Inhomogeneous spectral broadening and the decay kinetics of the luminescence spectra of prodan

The selectively excited steady-state luminescence spectra, as well as the decay time characteristics of the luminescence, of prodan in polar solvents excited by picosecond radiation are studied. The steady-state luminescence spectra exhibit a strong inhomogeneous broadening, which is the most pronounced at elevated solution viscosities. The temporal characteristics of the luminescence decay in different spectral ranges and the instantaneous spectra suggest the presence of relaxation processes resulting in a long-wavelength shift of the emission spectrum during the lifetime of the excited state. A relation between the relaxation shift of the emission spectrum and the intermolecular orientational relaxation of solvate molecules is established.     

Nonradiative energy transfer in a concentrated solution of prodan

The temporal characteristics of luminescence decay in concentrated solutions of prodan excited by picosecond laser radiation are studied The electronic spectra exhibit a strong inhomogeneity, which, in the case of elevated solution viscosity, manifests itself under steady-state conditions of measurements. The temporal characteristics of the luminescence decay and the time-resolved luminescence spectra point to the occurrence of relaxation processes causing a long-wavelength shift of the emission band with time. An increase in the prodan concentration from 10^?4 to 5 × 10^?2 M leads to a faster increase in the luminescence lifetime in the long-wavelength spectral region and to a higher rate of shifting of the instantaneous spectra, which is related to energy transfer over the states of inhomogeneous broadening of the luminophore.     

Red luminescence decay kinetics in Brazilian diamonds

Luminescence kinetics in the temperature range of 80–480 K and the red region of the spectrum is studied for Brazilian diamonds. Components with decay time constants of 23 and 83 ns are observed at room temperature after being excited by laser radiation with wavelengths of 375 and 532 nm, which differs considerably from the data published earlier for the luminescence kinetics of NV⁰- and NV^–-centers.     

Femtosecond luminescence decay due to exciton energy transfer in single-walled carbon nanotube bundles

We investigated luminescence decay kinetics in single-walled carbon nanotubes in large bundles excited by femtosecond pulses. The time constant of luminescence decay becomes longer with decrease in photon energy: 40 fs at 1.2 eV and 380 fs at 0.6 eV. This behavior is explained by exciton energy transfer from an excited to neighboring tubes.     

Simultaneous decay kinetics of drops and excitons luminescence in silicon

The lifetime of drops and the enhancement factor in silicon are deduced from simultaneous decay kinetics of drops and exciton luminescence.The determination of the drops lifetime does not require the knowledge of the exciton lifetime.The results yield: τ_g = 105 ηsec? = 9.     

The decay kinetics of radical-recombination luminescence in crystal phosphors

The features of the decay kinetics of radical-recombination luminescence (RRL) in crystal phosphors excited by atomic hydrogen have been studied. It is shown that the kinetics of the RRL decay can be determined both by the processes in the gas phase (decrease in the hydrogen-atom concentration as a result of their recombination at the walls of the reaction vessel after the atom-generation source has been switched off) and by the processes in the solid itself. Some conclusions are drawn concerning the mechanism of recombination for the RRL of the experimental phosphors.Translated from Izvestiya VUZ. Fizika, No. 12, pp. 16–19, December, 1973.     

Temporal dependences of dipole moments of prodan molecules

The fluorescence spectra of 6-propyl-2-dimethylaminonaphtalene (prodan), 1-(phenylamino)naphthalene (1-PAN), and 3-aminophthalimide are measured in glycerol with a picosecond resolution. The instantaneous fluorescence spectra and the correlation functions of the time-dependent Stokes shift of the fluorescence spectra of the two latter probes are used to find the time dependence of the dielectric response function of glycerol, which is necessary for calculating the charge transfer kinetics in prodan molecules. Based on the solvatochromism theory and using the experimental dependences of the time-dependent shift of the fluorescence bands for prodan molecules, which are characterized by efficient charge transfer in the excited electronic state, the kinetics of the electric dipole moment of the first singlet state is calculated.     

