Luminescence Spectroscopy Studies Research Articles

A luminescence and absorption spectroscopy study of KH2PO4 crystals doped with Tl+ ions

We report experimental study on luminescence and optical properties of single crystals KH2PO4 (KDP) doped with Tl+ ions (KDP:Tl) carried out at 10–480K. The 4.5eV photoluminescence (PL) of KDP:Tl originates from radiative electronic transitions 3P1→1S0 in the Tl+ ions upon excitation by UV-photons, X-rays, and electron beam. This luminescence can be induced by direct photoexcitation, or through the recombination process with participation of the lattice defects located in the vicinity of Tl+ ion. These excitation mechanisms lead to different temperature behavior of the luminescence intensity. The PL excitation spectra of KDP crystals containing a small amount of the Tl+ ions (0.001–0.008wt.%) comprises peaks at 5.7–5.8, 6.9, and 7.3–7.4eV, corresponding subsequently to the A-, B- and C-optical transitions in Tl+. The PL time response has single-exponential behavior with an average lifetime of τ=280±8ns. Under exposure to ionizing radiation (X-rays, or electron beam) the intensity of the Tl+ luminescence increases depending on the exposure time. The origin of this phenomenon was associated with creation of defects in the hydrogen sublattice of KDP.

A time-resolved luminescence spectroscopy study of non-linear optical crystals K2Al2B2O7

We report the results of complex study of luminescence and dynamics of electronic excitations in K2Al2B2O7 (KABO) crystals obtained using low-temperature luminescence-optical vacuum ultraviolet spectroscopy with sub-nanosecond time resolution under selective photoexcitation with synchrotron radiation. The paper discusses the decay kinetics of photoluminescence (PL), the time-resolved PL emission spectra (1.2–6.2eV), the time-resolved PL excitation spectra and the reflection spectra (3.7–21eV) measured at 7K. On the basis of the obtained results three absorption peaks at 4.7, 5.8 and 6.5eV were detected and assigned to charge-transfer absorption from O2− to Fe3+ ions; the intrinsic PL band at 3.28eV was revealed and attributed to radiative annihilation of self-trapped excitons, the defect luminescence bands at 2.68 and 3.54eV were separated; the strong PL band at 1.72eV was revealed and attributed to a radiative transition in Fe3+ ion.

Heterometallic, Hybrid, Heavy Main‐Group Iodometallates Containing Lanthanide Complexes: Template Synthesis, Structures, Thermal, Optical, Luminescent and Magnetic Properties

AbstractUsing [Ln(L)8]3+ [Ln = Tb, Y; L = dimethyl sulfoxide (DMSO), N,N‐dimethylformamide (DMF)] cations as templating reagents, the syntheses and crystal structures of the following new metal organic–inorganic hybrid complexes based on either discrete clusters or 1D chains of an iodoplumbate or‐bismuthate moiety are reported: [Tb(DMSO)8]2[(DMSO)2Pb5I16] (1), [Tb(DMF)8][Pb3I9]1∞·DMF (2) and [Ln(DMF)8][Bi2I9] [Ln = Y (3), Tb (4)]. These derivatives were characterized by thermogravimetric analysis (TGA), diffuse‐reflectance spectroscopy, luminescence spectroscopy and magnetic studies. TGA studies show that the thermal stability of these complexes decreases in the order 2 > 3 ≈ 4 > 1. An optical band‐gap in the range 1.90–2.15 eV in the diffuse‐reflectance spectra of 1–4 indicate their potential use as semiconductors, 3 and 4 being the most promising because of their low band gap values. Compared to the precursors [Tb(DMSO)8]I3 and [Tb(DMF)8]I3, the high energy transitions in the excitation spectra of 1, 2 and 4 are quenched by a process that is best attributed to the autoionization of the carriers in the material. The temperature dependence of the magnetic susceptibilities of 1, 2 and 4 was reproduced well by a Curie–Weiss plot at 2–300 K.

