Dysprosium doped alkali fluoroborate glasses—Thermal, structural and optical investigations

Thermal, structural and optical properties of Dy³⁺-doped alkali fluoroborate glasses with composition (in mol%), 49B₂O₃+25XO+25NaF+1Dy₂O₃ (where X=Li₂, Na₂, K₂, Mg and Ca), have been investigated. Thermal analysis revealed the homogeneous formation of the glasses. The FTIR spectra reveal that the glasses contain BO₃, BO₄ non-bridging oxygen atoms and strong OH⁻ bonds. From the optical absorption spectra, Judd-Ofelt intensity parameters (Ω_λ, λ=2, 4 and 6) have been evaluated and are in turn used to predict radiative properties such as radiative transition probability (A), stimulated emission cross-section () and branching ratios (β_R) for the excited levels of Dy³⁺ ions in alkali fluoroborate glasses. The dependence of the spectral characteristics of Dy³⁺ ions due to compositional changes has been examined and reported.     

13C MAS NMR investigations of alkali doped C60

Results of¹³C MAS NMR measurements of the Rb _x C₆₀ system (x=2.75, 3, 4, 6) and the A₆C₆₀ compounds (A=K, Rb, Cs) are presented. Special attention was paid to sample preparation in order to suppress effects of impurities and lattice defects due to imperfect C₆₀ starting material. The¹³C MAS NMR measurements of the Rb _x C₆₀ system demonstrate the usefulness of this method to reveal valuable information about its phase diagram. The existence of underdoped Rb₃C₆₀ is proved. Well resolved lines in all investigated A₆C₆₀ compounds confirm the orientational order of the C₆₀ ions. An assignment of the signals to the three magnetically inequivalent carbon atom positions in the crystal structure is proposed.     

Optical spectroscopic investigations on silver doped sodium phosphate glass

This research investigates the optical spectroscopic characteristics of silver-doped phosphate antibacterial glasses with chemical compositions 42P₂O₅–42ZnO–(16?x) Na₂O, (where x = 0, 0.4, 0.8, 1.2, 1.6 Ag₂O). The glass samples were prepared by conventional melting quenching techniques. The structures of all the homogenous prepared glasses were studied by XRD, and UV–Vis spectroscopy. The glass formability was tested and the amorphous nature was approved using XRD-technique. Archimedes method has been employed to measure the density of the samples hence, the molar volume was calculated. The molar volume and density shows discontinuity of measurements under effect of increasing Ag₂O concentration. The optical spectroscopic analyses for the obtained glass samples has been investigated over the whole range (190–2500 nm) for studying the effect of bandpass absorption glass filter, its color peak center and UV cut-off. Transmittance of some glass samples showed cut-off for UV and short visible wavelengths in some glass samples, so these samples composition can be considered as long-pass edge filters and from band stop ranges started from 190 to 515 nm and increase by increasing doped silver concentration. The optical energy gap decreases by increasing the Ag₂O concentration from 4.43 to 3.61 eV. The refractive index and extinction coefficient and some optical properties are studied and the results indicate clearly that there is no high remarkable change with changing wavelength. The refractive index is found to be increased by increasing the Ag₂O content. The wavelength dependence of extinction coefficient and the dielectric constants exhibit higher values for higher Ag₂O contents.     

Ionic conductivity in borate glasses with three types of mixed alkali cations

We have investigated the temperature- and frequency-dependent ionic conductivity in (Li_0.67 ? xNa_0.33 Rb_x)₂B₄O₇ (LNRBO) glasses with x = 0, 0.07, 0.2, 0.33, 0.47, and 0.6. The mixed alkali effect of the ternary mixed alkali system LNRBO is compared with that of the binary mixed alkali systems (Li_1 ? xNa_x)₂B₄O₇ (LNBO), (Li_1 ? xRb_x)₂B₄O₇ (LRBO) and the single alkali glass Rb₂B₄O₇ (RBO). From the results of the dc conductivity and dc activation energy, we observe that the LNRBO system exhibits the combined characteristic of binary mixed alkali systems LNBO and LRBO. It is found that the power-law exponent n for binary alkali glass is the same as that for ternary alkali glass but it is lower than that for single alkali glass. This indicates that the dimensionality of conducting pathway in the mixed alkali glasses of LNBO, LRBO and LNRBO is lower than that in the single alkali RBO. We discuss the concentration dependence of the dc conductivity and dc activation energy in the framework of the bond valence technique to reverse Monte Carlo produced structural model [Phys. Rev. Lett. 90, 155507 (2003)].     

