Li2B4O7晶体的晶格振动光谱

在室温下测量了Li₂B₄O₇单晶的各种振动类的偏振Raman散射谱和该晶体粉末样品的红外吸收谱(200—4000cm^-1)。根据LO-TO劈裂的实验结果,计算出该晶体极化模的有效电荷和振子强度。通过与BBO和LBO晶体的结构和B—O伸缩振动模频率比较,得出:Li₂B₄O₇晶体可能有较大的非线性光学系数。 关键词：     

Vibrational spectrum of Li2B4O7 crystals

Polarized IR reflection spectra of Li₂B₄O₇ crystals are studied in a spectral range of 80–1600 cm^?1 and compared with their Raman spectra. Based on the results of the dispersion analysis of the spectra, the frequencies, damping constants, and oscillator strengths of all vibrations are determined. The inversion of frequencies of the longitudinal and transverse vibrations of the A ₁ and E symmetry in a range of 900–1150 cm^?1 is found. Based on the data thus obtained, the effective charges are calculated and the types of chemical bonds are analyzed for structural groups of the Li₂B₄O₇ crystal.     

非晶态离子导体Li2B2O4的核磁共振研究

本文报道了非晶态离子导体Li₂B₂O₄的⁷Li核磁共振研究。测量了⁷Li核磁共振谱与温度的关系。实验中发现,Li₂B₂O₄的晶态、非晶态和部分晶化样品的⁷Li核磁共振谱有很大的不同,且在部分晶化样品的⁷Li核磁共振谱上有附加的小峰,它与LiCl(Al₂O₃)的⁷Li核磁共振谱上附加的小峰相类似。我们也对非晶态离子导体B₂O₃-0.7Li₂O-0.7LiCl进行了⁷Li核磁共振研究,其结果与上面的类似。研究结果表明,它们都起因于非晶母体与微晶的界面效应。 关键词：     

Structural and photoluminescence properties of Dy3+ doped different modifier oxide-based lithium borate glasses

Structural and photoluminescence properties of Dy³⁺ doped lithium fluoro-borate glasses with the compositions Li₂B₄O₇–BaF₂–NaF–MO (where M=Mg, Ca, Cd and Pb), Li₂B₄O₇–BaF₂–NaF–MgO–CaO and Li₂B₄O₇–BaF₂–NaF–CdO–PbO have been investigated through XRD, FTIR, optical absorption, emission and decay measurements. 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 probabilities (A_T), branching ratios (β_r) and stimulated emission cross sections (σ_p) for all emission levels of Dy³⁺ ion in different lithium fluoro-borate glass matrices. From the emission spectra, chromaticity color coordinates have been calculated and indicated emission color for all glass matrices. The nature of decay profiles of ⁴F_9/2 state of Dy³⁺ in all the glass matrices are analyzed.     

Thermoluminescence studies on Cu-doped Li2B4O7 single crystals

Lithium tetraborate (Li₂B₄O₇) is a tissue equivalent material and single crystals of this material doped with Cu are promising for dosimetric applications. In the present study highly transparent single crystals of lithium tetraborate (Li₂B₄O₇) doped with Cu (0.5 wt%) have been grown using the Czochralski technique. The Li₂B₄O₇:Cu crystals were studied using photoluminescence, X-ray diffraction (XRD), UV-vis transmission, time resolved fluorescence and thermoluminescence (TL) techniques. The TL readout of Li₂B₄O₇:Cu crystals showed two well-defined glow peaks at 402 K (peak-1) and 513 K (peak-2) for a 4 K/s heating rate. While the low temperature TL peak-1 fades completely within 24 h at room temperatures, the main dosimetric peak-2 remains the same. The TL sensitivity of the grown single crystal is found to be 3.3 times that of a conventional TL phosphor, TLD-100. The Li₂B₄O₇:Cu crystals showed a linear TL dose-response in the range from 1 mGy to 1 kGy. The TL analysis using a variable dose method revealed first order kinetics for both the peaks. Trap depth and frequency factor for peak-1 were found to be 0.81 eV and 5.2×10⁹ s⁻¹, whereas for peak-2 the values were 1.7 eV and 1.7×10¹⁶ s⁻¹, respectively.     