Speciation of U(VI) sorbed onto ZrP2O7 in the presence of citric and oxalic acid

Abstract In the field of nuclear waste management, prediction of radionuclide migration through the geosphere has to take into account the effects of organic matter. This work deals with the effects of organic acids (citric and oxalic acid) on speciation of uranium(VI) sorbed onto zirconium diphosphate (ZrP2O7). Surface properties of zirconium diphosphate and its uranium(VI) sorption capability in the presence and absence of organic acids were previously studied. The preliminary study suggested that organic acids take part in the sorption equilibria. In order to understand the interactions between organic ligands (citrate or oxalate), uranium(VI) and zirconium diphosphate, a luminescence spectroscopy study was carried out. Luminescence measurements indicated that only one uranium(VI) surface complex is formed when citric or oxalic acid is present. Moreover, the total carbon content in the studied samples indicated that organic ligands remain on the surface when uranium(VI) sorption is carried out. Uranium sorption edges were then fitted with the FITEQL4.0 code [15] and the constant capacitance model (CCM). Spectroscopy information was used to constraint the modeling. The best fit for the U(VI)/citrate/ZrP2O7 and U(VI)/oxalate/ZrP2O7 systems considered the formation of a ternary surface complex.

XANES, UV-VIS and luminescence spectroscopic study of chromophores in ancient HIMT glass

A series of Late Roman glass fragments belonging to the peculiar group called HIMT (High Iron Magnesium Titanium glass), coming from two archaeological sites in Northern Italy (Modena province and Galeata excavations) and from Catania Roman amphitheatre, were studied by XANES, UV-VIS and luminescence spectroscopies to determine the distribution of the oxidation states of the two chromophores Fe and Mn. The samples, characterized by different colour nuances, were previously chemically characterized. In all the ancient glass samples, Fe results to be mostly in the trivalent state. XANES data indicate that the prevalent Mn oxidation state is 2+, however the presence of minor amounts of Mn 3+ is clearly proved by UV-VIS investigations. The different spectroscopic techniques, used in a combined approach, allow for the interpretation of the apparent anomalous colour of some of the ancient glass samples.

Structural and time resolved emission spectra of Er 3+: Silver lead borate glass

The structural properties of Er 3+: silver lead borate glass is assessed by means of SEM, X-ray mapping, EDS and Raman analysis. In order to verify the time dependency of emission spectra, steady-state luminescence spectroscopy (SSLS) and time-resolved emission spectroscopy (TRES) studies have been performed. The stimulated emission cross-sections for the NIR emission transition 4I 13/2 → 4I 15/2 (1535 nm) at 970 nm excitation are reported. The decay times were obtained by fitting one ( τ m = 0.301 ms) and two ( τ m1 = 0.141 ms, τ m2 = 0.368 ms) distributions for the NIR transition. Furthermore, by making use of TRES measurements the decay associated spectra were obtained allowing the time dependency for the different emission bands to be elucidated.

Determination of uranium(VI) sorbed species in calcium silicate hydrate phases: A laser-induced luminescence spectroscopy and batch sorption study

Batch sorption experiments and time-resolved luminescence spectroscopy investigations were carried out to study the U(VI) speciation in calcium silicate hydrates for varying chemical conditions representing both fresh and altered cementitious environments. U(VI) uptake was found to be fast and sorption distribution ratios (Rd values) were very high indicating strong uptake by the CSH phases. In addition a strong dependence of pH and solid composition (Ca:Si mol ratio) was observed. U(VI) luminescence spectroscopy investigations showed that the U(VI) solid speciation continuously changed over a period up to 6months in contrast to the fast sorption kinetics observed in the batch sorption studies. Decay profile analysis combined with factor analysis of series of spectra of U(VI) – CSH suspensions, recorded with increasing delay times, revealed the presence of four luminescent U(VI) species in CSH suspensions, in agreement with the batch sorption data. Along with the aqueous UO2(OH)42- species and a Ca–uranate precipitate, two different sorbed species were identified which are either bound to silanol groups on the surface or incorporated in the interlayer of the CSH structure.

