Lanthanum Aluminosilicate Glasses Research Articles

Broadband near-infrared emission in barium gallo-germanate glasses co-doped with bismuth, chromium and erbium ions

This work presents barium gallo-germanate glasses co-doped with Bi+/Er3+ and Cr3+/Er3+ ions for NIR luminescence. The addition of Al2O3 content in the glass matrix made it possible to obtain luminescence corresponding to the 3P1→3P0 transition of Bi+ ions. Co-doping with the Bi+/Er3+ system resulted in a broad luminescence spectrum of 1.0-1.6 µm and Cr3+/Er3+ co-doping in selected glass matrix resulted in luminescence in 0.9-1.6 µm band. However, the luminescence of the Cr3+ ions is much lower than that of Er3+ ions. Full Text: PDF References T. Suzuki, G.S. Murugan, and Y. Ohishi, 'Optical properties of transparent Li2O-Ga2O3-SiO2 glass-ceramics embedding Ni-doped nanocrystals', Appl. Phys. Lett., 86(13), 131903 (2005). CrossRef N.V. Golubev et al., 'Pre-crystallization heat treatment and infrared luminescence enhancement in Ni2+-doped transparent glass-ceramics', J. Non-Cryst. Solids, 515, 42 (2019) CrossRef Z. Xu, W. Feng, T. Chen, X. Liu, and J. Qiu, 'Tuning optical properties in PbSe quantum dot-doped borosilicate glass fiber by modulation of network topology', Opt. Laser Technol., 158, 108910 (2023). CrossRef M.A. Hughes, T. Suzuki, and Y. Ohishi, 'Spectroscopy of bismuth-doped lead-aluminum-germanate glass and yttrium-aluminum-silicate glass', J. Non-Cryst. Solids, 356(44), 2302 (2010). CrossRef J. Song, Z. Zhou, B. Zhong, M. Zhang, J. Huang, and L. Han, 'Ultra-broadband near-infrared Cr3+-doped multi-phase glass-ceramics realized by the selective enrichment strategy for near-infrared spectroscopy applications', J. Alloys Compd., 968, 172126 (2023). CrossRef M.A.U. Martines, M.R. Davolos, M.J. Júnior, D.F. de Souza, and L.A.O. Nunes, 'Cr3+ and Cr4+ luminescence in glass ceramic silica', J. Lumin., 128(11), 1787 (2008). CrossRef S. Zhou, H. Dong, H. Zeng, J. Hao, J. Chen, and J. Qiu, 'Infrared luminescence and amplification properties of Bi-doped GeO2−Ga2O3−Al2O3 glasses', J. Appl. Phys., 103(10), 103532 (2008). CrossRef T. Suzuki and Y. Ohishi, 'Ultrabroadband near-infrared emission from Bi-doped Li2O-Al2O3-SiO2 glass', Appl. Phys. Lett., 88(19), 191912 (2006). CrossRef T. Minh Hau et al., 'Super broadband near-infrared emission and energy transfer in Bi-Er co-doped lanthanum aluminosilicate glasses', Opt. Mater., 35(3), 487 (2013). CrossRef H.K. Dan et al., 'Effects of Y3+on the enhancement NIR emission of Bi+-Er3+ co-doped in transparent silicate glass-ceramics for Erbium-doped fiber amplifier (EDFA)', J. Lumin., 219, 116942 (2020). CrossRef E.M. Dianov, 'Bismuth-doped optical fibers: a challenging active medium for near-IR lasers and optical amplifiers', Light Sci. Appl., 1(5) (2012). CrossRef L. Wang, L. Tan, Y. Yue, M. Peng, and J. Qiu, 'Efficient Enhancement of Bismuth NIR Luminescence by Aluminum and Its Mechanism in Bismuth‐Doped Germanate Laser Glass', J. Am. Ceram. Soc., 99(6), 2071 (2016). CrossRef Z. Jiang et al., 'Effects of Al2O3 composition on the near-infrared emission in Bi-doped and Yb-Bi-codoped silicate glasses for broadband optical amplification', J. Non-Cryst. Solids, 383, 196 (2014). CrossRef

