Emission Band Shape Research Articles

Ab initio calculations on the local structure and the 4f–5d absorption and emission spectra of [formula omitted]-doped YAG

The 4 f ↔ 5 d absorption and emission spectra of Ce 3 + -doped YAG ( Y 3 Al 5 O 12 ) are simulated with a quantum chemical ab initio embedded cluster approach applied to Ce 3 + substitutional defects of D 2 local symmetry. The only empirical information used is the structure of the pure host. The simulated absorption spectrum is calculated with overestimations of 2300– 3300 cm - 1 , which became 4600 cm - 1 in the luminescence. The three 4 f → 5 d observed absorptions were assigned and the energies of the two remaining ones, which are hidden by the absorption of the pure host, were predicted. The lowest 5 d → 4 f emission was found to take place from Γ 5 ( 2 2 A ) and the next emission from Γ 5 ( 3 2 B 3 ). Good absorption and emission band shapes and relative intensities are obtained. A large underestimation of the Stokes shift is found, which suggests an underestimation of the relaxation on the emitting state.

Electronic and Optical Properties of Ladder‐Type Heteraborins

Ladder-type pi-conjugated molecules bearing heteraborin (azaborine or thiaborin) units were synthesized, and X-ray crystallographic analysis of pentacene-type molecules showed that these molecules have rigid and planar structures. UV-visible spectroscopy and theoretical calculations revealed the enhancement of electronic interaction between heteraborin units, the decrease in HOMO-LUMO energy gaps, and the strong effect of the bridging main-group elements (nitrogen or sulfur) on the electronic states. The ladder-type molecules emitted strong fluorescence both in solution and in the solid state, and the emission-band shapes were different from each other, indicating the existence of intermolecular interactions in the solid state. Complex formation of the ladder molecules with fluoride ion was monitored by UV-visible spectroscopy, which revealed that the Lewis acidity of these molecules can be controlled by the elongation of pi systems and the change of the bridging main-group elements.

Probing Excitation Delocalization in Supramolecular Chiral Stacks by Means of Circularly Polarized Light: Experiment and Modeling

Photoexcitations in helical aggregates of a functionalized, chiral oligophenylenevinylene (MOPV) are described going beyond the Born-Oppenheimer approximation, in the form of dressed (polaronic) Frenkel excitons. This allows for accurate modeling of the experimentally observed wavelength dependence of the circular polarization in fluorescence, which directly probes the non-adiabatic nature of the electron-vibration (EV) coupling in this system. The fluorescence photon is emitted from a nuclear geometry in which one MOPV and its two nearest neighbors have a nuclear equilibrium that differs appreciably from the ground state due to the presence of the excited state. The absorption and emission band shape and the circular dichroism are consistent with a coherence range of the emitting excitation of approximately two neighboring molecules. Random fluctuations in the zero-order excited-state energy of the MOPVs (disorder) limit the exciton delocalization and can be described by a Gaussian distribution of energies with a width sigma=0.12 eV and a spatial correlation length l0 approximately 5 molecules. We find that disorder and EV coupling act synergistically in localizing the emitting exciton to a single MOPV in the aggregate with 95% probability.

Radiative Relaxation of Sepia Eumelanin is Affected by Aggregation¶

The steady-state and time-resolved emission properties of aqueous solutions containing different aggregation state distributions of eumelanin are reported. Excitation spectra of the size-selected samples reveal, for the first time, differences in absorption bands due to varying levels of aggregation. These size-dependent absorption properties result in size-dependent emission band shapes and quantum yields. For all size fractions, absorption and emission overlap significantly. The emission yield for small eumelanin aggregates is 5.7 times greater than that for large eumelanin aggregates. Time-resolved population decays reveal that small eumelanin aggregates are responsible for long-lived emission dynamics (lifetimes greater than 1 ns), while large eumelanin aggregates are the source of short emission decay (lifetimes less than 1 ns). Polarized emission decays for the large and small aggregates reveal that energy transfer occurs both within the same and between the separate fundamental building blocks of eumelanin. The observed energy transfer dynamics can be accounted for using Förster theory.

