Sodium Borate Glasses Research Articles

Role of Eu ions and defect centers in formation of high-temperature persistent spectral holes in glass

The mechanism of room temperature persistent spectral hole burning was investigated using Eu-doped sodium borate glass (35Na 2O–65B 2O 3). The concentrations dependence of defect centers on the extent of hole burning was investigated for several Eu concentrations because the mechanism proposed so far are of two types: electron transfer to Eu 3+ from Eu 2+ and from defect centers in the glass. When the defect concentration increased due to X-ray irradiation, a high-temperature hole burning was observed at a Eu concentration (0.3 mol%) ; where the phenomenon is not observed in a normal sample without X-ray irradiation. When the Eu concentration was very low (0.1 mol%) , a spectral hole was observed only at low temperatures even when the concentration of defect centers became saturated due to X-ray irradiation. Furthermore, a concentration quenching of fluorescence from Eu 3+ became obvious at Eu concentrations of more than ca. 1 mol% . Hole burning became obvious at the same concentration. These findings indicate that the mechanism is an energy transfer from selectively excited Eu 3+ to adjacent Eu 2+ and subsequent electron transfer from Eu 2+ to Eu 3+. Defect centers in the glass reduce the barrier height of this electron transfer.

Effect of the addition Y2O3 on persistent spectral hole burning in europium doped sodium borate glass

Persistent hole burning is observed in a europium doped sodium borate glass from 10 to 100 K. Hole burning efficiency increased 18× when 5% yttrium oxide was added to the glass mixture. Hole burning was observed up to 300 K in Eu3+, Y3+ Co-doped glass.

Laser- and γ-inducedtransformations of optical spectra of indium-doped sodium borate glass

The optical absorption and luminescence properties ofindium-doped sodium borate glass irradiated by γ-raysand by powerful UV lasers within the impurity-related absorption band areinvestigated experimentally. It is demonstrated that both the laser- and γ-irradiationcause similar transformations of optical spectra in the UV and visible regions. Thechanges of the spectra observed are described with the use of a model whichincludes three types of impurity centres formed by differently charged indium ions.

Structural investigation of sodium borate glasses and melts by Raman spectroscopy. II. Conversion between BO 4 and BO 2O − units at high temperature

Raman scattering spectra were recorded for pure boron oxide and sodium borate glasses and their melts at the temperature ranging from room temperature to 1200 °C to investigate the structural changes occurring in the melts. The amounts of short-range order structures (SRO), BO 2O − and BO 3, were estimated from the high frequency bands at 1100–1600 cm −1. The ratio of 4-fold coordinated boron oxide BO 4, N 4, at high temperature could be derived for the glass melts as a function of Na 2O concentration. In Na 2O ⩽20 mol% region, N 4 showed a slight decrease while the remarkable decrease of N 4 was found in the region of Na 2O ⩾25 mol% with increasing temperature. The enthalpy of the equilibrium reaction, BO 4↔ BO 3+ NBO monotonously increased from 20 to 80 kJ/mol with an increase in Na 2O. A characteristic temperature T X SRO was found to exist, which defines the temperature sensitive–nonsensitive transition point of the above conversion of the structures of SRO, and did not necessarily coincide with the glass transition temperature. T X SRO plots were located between the liquidus line and the immiscibility dome in the phase diagram. Using this temperature and composition relationship, anomalous behavior of isothermal viscosity and strong-fragile characteristics of melts could be explained quantitatively.