Study of Raman spectra in the processes of glass formation,crystallization, and melting of strontium diborate

The behavior of the Raman spectra of SrB₄O₇ (SBO) and Li₂B₄O₇ crystals upon melting and glass formation is studied by high-temperature Raman spectroscopy (HTRS). The character of formation of boron–oxygen fragments in different aggregate states of SBO is discussed based on an analysis of the Raman spectra in the crystalline, glassy, and molten states.     

Neutronendosimetrie mit dem Thermolumineszenzleuchtstoff Li2B4O7:Mn

Der Thermolumineszenzleuchlstoff Li₂B₄O₇, :Mn mirde durch Anwendung eines besonderen Herstellungsverfahrens für klerhine Substanzmengen unter Verwendung von ⁶Li-Verbindungen präpariert. Die experimentell bestimmte relative Neutronenempfindlichkeit des erhaltenen ⁶Li₂B₄O₇.Mn steigt bei etwa gleichbleibender Lichtausbeute entsprechend der Zunahme an⁶Li im Thermoluminophor an und erreicht Werte, die denen von ⁶LiF nahekommen. Der hergeslellte Leuchtsloff ist daher zur Dosimetrie thermischer Neutronen gut geeignet, seine Eigenschaften als Dosimeter für γ-Strahlung enlsprechen denjenigen von?Dohna-lum-Li₂B₄O₇:Mn”.     

Synthesis and characterization of thermoluminescent Li2B4O7 nanophosphor

Lithium borate (Li₂B₄O₇) is a low Z_eff, tissue equivalent material that is commonly used for medical dosimetry using the thermoluminescence (TL) technique. Nanocrystals of lithium borate were synthesized by the combustion method for the first time in the laboratory. TL characteristics of the synthesized material were studied and compared with those of commercially available microcrystalline Li₂B₄O₇. The optimum pre-irradiation annealing condition was found to be 300 °C for 10 min and that of post-irradiation annealing was 300 °C for 30 min. The synthesized Li₂B₄O₇ nanophosphor has very poor sensitivity for low doses of gamma up to 10¹ Gy whereas from 10¹ to 4.5×10² Gy this phosphor exhibits a linear response and then from 4.5×10² to 10³ Gy it shows supralinearity. Thermoluminescence properties of Li₂B₄O₇ nanophosphor doped with Cu has also been investigated in this paper. It shows low fading and a linear response over a wide range of gamma radiation from 1×10² to 5×10³ Gy. Therefore the synthesized lithium borate nanophosphor doped with Cu may be used for high dose measurements of gamma radiations.     

Effect of doping on the luminescence properties of Li2B4O7

In this work, we have investigated the influence of doping agents on the luminescence properties of multiply doped Li₂B₄O₇ and the temperature lag between TSL materials and the heating element. The results of thermoluminescence studies show that the Ag doping leads to the appearance of a new glow curve peak at 165 °C and the increasing sensitivity of Li₂B₄O₇:Cu,Ag,P is correlated with copper and phosphate concentrations. Under the excitation at 245 nm the emission spectra show maxima at 365 and 450 nm in the ceramic, crystal and glass. The low energy shift in the latter system might be related to the local structural distortion in the glass around Cu⁺ ions.     

Li2O-(LiCl)2-B2O3-Al2O3系统玻璃的Raman光谱研究

我们用Raman光谱研究了Li₂O(LiCl)₂B₂O₃-Al₂O₃系玻璃的结构,着重研究了Al₂O₃的影响。对于Li₂O-B₂O₃系玻璃,Li₂O含量增加使玻璃中存在的BO₃三角体转变为BO₄四面体, 关键词：     

Kinetics of thermally stimulated recombination processes in lithium borate crystals

This paper reports on the results of the experimental and theoretical investigations of thermally stimulated recombination processes in crystals of the lithium borates Li₂B₄O₇ and LiB₃O₅. For both types of crystals, the measurements of thermally stimulated luminescence curves, spectra, and temperature dependences of the intensities of steady-state X-ray luminescence have been performed in a single experimental cycle. In the framework of a unified model for the Li₂B₄O₇ and LiB₃O₅ crystals, the thermally stimulated recombination processes have been calculated and the obtained results have been interpreted talking into account all available experimental data.     