Application of Asymmetric Model in Analysis of Fluorescence Spectra of Biologically Important Molecules

Having a valid mathematical model for structureless emission band shapes is important when deconvoluting fluorescence spectra of complex molecules. We propose a new asymmetric model for emission spectra of five organic molecules containing aromatic ring: catechol, coniferyl alcohol, hydroquinone, phenylalanine and tryptophan. For each molecule, a series of emission spectra, varying in excitation wavelength, were fitted with the new model as well as with two other analytical expressions: log-normal, described previously in the literature, and sigmoid-exponential. Their deconvolution into two, three and four Gaussian components was also performed, in order to estimate the number of symmetric components needed to obtain a better fitting quality than that of the asymmetric models. Four subtypes of the new model, as well as the log-normal one, did not differ significantly in their fitting errors, while the sigmoid-exponential model showed a significantly worse fit. Spectra of two mixtures: hydroquinone-coniferyl alcohol and hydroquinone-tryptophan were deconvoluted into two asymmetric and four Gaussian components. Positions of asymmetric components of mixtures matched those of separate molecules, while Gaussian did not. Component analysis of a polymer molecule, lignin, was also performed. In this more complex case asymmetric and Gaussian components also grouped in alternating positions.

Nanosized LiSrPO 4:Eu 2+ phosphor with blue-emission synthesized by the sol–gel method

A novel nanosized phosphor, LiSrPO 4:Eu 2+, was prepared by the sol–gel method with a precursor (Li/Sr/Eu) polymerized citrate–polyethylene glycol, calcined at 950 °C for 3 h in a weak reductive atmosphere of active carbon. X-ray diffraction results confirmed the formation of LiSrPO 4:Eu 2+. Field-emission scanning electron microscopy observation showed an average diameter of about 15 nm for the particles with a spherical-like morphology. Photoluminescence measurements results indicated that upon excitation with 346 nm light, the nanosized LiSrPO 4:Eu 2+ showed intensely blue-emission peaked at about 445 nm. Compared with the microsized phosphor obtained by the solid-state reaction method, the main peaks in the emission and excitation spectra of the nanoparticles shifted to shorter wavelength, and the nanoparticles exhibited longer decay time. The symmetric emission band shape implies that Eu 2+ ions just occupy one kind site in the LiSrPO 4 lattice by substituting Sr 2+ ions.

Wavelength despersive spectroscopy analysis at high spectral resolution: application to the study of Mo/Si multilayers

AbstractWe show that x‐ray emission spectroscopy (XES) induced by electrons, analyzed at high spectral resolution by a WDS Johann‐type spectrometer, is a powerful technique to characterize in a nondestructive way the interlayers in Mo/Si multilayers. The analysis is performed using the IRIS (Instrument de Recherche sur les Interfaces et Surfaces) apparatus equipped with a curved crystal. Within those experimental conditions the spectral resolution E/ΔE is about 2000 in the 1800–1900 eV photon energy range. Because of the high resolution of the spectrometer, the evolution of the shape of the Si Kβ emission band (3p − 1s transition) as a function of the chemical environment of the Si atoms is easily evidenced. We study a series of Mo/Si multilayers, where the thickness of the Si layers is 2 nm and that of the Mo layers is 1, 2, 3 or 4 nm. It clearly appears that the emission band from the Si atoms within the multilayers is different from that of amorphous Si (a‐Si), which should be observed if no diffusion process takes place at the interfaces. By comparing the observed emission band to that of a‐Si and molybdenum silicides and using a simple diffusion model, we deduce the composition of the interlayers. Their thickness is deduced and estimated to be 0.4 ± 0.1 nm or 0.8 ± 0.2 nm depending on the samples. Copyright © 2007 John Wiley & Sons, Ltd.

