Luminescence Excitation Spectra Research Articles

Heterogeneous and hyperfine interactions between valence states of molecular iodine correlating with the I((2)P1/2) + I((2)P1/2) dissociation limit.

Detailed analysis of interactions between all 0g (+), 1u, and 0u (-) weakly bound states of iodine molecule correlating with the I((2)P1/2) + I((2)P1/2) (bb) dissociation limit has been performed. For this purpose, the 0u (-) (bb) state has been described using analysis of rotationally resolved excitation spectra of luminescence from the g0g (-) state populated in a three-step three-color perturbation facilitated excitation scheme via the 0u (-) state. Energies of 41 rovibrational levels, molecular constants, and potential energy curve have been determined. Energy gaps between closest rovibrational levels of the 0u (-) and 0g (+), 1u (bb) states are found to be large, ∼6 cm(-1). However, interaction of all three 0g (+), 1u, and 0u (-) (bb) states has been observed. It has been found that the 0u (-) and 1u electronic states are mixed by heterogeneous interactions, while their mixing with the 0g (+) one is due to hyperfine interactions predominantly. Admixture coefficients and electronic matrix elements of the coupling between the 0g (+) ∼1u, 0g (+)∼0u (-), and 0u (-) ∼1u states have been estimated.

Geochemical study of the mobile metal/metalloid fraction and the fluorescent properties of the aqueous extracts of dissolved organic matter present in marine sediments from the Messiniakos gulf at the southern part of Greece

Sediment samples from the Messiniakos gulf, at the southern part of Greece, were studied for the metals/metalloid content in the non-residual fraction and the fluorescent properties of the aqueous extracts of dissolved organic matter as both groups of metals/metalloid and dissolved organic matter are highly important from an environmental aspect. Applying the useful tool of Kriging method, prediction surfaces for each non-residual metal/metalloid were produced. Hierarchical cluster analysis and factor analysis with varimax rotation were performed on the data for the non-residual metal/metalloid content in sediments. The aqueous extracts of dissolved organic matter were characterized by fluorescence spectroscopy recording mono dimensional emission, excitation, synchronous-scan excitation and total luminescence spectra for the classification of chromophoric units present.In general, it was found that sediments from the central part of the gulf correspond to mobile metal fraction enrichment while those from the western gulf had lower values. Fluorescence studies in the DOM extracted from sediments revealed the presence of autochthonous organic matter with a low degree of aromatic polycondensation and a low level of conjugated chromophores. Fluorescence intensity and humification decrease in buried sediments. Samples with more humificated structures were also the ones having more intense peaks.Spatial and vertical distributions of temperature, salinity and chlorophyll content in the water column were also studied.

Specifics of the spectral and luminescent properties of ensembles of colloidal quantum dots

Using colloidal solutions of ZnS-shell indium phosphide quantum dots with two average sizes of 2.1 and 3.0 nm and a size distribution variance of 10%, it has been shown that the luminescence and the luminescence excitation spectra of the colloidal quantum dots substantially depend on the wavelength of exciting light and the detection wavelength, respectively, with both the relationships being nonlinear in character, which may indicate the bimodal type of the size distribution function. Similar measurements for CdSe colloidal quantum dots with an average particle size of dav = 2.5 nm and a variance of 6% have shown that the effect of dependence of the luminescence peak position on the excitation wavelength is manifested to a much lesser extent.

Recombination luminescence of Cu and/or Ag doped lithium tetraborate single crystals

Complex investigations of thermostimulated luminescence (TSL) and radioluminescence properties of Li2B4O7 (LTB), LTB:Cu, LTB:Ag and LTB:Cu, Ag crystals suitable for tissue equivalent dosimeters were carried out in the temperature range 4.2–700K. TSL, cathodoluminescence and X-ray excited luminescence spectra are compared to those measured under photoexcitation. The emission band at 4.6eV in LTB:Ag is reliably related to Ag+ ions based on the comparison of the results of optical spectroscopy studies and first principle calculations. Energy transfer from the relaxed exited state of the Ag+ ion to the Cu+ ion in double-doped LTB:Cu, Ag crystals is demonstrated. Thermostimulated recombination of charge carriers in irradiated crystals is seen to take place mainly at oxygen sites at low temperatures and at impurity sites at high temperatures. For the first time, the appearance of the low-temperature TSL peak at 90K is assigned to ionic processes in LTB crystals. The appearance of pyroelectric flashes due to the lattice relaxation in the temperature region 90–240K is demonstrated and their surface-related nature clarified. In accordance with EPR studies the dosimetric TSL peaks in copper and silver doped LTB crystals are attributed to thermally released electrons recombining with Cu2+ and Ag2+ centres.

