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International audience; This paper reports on the Raman spectroscopy and the photoluminescence spectra of Nd- and W- doped BaTiO3 (BT) ceramics prepared using the molten-salt method. The samples were subjected to annealing at a temperature of 900 °C. Raman spectroscopy was carried out at room temperature on doped ceramics and pure BT. The incorporation of Nd3+ for Ba2+ in A site and W6+ for Ti4+ in B site into BT lattice was also discussed. Moreover, we controlled the frequency and damping of the main optic modes. No significant change was observed in the frequency and damping. But the only frequency of A1[TO3] mode was slightly sensitive to the Nd and W doping. This could reflect the effect of these ions on the Ti site, since this mode corresponds to a distortion of O octahedron around the central Ti ion.In addition, three different exciting laser lines were used for enlightening the Nd3+ emission effect and the contribution of the luminescence processes in the “abnormal” Raman spectra recorded for 785 nm. These abnormal Raman signals originate from a fluorescent effect corresponding to 4F5/2,3/2 →4I9/2 transitions of Ba-site Nd3+ ions. This behavior is confirmed by photoluminescence data at room temperature under 514.5 nm excitation via the presence of two peaks located at 880 nm and 909 nm corresponding to the 4F5/2,3/2 →4I9/2 transition levels, respectively, which also showed a decrease in the intensity of emission spectra following the incorporation of W6+ ions into the Ti site. The fluorescent signals were so intense that they overwhelmed the traditional Raman spectra of our compounds.

The THz and sub-THz polarized Raman response was measured in tetragonal and cubic phases of single domain BaTiO

BaTiO3 (BTO) is considered as a textbook material for the description of structural phase transitions (SPT) and the appearance of ferroelectricity. [...]

International audience; We show the interest in recording both Stokes and anti‐Stokes Raman spectra in two peculiar applications. In one case, the comparison between these two parts of the spectrum, measured at one temperature only, allows to distinguish between first‐ and second‐order phonon bands. In the second example, the difference between Stokes and anti‐Stokes spectra provides separation between vibrational and emission lines. We describe the different stages needed in the measurements and data treatment.

Transmission Raman spectroscopy experiments were performed on iron doped congruent lithium niobate within two –in principle equivalent- configurations, namely Y(ZX)Y and Y(XZ)Y. While the former respects the Raman selection rules, the other configuration gives a time dependent spectrum that, after a transient time of several minutes, finally results in a mixture of expected and forbidden modes. This breaking of Raman selection rules is caused by the spontaneous conversion of a part of the ordinarily polarized pump beam into an extraordinarily polarized beam by photorefractive anisotropic self-scattering. A numerical modelling of the phenomenon is developed and fairly reproduces the time dependence of conversion energy.

International audience; Raman measurements were carried out on Ho3+ doped Lithium Niobate crystals. When the excitation wavelength of 532nm is used, in addition of expected Raman modes, forbidden bands are detected, while when exciting with 785nm, “classical” Raman spectrum was recorded with expected modes according to Raman selection rules. Additional lines are attributed to emission lines of Ho doped crystals. We detect, within a very good resolution, in the same Stokes spectrum, the transitions between the electronic states, and the vibrational states as well. We report on the analysis of these data as function of Ho-content, for different polarizations and wavelengths, of the incident laser beam.

International audience; We investigate Raman scattering measurements on polycrystalline LiH2PO 4 (LDP) between 30 and 240°C, in order to detect phase transformations. The thermal behavior of main lines in different wavenumber ranges is discussed and analyzed. Raman spectra show two anomalies at 176°C and 210°C, reflecting changes in chemical bonds, and are attributed to progressive polymerization, in agreement with earlier electrical measurements.

