Li2B4O7 Glasses Research Articles

Spectroscopy of the CaB4O7 and LiCaBO3 glasses, doped with terbium and dysprosium

A series of borate glasses of high optical quality with CaB4O7:Tb, LiCaBO3:Tb, CaB4O7:Dy, and LiCaBO3:Dy compositions containing 0.5 and 1.0mol% Tb2O3 and Dy2O3 impurity compounds were obtained from corresponding polycrystalline compounds using standard glass technology. By electron paramagnetic resonance (EPR) and optical spectroscopy it was shown that the Tb and Dy impurities are incorporated as Tb3+ (4f8, 7F6) and Dy3+ (4f9, 6H15/2) ions in the Ca and Li(Ca) sites of CaB4O7 and LiCaBO3 glasses network, respectively. The luminescence excitation and emission spectra as well as luminescence kinetics of the Tb3+ and Dy3+ centres in the CaB4O7 and LiCaBO3 glasses have been investigated and analysed in comparison with obtained earlier results for Tb3+ and Dy3+ centres in the Li2B4O7 glasses. All observed f–f transitions of the Tb3+ and Dy3+ centres in the luminescence excitation and emission spectra have been identified. Luminescence kinetics show single exponential decay for Tb3+ and Dy3+ centres in the CaB4O7 and LiCaBO3 glass network. The lifetime values for the main emitting levels of the Tb3+ and Dy3+ centres in all investigated glasses were determined at room temperature and their dependencies on the basic glass compositions and impurity concentrations are discussed. The obtained results show that the CaB4O7 and LiCaBO3 glasses are promising luminescent materials, operating in green and yellow–blue spectral regions, when activated with Tb3+ and Dy3+ ions, respectively.

Effect of γ-irradiation on optical absorption of Al2O3–TeO2–Li2B4O7 glasses doped with MgF2

The effect of γ-radiation on the optical properties of the glassy system [xMgF2–10Al2O3-(40-x) TeO2–50Li2B4O7], (x=0, 15, 20 and 40mol%) has been investigated. Samples were prepared by conventional melt-quench technique. The density and molar volume were estimated and found to decrease with increasing MgF2 concentration. The obtained data indicate that the glass structure becomes less tightly packed with increasing the MgF2 concentration. The effect of γ-irradiation (5, 20, 40 and 70kGy) on optical absorption has been studied. It was observed that γ-radiation enhances the formation of NBOs. This leads to a decrease in the optical band gap energy. Radiation induced changes include hole trapping by bridging oxygen causing the increase of B–O bond length.

Optical harmonic transformations in borate glasses with Li2B4O7, LiKB4O7, CaB4O7, and LiCaBO3 compositions

A series of un-doped borate glasses with Li2B4O7, LiKB4O7, CaB4O7, and LiCaBO3 compositions of high optical quality and chemical purity were obtained from corresponding polycrystalline compounds using standard glass synthesis and technological conditions developed by authors. The optically thermopoled second harmonic generation (SHG) effect in the Li2B4O7, LiKB4O7, CaB4O7, and LiCaBO3 glasses were investigated and analyzed.

Kinetics of non-isothermal crystallization process in various sized Li2B4O7 glasses

We report the size dependence kinetics for non-isothermal processes of crystallization in lithium tetraborate (Li 2 B 4 O 7 :LBO) glass. We performed X-ray and the non-isothermal differential scanning calorimetry (DSC) measurements of the LBO glass particles for a couple of samples sized <63 and 180–212 μm. The activation energies for crystallization are obtained 5.4 eV for the <63 μm glass and 4.3 eV for the 180–212 μm glass, respectively. The surface tension energy may be dominant in determining the activation energy in the LBO glass system.

Charge transport in Li2B4O7 in single crystal and glassy states

The electrophysical properties of Li2B4O7 single crystals and glasses are studied in the temperature range 290–1100 K and the frequency range 1–1000 kHz. The strong frequency dispersion of ionic conductivity at temperatures close to room temperature is explained by the low-frequency hoppings of lithium ions from the basic to the interstitial positions. The dielectric relaxation accompanying the transport of lithium ions is analyzed within the framework of the Debye-Skanavi model. The minimum hopping length of Li+ ions and the height of the potential barrier between their closest positions are determined. The parameters obtained are compared with the known structural data.

Valency states of Yb, Eu, Dy and Ti ions in Li2B4O7 glasses

Abstract Absorption and emission spectra of Eu and Dy, Yb and Ti ions in Li2B4O7 glasses grown in oxygen and hydrogen gas atmospheres were measured for valency states and lattice-sites analysis. For the Li2B4O7 glass doped with Eu2+, Eu3+ and Dy3+ ions which were grown in oxidizing and reducing atmospheres, absorption and emission bands due to these ions were investigated before and after γ-irradiation. For the Yb3+-doped Li2B4O7 glass, a weak, broad band was observed near the sharp 976.3 nm absorption band. The origin of this band is discussed in comparison with other glasses. Moreover, irradiation experiments using γ-rays were also performed in order to investigate the possibility of valency change of Yb ions. It was found that Ti4+ ions, which are produced under oxidizing atmosphere, change to Ti3+ ions after γ-irradiation with a dose of 105 Gy. An additional absorption band observed at about ∼500 nm is due to the Ti3+ ions accompanied by charge-compensating vacancy and does not give any emission.

Li2B4O7 glasses doped with Cr, Co, Eu and Dy

Abstract Absorption and emission spectra of Cr, Co, Eu and Dy ions in Li2B4O7 glasses melted in oxygen and hydrogen were measured for valency states analysis. It was stated that the presence of Cr6+ ion is limited by composition of the starting mixture and atmosphere of the melting and that this ion arises as Cr6+O− complex. Independently of the above factors in all the glasses there were present Cr3+ ions. Under γ-irradiation Cr6+–O− complex of 3d0 configuration can be disintegrated giving additional absorption band of Cr3+ and may be Cr4+ and higher valency centers. Corresponding photoluminescence is centered at about 430 nm. Absorption of Li2B4O7:Co glasses obtained in oxygen atmosphere reveals Co2+ and Co3+ ions which does not give any emission in the UV–VIS and near-infrared region of luminescence spectrum. The content and optical characteristics of Eu2+ and Eu3+-doped Li2B4O7 glasses are dependent of the growth atmosphere.