Influence of the “Innocent” Ligands on the MLCT Excited-State Behavior of Mono(bipyridine)ruthenium(II) Complexes: A Comparison of X-ray Structures and 77 K Luminescence Properties

The variations in the nonchromophoric ligands of [Ru(L)4bpy]2+ complexes are shown to result in large changes in emission band shapes, even when the emission energies are similar. These changes in band shape are systematically examined by means of the generation of empirical reorganizational energy profiles (emreps) from the observed emission spectra (Xie, P.; et al. J. Phys. Chem. A 2005, 109, 4671), where these profiles provide convenient probes of the differences in distortions from the ground-state structures of the 2,2-bipyridine (bpy) ligands (for distortion modes near 1500 cm(-1)) in the metal-to-ligand charge-transfer (MLCT) excited states for a series of complexes with the same ruthenium(II) bipyridine chromophore. The bpy ligand is nearly planar in the X-ray structures of the complexes with (L)4 = (NH3)4, triethylenetetraamine (trien), and 1,4,7,10-tetraazacyclododecane ([12]aneN4). However, for (L)4 = 5,12-rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, the X-ray crystal structure shows that the bpy ligand is twisted in the ground state (a result of methyl/bpy stereochemical repulsion) and the emrep amplitude at about 1500 cm(-1) is significantly larger for this structure than for the complex with (L)4 = 1,4,8,11-tetraazacyclotetradecane, consistent with larger reorganizational energies of the bpy distortion modes in order to form a planar (bpy(-)) moiety in the excited state of the former. The trien and [12]aneN4 complexes have very nearly the same emission energies, yet the 40% smaller vibronic sideband intensity of the latter indicates that the MLCT excited state is significantly less distorted; this smaller distortion and the related shift in the distribution of distortion mode reorganizational energy amplitudes is apparently related to the 36-fold longer lifetime for (L)4 = [12]aneN4 than for (L)4 = trien. For the majority (77%) of the [Ru(L)4bpy]2+ complexes examined, there is a systematic decrease in emrep amplitudes near 1500 cm(-1), consistent with decreasing excited-state distortion, with the excited-state energy as is expected for ground state-excited state configurational mixing in a simple two-state model. However, the complexes with L = [12]aneN4, 1,4,7,10-tetraazacyclododeca-1-ene, and (py)4 all have smaller emrep amplitudes and thus less distorted excited states than related complexes with the same emission energy. The observations are not consistent with simple two-state models and seem to require an additional distortion induced by excited state-excited state configurational mixing in most complexes. Because the stereochemical constraints of the coordinated [12]aneN4 ligand restrict tetragonal distortions around the metal, configurational mixing of the 3MLCT excited state with a triplet ligand-field excited state of Ru(II) could account for some of the variations in excited-state distortion. The large number of vibrational distortion modes and their small vibrational reorganizational energies in these complexes indicate that a very large number of relaxation channels contribute to the variations in 3MLCT lifetimes and that the metal-ligand skeletal modes are likely to contribute to some of these channels.

Probes of the Metal-to-Ligand Charge-Transfer Excited States in Ruthenium-Am(m)ine-Bipyridine Complexes: The Effects of NH/ND and CH/CD Isotopic Substitution on the 77 K Luminescence

The effects of ligand perdeuteration on the metal-to-ligand charge-transfer (MLCT) excited-state emission properties at 77 K are described for several [Ru(L)(4)bpy](2+) complexes in which the emission process is nominally [uIII,bpy-] --> [RuII,bpy]. The perdeuteration of the 2,2'-bipyridine (bpy) ligand is found to increase the zero-point energy differences between the ground states and MLCT excited states by amounts that vary from 0 +/- 10 to 70 +/- 10 cm(-1) depending on the ligands L. This indicates that there are some vibrational modes with smaller force constants in the excited states than in the ground states for most of these complexes. These blue shifts increase approximately as the energy difference between the excited and ground states decreases, but they are otherwise not strongly correlated with the number of bipyridine ligands in the complex. Careful comparisons of the [Ru(L)(4)(d(8)-bpy)](2+) and [Ru(L)(4)(h(8)-bpy](2+) emission spectra are used to resolve the very weak vibronic contributions of the C-H stretching modes as the composite contributions of the corresponding vibrational reorganizational energies. The largest of these, 25 +/- 10 cm(-1), is found for the complexes with L = py or bpy/2 and smaller when L = NH(3). Perdeuteration of the am(m)ine ligands (NH(3), en, or [14]aneN(4)) has no significant effect on the zero-point energy difference, and the contributions of the NH stretching vibrational modes to the emission band shape are too weak to resolve. Ligand perdeuteration does increase the excited-state lifetimes by a factor that is roughly proportional to the excited-state-ground-state energy difference, even though the CH and NH vibrational reorganizational energies are too small for nuclear tunneling involving these modes to dominate the relaxation process. It is proposed that metal-ligand skeletal vibrational modes and configurational mixing between metal-centered, bpy-ligand-centered, and MLCT excited states are important in determining the zero-point energy differences, while a large number of different combinations of relatively low-frequency vibrational modes must contribute to the nonradiative relaxation of the MLCT excited states.