Structural investigation of sodium borate glasses and melts by Raman spectroscopy.: I. Quantitative evaluation of structural units

Short-range and intermediate range structures of the sodium borate glass system were investigated using Raman spectroscopy to quantify their dependence on Na 2O concentration. High-resolution spectra were collected by Raman spectroscopy using the Q-switched, second-harmonic pulse of a Nd:YAG laser as an excitation source. The system was designed for measurement of the spectra of glasses and melts up to temperatures over 1000 °C with high signal to noise ratio. Use of polarized light and the simultaneous analysis of HH and VH spectra allowed deconvolution of Raman spectra into appropriate bands with high reproducibility. The deconvoluted bands in the high-frequency region of 1100–1600 cm −1 could be assigned to the vibration modes due to the short-range structures of BO 3 and BO 2O − units in the glasses. The band intensity ratios showed a simple linear relationship with the molar ratio, symmetric BO 3 triangle unit, N 3s, to asymmetric BO 2O − triangle unit, N 3a, obtained from 11B-NMR results. These results allowed a quantitative measure for normalizing the spectra leading to a direct comparison of the band intensities. The ring-structures of intermediate range order, boroxol, pentaborate, tetraborate and diborate groups, could be quantified from the spectra in the middle-frequency region. Their trends with Na 2O concentration showed a good consistency with 10B-NMR results and also Krogh-Moe’s model.

Structural investigation of sodium borate glasses and melts by Raman spectroscopy. III. Relation between the rearrangement of super-structures and the properties of glass

The structure of the intermediate range order (IRO) of sodium borate glasses and melts were quantitatively investigated by the analysis of high-temperature Raman scattering spectra. Raman bands at the middle frequency region of 700–950 cm −1 were normalized using the bands at high frequency spectra and their intensities were compared among the spectra collected from the melts with different composition at various temperature. Bands at 805, 780, 750 and 720 cm −1 were focused and their intensity changes were quantified. The exceeds of temperature over the glass transition temperature did not necessarily cause the decrease of all the band intensities. At Na 2O<15 mol%, 805 cm −1 band was the most sensitive to temperature, while at 15<Na 2O<30, it was switched to 780 cm −1 band and 805 cm −1 band became insensitive. When Na 2O concentration exceeded 30 mol%, 750 and 720 cm −1 bands were decreased with temperature. Accompanying the previous analysis on the structures of short range-order (SRO) of boron atoms [J. Non-Cryst. Solids, in this issue], some models of the structural rearrangement along with temperature were proposed. The combination of the obtained structural informations of IRO and SRO was found to explain the mechanisms causing various characteristic properties of borate glasses and melts, especially immiscibility and boron oxide anomaly of thermal expansion coefficient from the microscopic and dynamic points of view of the vitrification process in melt.

Function of Eu ion and defect centers in photochemical hole-burning of Eu-doped sodium borate glass

Function of Eu ion and defect centers in photochemical hole-burning of Eu-doped sodium borate glass

Laser- and g-induced optical absorption of indium-doped sodium-borate glass

Laser- and g-induced optical absorption of indium-doped sodium-borate glass

Preparation and physical properties of nickel phthalocyanine-substituted sodium borate glass

Electrical conductivity and optical absorption of nickel phthalocyanine (NiPc)-substituted sodium borate glass is reported here. We have successfully prepared NiPc-substituted sodium borate glass at 830 °C, and some preliminary studies on this glass are reported. Activation energy and optical band gap were determined for the glass from the Arrhenius plot of conductivity and optical absorption spectra, respectively.

Photochemical reactions of samarium ions in sodium borate glasses irradiated with near-infrared femtosecond laser pulses

Photoinduced processes of Sm 3+-doped sodium borate glasses under high-power, 800 nm femtosecond laser irradiation have been studied. Both the photoreduction of Sm 3+ to Sm 2+ and the formation of intrinsic defects are observed at an irradiance well below the threshold for laser-induced damage. We propose that these photoinduced processes arise from the linear and two-photon absorption of the short-wavelength component of the supercontinuum and the subsequent ionization of the glass matrix. Photochemical hole burning (PHB) has been observed for 5 D 0– 7 F 0 transition of Sm 2+ in the sodium borate glasses irradiated with near-infrared femtosecond laser pulses. The efficiency of hole burning at 77 K was about 5 times higher in the irradiated glasses than in thermally reduced glasses. We consider that both the metastable Sm 2+ and the intrinsic defects were responsible for the highly efficient PHB phenomenon.