A luminescence spectroscopy and theoretical study of 4f–5d transitions ofCe3 + ionsin SrAlF5 crystals

This research is focused on the 4f–5d transitions inCe3 + centers dopedinto tetragonal β-SrAlF5 single crystalsbelonging to the I41/a space group. The presence of four non-equivalentSr2 + sites in this compound leads to the appearance of three spectroscopically non-equivalentCe3 + luminescence centers, which can be well distinguished using a time-resolvedlaser spectroscopy technique. All 4f–5d transitions have slightly varyingexcitation and emission energies with characteristic probabilities resultingin several decay times that can be determined experimentally. One of thesecenters experiences strong perturbation due to a defect nearby, probably theO2 − impurity ionsubstituting for the F − ion and acting as a charge compensator as well. Identification of thesephotoluminescence centers is performed using crystal field calculations. The crystal fieldparameters are calculated for two identified centers using the structural data forSrAlF5; diagonalization of the crystal field Hamiltonian results in obtaining the splitting of theCe3 + 5d states. This method allows ‘regular’ unperturbedCe3 + centers withselected Sr2 + sites to be assigned.

NMR and luminescence spectroscopy study of the formation of mixed europium β-diketonate complexes with trifluoroacetic acid in nonaqueous solutions

The ligand substitution in Eu(AA)3 · Phen-CDCl3-TFA systems, where AA is acetylacetone, Phen is 1,10-phenanthroline, and TFA is trifluoroacetic acid was studied at various molar ratios (m) of competing ligands (m = TFA/AA) using NMR (1H, 19F) and luminescence spectroscopy. The formation of mixed Eu(AA)2(TFA) · Phen and Eu(AA)(TFA)2 · Phen complexes in the resultant solutions was attested. The luminescence spectra were studied. The competitive capacity of TFA was ascertained to be higher than that of AA. Depending on the m value, the substitution of acido ligands was shown to occur successively according equations Eu(AA)3 · Phen + (TFA)n = Eu(AA)3 − n(TFA)n · Phen + (AA)n (n = 1, 2, 3).

Comparative study on protection properties of anionic surfactants (SDS, SDBS) and DNA covering of single‐walled carbon nanotubes against pH influence: luminescence and absorption spectroscopy study

AbstractThe pH effect on luminescence and absorption spectra of semiconducting Single‐walled carbon nanotubes (SWNTs) (produced by CoMoCAT® method) covered with anionic surfactants (sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS)) or DNA in aqueous solutions have been studied in visible and near‐infrared (NIR) ranges. With lowering pH from 11 till 3 the emission intensity of SWNTs decreases, the largest luminescence quenching was observed with nanotubes covered by SDS intensity of which dropped by 95% and the smallest one occurred in SWNTs covered by SDBS, which decreased by 35%. The absorption intensity of the most intensive band corresponding to (6,5) nanotube (E11S transition) covered by SDBS or DNA changes weakly in the range ph = 3–11, however, in SDS surrounding the intensity of this band is reduced essentially. This observation indicated that SDBS protection ability of SWNT against pH influence is more significant compared to that of SDS. DNA takes the intermediate position among surfactants studied. The possible reason of such pH influence on optical properties of SWNTs in different surfactants or polymer surrounding is discussed.Der Einfluss des pH‐Wertes auf die Lumineszenz‐ und Absorption‐Spektren von Kohlenstoffnanoröhren (CNT) (synthetisiert nach der CoMoCat Methode), die mit anionische Tensiden(SDBS oder SDS) oder DNA bedeckt sind, in wässriger Suspension wurde im sichtbaren Bereich und Nahinfrarotbereich untersucht. Bei Verringerung des pH‐Wertes von 11 bis auf 3 vermindert sich die Leuchtstärke der CNTs, wobei die größte Lumineszenzlöschung (um 95%) bei Nanoröhren mit SDS‐Funktionalisierung Beschichtung beobachtet wurde. Die geringste Lumineszenzlöschung (um 35%) wurde bei Nanoröhren mit SDBS‐Beschichtung beobachtet. Der Absorptionsgrad der intensiveren Bande, der einer (6,5)‐Nanoröhre mit SDBS‐ bzw. DNA‐Beschichtung entspricht (E11S‐Übergang), änderte sich wenig im pH‐Wert‐Bereich von 3 bis 11. Bei einer SDS‐Funktionalisierung sank die Intensität dieser Bande. Diese Beobachtung zeigt, dass SDBS den Einfluss des pH‐Wertes wesentlich besser zurückdrängen kann als SDS. DNA nimmt dabei einen Mittelwert ein. Mögliche Ursachen des Einflusses des pH‐Wertes auf die optische Eigenschaften der CNTs bei Beschichtung mit verschiedenen Tensiden oder Polymeren werden diskutiert.