Tm掺杂的激光晶体生长、结构和光谱性能研究

采用顶部籽晶生长法从K2Mo3O10-B2O3助熔剂中生长出15 mm×15 mm×25 mm优质TmxGd1-x Al3(BO3)4(x=1,0.06)晶体.利用X射线单晶衍射仪测定了TmAl3(BO3)4晶体的结构.对Tm3+GAB晶体进行定向切割,测量得到了σ和π方向的偏振的吸收和发射光谱,并根据Judd-Ofelt理论计算了Tm3+在GdAl3(BO3)4中的J-O参数、各个能级的振子强度、自发辐射几率、荧光分支比等参数.     

Absorption and emission properties of Nd in lithium cesium mixed alkali borate glasses

Lithium cesium mixed alkali borate glasses of the composition 67B₂O₃·xLi₂O·(32−x)Cs₂O (where x=8, 12, 16, 20 and 24) containing 1 mol% Nd₂O₃ were prepared by melt quenching. The absorption spectra of Nd³⁺ were studied from the experimental oscillator strengths and the Judd-Ofelt intensity parameters were obtained. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) (A_T), branching ratios (β) and integrated absorption cross-sections (Σ) of the Nd³⁺ transitions from the excited state J manifolds to the lower lying J′ manifolds. Radiative lifetimes (τ_R) are estimated for certain excited states of Nd³⁺ in these mixed alkali borate glasses. Luminescence spectra were measured and the emission cross-sections (σ_p) were evaluated for the three emission transitions. The variation of luminescence intensity with x was recorded for the three transitions at different excitation power to see the effect of mixed alkalies in these borate glasses.     

Compositional-dependent lead borate based glasses doped with Eu ions: Synthesis and spectroscopic properties

New multicomponent lead borate based glasses with various PbO/B₂O₃ weight ratio were prepared. The glass samples were analyzed in detail by using Raman and IR absorption spectroscopy. Optical properties of Eu³⁺ ions have been investigated in lead borate based systems, in which PbO/B₂O₃ weight ratios were changed from 1:2 to 8:1 in glass composition. The values of the phonon energy of the host and ⁵D₀ lifetime of Eu³⁺ decrease, whereas absorption and emission intensities, as well as bonding parameter increase with increasing PbO concentration. Additionally, spectral lines are shifted in direction to the lower frequency region. Non-monotonic dependence of the fluorescence intensity ratio R (⁵D₀-⁷F₂/⁵D₀-⁷F₁) upon PbO/B₂O₃ content has been observed in contrast to bonding parameter that is also non-linear but monotonic. Some structural and spectroscopic aspects for Eu-doped lead borate based glasses are presented.     

Optical and other spectroscopic studies of lead, zinc bismuth borate glasses doped with CuO

10MO·20Bi₂O₃·(70−x)B₂O₃·xCuO [M=Pb, Zn] with x=0, 0.4 and 0.8 (wt%) glasses were synthesized by the melt-quenching technique and were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Physical parameters, like density, and spectroscopic studies (optical absorption, EPR, FTIR and photoluminescence) were used to understand the role of modifier oxide and CuO in the glass matrix. A red shift of the absorption band corresponds to ²B_1g→²B_2g transition of Cu²⁺ ions from P2 to Z4 samples and the increase of hyperfine splitting factor (A_‖) from P2 to Z2 shows that with the integration of PbO by ZnO the electron density around copper ion is increased. It is also supported by the gradual increase in theoretical optical basicity values of ZnO mixed glasses, as compared to that of PbO mixed glass matrix. Reduced bismuth radicals are found in undoped and 0.4% CuO doped glasses of both the series. Analysis of the absorption and emission studies indicates that the concentration of luminescence centers of bismuth ions (Bi³⁺ ions in UV region) is decreased by the integration of ZnO as well as by increasing the dopant concentration. In lead series PbO₄ and BiO₃ units are increased from P2 to P4 and in zinc series BiO₃ units are decreased from Z0 to Z4. The conductivity of the glass matrices is increased in both the series with the dopant of CuO.     

Structural studies and mechanical properties of some borate glasses doped with different alkali and cobalt oxides

Mixed alkali borate glasses doped with CoO, have been prepared by the melt quenching technique. Elastic properties and FT-IR spectroscopic studies have been employed to study the role of CoO and the mixed alkali effect on the structure of the investigated glass system. Elastic properties and Debye temperature have been investigated using sound wave velocity measurements at 4 MHz at room temperature. The density, molar volume and glass transition temperatures were employed to investigate the structure of these glasses. Infrared spectra of these glasses revealed that the borate network is affected by the increase in the concentration of CoO content and the mixed alkali oxides. These results are interpreted in terms of the change in the topology of these glass structures. The elastic moduli are observed to increase with the increase of CoO content due to the increased average bond connectivity.     