International audience; The paper reports on a methodology for the determination, by means of Raman spectrometry, of the concentration of inorganic salts dissolved in aqueous solutions. This procedure is then applied to nitrate solutions with a varying content from 0 to 100 mM (mmol/l). For this we exploit the concentration dependence of the Raman peak lying at 1047 cm -1 specific to the NO 3- anion. Different signal processing and normalization methods are used and compared to deduce the most reliable and robust calibration. Then cross-validations are done using the “leave-one-out” method to validate the prediction models. Several figures of merit such as sensitivity, signal to noise ratio, limits of detection and quantification are calculated to estimate the efficiency of our methodology for nitrate solutions. Various sources of uncertainties are considered and evaluated according to the ISO GUM and the standard uncertainty of the concentration is then calculated.

International audience

Aircrafts and runways de-icing operations with anti-icing fluids are still the most commonly used methods, in spite of their environmental impacts and associated costs. Once applied, these fluids are diluted because of adverse weather water inputs, conducting to a freezing point getting closer to 0 °C. The characterization of their freezing points is therefore crucial. Four distinct anti-icing fluids, at concentrations ranging from their pure commercial form to an highly diluted rate were investigated by means of Raman spectroscopy and chemiometrics. The approach allowed the discrimination of the aircrafts anti-icing fluids between each other though containing the same active chemical compound, the rapid evolution towards 0 °C of their freezing temperatures with the water dilution, and of the concentrations in active compounds of each fluid, along with their forecast.

International audience; Transmission Raman spectroscopy experiments as a function on time were carried out on iron doped photorefractive congruent lithium niobate crystals. A big change with time in Raman spectra is observed when the incident light is polarized along ordinary axis. The mentioned breaking of Raman selection rules is originated by photorefractive properties of the crystal.

International audience; Les défauts jouent un rôle important dans les propriétés des solides. Que leur effet soit bénéfique (cas des dopants) ou non, leur étude est un enjeu essentiel pour la maîtrise et l’optimisation des matériaux. La spectroscopie Raman est une technique d’analyse de milieux permettant d’accéder à la structure par la caractérisation des vibrations des molécules. L’objectif de cet article est de décrire les effets causés par les défauts sur le spectre Raman : les modifications des raies propres de la matrice hôte, par l'apparition de raies spécifiques, ou par l’activation de raies normalement interdites par les règles de sélection.

International audience; Raman measurements were investigated on Zr-doped lithium niobate LiNbO3 crystals with different concentrations. Spectra were treated by fitting procedure and principal component analysis which both provide results consistent with each other. The concentration dependence of the frequency on the main low-frequency optical phonons provides an insight of site incorporation of Zr ions in the host lattice. The threshold concentration of about 2% is evidenced, confirming the interest of Zr doping as an alternative to Mg doping for the reduction of the optical damage in lithium niobate.

Polarized Raman measurements were carried out in a 3% Ca- doped BaTiO3 (BCT) single crystal and compared with those in undoped BaTiO3 (BT) in order to study the effect of Ca2+ incorporation into the BT lattice. Spectra recorded at room temperature in BCT show peaks unexpected by the Raman selection rules in BT, proving an off-centering of Ca with respect to the Ba site in BT. Main phonon lines A1 polarized along the ferroelectric c axis are notably shifted to lower frequency by Ca doping, while the phonons E in the plane normal to c are nearly unaffected. In addition, the modes A1 are highly anharmonic, even more than in BT, as revealed by the temperature dependences of their frequency and damping which are analyzed in terms of 3rd and 4th order anharmonic potential.

The temperature dependence of the Raman spectrum in LiNbO $$_3$$ is investigated from 100 to 700 K. The various sources of asymmetry of Raman bands and artefacts are discussed before analyzing the temperature dependence of A $$_1$$ and E first-order phonon lines. The phonon frequency downshift and damping increase on heating are interpreted in terms of normal volume expansion and third- and fourth-order anharmonic potentials. Anharmonic contributions are highly anisotropic and mainly explain the temperature dependences of both frequency and damping of A $$_1$$ optical vibrational modes along the ferroelectric axis. Results are consistent with Caciuc et al. (Phys Rev B 61:8806, 2000) predictions.

