Anti-Stokes Yb3+ emission--valuable structure information in spectra of rare earth compounds measured with FT-Raman spectrometers

Raman spectroscopy is a powerful and simple method which proved to be very useful in studies of solids. The most widely used Raman spectrometers are FT-Raman instruments with YAG:Nd(3+) laser as an excitation source. However, in the case of samples containing rare earth elements, the quality of FT-Raman spectra is often low due to strong fluorescence effects. We show that, in such cases, anti-Stokes part of the Raman spectra often contains strong, well resolved bands identified as multiphonon-assisted emission bands of Yb(3+) present as an impurity. We show on several examples that analysis of these bands may provide useful structure information, similar to that obtained by "Eu structure probe" method in optical spectroscopy. The Yb(3+) emission can be also measured using standard luminescence detection systems. However, the application of FT-Raman system allows one to obtain good quality spectra in a much cheaper, easier and faster way (in times as short as a few seconds). Moreover, high-sensitivity of FT-Raman spectrometers allows to detect even very small amounts of Yb(3+) impurity.     

Laser induced fluorescence bands in the FT-Raman spectra of bioceramics

A new fluorescence band at about 1930cm-1 has been observed in the FT-Raman spectra of some bioceramics. While a fluorescence band at about 760cm-1 has been already reported in the FT-Raman spectra of hydroxyapatite and related calcium phosphates, this new band is observed for the first time. This strong band is totally absent in the anti-Stokes side of the FT-Raman spectra and therefore has been assigned as a laser induced fluorescence band. It has been concluded that in recording FT-Raman spectra of minerals, all precautions about fluorescence bands should be considered, otherwise the FT-Raman spectra may well be misinterpreted.     

Double perovskite structure: a vibrational and luminescence investigation providing a perspective on crystal field strength

The luminescence spectra of Eu(3+) doped in a series of double perovskite lattices Ba(2)LnMO(6) (Ln = Y, Gd; M = Nb, Ta) have been recorded at room temperature and 10 K. Together with FT-IR and FT-Raman spectra and aided by DFT vibrational energy calculations, assignments have been made for the crystal field levels of the (5)D(J) (J = 0,1) and (7)F(J) (J = 0-2) multiplets. The luminescence spectra are consistent with monoclinic symmetry of these systems. The crystal field parameters from the fitting of the energy level data set of Ba(2)YNbO(6):Eu(3+) enable the crystal field strength to be calculated, and the order of magnitude is Cl(-) < O(2-) < F(-) for the EuX(6)(n-) (n = 6 for halogen, 9 for oxide) moieties. For these systems, an empirical linear relationship between crystal field strength and electronegativity of ligand X has been found. By contrast, the nephelauxetic series from the depression of the Slater parameter F(2) is Cl(-) ≈ O(2-) > F(-) > free ion for these systems.     

Yb3+ as an origin of the strong anti-Stokes luminescence in NIR FT-Raman spectra of some lanthanide sesquioxides

Strong anti-Stokes bands observed in FT-Raman spectra of Y2O3, Gd2O3 and Lu2O3 are explained by NIR luminescence of Yb3+ impurities present in sesquioxides after the excitation with the 1064 nm line of an Nd:YAG laser. Samples of Y2O3:Yb, Ga2O3:Yb, CeO2:Yb, Gd2O3:Yb and Lu2O3:Yb were prepared by solution combustion synthesis procedure using urea. All materials were investigated by FT-Raman and FT-NIR spectroscopy and characterized by X-ray powder diffraction.     

The observation of the first vibrational overtone of dihydrogen in the luminescence of zeolites at low temperatures

Dehydrated zeolites NaA, NaY, and barium-exchanged NaY luminesce when irradiated with the 1064 nm laser light of an FT-Raman instrument. When hydrogen is adsorbed in the zeolite, the luminescence is altered in several ways. Most remarkable is the appearance of "absorptions" in the positions of the first vibrational overtones of H(2) and HD. Although these features are in the expected positions with reasonable band profiles for overtone absorptions, the large extinction of the luminescent intensity requires a more efficient mechanism than simple reabsorption of emitted photons. In addition to the appearance of holes in the luminescence spectrum, other luminescent features are substantially quenched by the presence of hydrogen or, in one case, augmented.     

