affects the fluorescence emitted by the polymer. Thus, the incorporation of azo dyes can be used to modulate the fluorescence response of polymeric thin films.

Optical properties of self-assembled quantum dots (SAQDs) samples were investigated through photoluminescence (PL) with variation of temperature and excitation density. Two types of InAs SAQDs were studied: dots grown directly on GaAs, and dots grown inside an InGaAs quantum well, heterostructure known as dot-in-a-well (DWELL). The QDs structures were produced through conventional growth (with several deposition rates) as well as through pulsed growth mode, which consists in deposition cycles with growth interruption intervals. In the samples of QDs grown on GaAs, two PL peaks were identified and their behavior as a function of temperature can be explained by taking into account a bimodal distribution of dot sizes. For the DWELL sample only one PL peak was identified, which was assigned to the emission of the ground state of QDs belonging to a larger Gaussian distribution of dot sizes. SAQDs samples showed an anomalous behavior of the peak energy, integrated intensity and linewidth (FWHM) of the PL signal, as a function of temperature. To explain the observed results, a model was proposed that takes into account the size distribution of dots and the excited state emission of the family of larger dots. The QDs can be distributed in a bimodal size distribution, and the emission from the excited state can be observed, or not, depending on the growth conditions and on the potential profile of the dot. Such aspects can be combined to explain several peculiarities of the PL spectra observed in this and other published papers on SAQDs optical properties.

In the present paper the layer-by-layer self-assembly (LbL) technique was used to obtain poly( p -phenylenevinylene) (PPV) films exchanging the counter-ion Cl of the poly(xylylidene tetrahydrothiophenium) (PTHT ) precursor polymer by Congo Red (CR) azodye. The objective of the present paper is to study the azodye photoisomerization trans → cis → trans process as a function of the PPV thermal annealing procedure. The LbL PTHT/CR films were thermally converted into LbL PPV/CR films at low (110 °C) and conventional (230 °C) temperatures, and characterized through both absorption and emission techniques. We found that the unexpected emission band above 650 nm, attributed to the azodye, for LbL PPV/CR film thermally converted at lower temperature (110 °C) is an evidence of the considerable decrease of CR degradation in the polymeric matrix. Emission anisotropy and selective photoluminescence were carried out to characterize qualitatively the exciton energy transfer.

In this work, MEH-PPV and BDMO-PPV films were deposited by spin-coating on “dirty” textile substrates of canvas, nylon, canvas with resin, jeans and on glass and the temperature dependence of the optical properties of them was studied by photoluminescence and Raman (300 K) techniques. The temperature dependence of the energy, of the half line width at half height of the purely electronic peak, of the integrated PL intensity and of the Huang-Rhys factor, S = I (01) / I (00) , were obtained directly from the PL spectrum. For an analysis of the vibrational modes involved, Raman measurements were performed on substrates with and without polymers deposited and the results compared with those found in the literature. The films of MEH-PPV and BDMO-PPV showed optical properties similar to those films deposited on other substrates such as glass, metals, etc. It was observed an inversion of the first vibrational band in relation to the purely electronic peak with increasing temperature in the films deposited on nylon and canvas. The vibrational modes obtained by Raman were used to compose the simulation of the PL line shape of BDMO-PPV films on canvas and nylon, using a model proposed by Lin [29] .

This work reports on the results of magnetophotoluminescence (MPL) measurements carried out in a sample containing two Al 0.35 Ga 0.65 As/GaAs, coupled double quantum wells (CDQWs), with inter-well barriers of different thicknesses, which have the heterointerfaces characterized by a distribution of bimodal roughness. The MPL measurements were performed at 4 K, with magnetic fields applied parallel to the growth direction, and varying from 0 to 12 T. The diamagnetic shift of the photoluminescence (PL) peaks is more sensitive to changes in the confinement potential, due to monolayer variations in the mini-well thickness, rather than to the exciton localization at the local potential fluctuations. As the magnetic field increases, the relative intensities of the two peaks in each PL band inverts, what is attributed to the reduction in the radiative lifetime of the delocalized excitons, which results in the radiative recombination, before the excitonic migration between the higher and lower energy regions in each CDQW occurs. The dependence of the full width at half maximum (FWHM) on magnetic field shows different behaviors for each PL peak, which are attributed to the different levels and correlation lengths of the potential fluctuations present in the regions associated with each recombination channel.

In this work we simulate the photoluminescence (PL) spectra of BDMO-PPV thin films prepared by spin-coating technique on glass and on copper, as a function of temperature (12–300 K). Simulations were done using two theoretical models based on (i) the SSH theory where the line shape of the purely electronic transition is partly generated by localized states and partly by delocalized states and (ii) the semi-empirical model containing the coupling between localized molecular excitons and vibrational modes in Franck–Condon approach. Four active vibrational modes have been considered: C–C stretching coupled to a C–H bending of the phenyl ring at 1111.5 cm −1 , inter-rings C–C stretching at 1282.2 cm −1 , CC stretching coupled to a C–H bending of the vinyl group at 1309.3 cm −1 , C–C stretching of the phenyl ring at 1580.2 cm −1 . Additional vibrational mode of 403 cm −1 associated with C–C–C out-of-plane bending allowed leastwise for this material to adjust well with the characteristic asymmetry of the purely electronic transition. Finally, application of theoretical models are strongly dependent on the well-resolved PL spectra, i.e., electronic transition peak presented a relatively thinner HWHM and an asymmetric line shape.

In this work, we present a detailed study on the optical properties of two GaAs/Al 0.35 Ga 0.65 As coupled double quantum wells (CDQWs) with inter-well barriers of different thicknesses, by using photoluminescence (PL) spectroscopy. The two CDQWs were grown in a single sample, assuring very similar experimental conditions for measurements of both. The PL spectrum of each CDQW exhibits two recombination channels which can be accurately identified as the excitonic e 1 -hh 1 transitions originated from CDQWs of different effective dimensions. The PL spectra characteristics and the behavior of the emissions as a function of temperature and excitation power are interpreted in the scenario of the bimodal interface roughness model, taking into account the exciton migration between the two regions considered in this model and the difference in the potential fluctuation levels between those two regions. The details of the PL spectra behavior as a function of excitation power are explained in terms of the competition between the band gap renormalization (BGR) and the potential fluctuation effects. The results obtained for the two CDQWs, which have different degrees of potential fluctuation, are also compared and discussed.