International audience; Oxygen vacancies in reduced SrTiO3 are investigated by Raman spectroscopy and dynamic elastic modulus measurements. The anelastic spectrum is used to evaluate the amount and state of the O vacancies, which result to be almost completely paired and otherwise aggregated at a concentration of 0.5 mol. %, with only 1/6 of them isolated at room temperature. Raman spectra recorded as a function of temperature in as-grown and reduced samples are examined regarding the different processes which can contribute to them. Chemometric analysis is used to highlight the specific influence of oxygen vacancies on the Raman spectra. It is shown that oxygen vacancies induce a relaxation of selection rules leading to the activation of first-order lines even in the cubic phase. Furthermore, regions around oxygen vacancies are demonstrated to be responsible for the asymmetric broadening of Raman lines.

Raman spectra of potassium, sodium, and ammonium sulfates (K2SO4, Na2SO4, and (NH4)2SO4) are reported and analyzed. These sulfates have been investigated under two states: solid (anhydrous and hydrated) salts and aqueous solutions. The effects of monovalent ions (K+ , Na+ , and NH4+) and hydration on the position of Raman lines assigned to internal vibrations of sulfate anion SO42- are discussed. In solid salts, the line position of each Raman peak is shown to decrease with increasing radius of the cation. The main ν1 mode of sulfate molecule is particularly affected. It is emphasized that this sensitivity in solid sulfates vanishes in aqueous solutions. As a consequence, this mode can be probed by Raman spectroscopy as the main signature of SO42- to determine its concentration within a single calibration.

The temperature dependence of the optical phonon modes in the tetragonal BaTiO3 single crystal was investigated by means of polarized Raman spectroscopy measurements. A special attention was devoted to the Raman spectra deconvolution to separate between first- and second-order bands, which can be discriminated from the difference in the temperature behavior of scattered intensity. Both A 1 mode motions along the polar c axis and E vibrations (except the well-known soft mode) normal to c were studied and discussed. The temperature dependences of frequency and damping of each optical phonon were achieved and then interpreted in terms of third- and fourth-order anharmonic potential. It was derived from this analysis that the A 1 transverse optical phonon arising from the hardening of the soft phonon of the cubic phase possesses large anharmonic motion of Ti versus O ions. A significant anharmonicity was as well found for phonons associated with O octahedral distortion.

Raman spectroscopy was used to study the liquid–solid water phase transition. Special attention was devoted to the OHstretching band of the Raman spectrum, which shows monotonous changes in the temperature range between 10 and − 15 °C. The interpretation of this spectral change, as well as a careful analysis of its integrated scattered intensity, led to a spectral marker that allows the determination of the water phase (liquid or solid), and the efficient identification of the liquid–solid phase transition itself. Copyright © 2011 John Wiley & Sons, Ltd.

In this work we demonstrate the abilities of micro-Raman imaging in the study of ferroelectric domains and present its application to visualization of micro-scale periodical domain structures and nano-domains induced by laser irradiation in lithium niobate.

By means of Raman scattering spectroscopy we determine the site location occupied by Hf ions in photorefractive damage resistant Hf-doped LiNbO 3 . At room temperature the two lowest frequency phonons are related to sites B (Nb) and A (Li), and are used to directly probe the dopant ion. For the low concentration range, the Hf ions go into the sites A whereas, for high concentration, Hf ions occupy both sites A and B. Results are compared with data obtained for pure congruent and stoichiometric crystals, and the proposed mechanism of incorporation of Hf ions in the LiNbO 3 lattice explains the threshold in the behaviour of photorefractive properties.

Fe in—diffusion was performed by depositing a Fe film on X-cut LN substrates by sputtering and subsequent annealing in a controlled atmosphere. The photorefractive properties of the Fe:LN film were studied by confocal Micro–Raman spectroscopy. The presence of unexpected lines in the Raman spectra of the samples was detected and attributed to the activation by the photoinduced space charge field which is also the cause of the photorefractive effect. The results in Fe-doped samples are compared to those recorded in nominally pure congruent crystals.