Relationship between room temperature hole-burning in glasses and doped Eu-ion concentration

Photochemical hole-burning in sodium-borate glass (35Na 2O–65B 2O 3) was investigated as a function of doped Eu-ion concentration from 0.1 to 5 mol% both at room temperature and 12 K. In our preparation, 50–70% of Eu 3+ was reduced to Eu 2+. As the concentration of Eu ion exceeded 1 mol%, the fluorescence was quenched, and meanwhile the photochemical hole started burning. The spectral hole was most efficiently burnt at concentrations between 2 and 3 mol% at room temperature. Low temperature experiment showed that there are three kinds of processes for the hole formation. One is a transient process relaxed within 1–2 min. Another is observed only at low temperatures. The third one is observed persistently even at room temperature. The extent of these components depends on Eu-ion concentration. In view of these concentration dependences, the suggested mechanism of room temperature hole-burning is an energy or electron transfer between Eu 3+ and Eu 2+. Defect centers created by reduction process of the glass may play a role to help this transfer.

Preparation and physical properties of CuPc substituted sodium borate glass matrix

Electrical conductivity and optical absorption of copper phthalocyanine (CuPc) substituted sodium borate glass is reported here for the first time. We have successfully prepared CuPc substituted sodium borate glass at 830 °C and some preliminary studies on this glass are reported. Activation energy and optical band gap were determined for the glass from the Arrhenius plot of conductivity and optical absorption spectra, respectively.

Ultrasonic studies on irradiated sodium borate glasses

The ultrasonic velocity and attenuation coefficient have been measured at the frequency 4 MHz and at room temperature using the pulse echo technique. The effect of γ-radiation (1–10 Gy) on the ultrasonic attenuation, the internal friction and elastic properties inside the modified sodium borate glasses was studied. The used modification oxides are CaO, ZnO, MgO, BaO, and CdO. The results indicate the possibility for using modified sodium borate glasses as γ-ray dosimeters in the low γ-radiation doses.

Ultrashort-laser-pulse-induced persistent spectral hole burning of Eu^3+ in sodium borate glasses

We have observed persistent spectral hole burning (PSHB) in Eu(3+) -doped sodium borate glasses irradiated with near-IR femtosecond laser pulses. As-prepared glasses, i.e., glasses melted in air, do not show PSHB even at low temperatures (~77K) , but room-temperature PSHB occurs in the irradiated glasses. The exposure to IR radiation causes both the reduction of Eu(3+) to Eu(2+) and the formation of intrinsic defects. We propose that the photoinduced redistribution of electric charges between Eu(3+) to Eu(2+) is responsible for the occurrence of PSHB.

Effect of Al on the spectral and spectral-hole-burning properties of sodiumborate glasses doped with Sm 2+

Photoluminescence and absorption measurements of Sm 2+-doped aluminoborate glasses are reported. The effect of Al on the valence state of samarium and on its photoluminescence properties has been studied. Special attention was paid to the inhomogeneous widths of the 7F 0– 5D 0 transitions. Persistent spectral hole burning was performed at different temperatures to study the variation of homogeneous linewidths and hole-burning kinetics.

Electrical and optical properties of some sodium borate glasses

The dc-electrical conductivity of sodium borate glasses containing different metal oxides namely MgO, CaO, SrO, BaO, CdO and Al2O3 with different percents was measured in the temperature range 35–510°C. The activation energies of the electrical conduction and the glass transition temperature were calculated. DTA was carried out for the samples containing 5% MgO and 1% Al2O3 to identify phase transitions. All the results were discussed and correlated according to the molecular structure of the prepared glasses. Also, the absorption spectra were measured in the 190–900 nm range and interpreted in the terms of structural concepts. A resolution of the observed absorption spectra showed that four bands were induced with maxima at about 210, 270, 420 and 680 nm. Small deviations of these induced bands characteristic of the glass content were observed and explained in terms of the physical properties of the contained metal oxides.