Optical absorption and emission properties of Pr and Er in lithium cesium mixed alkali borate glasses

This article presents the optical absorption and emission properties of Pr³⁺ and Er³⁺ in mixed alkali borate glasses of the type 68B₂O₃·xLi₂O·(32-x)Cs₂O (where x=8, 12, 16, 20 and 24). The variation of Judd-Ofelt intensity parameters (Ω_λ), the peak wavelength of the hypersensitive transitions, radiative transition probabilities (A_rad) and peak emission cross-sections (σ_p) with x in the glass matrix have been discussed in detail. The changes in position of hypersensitive transition and intensity parameters with x are correlated to the structural changes in the host matrix. The estimated radiative lifetimes (τ_R) of certain excited states of both Pr³⁺ and Er³⁺ in lithium cesium mixed alkali borate glasses are reported. Branching ratios (β) and integrated absorption cross-sections (Σ) for certain important transitions are presented. Peak stimulated emission cross-sections (σ_p) are calculated for the observed emission peaks of Pr³⁺ and Er³⁺ ions in this glass matrix.     

Characterization of laser processing of single‐crystal natural diamonds using micro‐Raman spectroscopic investigations

The application of lasers for processing diamond has revolutionized the diamond industry and its applications in microelectronics, microelectromechanical system (MEMS) and microoptoelectromechanical system (MOEMS) technologies. The process quality can be evaluated using spectroscopic techniques. In the present investigation, four different types of Q‐switched solid‐state lasers (with different beam parameters), namely, a lamp‐pumped Nd:YAG laser operating at 1064 nm, a lamp‐pumped Nd:YAG laser operating at second harmonically generated 532 nm, a diode‐pumped Nd:YVO₄ laser operating at 1064 nm and a diode‐pumped Nd:YAG laser operating at 1064 nm, have been employed for the processing of a single‐crystal, gem‐quality, natural diamond. The main objective behind the selection of these lasers with different beam parameters was to study the effect of wavelength, pulse width, pulse energy, peak power and beam quality factor (M² factor) on various aspects of processing (such as microcracking, material loss and cut surface quality) and their relative merits and demerits. The overall weight loss of the diamond and formation of microcracks during processing have been studied for the above four cases. The characteristics of the graphite formed during processing, elemental analysis, surface morphology of the cut surface and process dynamics have been studied using micro‐Raman spectroscopy and scanning electron microscopy (SEM). We observed that laser cutting of single‐crystal diamonds used for industrial applications can be accomplished without microcracking or surface distortion using Q‐switched Nd:YAG lasers. This allows direct processing without extensive postgrinding and polishing stages. Very efficient diamond processing is possible using diode‐pumped lasers, which results in the lowest possible breakage rate, good accuracy, good surface finish and low weight loss. From the micro‐Raman and SEM studies, it is concluded that the surface quality obtained is superior when diode‐pumped Nd:YVO₄ laser is used, owing to its extremely high peak power. The maximum graphite content is observed while processing with lamp‐pumped Nd:YAG laser at 532 nm. An overall comparison of all the laser sources leads to the conclusion that diode‐pumped Nd:YAG laser is a superior option for the efficient processing of natural diamond crystals. Copyright © 2006 John Wiley & Sons, Ltd.     

Characterization of the Suzuki phase in doped alkali halides by Raman spectroscopy

The symmetries and frequencies of the Raman active modes of the Suzuki phase in the systems 6NaCl:CdCl₂; and 6NaCl:MnCl₂, have been calculated. Three of the four peaks allowed by symmetry (A_1g and 2F_g) agree to within 25% in position with the experimental values presented here and with other experimental results. The fourth peak (E_g) seems to be associated with a very soft mode, which explains why this peak has not been observed. The features of the Raman spectrum depend mainly upon the chlorine ions.     

Spectroscopic studies of tantalum doped borate glasses

Glasses with formula 30Li₂O 60B₂O₃xTa₂O₅ (10−x) Bi₂O₃ for x=0, 2, 4, 6 and 8 were prepared via normal melt quenching technique and characterized by refractive index and MDSC. Refractive index (μ) and glass transition temperature (T_g) are found to increase with increase in dopant concentration. Impedance spectra of the samples were recorded in the frequency range 100 Hz–5 MHz in the temperature range 175–275 °C. The plots are typical of those recorded for disordered systems. Conductivities and relaxation times are found to follow Arrhenius type of relation and activation energies are calculated. Optical absorption spectra were recorded in the wavelength range 200–900 nm range from which cutoff wavelength (λ_c) and optical band gap energy (E_g) are evaluated. λ_c is found to decrease while E_g to increase with increase in composition. FTIR spectra of the samples were recorded in the frequency range 400–1500 cm⁻¹ which exhibit characteristic bands corresponding to BO₃, BO₄ stretching vibrations and BO bending vibration. Tightening of the structure is indicated by increase in the vibration of BO₃ at the cost of BO₄ for 8 mol% of Ta₂O₅. This is in support of the highest value of T_g for this sample among the series. Raman spectra of the samples were recorded in the frequency range 200–1200 cm⁻¹. With successive addition of Ta₂O₅, increase in the vibration of Ta–O groups TaO₆ groups to be responsible for observed increase in μ and T_g. An attempt is made to prepare tantalum doped borate glasses and study them by spectroscopic techniques.     