We analyse the Raman spectrum recorded during scanning across the domain walls of a periodically poled lithium niobate single crystal. We show that the intensity of scattered light is sensitive to the stresses and electric fields in the vicinity of domain walls. These features are amplified due to large elasto-optic and electro-optic coefficients of lithium niobate.

The results of a comparative study of composition dependences of the light-induced refractive index change, photorefractive sensitivity, polaron luminescence, and intrinsic optical absorption in nominally pure LiNbO 3 and LiTaO 3 crystals are reported. Our investigation demonstrates that the particular light-induced defects traced by the photoluminescence are secondary photorefractive centers itself. The experimental results obtained are well described by light-induced dissociation of bipolarons into small polarons that are unstable at room temperature.

We report a study of periodically poled congruent LiNbO 3 by means of micro-Raman spectroscopy. We show that the Raman spectrum is sensitive to the structural changes in the regions close to the domain walls and therefore can be used for characterizing the ferroelectric domain structure.

International audience

In-depth micro-Raman profiling of He+-implanted LiNbO 3 has been performed. It is demonstrated that in the buried nuclear stopping layer a transition from point to extended defects occurs at threshold dose in the range 1 − 2 × 10 15 ions/cm 2 related to polarization nano-clusters formation.

The spectral widths of Raman lines in nominally pure lithium niobate are measured as a function of the cationic molar ratio, in a wide range from stoichiometry (50 mol% Li) to sub-congruent compositions (below 48.6 down to 47 mol% Li). The broadening observed on the sub-congruent side follows the same slopes as on the congruent-to-stoichiometric side. It is shown that micro-Raman analysis permits one to characterize short-range heterogeneities at the micron scale, such as growth striations in bulk crystals or lithium out-diffusion in the surroundings of titanium-diffused waveguides, with a typical accuracy of 0.04 mol%.

Temperature dependences of the piezoelectric modulus d31 and complex elastic compliance have been measured for a lithium niobate single crystal grown by the high temperature top-seeded solution growth technique. The results obtained have shown that the imaginary part of the elastic coefficient is probably sensitive to the lithium ion and proton migration inside the crystal. X-ray photoelectron spectroscopy has revealed the existence of some defects in the crystal structure. While these imperfections only weakly control the magnitude of the piezoelectric coefficients, they influence the elastic properties, even in the relatively low temperature range. It was found that the temperature dependence of the elastic properties is stable as long as a temperature of ~90 °C is not reached.

A complete Raman scattering study on a lithium tetraborate single crystal is reported. The frequency and scattered intensity of Raman modes are carefully determined in the various geometrical configurations. These Raman data are then used to relate to the electro-optical and non-linear optical properties. Raman scattering efficiencies of A1(a), A1(b) and E phonons are consistent with the values of the EO coefficients r13, r33 and r51 respectively.

The light depolarization and the Raman scattering spectrum were measured in a KTa1−xNbxO3 crystal with a dilute Nb concentration (1.2%). Measurements were performed on cooling to 10 K without and then with an electric field. The unexpected Raman lines detected well above TC are attributed to one-phonon density of states. The dependence of these lines as functions of temperature and electric field reveals the formation of polar clusters which grow in the paraelectric phase on cooling and some peculiarities in the mechanism of the phase transition. Copyright © 2005 John Wiley & Sons, Ltd.

We demonstrate that the Raman spectroscopy method may be effectively used for accurate determination of optical damage profiles in LiNbO3-based elements used in the various devices utilizing high-power laser beams. It has been established, that there is an irreversible fraction of the optical damage induced only by the high-intensity (≥25 kW/cm2) illumination for a long time, and it has accumulative character with exposure time in nominally pure crystals. This irreversible effect was related to the optical fatigue of a material. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

International audience; The frequency dependence of electro-optic co- efficients in congruent and stoichiometric LiNbO3 , LiTaO3 , β-BaB2O4 and KTiOPO4 was determined and compared to each other for the first time in a wide frequency range from DC up to 150 MHz. The measurements have been investigated as a function of laser wavelength from 0.5 to 1.3 µm. Clamped and unclamped electro-optic coefficients as well as the acoustic contribution have been established for each crystal.

