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We have investigated the molecular interface between an azo pigment and an α-phenylstilbene derivative where photocarriers are extrinsically produced from a microscopic viewpoint. From the measurement of the azo-pigment photoluminescence quenching by the α-phenylstilbene derivative, only the molecules that contact with the azo-pigment particles are known to promote generation of the photocarriers. The electron-transfer reaction at the interface for photocarrier generation is proven to occur adiabatically.

The non-radiative decay rate (at T=0) of photoexcited polarons in cis -polyacetylene is calculated using a lattice relaxation approach, treating the polaron state as a bound pair of kinks with position dependent mass. The required violation of Charge Conjugation Symmetry is provided by the emission of a phonon coupled to by second nearest-neighbour hopping. The resultant decay rates, though one to two orders of magnitude lower than those previously predicted using a multiphonon calculation [1], agree well with experiment.

Based on the theory of concentrational depolarization of photoluminescence (CDPL) worked out for three-dimensional systems [8] an extension has been made for two-dimensional systems. In the theory the excitation energy remigration and photoluminescence quenching by non-luminescent dimers have been taken into account as well. The expression obtained for emission anisotropy has been compared with the experimental results ofTrosper et al. [18] concerning CDPL of chlorophyll-a in two dimensional solutions. Good agreement of theory with experiment has been found for the values of critical distancesR0 smaller than those obtained in [18] as upper limits.

The non-radiative decay of photoinduced bond-alternation defects in cis-polyacetylene is considered within the SSH model [18]. The charge-conjugation symmetry of the simplest model Hamiltonian must be violated to explain the low photoluminescent yield (˜ 10-3 %) found experimentally. The simplest such route, that of electron-phonon coupling via second nearest-neighbour hopping is considered. It is found that a multiphonon process is required, the resulting decay rate being very sensitive to the parameters chosen. If this is the dominant non-radiative process, then it gives a potentially highly accurate method of determining the value of α, the nearest-neighbour electron-phonon coupling constant. The results for cis-polyacetylene can be generalized to give a qualitative understanding of photoluminescent properties of more complex conjugated molecules.

Optical properties of GaInAs/InP quantum wells at room temperature have been studied. Electric field induced exciton energy shifts, photoluminescence quenching and saturation of optical absorption have been observed.

The work has been supported from iCspec project, which received funding from the European Commission’s Horizon 2020 Research and Innovation Programme under grant agreement No. 636930, and also by the National Science Centre of Poland within Grant No. 2014/15/B/ST7/04663. Temperature-resolved photoluminescence studies were performed on tensely-strained AlSb/InAs/GaAsSb W-shaped type II quantum wells. They revealed two emission bands: one at lower energy of localized origin resulting from carrier trapping states at interfaces and dominates at low-temperature; and one corresponding to the fundamental optical transition in the type II quantum well. With the temperature increase to 170—200 K the low-energy emission is quenched and the high-energy band dominates and its intensity increases, indicating carrier transfer processes between the respective states at elevated temperatures. In addition, the integrated photoluminescence intensity was measured as a function of excitation power. At high excitation regime the emission intensity of the low-energy emission band saturated, indicating low density of states, thus confirming its localized nature. The depth of the localization potential at the InAs/GaAsSb interface was determined to be 13—15 meV. Publisher PDF

Porous silicon is a very attractive material due to its intense visible photoluminescence at room temperature. Its unique physical and chemical properties are determined by the porous structure where a nanosized silicon layer is formed during the electrochemical etching of crystalline silicon. So far, the high chemical reactivity of the porous silicon surface has prevented its extensive application in optoelectronics. Considerable effort has been put into the development of suitable techniques of stabilization. On the other hand, high chemical reactivity and sorption capacity of porous silicon represent the principal advantage for the construction of sensitive sensors of chemical species. This article provides a brief overview of the ongoing activities in the development of porous-silicon-based chemical sensors at the Charles University and at the Institute of Chemical Technology. So far, the detection of chemical species is based on the measurement of the changes in photoluminescence intensity and photoluminescence decay time, other complementary electrochemical and optical detection methods will follow in order to increase the selectivity of the detection. Another approach resulting in increased selectivity of sensor response utilizes the modification of porous silicon surface – either by physical adsorption or chemical derivatization – by various molecules with recognition properties. Due to the interdisciplinary nature of the research the involved scientists have built a network of collaborating laboratories specialized in various fields – material research, surface chemistry, design and synthesis of the molecules with recognition properties and sensor development.

We demonstrate that a DC voltage applied on a PbS quantum dot embedded organic light emitting diode can partially quench the quantum dot photoluminescence and propose a way to avoid this quenching.