Dielectric and spectroscopic investigations of lithium aluminium zirconium silicate glasses mixed with TiO2

Li₂O–Al₂O₃–ZrO₂–SiO₂ glasses mixed with different concentrations of TiO₂ (ranging from 0 to 5.0?mol%) were synthesised and their dielectric properties (dielectric constant, loss tan?δ, a.c. conductivity σ) investigated over wide ranges of frequency and temperature. Studies of optical absorption, ESR, infrared (IR) and photoluminescence properties have also been undertaken. A decrease in dielectric parameters with increasing concentrations of TiO₂ has been observed and this is attributed to an increasing proportion of titanium ions occupying network-forming positions rather than going into interstitial positions. A.C. conductivity in the high-temperature region appears to be connected both to electronic transfer and ionic movements, but conduction attributed to such processes seems to be hampered by the entry of titanium ions into the network-forming positions. Analysis of the results of the IR spectral studies have indicated that there is a decreasing degree of disorder in the glass network with increasing TiO₂ content. The optical absorption and ESR spectral studies have revealed that titanium ions exist in both Ti³⁺ and Ti⁴⁺ states in the glasses. Luminescence spectra exhibited an emission band in the visible region and the luminescence efficiency increased with TiO₂ content. The excitation of substitutionally positioned octahedral Ti⁴⁺ ions is identified as being responsible for the observed luminescence emission.     

Magnetoresistance of mixed valent Tm impurities

The resistivity of a metal due to an Anderson impurity with orbital degeneracy in the intermediate valence regime is calculated via the Kubo formula within a mode-mode decoupling scheme. The result depends on the relative occupation of the f-levels and shows a bump as a function of temperature. In the case of Tm the two ionic configurations are magnetic, and a considerable field dependence is obtained.     

Infrared spectroscopic investigations of bauxites

Journal of Applied Spectroscopy -     

Effect of Li2O content on physical and structural properties of vanadyl doped alkali zinc borate glasses

The effect of Li₂O content in vanadyl doped 20ZnO+xLi₂O+(30−x)Na₂O+50B₂O₃ (5≤x≥25) glasses has been studied with respect to their physical and structural properties. The absence of sharp peaks in XRD spectra of these glass samples confirms the amorphous nature. The physical parameters like density, refractive index, ionic concentration and electronic polarizability vary non-linearly with x mol% depending on the diffusivities of alkali ions. EPR and optical absorption spectra reveal that the resonance signals are characteristics of VO²⁺ ions in tetragonally compressed octahedral site. Spin-Hamiltonian, crystal field, tetragonal field and bonding parameters are found to be in good agreement with the other reported glass systems. The tetragonal distortion (g_⊥-g_∥) and Dt reveals that their values vary non-linearly with Li₂O content and reaches a minimum at x=10 mol%. An anomaly of character has been observed in all the properties of vanadyl doped glass systems, which gives a clear indication of mixed alkali effect.     

Tm3+掺杂硅酸镓镧(La3Ga5SiO14)晶体的结构与光学性能研究

利用X射线粉末衍射确定了Tm3+掺杂硅酸镓镧(La3Ga5SiO14,LGS)晶体的晶体结构;运用DICVOL91程序计算了该晶体不同部位的晶胞参数;测定了Tm:LGS晶体的室温吸收谱和470 nm光激发下的发射光谱;根据Judd-Ofelt理论拟合了Tm3+的三个晶场调节参数Ωt(t=2,4,6),分别为2.694×10-20 cm2,1.842×10-20 cm2,0.030 × 10-20 cm2;计算了各个能级跃迁的谱线强度、振子强度、吸收截面等,进而计算了3H4和3F4态的自发跃迁概率、辐射寿命、荧光分支比和积分发射截面,并对结果进行了分析.     

Terahertz spectroscopic investigations of explosives

Experimental measurement and theoretical analysis of THz spectrum for five different explosives and related compounds are introduced. The refractive index and absorption coefficient of the samples are measured in the region of 0.2–2.6 terahertz by time-domain spectroscopy. The simulated spectrum of γ-HNIW is in agreement with the experimental data.