The Raman scattering spectrum of the sodium niobate crystal, in both P and R phases, has been investigated from room temperature up to 440°C. The dependence of the low-frequency (LF) spectrum clearly reveals, for the first time, over a wide temperature range, the presence of a strong quasi-elastic scattering below a LF zone centre phonon. The phase transition mechanism is discussed, considering an order–disorder process induced by the relaxation of the Nb ions.

An investigation of the dielectric constant according to the frequency (20 Hz and 1 GHz) for as-grown and reduced samples of lithium tetraborate (LTB) is done. Anisotropy of e' and e at low frequency decreases by reducing crystal then at frequency higher the 104 Hz the reduced state does not affect e. The disappearance of relaxations in both real and imaginary part of e x in as-grown LTB, shows the unidirectional conductivity of the lithium ions along the 'Z' axis. When the samples are reduced we notice the appearance of relieving in the imaginary and real parts of e x and an increase in these relaxations for the two components of e z , that shows the appearance of a new mechanism of conduction in two directions X and Z other than that of lithium.

The properties of Cr 3+ in LiNbO 3 single crystals have been investigated by means of several experiments including the recordings of absorption and high resolution laser spectroscopy spectra with dye-laser excitation spectra, emission spectra and fluorescence decays under laser selective pumping. Measurements performed on crystals with composition varying between congruent and close to stoichiometry enabled new features to be revealed which lead us to re-interpret the optical spectra of chromium-doped LN. Three chromium centres are sufficient to explain the main optical features. The main chromium centre labelled γ , giving rise to the broad absorption and emission bands, corresponds to the low-crystal field scheme where the 4 T 2 level is lower than 2 E. The two other chromium centres α and β yield sharp lines in emission and correspond to the high-crystal field scheme. Their dependencies on both the chromium concentration and the composition were studied using emission spectroscopy at low temperature. The main centre γ seems slightly affected by chromium concentration or composition change. The centres α and β are shown to be strongly connected to the presence in their surrounding of intrinsic defects related to the crystal non-stoichiometry. From their behaviour versus Cr concentration, the origin of these centres is discussed in terms of perturbed substitution.

International audience; The relationships of the wavelength dependence of both the electro-optic and second harmonic generation coefficients are established within the same model applied to nonlinear optical materials. It is demonstrated that the dispersion of these coefficients can be obtained from the own dependence of the refractive indices only, without any fitted parameter. Solely the measurement of the coefficient at one wavelength is required within this approach. A very good agreement in the -dependence of electrooptic and second harmonic generation coefficients is achieved between calculated values and experimental data in SBN, DAST, KTP and KNbO3 crystals.

Raman scattering in nominally pure lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) crystals has been studied at high-intensity excitation. Significant photoinduced perturbations of Raman spectra of congruently melting LiNbO3 are discovered in contrast to Raman scattering observed in both nearly stoichiometric LiNbO3 and congruently melting LiTaO3. Our study allows assignment of these perturbations to the photorefractive (PR) effect and, therefore, comparison of the PR damage resistance of the crystals studied.

The LiNbO 3 crystals doped with Nd 3+ , Dy 3+ and Er 3+ ions were investigated by means of Raman scattering measurements. Data were compared with results recorded in undoped congruent crystal and highly Mg-doped samples. The doping dependence of frequency and damping in the E(TO 1 ) and the two lowest frequency A 1 (TO) phonon modes were employed to deduce the incorporation site of rare earth doping ions in LiNbO 3 lattice.

Photo-induced birefringence changes are investigated on several undoped LiNbO 3 crystals as a function of laser-irradiation time and intensity. Comparison points out that the changes are the smallest in the crystals grown from high temperature top seeded solution (TSS). It is concluded that the optical damage resistance in undoped LiNbO 3 crystals is increased with a decrease of the amount of intrinsic defects related to the non-stoichiometry. The necessity to carefully control the true crystal composition is stressed.