新型铕(Ⅲ)、穴醚[2.2]与α-噻吩甲酰三氟丙酮三元荧光配合物的合成与表征

首次合成两种穴醚[2.2](C[2.2]), α-噻吩甲酰三氟丙酮(HTTA)和稀土铕(Ⅲ)的三元混配配合物: 2Eu(TTA)3.2HTTA.C[2.2](A)和2Eu(TTA)3.C[2.2](B)。与传统的强荧光配合物Eu.(TTA)3.2H2O(C)相比, 有以下的相对荧光强度比例关系: I(A):I(B):I(C)=13.3:3.7:1, 且混配配合物荧光单色性好。配合物的差热热重、红外光谱、Raman光谱和荧光光谱表明, 三元配合物分子中共轭效应增强, 分子内能量转移效率提高; 配合物晶体场对称性提高; 同时消除了水分子对荧光的猝灭作用, 增强了三元混配配合物的荧光强度。     

Luminescence studies on europium-strontium phthalate system

New lanthanide luminescence materials were prepared. The main component lanthanide chelates generally need a relatively high content of rare earth. Inorganic luminescence materials only need low rare earth concentration using doped method. Similarly, lanthanide chelates can be added to complex matrix by doped method. In this way, low rare earth concentration emission was successful in the lanthanide chelates system as well. The influence of europium ion concentration on luminescence intensities was discussed. When the europium ion weight in the complex is only about 0.6%, the sample exhibits good luminescence properties. The fluorescence, Fourier transform infrared spectra, micro-Raman and electron spin resonance spectra of the samples were measured. And a possible luminescence mechanism was suggested by the inorganic doped mechanism and the luminescence of lanthanide complexes together.     

Synthesis and spectroscopic properties of monocyclic and bicyclic erbium phtalocyanines

Bimacrocyclic and monomacrocyclic erbium phtalocyanines have been synthesized and their luminescence spectra and lifetimes have been studied. The bi-planar structure of ErPc₂ complexes, although interesting at first sight, is non-luminescent because of a strong absorption band near 1.5 μm. However, the luminescence of the erbium ion can be recovered after oxidation or reduction of the macrocycle. Monomacrocyclic erbium phtalocyanines exhibit a strong luminescence of erbium as a result of the energy transfer between the excited phtalocyanine macrocycle and the erbium ion. With a perchlorinated phtalocyanine and a perdeuterated axial ligand in a deuterated solvent, the luminescence lifetime reaches 5 μs, which is the maximum lifetime found for conventional perdeutarated ligands. The large absorption cross-section of phtalocyanine in the red may counterbalance the fast luminescence lifetime, allowing the hope for a new all-organic integrated optical amplifier device.     

Luminescence of Sb3+ in rare earth orthoborates LnBO3 (Ln = Sc,Y, La,Gd, Lu)

The luminescence of several Sb³⁺-activated rare earth orthoborates (LnBO₃Sb³⁺; Ln = Sc, Y, La, Gd, Lu) are reported. In all compositions the Stokes shift of the Sb³⁺ luminescence is rather large, resulting in rather low quenching temperatures (200 K or lower). The Stokes shift appears to be dependent on the coordination number and on the radius of the host lattice cation. This is explained from the assumed tendency of the Sb³⁺ ion to occupy an off-center position which becomes more apparent when the space available for the Sb³⁺ ion increases. The present results are compared with those on LnBO₃Bi³⁺. It appears that the Stokes shift of the Bi³⁺ luminescence is more sensitive to the host lattice and is smaller than the Stokes shift of the Sb³⁺ luminescence. This is explained by the large radius of the Bi³⁺ ion compared to the Sb³⁺ ion. In GdBO₃Sb³⁺ thermally activated energy transfer is observed from Gd³⁺ to Sb³⁺.     