Preparation and optical properties of thulium doped lanthanum aluminum silicate glass photonic crystal fiber

Lanthanum aluminum silicate glass has excellent optical properties, such as high solubility of rare earth ions, good thermal stability, and excellent physicochemical properties. Some of its physicochemical properties are similar to those of silica glass, so it is easy to combine with silica glass to fabricate special optical fibers. It is considered to be an ideal laser glass matrix material. In this paper, a series of Tm<sup>3+</sup> doped lanthanum aluminum silicate glasses with different concentrations for <i>x</i>Tm<sub>2</sub>O<sub>3</sub>-(70–<i>x</i>)SiO<sub>2</sub>-21Al<sub>2</sub>O<sub>3</sub>-9La<sub>2</sub>O<sub>3</sub> (<i>x</i> = 0.2%, 0.4%, 0.6%, 0.8%, 1%, mole fraction) are successfully developed by the traditional high-temperature melting method. Using thulium-doped lanthanum aluminum silicate glass as the fiber core, thulium-doped double-cladding photonic crystal optical fibers are prepared by the stack-and-draw technique and rod in tube method. The core diameter of the thulium-doped lanthanum aluminosilicate glass double-clad photonic crystal fiber is as long as 21.7 μm, the inner cladding diameter is about 119.3 μm, and the outer diameter is about 236.8 μm. The optical properties of thulium-doped lanthanum aluminum silicate glass and its optical fiber are studied experimentally. Under the excitation of a 793 nm laser, the fluorescence bandwidth of thulium-doped lanthanum aluminum silicate glass reaches 223 nm in a wavelength range of 1550–2050 nm. The fiber laser constructed with thulium-doped lanthanum alumino-silicate glass fiber achieves a laser operating at around 2 μm. The fiber laser resonant cavity consists of a pair of dichroic mirrors. The front dichroic mirror has high transmittance for light at 793 nm and high reflectivity (99.9%) for the light within a wavelength range of 1850–2050 nm. The back dichroic mirror has high reflectivity (99.9%) for light at 793 nm and high transmittance (~ 15%) at 2050 nm. Under the experimental conditions in our laboratory, the laser power reaches 253 mW. The highest slope efficiency is 9.67%, which is close to that of the thulium-doped glass fiber laser reported in the literature. It is also found that the central wavelength of fiber laser is shifted toward the longer wavelength with the increase of the optical fiber's length. These results suggest that thulium-doped lanthanum aluminum silicate glass and thulium-doped photonic crystal fiber are suitable for 2-μm fiber laser.

Fabrication and optical properties of Tm3+/Ho3+ co-doped lanthanum aluminosilicate photonic crystal fiber for 2 μm fiber lasers

In this study, the Tm3+/Ho3+ co-doped lanthanum aluminosilicate glass was prepared using the melt-quenching method. The absorption and emission properties of glass were studied. A Tm3+/Ho3+ co-doped lanthanum aluminosilicate photonic crystal fiber (PCF) was fabricated using the stacking and drawing method. The PCF structure effectively enhanced the laser performance and generated laser emission centered at 2051 nm. The max output power of the PCF laser was 256 mW under existing conditions and the optical-to-optical efficiency was 6.37%. In addition, the broadband luminescence characteristics strongly influenced by the length of fibers were presented. The results indicated that the Tm3+/Ho3+ co-doped lanthanum aluminosilicate PCF could be potentially used for 2 μm fiber lasers and amplifiers.

Influences of copper-potassium ion exchange process on the optical bandgaps and spectroscopic properties of Cr3+/Yb3+ co-doped in lanthanum aluminosilicate glasses.

In this study, lanthanum aluminosilicate glasses with compositions of 45SiO2–20Al2O3–12.5LaF3–10BaF2–9K2O–1Cr2O3–2.5Yb2O3 (SALBK) were prepared using the conventional melting method and copper–potassium ion exchange process. Influences of the ion exchange process between copper and potassium on the visible, upconversion, and near-infrared luminescence spectra of Cr3+/Yb3+ co-doped under excitations of 343, 490, and 980 nm LD were investigated. The EDS analysis of SALBK glasses was measured to confirm the presence of atoms in the glasses. The values of direct and indirect bandgaps of Cr3+/Yb3+ co-doped SALBK glasses were calculated and analyzed. Besides, the energy exchange processes between Cu+, Cu2+ ions, and Cr3+, Yb3+ ions were also proposed and discussed.