The defect structure of Mg-doped lithium niobate crystals was studied with varying Mg doping concentration by means of Raman scattering measurements. The Mg content dependences of both the frequency and damping of the two lowest-frequency A1(TO) phonon modes were used to derive the Mg incorporation mechanism in the LiNbO3 lattice. Results indicated that Mg ions are located on the Li site for low doping and then replace both Li and Nb ions for larger concentration.

We report the electro-optic properties in iron-doped LiNbO 3 crystals. We investigated samples with various crystal compositions and the same doping concentration. The value of the electro-optic coefficient r c monotonously decreases with respect to the crystal composition. To separate the influence of the intrinsic defects related to the non-stoichiometry and the effect of the introduction of iron, we compared the results with data obtained in pure LiNbO 3 crystals. The effect of Fe ions on the composition of the crystal and the electro-optic properties is discussed from their site occupation in LiNbO 3 lattice.

Dielectric studies of a PbHfO3 (lead hafnate) single crystal undergoing two structural phase transformations at about 163°C (436 K) and 209°C (482 K) were performed in broad frequency and temperature range. Special attention was paid to the paraelectric phase. Investigations of the complex dielectric permittivity in the frequency range 10 Hz to 10 MHz revealed two relaxations of polydispersive and nearly monodispersive (Debye-like) character connected with space charge behaviour. In the frequency range of 106-109Hz a polar relaxation mode has been found and related to a disorder in the Pb sublattice. Temperature dependence of the dielectric step of this relaxation corresponds to a sharp anomaly of the e(T) function at the phase transition from the paraelectric to antiferroelectric state. Analysis of temperature evolution of the first order Raman light scattering spectra showed existence of a soft line at this transformation. Crossover of the displacive and order-disorder type of the transformatio...

We have studied Cr3+ emission in LiNbO3 crystals with compositions close to stoichiometry, which were not investigated up to now. The emission spectra recorded at low temperature exhibits new peaks at 13 555 and 13 415 cm−1. The measurement of the fluorescence decays and the recording of the excitation spectra monitored at all the emission peaks were performed in order to determine the different Cr3+ centres in lithium niobate as well as their energy levels contributing to the emission experiments. Three Cr3+ centres permit to describe the various features of the emission spectra. The main centre corresponds to the weak crystal field scheme and yields the broad emission band as well as the new peaks which have a vibronic origin. The two other Cr3+ centres agree with the high crystal field scheme and display the sharp R-lines at 13685 and 13614 cm−1.

We report the dependence of the unit cell parameters and the EO coefficients on Zn doping in optical-damage-resistant LiNbO3:Zn crystals. Both properties depend in a non-monotonic manner on the Zn content. This is accounted for by different types of Zn ion incorporation into the lattice depending on the Zn concentration in the melt. Extrema observed in the concentration dependence of the EO coefficients at about 2–3 and 6.4 mol.% Zn correlate with an unusual concentration dependence of the unit cell parameters a and c. The low-concentration anomalies may be accounted for by a decrease of the Li vacancy concentration due to the Zn incorporation into Li sites. Anomalies at high concentrations are obviously due to a partial incorporation of Zn ions on Nb sites, which is reflected in the structure data. Anomalies in the concentration dependence of other optical properties at about 6–7 mol.% Zn reported recently are obviously related to a change in the localization of the Zn ions. The combination of high EO coefficients with a reduced optical damage for these concentrations make these crystals attractive for applications as Q-switching or electrooptical modulation.

In this paper we show how the Raman microprobe can be used for characterization of the domain structure in periodically poled lithium niobate (PPLN). The Raman scattered intensity of the transverse and longitudinal optical phonons was recorded across the stripe ferroelectric domains at the surface of a z-cut congruent PPLN sample. The change of integrated intensities across the domain structure was attributed to the influence of mechanical stresses and partially screened depolarization fields.