Room-temperature photochemical hole burning of Eu3+ in sodiumborate glasses

Persistent spectral hole burning (PSHB) has been observed at 77 K to roomtemperature for Eu3+ in sodium borate glasses with compositions of xNa2O·(100-x)B2O3 (x = 10,25,35). Glasses meltedin air do not show the phenomenon of PSHB, while room-temperature PSHB occursin the glasses prepared by melting in reducing conditions. 151EuMössbauer spectra reveal that europium ions are present as both Eu3+and Eu2+ in glasses melted in reducing conditions. The relative hole areaincreases with an increase in the molar ratio of Eu2+ to Eu3+ whenthe content of Eu2+ is low, whereas the relative hole is almostindependent of the molar fraction of Eu2+ when the content of Eu2+is high. Furthermore, a comparison of hole burning among sodium borate glasseswith the molar fraction of Eu2+ being almost the same as one anothershows that the hole area grows larger as the content of Na2O becomeshigher. These observations are interpreted in terms of the photoinducedredistribution of electric charges between Eu3+ and Eu2+. The effectof the glass composition on hole widths is also discussed based on thestructural change in sodium borate glasses.

Photochemical Hole Burning of Sm2+ in Sodium Borate Glasses Induced by Near-Infrared Femtosecond-Laser Irradiation.

We report on photochemical hole burning of Sm2+ in sodium borate glasses irradiated with femtosecond-laser pulses of 800nm wavelength. The irradiation of Sm3+-doped sodium borate glasses with femtosecond-laser pulses causes electron-trapped Sm3+, i.e., Sm2+ and point defects such as an oxygen hole center and an electron trapped near Na+. The measurements of spectral hole burning were carried out for the 5D0-7F0 transition of Sm2+ using a DCM dye laser. Photoionization hole burning is observed at 77K to room temperature for the glasses exposed to femtosecond-laser pulses, and also for the glasses prepared by melting under reducing conditions. The hole-burning efficiency of Sm2+ produced by the photoinduced process is about twice higher than that by the thermal process. It is thought that the metastable Sm2+ ions and oxygen hole centers induced by femtosecond-laser irradiation are responsible for the observed phenomenon. We propose that the efficient photoionization hole burning is caused by the photostimulated recombination of the electron trapped by Sm3+ with the oxygen hole center.

Influence of Residual Water in a Glass on Its Rheological and Relaxation Properties (by the Example of a 5Na2O · 95B2O3Glass)

Glasses of the 5Na2O · 95B2O3(mol %) composition synthesized at a temperature of 1100°C for 180 and 20 min are studied. The temperature dependences of the viscosity and the thermal expansion of glasses are obtained. The thermal expansion coefficients and glass transition temperatures of the studied glasses are determined, and the parameters of structural relaxation (the constant characterizing the width of the spectrum of relaxation times, the relaxation modulus equal to the ratio of the viscosity to the relaxation time, and the relaxation time at zero reciprocal temperature) are calculated from the dilatometric curves measured at temperatures close to the glass transition range. The water content in the studied glasses is estimated by comparing the obtained dependence of the viscosity on the water content with the data available in the literature for glasses of a similar composition. The assumption is made that the structural relaxation time in sodium borate glass decreases with an increase in the water content.

Mössbauer and electrical investigation of sulfur-doped sodium borate glasses containing iron

Three series of sulfur-doped sodium tetraborate glasses containingiron was prepared with the composition (Na2 B4 O7 ) 1–x (Fe2 O 3 ) x , wherex equals 0.1, 0.2 and 0.3. One series of the glass was left free of sulfur,while sulfur was added to the other two series of 2.5 and 5 wt%, respectively,to investigate the role of sulfur ions on some physical properties of thistype of glass. Melting process was carried out in platinum crucibles at 1100°C for one hour. The glasses were quenched in air at room temperature.X-ray diffraction measurement was carried out to be sure that the pure glassystate is obtained. 57Fe Mossbauer spectroscopy and dc conductivitymeasurements were carried out. It was found that iron is present in form ofFe2+ and Fe 3+ ions. Sulfur ions increased the valuesof dc conductivity. The isomer shift of the two states of iron is stable whilethe quadrupole splitting value changed with increasing Fe2 O3 content or as sulfur was added.