Benzene ring impact on energy transfer system of Eu(TTA) 3DPBT

Eu(TTA) 3DPBT was found most likely to lead a special singlet photosensitization pathway by means of time-resolved luminescence spectroscopic studies. For further understanding of its intra-molecular energy transfer mechanism, another lanthanide complex Eu(TTA) 3BDDT was synthesized, using a related ligand BDDT, changing the D-p-A structure of DPBT to the D-A structure of BDDT. The luminescence characteristics of both complexes were investigated and compared. Results show that p bridge plays an important role in the energy transfer process. p bridge can change the charge separation strength by affecting the electron-density distribution over the diethylaniline and the dipyrazoletriazine moieties. Without the p bridge connection, the benzene ring, BDDT gets a smaller conjugated system, and the absorption peak in the UV-Vis spectrum of BDDT has a blue shift of 114 nm relative to that of DPBT. So the energy level of ligand BDDT and the central ion Eu(III) does not match well, and the energy transfer efficiency drop 33%.

Synthesis and optical properties of nanostructured Ce(OH)4

Nanocrystalline cerium hydroxide (NCs-Ce(OH)4) is a intermediate product of CeO2, synthesized successfully using a novel and simple wet chemical rout at an ambient temperature for the preparation of NCs CeO2 powder and film on mass scale for various purposes. The synthesized NCs-Ce(OH)4 was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA), Fourier transform infrared (FTIR), UV-visible and photoluminescence (PL) spectroscopy. The average crystallite size of NCs-Ce(OH)4 has been estimated by the Scherrer equation to be 3–4 nm. The SEM examinations show that the surface texture was uniformly agglomerated and homogeneous. Thermal analysis suggests that cerium (IV) ion is in the tetra hydrated form. Absorption and luminescence spectroscopic studies have been examined for future application in the development of optical devices.

Binding of Europium(III) to a Non-Nucleosidic Phenanthroline Linker in DNA

Eu(III) complexes of DNA containing a non-nucleosidic linker, a derivative of 1,10-phenanthroline-2,6-dicarboxamide (Q), are studied with the goal of forming novel lanthanide ion binding sites that are incorporated in the backbone of DNA. One oligonucleotide is short and unstructured (TTTQTTT (QT6)) and the other (5'-AGCTCGGTCAQCGAGAGTGCA-3' (SQ)) is studied both in single-stranded form and in the presence of a partially complementary DNA strand. Luminescence spectroscopy studies show that Eu(III) binds to SQ, QT6, AQB, or QB 1100-, 56-, 23-, or 27-fold more tightly, respectively, than to a simple 1,10-phenanthroline-2,6-dicarboxamide ligand (Q1). Direct excitation and phenanthroline sensitized luminescence spectroscopy supports binding of Eu(III) to the phenanthroline linker in QT6 and in double-stranded DNA formed from SQ and partially complementary sequences that place Q in a bulge-like position. Eu(III) hydration numbers range from 3 to 5 when bound to the phenanthroline moiety in modified DNA, consistent with binding to the tetradentate linker and, in some cases, coordination to other groups in the DNA. Thermal melting experiments show that Q in a bulge-like structure stabilizes double-stranded DNA and that Eu(III) binding does not markedly affect the stability of the duplex.

Atmospheric Barrier–Torch Discharge Deposited ZnO Films: Optical Properties, Doping and Grain Size Effects

Technology aspects, structure and characteristic properties of the atmospheric barrier torch discharge technique grown nominally pure and Al (0.1-5%) and Mn (0.05-0.5%) doped ZnO nanocrystalline thin films deposited on fused quartz substrates are reported. The set of films with various thicknesses in the range from 70 nm to 1000 nm were prepared for each composition. XRD and AFM analysis show well formed [001] preferably oriented hexagonal high quality films witch could be operatively fabricated in air atmosphere with controlled grain size. All films under study revealed n-type conductivity except some Mn doped films, which revealed p-type. Spectroscopic optical ellipsometry and luminescence spectroscopy studies evidenced luminescence properties typical for well formed ZnO and appreciable influence of Al doping and grain size on the optical absorption edge. Al doping shifts strongly absorption edge to the higher energies. The grain size decreasing (from 100 to 15 nm) leads to distinct diffusing of the absorption edge accompanied by increase of absorption in the near band edge region. For the smallest grains the pronounced Urbach-type absorption tail can be observed manifesting films inhomogeneity development.

