Search results for "Ultrafast laser"
showing 10 items of 100 documents
Charge injection and trapping at perovskite interfaces with organic hole transporting materials of different ionization energies
2019
The extraction of photogenerated holes from CH3NH3PbI3 is crucial in perovskite solar cells. Understanding the main parameters that influence this process is essential to design materials and devices with improved efficiency. A series of vacuum deposited hole transporting materials (HTMs) of different ionization energies, used in efficient photovoltaic devices, are studied here by means of femtosecond transient absorption spectroscopy. We find that ultrafast charge injection from the perovskite into the different HTMs (<100 fs) competes with carrier thermalization and occurs independently of their ionization energy. Our results prove that injection takes place from hot states in the valence…
Role of Shallow Electron Traps in the Fast Transient Optical Phenomena of Alkali Halide Crystals
2002
We present additional evidences that the same shallow electron traps-atomic alkali impurity centres [M + ] c 0 e - are responsible for both classes (A and B) of the transient IR-absorption bands: (A) bands with maximum at 0.27-0.36 eV in NaCl, KCl, KBr, KI and RbCl (due to shallow electron traps or bound polarons) and (B) bands with maximum at 0.15-0.36 eV in NaI, NaBr, NaCl:I, KCl:I, KBr:I, RbCl:I and RbBr:I (due to on-centre STE or on-centre STE localised at iodine dimer). Both classes of the IR bands have the same location, similar shape (both exactly coincide for KCl:I and KCl at 10 or 80 K), half-width, vibration structure. It is established that the same Mollwo-Ivey plot curves E o =a…
Transient absorption with a femtosecond tunable excitation pump reveals the emission kinetics of color centers in amorphous silica.
2021
We report a set of femtosecond (fs) transient absorption (TA) measurements following the dynamics of the so-called nonbridging oxygen hole center in silica, a model color center in wide bandgap amorphous solids, characterized by a very large Stokes shift between the UV excitation and its associated red emission at 1.9 eV. The changes in the TA spectrum were probed in the UV-visible range at various delays after photoexcitation and analyzed as a function of the UV excitation energy, in single-photon absorption conditions. The combination of the experiments helps to clarify the defect photocycle, highlighting how TA measurements with tunable UV excitation could represent a powerful tool to in…
Luminescence Center Excited State Absorption in Calcium and Zinc Tungsates
2002
The tungstate crystals are well known scintillators. The mechanism of luminescence center formation and the luminescence center model are under discussion today. The results of time-resolved spectroscopy of luminescence center in ZnWO4 and CaWO4 in wide temperature regions was presented. The luminescence and induced absorption under pulsed electron beam excitation (pulse duration 10 ns, 0.26 MeV) were studied. The experimental equipment used allows one to obtain the transient absorption spectra, luminescence decay kinetics and transient absorption relaxation times.
Real-time observation of the intravalley spin-flip process in single-layer WS2
2019
We use helicity-resolved transient absorption spectroscopy to track intravalley scattering dynamics in monolayer WS2. We find that spin-polarized carriers scatter from upper to lower conduction band by reversing their spin orientation on a sub-ps timescale.
Transient absorption and luminescence of LiNbO3 and KNbO3
2001
Abstract The results of time-resolved optical absorption spectra in congruent and stoichiometric LiNbO3 as well as KNbO3 crystals are reported. The role of different polaron types in transient absoiption and luminescence spectra and decay kinetics are discussed.
Luminescence and Transient Optical Absorption in CdWO<sub>4</sub>
1997
Photodynamics at the CdSe Quantum Dot–Perylene Diimide Interface: Unraveling the Excitation Energy and Electron Transfer Pathways
2021
Excitation energy and charge transfer processes in perylene diimide dye–CdSe quantum dot complexes have been studied by femtosecond transient absorption spectroscopy. After excitation of the quantu...
Relaxation of electronic excitations in LiNbO3crystals
2001
Transient absorption both in stoichiometric and Mg doped congruent LiNbO was observed after pulsed electron beam excitation. The luminescence spectra and decay kinetics in these materials show different excitonic relaxation possibilities. The dependence on sample stoichiometry is also discussed.