Effects of Ce3 + sensitizer on the luminescent properties of Tb3 +-activated silicate oxyfluoride scintillating glass under UV and X-ray excitation

Novel Tb3+ or Ce3+ doped and Tb3+/Ce3+ codoped silicate oxyfluoride scintillating glasses were synthesized by melt-quenching method. The luminescent properties were studied by transmission spectra, photoluminescence excitation (PLE) and photoluminescence (PL) spectra, X-ray excited luminescence (XEL) spectra and luminescence decay curves in order to reveal the roles of Ce3+ sensitizer in the luminescence process of Tb3+-activated silicate oxyfluoride scintillating glass under UV and X-ray excitation. As for Tb3+/Ce3+ codoped scintillating glasses, the Ce3+ ions strongly sensitized the luminescence of the Tb3+ ions by energy transfer process from Ce3+ to Tb3+ ions under UV excitation. The optimal doping concentration of Ce2O3 in Tb3+/Ce3+ codoped scintillating glasses can be determined to be 0.6mol%. But under X-ray excitation, the enhancement of Tb3+ ions emission intensity caused by Ce3+ codoping is not as obvious as that under UV excitation, which is mainly due to the low energy transfer efficiency from host glass to Ce3+ ions. Under X-ray excitation, the intensity of 544nm emission in Tb3+/Ce3+ codoped scintillating glasses with 0.6mol% of Ce2O3 was 6 times than that of 500nm emission in the commercial Bi4Ge3O12 (BGO) crystals. The integral scintillation efficiency was about 83% of the BGO crystals. These results imply that the developed silicate oxyfluoride scintillating glasses in our case can be potential candidate for high-resolution medical X-ray imaging.

Spectroscopy and quantum-chemical calculations of nitro-bis-bipyridyl complexes of ruthenium(II) with 4-substituted pyridine ligands

The luminescence, absorption, and luminescence excitation spectra of complexes cis-[Ru(bpy)2(L)(NO2)]+ [bpy = 2,2′-bipyridyl, L = pyridine, 4-aminopyridine, 4-dimethylaminopyridine, 4-picoline, isonicotinamide, or 4,4′-bipyridyl] in alcoholic (4 : 1 EtOH–MeOH) solutions are studied at 77 K. A linear correlation is established between the energy of the lowest electronically excited metal-toligand charge transfer state d π(Ru) → π*(bpy) of the complexes and the pKa parameter of the free 4-substituted pyridines used as ligands L. The B3LYP/[6-31G(d)+LanL2DZ(Ru)] hybrid density functional method is used to optimize the geometry of complexes and calculate their electronic structure and the charge distribution on the atoms of the nearest environment of ruthenium(II) ions. It is shown that there exists a mutually unambiguous correspondence between the charge on the nitrogen atom of ligands L coordinated in the complex and the pK a parameter of ligands. The calculated energies of the electronically excited metal-to-ligand charge transfer states of complexes linearly (correlation coefficient 0.99) depend on the charge on the nitrogen atom of ligands L, which completely agrees with the experimental data.

Fabrication and X-Ray Excited Luminescence of Ga- and In-Doped ZnO Nanorods

Ga- and In-doped ZnO nanorods were prepared by low temperature hydrothermal method, and their structure, morphology and luminescence properties were investigated through X-ray diffraction, scanning electron microscopy, photoluminescence and X-ray excited fluorescence spectrometers. The results indicated that the nanorods had a hexagonal wurtzite structure, and the average diameter and length of the nanorod were about $1~\mu\hbox{m}$ and $10~\mu\hbox{m}$ , respectively. Ultraviolet and X-ray excited luminescence spectra of the nanorods show a relatively strong visible emission peak located around 450-750 nm. The In-doped ZnO nanorods exhibited a superior X-ray excited luminescence performance, which implies that it is expected to be a promising candidate for applications in high-spatial-resolution and fast X-ray imaging detector.