Red emission in B- and Li-doped SrAl2O4:Eu phosphor under UV excitation

Samples of SrAl₂O₄:Eu³⁺ doped with B³⁺ and SrAl₂O₄:Eu³⁺ co-doped with B³⁺ and Li⁺ have been prepared by the solid-reaction method. The influence of B³⁺ and Li⁺ contents on luminescence property has been investigated. It is found that the substitution of B³⁺ for Al³⁺ greatly improves red emission intensity at 591, 615 and 701 nm. The dopant Li⁺ as charge compensator in SrAl₂O₄:Eu³⁺, B³⁺ can further enhance luminescence intensity. The strongest red emission is obtained in the Sr(Al_1.9, B_0.1)O₄:Eu_0.02³⁺, Li⁺_0.02 sample. The developed phosphors can be efficiently excited by ultraviolet (UV) light from 350 to 480 nm, which indicates that B³⁺ and Li⁺ co-doped SrAl₂O₄:Eu³⁺ is a good candidate phosphor applied in solid-state lighting in conjunction with white UV light-emitting diodes (LEDs).     

Glass formation in the system Li2B4O7–Pb3O4–CuO using X-ray diffraction

X-ray diffraction was performed to construct the phase diagram for the ternary Li₂B₄O₇–Pb₃O₄–CuO glass system. Three principal regions were identified: (1) a glass-forming region observed at the composition (75 < Li₂B₄O₇ < 100) mol%, (0 < CuO < 35) mol% and (0 < Pb₃O₄ < 70) mol% in the ternary system, and (100 ? x) mol% Li₂B₄O₇–x mol% Pb₃O₄ where x = 0 up to 70, (100 ? y) mol% Li₂B₄O₇–y mol% CuO where y = 0 up to 25 in the binary system;. (2) a crystalline region: all compositions prepared from the binary system Pb₃O₄–CuO and the ternary system containing Li₂B₄O₇ up to 60 mol%; (3) a partially crystalline region formed between the glass and crystalline regions.     

Effect of gamma irradiation on internal friction in lithium tetraborate

The effect of gamma irradiation on the mechanical properties of lithium tetraborate Li₂B₄O₇ in the single-crystal and vitreous states is investigated. It is found that, after irradiation of the Li₂B₄O₇ single crystal, the temperature range of the dissipative process initially occurring at 380–420 K becomes broader and the fine structure of the peak in the temperature dependence of the internal friction Q^?1(T) undergoes a substantial trans-formation. After irradiation of the vitreous Li₂B₄O₇ sample, the increase in the internal friction, which is characteristic of the onset of the α relaxation in this material, is not observed in the dependence Q^?1(T) up to a temperature of 570 K. It is shown that the mechanical properties of the irradiated samples are almost completely recovered after annealing at 570 K for 1 h.     

TL and OSL studies on lithium borate single crystals doped with Cu and Ag

Lithium borate (LBO) single crystals doped with Cu and Ag (0.25 mol% each) (Li₂B₄O₇:Cu,Ag) are grown by the Czochralski method. The thermoluminescence readout on Li₂B₄O₇:Cu,Ag crystals showed three glow peaks at～375, 441 and 516 K for the heating rate of 1  K/s. The thermoluminescence sensitivity of the grown Li₂B₄O₇:Cu,Ag single crystals is found to be 5 times TLD-100 and a linear dose response in the range 1 mGy to 1 kGy. The glow curve deconvolution reveals nearly first order kinetics for all the three peaks with trap depths 0.77, 1.25 and 1.34 eV respectively and corresponding frequency factors 1.6×10⁹, 1.3×10¹³ and 6.8×10¹¹ s^?1. The continuous wave optically stimulated luminescence (CW-OSL) measurements were performed on the LBO:Cu,Ag single crystals using blue light stimulation. The traps responsible for the three thermoluminescence peaks in Li₂B₄O₇:Cu,Ag are found to be OSL sensitive. The qualitative correlation between TL peaks and CW-OSL response is established. The photoluminescence studies show that in case of co-doping of Ag in LBO:Cu the emission at 370 nm in Cu states dominates over the transitions in Ag states implying doping of Ag plays a role as sensitizer when co-doped with Cu and increases overall emission.     