Micro-thermal analysis, FTIR- and Raman-microscopy of (R,S)-proxyphylline crystal forms

Three modifications of (R,S)-proxyphylline have been characterized by hot stage microscopy, FTIR- and FT-Raman microspectroscopy as well as differential scanning calorimety, X-ray powder diffractometry and helium pycnometry. Mod. I (m.p. 136°C) is thermodynamically stable in the entire temperature range and the only form which crystallizes from organic solvents or water. The metastable mod. II (m.p. 113–116°C) was prepared in gram quantities from the supercooled melt and shows considerable kinetic stability under dry atmospheric conditions. Mod. III (m.p. 82–85°C) is a new, kinetically very unstable form, which can only be produced in microscopic amounts along with mod. II. The metastable forms are monotropically related to mod. I. FTIR- and FT-Raman micro-spectroscopy, in combination with thermal analysis, are demonstrated to be powerful tools for the characterization of microphases and unstable modifications of polymorphic systems, providing information beyond the commonly phenomenological reports on such forms.     

A study of amber and copal samples using FT-Raman spectroscopy.

FT-Raman spectra were collected from fossil resins originating from a variety of geographical locations. The spectral profiles of most of the fossil resins could be related to modern resins containing diterpenoid components with predominantly labdane skeletons. The spectra collected from the fossil resin sample from Borneo differed from other fossil resins and was found to contain triterpenoid components. The differences in the spectral profile of fossil resins containing diterpenoid components are shown to relate to differences in level of maturation rather than geographical origin. FT-Raman spectra of fossil resins cannot be used to distinguish source although the degree of maturation can be used as an indicator to narrow the range of possible geographical origins.     

Physicochemical Characterization of the Loganic Acid–IR,Raman, UV-Vis and Luminescence Spectra Analyzed in Terms of Quantum Chemical DFT Approach

The molecular structure and vibrational spectra of loganic acid (LA) were calculated using B3LYP density functional theory, the 6–311G(2d,2p) basis set, and the GAUSSIAN 03W program. The solid-phase FTIR and FT-Raman spectra of LA were recorded in the 100–4000 cm⁻¹ range. The assignment of the observed bands to the respective normal modes was proposed on the basis of the PED approach. The stability of the LA molecule was considered using NBO analysis. The electron absorption and luminescence spectra were measured and discussed in terms of the calculated singlet, triplet, HOMO, and LUMO electron energies. The Stokes shift derived from the optical spectra was 20,915 cm⁻¹.     

A New Analytical Method for the Lanthanide Ions Using the Luminescence Enhancement by the Treatment of o-Phenanthroline on the Solid Medium

A new analytical luminescence method for the lanthanide ions was studied using the luminescence enhancement by the treatment of the o-phenanthroline on the solid medium, such as TLC and nylon membrane. Compared to the specific emission intensity of the ion, if the ion solution is spotted on the solid medium,the luminescence intensity was extremely enhanced.     

BaFCl：Ce^3＋和BaFCl：Gd^3＋晶体中的发光中心

运用不同的固相反应条件制备或后处理了几种BaFCl:RE~(3+)(RE=Ce或Gd)晶体,测定了它们的荧光光谱,对照并分析光谱数据和不同条件下可能引入晶体缺陷的情况,推论出晶体中存在有2类发光中心,即由RE_(?)-F_(?)和RE_(?)-F_(?)缔合体构成的中心。     

Role of the antenna in tissue selective probes built of lanthanide-organic chelates

The role of the antenna in the process of the host sensitized luminescence of the DOTA cage coordinated with the Eu ion is investigated. The analysis of the optimal geometries of DOTA modified by several antennas is based on the results of density functional theory (DFT) calculations. The physical environment of the luminescence center (the lanthanide ion) is illustrated by charge density maps and described by the values of the crystal field parameters directly evaluated. The conclusions derived from this theoretical analysis support earlier observations that antennas attached to the cage play the sole role of harvesting and transferring the energy to the lanthanide ion, whereas the cage perturbs the symmetry of the environment of the lanthanide ion, giving rise to the sensitized luminescence. The implications of the separation of the two parts of the organic chelate, cage and antenna, are discussed within the theoretical models of the energy transfer and of forced f <--> f electric dipole transitions.     

Inhomogeneous broadening, luminescence origin and optical amplification in bismuth-doped glass

Absorption and luminescence spectra and optical amplification in bismuth-doped germanate silicate glass were investigated. Two kinds of bismuth ion valence states could exist in the glass. One is Bi2+, which has shown red luminescence, another might be Bi+, which is the active center for infrared luminescence. The infrared luminescence excited at 700, 800, and 980 nm should be ascribed to the electronic transition 3P1 --> 3P0 of Bi+ ions in three distinct sites. The shifting, broadening, and multiple configuration of the luminescence could be due to the randomly disorder of local environment and multiple sites of the active centers. In this glass, obvious optical amplification was realized at 1300 nm wavelength when excited at 808 and 980 nm, respectively.     