Interaction of Eu3+ with N,N,N′,N′-tetraoctyl diglycolamide: A time resolved luminescence spectroscopy study

N,N,N′,N′-tetraoctyl diglycolamide (TODGA) has been identified as one of the promising extractants for the partitioning of minor actinides from high-level nuclear waste solutions. Solvent extraction studies have shown that stoichiometry of the extracted species of Eu3+ with TODGA depend on the nature of diluent. Time resolved luminescence spectroscopy (TRLS) has been employed to investigate the complexation of Eu3+ with TODGA under different experimental conditions. The effects of different experimental parameters such as aqueous phase acidity, nature of diluent, and TODGA concentration on the luminescence lifetime of Eu3+ ions have been investigated. The lifetime measurements of the complexed fraction of Eu3+ with TODGA suggested the absence of water molecules in the inner coordination sphere of the metal ion in different solvents. In ethanol–water (60/40%) mixture, the complexation of Eu3+ with TODGA under varying ligand-to-metal ratios suggested the formation of 1:1, 1:2, and 1:3 species, viz., Eu(TODGA)3+, Eu(TODGA)23+, and Eu(TODGA)33+, respectively. The conditional stability constants logβ1, logβ2, and logβ3 were calculated as 6.1±0.5, 10.8±0.7, and 14.3±0.6, respectively. The nature of diluent did not influence the luminescence spectra of Eu3+ in the presence of TODGA.

Synthetic, structural, photophysical and computational studies on 2-arylethynyl-1,3,2-diazaboroles

New 2-arylalkynyl benzo-1,3,2-diazaboroles, 2-(4'-XC(6)H(4)C[triple bond, length as m-dash]C)-1,3-Et(2)-1,3,2-N(2)BC(6)H(4) (X =Me ; MeO ; MeS ; Me(2)N ), were prepared from B-bromodiazaborole, 2-Br-1,3-Et(2)-1,3,2-N(2)BC(6)H(4), with the appropriate lithiated arylacetylene, ArC[triple bond, length as m-dash]CLi. Molecular structures of , and were determined by X-ray diffraction studies. UV-vis and luminescence spectroscopic studies on these diazaboroles reveal intense blue/violet fluorescence with very large quantum yields of 0.89-0.99 for . The experimental findings were complemented by DFT and TD-DFT calculations. The Stokes shift of only 2600 cm(-1) for , compared to Stokes shifts in the range of 5900-7300 cm(-1) for , is partly explained by the different electronic structures found in compared to (X = H). The HOMO is mainly located on the aryl group in and on the diazaborolyl group in whereas the LUMOs are largely aryl in character for all compounds. Thus, in contrast to other conjugated systems containing three-coordinate boron centers such as B(Mes)(2), (Mes = 2,4,6-Me(3)C(6)H(2)), in which the boron serves as a pi-acceptor, the 10-pi electron benzodiazaborole moiety appears to function as a pi-donor moiety.

Crystal structure and spectroscopic properties of ciprofloxacinium pentachloroantimonate(III) monohydrate (C17H19N3O3F)SbCl5 · H2O

Synthesis, X-ray diffraction, IR and luminescence spectroscopic studies of the monohydrate of pentachloroantimonate(III) of doubly protonated ciprofloxacin (C17H19N3O3F)SbCl5 · H2O (I) were performed. The structure of I is formed by SbCl6 octahedra combined into polymeric chains [SbCl5]n2n− through common vertices, ciprofloxacinium cations (CfH3)2+, and water molecules linked by hydrogen bonds. CfH is protonated at the carbonyl oxygen atom and the terminal nitrogen atom of the piperazinyl group. The electronic and geometric aspects determining the luminescence properties of I and of related compounds are discussed.