Effect of Sample Preparation and Excitation Conditions on the Single Molecule Spectroscopy of Conjugated Polymers

Extensive new single molecule spectroscopy (SMS) data on the conjugated polymer MEH-PPV at low temperature were obtained. In particular, the combined effects of sample preparation and excitation condition were explored in detail. The data confirm previous observations from this laboratory that (i) the distribution of emission maxima of single MEH-PPV molecules has a bimodal distribution and (ii) the single molecule emission spectrum of MEH-PPV exhibits few time-dependent fluctuations of the emission intensity, band shape, or spectral maxima. These data also help explain the discrepancy among the various published SMS data on this compound and suggest that environmental impurities, long irradiation times, nearby interfaces, and incomplete data sampling may account for some of the discrepancies among the published data.

Emission band shape probes of the mixed-valence excited state properties of polypyridyl-bridged bis-ruthenium(II) complexes

The absorption spectra and emission spectral band shapes of several polypyridine-ligand (PP) bridged bis-ruthenium(II) complexes imply that the Ru(II)/Ru(III) electronic coupling is weak in their lowest energy metal to ligand charge transfer (MLCT) excited states. Many of these PP-bridging ligands contain pyrazine moieties and the weak electronic coupling of the excited states contrasts to the strong electronic coupling inferred for the correlated mixed-valence ground states. Although the bimetallic complexes emit at significantly lower energy than their monometallic analogs, the vibronic contributions to their 77 K emission spectra are much stronger than expected based on comparison to the monometallic analogs (around twofold in some complexes) and this feature is characteristic of bimetallic complexes in which the mixed-valence excited states are electronically localized. The weaker excited state than ground state donor/acceptor electronic coupling in this class of complexes is attributed to PP-mediated super-exchange coupling in which the mediating orbital of the bridging ligand (PP-LUMO) is partly occupied in the MLCT excited states, but is unoccupied in the ground states; therefore, the vertical Ru(III)-PP − (MLCT) energy is larger and the mixing coefficient smaller in these excited states than is found for Ru(II)-PP in the corresponding ground states.

Near-infrared speckle interferometry and radiative transfer modelling of the carbon star LP Andromedae