Raman spectrometry and neural networks for the classification of wood types—1

In this work the coupling of near infrared (NIR) Fourier-transform (FT) Raman spectroscopy and neural computing for spectral feature extraction and classification of woods is reported. A NIR FT-Raman spectrometer operating at 1064 nm was used for all measurements; particular attention was paid to the effects of sample fluorescence and heating. It was demonstrated that fluorescence rejection is accomplished only for the lighter colored woods and that fluorescence was found to be severe for 10 of the 71 woods studied in this work even using excitation at 1064 nm. It was further found that hardwoods were no more or less susceptible to sample heating than softwoods. Feed-forward neural networks were used to extract the principal features of wood spectra at resolutions of 4, 8 and 16 cm⁻¹ and to classify spectra as either temperate hardwoods or temperate softwoods. Neural networks were constructed using zero and two processing elements in the hidden layer. It was shown that neural networks with two hidden processing elements perform near optimally, since each hidden layer processing element may function as either a hardwood or softwood feature detector. This work represents the first time that FT-Raman spectroscopy and neural network technology have been coupled for spectral feature extraction and classification.     

First FT-Raman and H NMR comparative investigations in ring opening metathesis polymerization

Kinetics of ring-opening metathesis polymerization (ROMP) of exo,exo-5,6-di(methoxycarbonyl)-7-oxabicyclo[2.2.1]hept-2-ene, promoted by the Grubbs’ 1st generation precatalyst, has been effectively monitored by FT-Raman and NMR spectroscopy. Both techniques evidenced similar monomer conversions to be attained under the same reaction conditions. The present FT-Raman study provided information on the polymer steric configuration, the Raman bands at 1670 and 1677 cm⁻¹ being specifically assigned to stretching vibrations of double bonds from the cis- and trans-polymer, respectively. The trans/cis ratio observed by FT-Raman parallels the corresponding result from ¹H NMR. For the first time, a comparison was made on application of these complementary methods on the same ROMP reaction, evidencing their assets and disadvantages and reliability of FT-Raman.     

Determination of medicinal preparations,salts of organic bases,by the effect of their anions on the luminescence of lanthanide complexes

The luminescence parameters of Eu(III) and Tb(III) complexes with fluorinated amide derivatives of hydroxyquinoline carboxylic acid (L_1–8) were studied. It was shown that medicinal preparations, salts of organic bases, can be determined from the effect of their anions on the luminescence of Eu(III)-sensitizing ligand complexes. The Eu(III)-L₁-citrate ion and Eu(III)-L₂-tartrate ion complexes were proposed for the luminescence determination of clomiphene and tamoxifen citrates and platyphyllin tartrate, respectively. The detection limits were 0.30 μg/mL for clomifene (tamoxifen) citrate and 0.85 μg/mL for platyphyllin tartrate.     

A comparison between PA-FTTR and FT-Raman spectroscopies in the structural analysis of annealed injected-moulded poly (ethylene terephthalate)

With the introduction of the Fourier Transform technique in Raman spectroscopy (FT-Raman) and the development of new methods in FTIR, such as FTIR with photoacoustic detection (PA-FTTR), vibrational spectroscopy has been launched into a new era of application in polymer chemistry and physics. This work provides a comparative study between PA-FTIR and FT-Raman techniques in which the potentials and limitations of these two methods are investigated by following and analyzing structural variations that take place in annealed injected-moulded poly(ethylene terephthalate) (PET). Both spectroscopic techniques appear to be suitable to detect structural changes that occur in PET submitted to different annealing temperatures. We suggest that these variations are directly related to conformational rather than crystallinity changes. The main drawbacks of PA-FTIR are the lengthy adquisition time of spectra and the photoacoustic saturation that can appear in regions with quite high optical absorption coefficient. Conversely, FT-Raman technique does not suffer from neither of these problems. However, the sensitivity to structural changes of certain infrared bands seems to be higher than that of analogous Raman bands and small structural details such as the regularity of chain folding, can only be detected in the infrared spectra.