Structure of zinc-borate low-melting glasses derived from IR spectroscopy data

The IR spectra of glasses of the ZnO—SrO—B₂O₃ system with constant additions of PbO, Al₂O₃, and Li₂O (20 mol. % in sum) were studied. It is established that on replacement of B₂O₃ by ZnO, the structure of the glasses is characterized by the presence of groupings with the bridge bonds B^III— O—B^III, B^III—O—B^IV, B^IV—O—B^IV and end groups B^III— O⁻; ZnO practically exerts no influence on the coordination transition [BO₃] → [BO₄]. At a high content of ZnO, zinc ions are present in both a six-and a four-coordinated state. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 778–781, November–December, 2005.     

Eu3+ emission in SrAl2B2O7 based phosphors

Eu³⁺ doped SrAl₂B₂O₇ phosphors were fabricated by the wet method. The structures of the phosphors were characterized by XRD. The doping content of Eu³⁺ ions in SrAl₂B₂O₇:Eu³⁺ phosphors are 1%, 4%, 6%, 8%, 10% (molar fraction), respectively. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. The luminescent properties of SrAl₂B₂O₇:Eu³⁺ phosphors are discussed. It is shown that from 4% to 6% of doping content of Eu³⁺ ions under 392 nm excitation in SrAl₂B₂O₇:Eu³⁺ phosphors is optimum.     

Radioluminescent mechanism of Li2B4O7:Cu crystal

The structure of the radioluminescent (RL) spectrum of Li₂B₄O₇:Cu crystal is complex, having no normal Gauss peaks. The RL spectrum recorded showed one sharp and strong peak near 365 nm. For the purpose of explaining this phenomenon, we used the self-trapped exciton (STE) model to analyze experimental data of absorption spectrum, emission spectrum, radioluminescence spectrum and decay-time curves. We found a short lifetime component (of the order of ns) from phosphorous signals of Li₂B₄O₇:Cu. We realized that the short lifetime component related to inherent signal of host lattice and the d-p transitions of Cu⁺. This result is applicable in the detector system with high time resolution.     

Effect of modifier oxides on absorption and emission properties of Eu doped different lithium fluoroborate glass matrices

Eu³⁺ doped lithium fluoroborate glass with different modifier oxides (Li₂B₄O₇–BaF₂–NaF–MO where M=Mg, Ca, Cd and Pb) and combinations of modifier oxides (Li₂B₄O₇–BaF₂–NaF–MgO+CaO, Li₂B₄O₇–BaF₂–NaF–CdO+PbO) were prepared by means of melt quenching method. These glass samples were analyzed by absorption, photoluminescence and decay curve measurements. The relative merits of thermal correction to the spectral intensities originating from the ground state (⁷F₀) of different absorption bands of Eu³⁺ are calculated. From the optical absorption measurements and using the Judd–Ofelt (J–O) theory, J–O parameters (Ω_λλ=2, 4 and 6) have been obtained which are used to predict the radiative properties such as radiative transition probabilities (A), radiative life-times (τ_R), and branching ratios (β_r) for certain transitions in all the glass matrices. From the emission spectra, peak stimulated emission cross-sections (σ_P) are obtained for the emission transitions, ⁵D₀→⁷F₁, ⁵D₀→⁷F₂, ⁵D₀→⁷F₃ and ⁵D₀→⁷F₄ of Eu³⁺ in lithium fluoroborate glass matrix with different modifier oxides. The fluorescence decay curves of the ⁵D₀→⁷F₂ transition have been measured and analyzed for all the glass matrices.     

Raman scattering in Li2B4O7 crystals with impurities

Raman spectra of an Li₂B₄O₇ crystal containing potassium and silver impurity ions with a concentration in a range of 0.1–0.2% were studied in detail. In the scattering geometries corresponding to manifestation of totally symmetric polar vibrations, the redistribution of spectral intensity for some lines in a region of 450–570 cm^?1 was observed. Using the model of weakly interacting oscillators, parameters of vibrations in this region were determined. On the basis of present-day concepts of the theory of light scattering by impurities, the position of impurity ions in a crystal lattice is discussed.