Optical and luminescence properties of Li2O[sbnd]Gd2O3[sbnd]MO[sbnd]B2O3[sbnd]Sm2O3 (MO[dbnd]Bi2O3, BaO) glasses

Spectroscopic properties of Sm3+ ion in borate based glasses (Li2OGd2O3-MO-B2O3 where MOBi2O3, BaO) have been investigated. Glasses are prepared by melt quenching technique and their properties are investigated using different techniques which include absorption, photoluminescence (PL), X-ray excited luminescence (XEL) spectra and decay rate analysis. Furthermore, other related physical and optical properties have been calculated. From absorption spectra the most intense and hyper sensitive transition is 6H5/2 → 6P3/2 at 403 nm. Under 403 nm excitation wavelength, four prominent emission peaks are observed at 563, 599, 645 and 707 nm. For Sm3+ ion the quenching points are observed at 2.0 and 1.5 mol% of LGBiBSm and LGBaBSm, respectively. Measured XEL spectra of the glass samples are found in agreement with that of PL emission spectra. The experimental decay rate follows non exponential behavior at higher concentrations and well fitted to the IH model for S = 6. The obtained color coordinates of the prepared glass matrix fall in the orange region of the CIE diagram. Comparing with LGBiBSm glass, LGBaBSm is transparent and exhibits long decay time value. Moreover, LGBaBSm shows high luminescence properties with excellent energy transfer from the host matrix to the luminescence center. On the basis of the observed properties of the developed glasses, it is expected that they will be best for the orange LEDs.

Spectral characteristics and energy transfer from Ce3+ to Tb3+ in compounds Lu1 – x – y Ce x Tb y BO3

The structure, IR absorption spectra, morphology, and spectral characteristics of compounds Lu1 – x – y Ce x Tb y BO3 have been investigated. It has been shown that the Tb3+ luminescence excitation spectrum of the Lu1 – x – y Ce x Tb y BO3 compounds is dominated by a broad band coinciding with the excitation band of Ce3+ ions, which clearly indicates energy transfer from the Ce3+ ions to the Tb3+ ions. The spectral position of this band depends on the structural state of the sample: in the structures of calcite and vaterite, the band has maxima at ~339 and ~367 nm, respectively. By varying the ratio between the calcite and vaterite phases in the sample, it is possible to purposefully change the Tb3+ luminescence excitation spectrum, which is important for the optimization of the spectral characteristics of Lu1 – x – y Ce x Tb y BO3 when it is used in light-emitting diode sources. An estimate has been obtained for the maximum distance between Ce3+ and Tb3+ ions, which corresponds to electronic excitation energy transfer. It has been shown that the high intensity of Tb3+ luminescence in these compounds is due to the high efficiency of electronic excitation energy transfer from the Ce3+ ions to the Tb3+ ions as a result of the dipole–dipole interaction.

Spectroscopy of the Er-doped lithium tetraborate glasses

The electron paramagnetic resonance (EPR), optical absorption, and luminescence (emission and excitation) spectra as well as luminescence kinetics of the Er-doped glasses with Li2B4O7 composition were investigated and analysed. The high optical quality glasses with Li2B4O7:Er composition containing 0.5 and 1.0mol.% Er2O3 were obtained from corresponding polycrystalline compound by standard glass synthesis. The EPR spectroscopy in the 4.2–300K temperature range and optical spectroscopy at 300K show that the Er impurity is incorporated into the network of Li2B4O7 glass as Er3+ (4f11, 4I15/2) ions, exclusively. The local structure of the Er3+ luminescence centres in Li sites of the glass network is proposed. Based on the standard Judd–Ofelt theory the oscillator strength (Pcal) and experimental oscillator strength (Pexp) for observed absorption transitions as well as phenomenological intensity parameters (Ω2, Ω4, Ω6) for Er3+ centres in the Li2B4O7:Er glass containing 1.0mol.% Er2O3 were calculated. Spectroscopic parameters of relevance for laser applications, including emission probabilities of transitions (Wr), branching ratios (β), and radiative lifetime (τrad) have been calculated for main observed emission transitions of the Er3+ centres in Li2B4O7:Er glasses. Experimental and calculated lifetimes were compared and quantum efficiency (η) for green (4S3/2→4I15/2 transition) and infrared (4I13/2→4I15/2 transition) emission bands has been estimated.