We present the near-infrared speckle interferometry for LP And in the H and $K^{\prime}$ bands with diffraction-limited resolutions of 56 and 72 mas, new $\it JHKLM$ photometry, and the results of our radiative transfer modelling of this carbon star. The reconstructed visibility reveals a spherically-symmetric envelope surrounding the central star. To determine the physical parameters of the latter and the properties of its dusty envelope, we performed extensive radiative transfer calculations. The well-defined spectral energy distribution of LP And in the entire range from the near-IR to millimeter wavelengths (including the absorption feature visible in the stellar continuum at 3 ${\mu}$m and the shapes of the dust emission bands at 11 and 27 ${\mu}$m), together with our H -band visibility can be reproduced by a spherical dust envelope with parameters that are very similar to those of CW Leo (IRC +10 216), the best studied carbon star. For the newly estimated pulsation period $P = 617 \pm 6$ days and distance $D = 740 \pm 100$ pc, our model of LP And changes its luminosity $L_{\star}$ between 16 200 and 2900 $L_{\odot}$, its effective temperature $T_{\star}$ between 3550 and 2100 K, and its radius $R_{\star}$ between 340 and 410 $R_{\odot}$. The model estimates the star's mass-loss rate $\dot{M} \approx 1.9 \times 10^{-5}$ $M_{\odot}$ yr - 1 , assuming a constant outflow velocity $v = 14$ km s -1 . If the latter also applied to the innermost parts of the dusty envelope, then presently the star would be losing mass at a rate $\dot{M} \approx 6.0 \times 10^{-5}$ $M_{\odot}$ yr -1 . However, we believe that the inner wind velocity must actually be closer to $v \approx 4$ km s -1 instead, as wind acceleration is expected in the dust-formation zone. The dusty envelope of LP And extends from $R_1 \approx 2$ $R_{\star}$ to distances of $R_2 \approx 3$ pc from the star. The total mass of the envelope lost by the central star is $M = 3.2$ $M_{\odot}$ assuming a dust-to-gas mass ratio of $\rho_{\rm d}/\rho$ = 0.0039. The circumstellar optical depth towards the star is $\tau_{V} = 25$ in the visual. The dust model contains small silicon carbide grains, inhomogeneous grains made of a mixture of SiC and incompletely amorphous carbon, and thin mantles made of iron-magnesium sulfides. This dust mixture perfectly fits the infrared continuum and both the 11.3 ${\mu}$m and 27 ${\mu}$m emission bands. We find that our $K^{\prime}$-band visibility could not be fitted by our spherical model, so we discuss possible reasons for this interesting result. More observations are required in order to determine what causes this effect. If slight deviations from spherical geometry in its envelope are the reason, then the object's evolutionary stage would be even more similar to that of CW Leo. It appears that LP And is a highly-evolved intermediate-mass star (initial mass $M^0_{\star}$ ≈ 4 $M_{\odot}$) at the end of its AGB phase.

The Effect of the Diphosphine Basicity on the Excited-State Properties of trans-(N2)2W(R2PCH2CH2PR2)2: Identification of Near-Degenerate, Luminescent 3MLCT and 3LF Terms

Absorption spectra (77 and 298 K), luminescence spectra (5-80 K), and luminescence lifetimes (5-80 K) for the title complexes have been correlated to increasing diphosphine basicity (R = 4-CF(3)-Ph < 4-H-Ph < 4-CH(3)O-Ph < Et). As a consequence, spectral peaks have been assigned to (1,3)MLCT (B(1u), W --> phosphorus) and (1,3)LF (B(2g)) terms. As the ligand basicity increases, the (3)MLCT bands observed in absorption blue-shift nearly 8000 cm(-1) and the vibrationally structured (3)LF bands observed in emission red-shift approximately 1300 cm(-1). (3)LF terms lie lowest in energy in the 4-H-Ph, 4-CH(3)O-Ph, and Et compounds, and temperature-dependent lifetime data suggest emission from each be assigned to the equilibrated, spin-orbit split levels of the (3)LF term. The (3)LF and (3)MLCT excited-state terms lie close in energy in the 4-CF(3)-Ph compound, resulting in an emission band shape that is temperature-dependent. At 77 K, the emission band is broad and structureless and is assigned to arise primarily from the (3)MLCT term. As the temperature is lowered toward 5 K, the (3)MLCT emission diminishes in intensity accompanied by the development of a vibrational structure that is characteristic of emission from the (3)LF term. These excited-state terms satisfy the requirements (different orbital origins, near-degeneracy) for separation by a Franck-Condon energy barrier, resulting in simultaneous emission from both terms between 5 and 77 K.

Putative phototautomerization of 4-thiouridine in the S 2 excited state revealed by fluorescence study using picosecond laser spectroscopy