Luminescence of Pr 3+ doped K 2LaCl 5 microcrystals encapsulated in KCl host

Scanning electron microscopy and luminescence spectroscopy studies have shown the formation of Pr 3+ doped K 2LaCl 5 microcrystalline phase embedded in KCl host after annealing of KCl–LaCl 3 (0.5 mol.%)–PrCl 3 (0.05 mol.%) at 250 °C. The luminescent characteristics of KCl–LaCl 3 (0.5 mol.%)–PrCl 3 (0.05 mol.%) are found to be similar with those of K 2La x Pr 1− x Cl 5 bulk crystals. The luminescence of Pr 3+ ion is observed from KCl–LaCl 3 (0.5 mol.%)–PrCl 3 (0.05 mol.%) due to the radiative transitions within Pr 3+ 4f 2 configuration whereas Pr 3+ 4f5d → 4f 2 emission is not revealed. Excitonic mechanism of energy transfer to the Pr 3+ activator centers in KCl–LaCl 3 (0.5 mol.%)–PrCl 3 (0.05 mol.%) crystal is considered.

The nature of unusual luminescence in natural calcite CaCO3

The unusual luminescence of particular varieties of natural pink calcite (CaCO{sub 3}) samples was studied by laser-induced time-resolved luminescence spectroscopy at different temperatures. The luminescence is characterized by intense blue emission under short-wave UV lamp excitation with an extremely long decay time, accompanied by pink-orange luminescence under long wave UV excitation. Our investigation included optical absorption, natural thermostimulated luminescence (NTL) and Laser-Induced Breakdown Spectroscopy (LIBS) studies. Two luminescence centers were detected: a narrow violet band, with {lambda}{sub max} = 412 nm, {Delta} = 45 nm, two decay components of {tau}{sub 1} = 5 ns and {tau}{sub 2} = 7.2 ms, accompanied by very long afterglow, and an orange emission band with {lambda}{sub max} = 595 nm, {Delta} = 90 nm and {tau} = 5 ns. Both luminescence centers are thermally unstable with the blue emission disappearing after heating at 500 C, and the orange emission disappearing after heating at different temperatures starting from 230 C, although sometimes it is stable up to 500 C in different samples. Both centers have spectral-kinetic properties very unusual for mineral luminescence, which in combination with extremely low impurity concentrations, prevent their identification with specific impurity related emission. The most likely explanation of these observationsmore » may be the presence of radiation-induced luminescence centers. The long violet afterglow is evidently connected with trapped charge carrier liberation, with their subsequent migration through the valence band and ultimate recombination with a radiation-induced center responsible for the unusual violet luminescence.« less

Heteronuclear bipyrimidine-bridged Ru–Ln and Os–Ln dyads: low-energy3MLCT states as energy-donors to Yb(iii) and Nd(iii)

The complexes [Ru((t)Bu(2)bipy)(bpym)X(2)] (X = Cl, NCS) and [M((t)Bu(2)bipy)(2)(bpym)][PF(6)](2) (M = Ru, Os) all have a low-energy LUMO arising from the presence of a 2,2'-bipyrimidine ligand, and consequently have lower-energy (1)MLCT and (3)MLCT states than analogous complexes of bipyridine. The vacant site of the bpym ligand provides a site at which [Ln(diketonate)(3)] units can bind to afford bipyrimidine-bridged dinuclear Ru-Ln and Os-Ln dyads; four such complexes have been structurally characterised. UV/Vis and luminescence spectroscopic studies show that binding of the Ln(III) fragment at the second site of the bpym ligand reduces the (3)MLCT energy of the Ru or Os fragment still further. The result is that in the dyads [Ru((t)Bu(2)bipy)X(2)(mu-bpym)Ln(diketonate)(3)] (X = Cl, NCS) and [Os((t)Bu(2)bipy)(2)(mu-bpym)Ln(diketonate)(3)][PF(6)](2) the (3)MLCT is too low to sensitise the luminescent f-f states of Nd(III) and Yb(III), but in [Ru((t)Bu(2)bipy)(2)(mu-bpym)Ln(diketonate)(3)][PF(6)](2) the (3)MLCT energy of 13,500 cm(-1) permits energy transfer to Yb(III) and Nd(III) resulting in sensitised near-infrared luminescence on the microsecond timescale.