Luminescence of LiF Crystals Doped with Metal Oxide Impurities

The luminescence spectra and luminescence excitation spectra have been investigated in the spectral range of 6.5–4.4 eV. Pulsed cathodoluminescence of LiF-WО3 and LiF-TiО2 crystals has been studied in the temperature range of 20–300 K. All LiF crystals doped with metal oxides are found to have similar luminescent properties and identical structure of the luminescence centers. It is assumed that photon and electron bombardment induces excitation of different types of О2− oxygen centers perturbed by impurities and Fe2О3, WО3 and TiО2 included in the oxygen complexes.

Luminescent and thermochromic properties of tellurium(IV) halide complexes with cesium

The spectral−luminescent and thermochromic properties of complex compounds of the composition Cs2TeHal6 (Hal = Cl, Br, I) are studied. The interrelation between the geometric structure and spectral–luminescent properties is studied using the example on complex compounds of tellurium(IV) halides with cesium. The Stokes shift and the luminescence intensity of Тe(IV) ions with island octahedral coordination are found to depend on the position of the A band in the luminescence excitation spectra, the diffuse reflection, and the energy of the luminescent 3P1 → 1S0 transition of the tellurium(IV) ion. The maximum luminescence intensity and the minimum Stokes shift at 77 and 300 K are observed for Cs2TeСl6. The geometrical and electronic factors responsible for luminescence intensification in Te(IV) complexes under study are analyzed.

The ArI2(ion-pair states) van der Waals complexes

The ArI2(E0g+) van der Waals complexes have been observed and studied for the first time. Analysis of the luminescence excitation spectra as well as luminescence spectra themselves in the spectral ranges, where the I2(E0g+→B0u+,D0u+→X0g+,β1g→A1u and D′2g→A′2u) transitions can occur, has been carried out. It has been shown that the I2(D→X, β→A and D′→A′) luminescence is due to ArI2(E←B) transitions with subsequent predissociation. We have determined the spectroscopic parameters of the ArI2(E,νE=0–3) complexes.It has been shown that rate of vibrational predissociation is ∼10 times less than total rate of the ArI2(E,νE=0–3)→Ar+I2(D, β, D′) electronic predissociation.

Low and high field sites of Cr3+ ions in calcium tetraborate glasses

This paper presents electron paramagnetic resonance and detailed optical spectroscopic characterization of CaB4O7 glasses doped with Cr3+. The luminescence excitation spectrum consists of two broad bands related to transitions from the ground state 4A2g to the excited states 4T1g and 4T2g of the octahedrally coordinated Cr3+ ions. The photoluminescence spectrum is a superposition of the R line related to the 2Eg→4A2g transition and broad band related to the 4T2g→4A2g transition. The analysis of electron paramagnetic resonance spectra allowed to distinguish different Cr3+ sites, whereas the analysis of luminescence and luminescence excitation spectra allowed to characterize the crystal field distribution in the glass host.

Electronic structure and inner-shell excited luminescence in gadolinium molybdate single crystals

An electronic structure of Gd2(MoO4)3 was studied using methods of luminescence and X-ray photoelectron spectroscopy. Luminescent properties under excitation were investigated in energy ranges 125–165 and 526–553 eV which correspond to Gd4d and O1s shells. Luminescence excitation spectra were antibate to X-ray absorption spectra. The X-ray photoelectron spectroscopy appended these data by density of states in energy ranges where no resonant structures in excitation spectra were found. A low-temperature emission of Gd3+ ions was registered in gadolinium molybdate for the first time. Possible models of energy transfer in cation sublattice are discussed.

Visible luminescent lanthanide ions and a large π-conjugated ligand system shake hands.

Visible luminescence europium(iii) complexes with large π-conjugated systems were theoretically and experimentally studied. A strategy for extending the π-conjugation of a ligand for use with europium(iii) ions was found on the basis of fragment molecular orbital and density functional theory calculations. Using this method, a novel europium complex was designed and synthesized. Its excited state properties were assessed from the luminescence spectrum, excitation spectrum, luminescence lifetime, and luminescence quantum yield. In this study, the novel photophysics induced by the combination of visible luminescent europium(iii) ions and large π-conjugated systems are described.