The stationary and dynamic properties of S 2 → S 0 fluorescence of 2′,3′,5′-tri- O-acetyl-4-thiouridine (TU) in acetonitrile solution at room temperature have been studied. In the emission spectra of the sample, measured upon excitation with picosecond laser pulses, changes in fluorescence intensity and emission band shape have been observed with increasing time of excitation. The fluorescence intensity increases and the band maximum moves to the shorter wavelength until the steady-state condition is achieved. These changes are fully reversible indicating that they are not related to the formation of stable photoproducts. No such changes have been observed in the fluorescence spectrum recorded upon excitation of the same sample of TU with continuous light from xenon lamp. Under the latter conditions the fluorescence is very weak ( ϕ F = 1 × 10 −4) and the band exhibit a maximum at λ max F = 420 nm . The decay kinetics was measured using a two-stage method in order to estimate the number of emitting species and determine the parameters characterizing their emission. Analysis of the experimental fluorescence decays at λ F = 400, 430 and 450 nm measured upon various time intervals (<20 min) of the sample excitation with laser pulses has shown that the best fit of experimental to theoretical curve is obtained assuming the presence of three emitting species with lifetimes of τ 1 = 5 ± 1 ps, τ 2 = 80 ± 20 ps and τ 3 = 600 ± 100 ps. In contrast to the lifetimes the values of fractional coefficients depend on λ F and the time of measurement. The results of the fluorescence study of TU with picosecond laser spectroscopy are discussed in terms of phototautomerization of TU (2-keto-4-thione) in the S 2 state leading to its two possible tautomers: 4-thione, 2-hydroxy form in the S 2 state and 4-thiol, 2-keto form in the S 1 state. The models of the tautomers of TU were synthesized and their absorption and emission features were determined.

The Characterization of the High-Frequency Vibronic Contributions to the 77 K Emission Spectra of Ruthenium−Am(m)ine−Bipyridyl Complexes, Their Attenuation with Decreasing Energy Gaps, and the Implications of Strong Electronic Coupling for Inverted-Region Electron Transfer

The 77 K emission spectra of a series of [Ru(Am)6-2n(bpy)n]2+ complexes (n = 1-3) have been determined in order to evaluate the effects of appreciable excited state (e)/ground state (g) configurational mixing on the properties of simple electron-transfer systems. The principal focus is on the vibronic contributions, and the correlated distortions of the bipyridine ligand in the emitting MLCT excited state. To address the issues that are involved, the emission band shape at 77 K is interpreted as the sum of a fundamental component, corresponding to the {e,0'} --> {g,0} transition, and progressions in the ground-state vibrational modes that correlate with the excited-state distortion. Literature values of the vibrational parameters determined from the resonance-Raman (rR) for [Ru(NH3)4bpy]2+ and [Ru(bpy)3]2+ are used to model the emission spectra and to evaluate the spectral analysis. The Gaussian fundamental component with an energy Ef and bandwidth Deltanu1/2 is deconvoluted from the observed emission spectrum. The first-, second-, and third-order terms in the progressions of the vibrational modes that contribute to the band shape are evaluated as the sums of Gaussian-shaped contributions of width Deltanu1/2. The fundamental and the rR parameters give an excellent fit of the observed emission spectrum of [Ru(NH3)4bpy]2+, but not as good for the [Ru(bpy)3]2+ emission spectrum probably because the Franck-Condon excited state probed by the rR is different in symmetry from the emitting MLCT excited state. Variations in vibronic contributions for the series of complexes are evaluated in terms of reorganizational energy profiles (emreps, Lambdax) derived from the observed spectra, and modeled using the rR parameters. This modeling demonstrates that most of the intensity of the vibronic envelopes obtained from the frozen solution emission spectra arises from the overlapping of first-order vibronic contributions of significant bandwidth with additional convoluted contributions of higher order vibronic terms. The emrep amplitudes of these complexes have their maxima at about 1500 cm(-1) in frozen solution, and Lambdax(max) decreases systematically by approximately 2-fold as Ef decreases from 17,220 for [Ru(bpy)3]2+ to 12,040 cm(-1) for [Ru(NH3)4bpy]2+ through the series of complexes. Corrections for higher order contributions and bandwidth differences based on the modeling with rR parameters indicate that the variations in Lambdax(max) imply somewhat larger decreases in first-order bpy vibrational reorganizational energies. The large attenuation of vibrational reorganizational energies of the [Ru(Am)6-2n(bpy)n]2+ complexes contrasts with the apparent similarity of reorganizational energy amplitudes for the absorption and emission of [Ru(NH3)4bpy]2+. These observations are consistent with increasing and very substantial excited-state/ground-state configurational mixing and decreasing excited-state distortion as Ef decreases, but more severe attenuation for singlet/singlet than triplet/singlet mixing (alphage > alphaeg for the configurational mixing coefficients at the ground-state and excited-state potential energy minima, respectively); it is inferred that 0.18 > or = alphage2 > or = 0.09 for [Ru(bpy)3]2+ and 0.37 > or = alphage2 > or = 0.18 for [Ru(NH3)4bpy]2+ in DMSO/water glasses, where the ranges are based on models that there is or is not a spin restriction on configurational mixing (alphage > alphaeg and alphage = alphaeg), respectively, for these complexes.