Effect of proton-donor solvent and structural flexibility of prodan and laurdan molecules on their spectral-luminescent properties

The influence of structural flexibility on dipole moments, energy-level locations, and charge distributions in prodan and laurdan molecules was studied. A quantum-chemical calculation of isolated prodan and laurdan molecules in the fluorescent state geometry was conducted. Rate constants for radiative and non-radiative processes and fluorescence quantum yields for these probe molecules were calculated. Interaction centers of prodan and laurdan with a proton-donor solvent were estimated quantitatively. The possibility of using fluorescent probes for estimating the polarity of proton-donor and proton-acceptor solvents was shown. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 334–341, May–June, 2009.     

Effect of phonon-induced desorption of oxygen molecules from the surface of a solid on adsorbate luminescence kinetics

A mathematical model to describe the pulse shape of delayed adsorbate fluorescence is proposed that accounts for desorption of oxygen molecules from the surface of a substrate induced by interaction with phonons. A numerical study of the temperature dependence of the probability of desorption of oxygen molecules from the substrate surface and of the luminescence intensity is carried out.     

Picosecond decay kinetics of CdS luminescence studied by a streak camera

Using a picosecond laser and a streak camera we have observed the time dependence of the luminescence intensity of free excitons, bound excitons, and excitonic molecules in CdS. The observed kinetics show that the P band is due to bimolecular emission from free excitons and that bound excitons are generated from free excitons through monomelecular process and excitonic molecule through bimolecular process.     

Investigation on luminescence and energy transfer in Tb-doped lead telluroborate glasses

This work reports on the visible luminescence properties and energy transfer processes responsible for non-exponential nature of the decay curves and also quenching of luminescence intensity of the ⁵D₃→⁷F_J transitions of Tb³⁺ ions in lead telluroborate (PTB) glasses containing different Tb³⁺ concentrations. The XRD and FT-IR spectra were measured to study the glassy nature and composition of the prepared glasses. The radiative properties are determined using the Judd-Ofelt theory to judge the suitability of studied glasses as practical photonic material. These parameters suggest that the PTBTb20 glass has the potential to produce intense green emission (544 nm) through the ⁵D₄→⁷F₅ transition.     

Luminescence self-quenching in Tm3+: YLF crystals: II. The luminescence decay and macrorates of energy transfer

Microparameters of migration and self-quenching of luminescence from the (³ P ₀, ¹ I ₆) levels of Tm ³⁺ ions are calculated and the luminescence decay from the ³ H ₄, ¹ G ₄, and ¹ _{D 2} levels are analyzed in the concentration series of LiY_1?x Tm_xF₄(x=0.5–10 at. %) crystals upon weak selective excitation. It is shown that the luminescence decay of a thulium ion concentration higher than 0.5 at. % cannot be described by the energy transfer that takes into account only the dipole-dipole interaction. The comparison of experimental kinetic curves with theoretical curves calculated within the framework of the known energy transfer models showed that multipole-multipole interaction is responsible for the self-quenching of the thulium levels. Contributions of higher multipole interactions to the self-quenching are estimated. The decay of luminescence from the ³ H ₄, ¹ G ₄, and ¹ D ₂ levels of Tm³⁺:YLF crystals with different concentrations of thulium ions is described analytically.     

Non-exponential decay kinetics: correct assessment and description illustrated by slow luminescence of Si nanostructures

The treatment of time-resolved (TR) photoluminescence (PL) decay kinetics is analysed in details and illustrated by experiments on semiconductor quantum dots, namely silicon nanocrystals (Si NCs). We consider the mono-, stretch- and multi-exponential as well as lognormal (LN) and some complex decay models for continuous and discrete distribution of rates (lifetimes). A particular attention is devoted to the thorough analysis of non-exponential decay kinetics. We explicitly show that a LN distribution of emitter sizes may results in LN distribution of decay rates. On the other hand, the distribution of rates cannot be, strictly speaking, Levy stable distribution (that results in the stretched-exponential decay). We introduce theoretical background and derive expressions to calculate the average decay lifetimes for some common decays with practical examples of their applications. Experimental aspects are discussed with special attention devoted to the major problems of the accurate TR PL data treatment, including background uncertainty, pulse duration, system response function etc. Finally, a thorough literature survey of TR PL in Si NCs is given. The methods and definitions outlined in this systematic review are applicable to various other material systems with slow decay like rare-earth and transition metal-doped materials, amorphous semiconductors, type-II heterostructures, singlet oxygen phosphorescence etc.