Characterization of the novel 4-thiazolidinone derivatives: luminescence spectra and potential antitumor activity

This study was aimed at measurement of the transmission, luminescence spectra, and luminescence excitation spectra of three novel anticancer 4-thiazolidinone derivatives (ID 3288, ID 3882, ID 3833) in order to characterize the photoinduced cytotoxicity of these compounds against murineleukemia L1210 cell line. The luminescence and luminescence excitation spectra of the ID 3288, ID 3882 and ID 3833 powders differed significantly from those measured in aqueous solution. Furthermore, the luminescence of the ID 3288 powder had lower intensity as compared to that of the ID 3882 and ID 3833 powders. The luminescence of the ID 3882 aqueous solution showed the lowest intensity, while the ID 3833 demonstrated the highest intensity. The potential of application of the obtained results in the photodynamic anticancer chemotherapy has been discussed.

Editors' Choice—Investigation of Luminescence and Photoacoustic Properties in Ce3+-Doped Ln3Al5O12 (Ln = Lu, Y, Gd) Garnet

Optical and photoacoustic properties of Ce3+-doped lanthanide (Lu, Y, Gd) aluminum garnet were investigated. In the photoacoustic (PA) spectra, the 5d1 (lowest 5d level) band of Ce3+ was observed at around 450 nm in the obtained Ce3+-doped garnet samples. This result shows that a part of the excited energy is converted to thermal energy, which is generated by some nonradiative processes. In Y3Al5O12:Ce3+, the 5d1 PA peak wavelength is shorter than the 5d1 photoluminescence excitation peak wavelength, which indicates that part of the heat generation is caused by the phonon relaxation process within 5d1 state. The PA intensity and luminescence quantum efficiency of the Ce3+-doped gadolinium yttrium aluminum garnets ((Gd0.5Y0.5)3Al5O12, (Gd0.75Y0.25)3Al5O12) are much stronger and smaller, respectively, than those of Y3Al5O12:Ce3+. Based on these results and the persistent luminescence excitation spectra, we conclude that (Gd0.5Y0.5)3Al5O12:Ce3+ and (Gd0.75Y0.25)3Al5O12:Ce3+ possess the additional heat generation process explained by the thermal ionization.

Sb/Mn co-doped oxyfluoride silicate glasses for potential applications in photosynthesis

A series of Sb/Mn co-doped oxyfluoride silicate glasses were prepared via the melt-quenching method to explore red luminescent materials for potential applications in photosynthesis of green plants, and these glasses are investigated by means of luminescence decay curves, absorption, emission, and excitation spectra. We find that the as-prepared glasses are transparent in the visible region and can emit strong red light under ultraviolet, purple, and green light excitations. Furthermore, energy transfer from Sb3+ to Mn2+ ions occurs in Sb/Mn co-doped glasses. The results demonstrate that the as-prepared Sb/Mn co-doped oxyfluoride silicate glasses may serve as a potential candidate for developing glass greenhouse, which can enhance the utilization of solar energy for the photosynthesis of the green plants.

Pressure-Stimulated Synthesis and Luminescence Properties of Microcrystalline (Lu,Y)₃Al₅O₁₂:Ce³⁺ Garnet Phosphors.

The Lu2.98Ce0.01Y0.01Al5O12 and Y2.99Ce0.01Al5O12 phosphors were synthesized by solid state reaction at temperature 1623 K and pressure 1.5 × 10(7) Pa in (95% N2 + 5% H2) atmosphere. Under the conditions, the compounds crystallize in the form of isolated euhedral partly faceted microcrystals ∼19 μm in size. The crystal structures of the Lu2.98Ce0.01Y0.01Al5O12 and Y2.99Ce0.01Al5O12 garnets have been obtained by Rietveld analysis. The photoluminescence (PL) and X-ray excited luminescence (XL) spectra obtained at room temperature indicate broad asymmetric bands with maxima near 519 and 540 nm for Y2.99Ce0.01Al5O12 and Lu2.98Ce0.01Y0.01Al5O12, respectively. The light source was fabricated using the powder Lu2.98Ce0.01Y0.01Al5O12 phosphor and commercial blue-emitting n-UV LED chips (λ(ex) = 450 nm). It is found that the CIE chromaticity coordinates are (x = 0.388, y = 0.563) with the warm white light emission correlated color temperature (CCT) of 6400 K and good luminous efficiency of 110 lm/W.