Laser processing and characterization of ZnS–Cu thin films

ZnS films were deposited using an original chemical method under atmospheric pressure on to a glass and ceramics substrates. The ZnS films were doped with Cu, Cl by a thermal diffusion method from a ZnS–Cu, Cl powder. Laser processing realized by a pulse nitrogen laser (337 nm) with a pulse time 5 ns. The power density varied from 10 to 32 MW/cm 2. The morphology of films was investigated by atomic force microscopy (AFM). It was found that the luminescent properties and the surface morphology of the ZnS–Cu film undergo a change starting with the power density of 20 MW/cm 2. The analysis of results shows that optimum dose is 23 MW/cm 2. There is a laser ablation of the layer surface ZnS film during laser processing at the power densities greater than 20 MW/cm 2. Basic roughness of the surface film was 55 nm.The laser processing resulted in the smoothing of surface. The roughness decreases to 27 nm. The emission and the excitation spectra measured before the laser processing and later are different. The excitation spectra consist of two bands at 337 and 375 nm. The laser processing changes the ratio of the bands intensities. The emission band maximum is 525 nm. The maximum shifts to 521 nm after the laser irradiation. The emission band shape changes too. It becomes asymmetric because of increase short-wave wing. An analysis of the available data is accomplished taking into account two alternative possibilities: an inhomogeneous distribution of the emission centers along the direction of the growth of the film and the laser processing of ZnS–Cu film.

Effects of the spin-triplet states mixture and electron-phonon coupling in Y3Al5O12:Cr4+

The exchange charge model of the crystal field is applied to calculate the complete energy level scheme of the Cr 4+ ions in Y 3 Al 5 O 12 using symmetry at the Cr 4+ position. Mixture of the spin-triplet states arising from the and terms of the 3 d 2 -electron configuration is shown to have a profound effect on the energy levels sequence. Large splittings of the orbital triplets originating from the “parent” T d symmetry are explained by large contribution of the low-symmetry component of the crystal field. Huang-Rhys parameter and effective phonon energy are evaluated from the experimental spectroscopic data available in the literature. Temperature-dependent probability of the nonradiative transition between the ground and first excited states is drawn; the emission band shape is obtained using the single configuration coordinate model.

Broadband emission of dye mixtures in films and polymer matrices

Emission of mixtures of organic compounds in thin acrylic films and matrices is investigated from the blue to red range of the spectrum. The present paper is aimed at studying the feasibility of obtaining white light by conversion of output diode radiation (379 nm) using a mixture of fluorophors. It is demonstrated that the emission band shape depends on ratios of dye concentrations and geometry of excitation and registration that must be taken into account in the development of devices based on these compounds.

The room temperature emission band shape of the lowest energy chlorophyll spectral form of LHCI

Selective excitation, at room temperature, in the long wavelength absorption tail of the photosystem I antenna complexes, known as light harvesting complex I, induces pronounced pre-equilibration fluorescence from the directly excited pigment state. This has allowed determination of the fluorescence band shape of this low energy photosystem I chlorophyll antenna state, at room temperature, for the first time. The emission maximum is near 735 nm. The remarkable band width (55 nm) and asymmetry have never been previously reported for chlorophyll a states.

Photoluminescence from localized states in rutile by Ar +-ion laser excitation

We report on a photoluminescence (PL) band at around 2.2 eV for rutile through an Ar +-ion laser excitation. The PL consists of two sub-bands which are located at 2.22 eV and 2.28 eV , respectively, and have bandwidths of 0.06– 0.07 eV . The emission and absorption band shapes, which are composed of two asymmetrically distorted sub-peaks, are examined and considered in detail. The PL emissions are proved to originate in the localized states and the Stokes shift are estimated to be 0.12–0.16 and 0.15 eV . The radiative centres for these PL are found to be those reported for the interstitial Ti 3+ ions.