Femtosecond Laser Pulse-Induced Structural Modification of Lanthanum Aluminosilicate Glasses: Refractive Indices in Visible Vs. Terahertz Frequency Regions

We studied femtosecond laser modifications of lanthanum aluminosilicate (SAL) glasses with 11–23 mol% La2O3 content. Refractive indices of these glasses were measured in the visible and terahertz frequencies and correlated to the change in the glass structure. The role of lanthanum provided a comparison to traditional glass modifiers within the glass network in terms of polarizability and optical basicity for femtosecond laser irradiation modification of the refractive index. 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) was used to identify aluminum speciation within the SAL glasses. We used prism-coupling and terahertz time-domain spectroscopy (THz-TDS) for visible and THz refractive index measurements, respectively. Our results show a linear correlation between refractive index measurements in visible and terahertz frequencies with systematic rare-earth ion inclusions. In addition, our results demonstrate that THz-TDS can be utilized as a means of extending the detectable limits in refractive index measurements of disordered glass structures.

Effects of Al3+/La3+ ratio on the DSC/DTA and luminescence properties of Bi-doped lanthanum aluminosilicate glasses

The Bi-doped in 55SiO2–xAl2O3–(40–x) La2O3–5TiO2–1Bi2O3 (x = 10, 15, 20, 25, 30, 32 and 35) lanthanum aluminosilicate glasses were fabricated by conventional melting-quenching technique. Effects of Al3+/La3+ ratio on the Differential scanning calorimetry/Differential thermal analysis (DSC/DTA) and luminescence properties of Bi-doped in SiO2–Al2O3–La2O3–TiO2 lanthanum aluminosilicate glasses was investigated. The Fourier transform infrared (FTIR) spectroscopy has also been investigated for structural analysis of the glasses. Near-infrared (NIR) emissions spectra of Bi-doped peaks exist at ~1120 and 1275 nm have originated from Bi0 and Bi+ ions, respectively, with the full-width at half-maximum (FWHM) lager than 250 nm was strongly observed. The visible luminescence of Bi-doped bands centered at ~430 and 660 nm arises from Bi3+ and Bi+ ions respectively were also observed. The emissions intensity of Bi-doped bands centered at ~660, 1120 and 1275 nm were significantly increased with the increasing of Al3+/La3+ ratio from 1:3 up to 3:1 ratio. Simultaneously, the visible emission intensity of Bi-doped band centered at 430 nm was decreased with the increasing of Al2O3 concentration.

Deconvolution method of 29Si MAS NMR spectra applied to homogeneous and phase separated lanthanum aluminosilicate glasses

The structural and microstructural properties of both homogeneous and phase separated lanthanum aluminosilicate (La2O3-Al2O3-SiO2 i.e. LaAS system) glasses were investigated. The microstructural observations and the structural characterization by X-ray Diffraction and by Nuclear Magnetic Resonance have highlighted the role of aluminum to favor a homogeneous vitreous aluminosilicate network by a high-level of Al/Si intermixing. A qualitative and simplified structure description is proposed from 29Si nuclear magnetic resonance spectra assignment according to Qn(mAl) species by controlling the deviation of chemical parameters. According to this approach, a homogeneous distribution of non-bridging oxygen in the aluminosilicate network and Al-O-Al linkages are considered for homogeneous glasses with high Al/Si atomic ratio. Phase separated samples are characterized by a low Al/Si atomic ratio inducing spinodal or nucleation/growth phase separation according to the depolymerization level. Homogeneity degree of the samples is discussed according to the intermixing level between silicon tetrahedra and aluminum polyhedra as a function of the proportion of Qn and Qn(mAl) species.

Distribution and stabilization of bismuth NIR centers in Bi-doped aluminosilicate laser glasses by managing glass network structure

Bismuth NIR emission centers can be stabilized or destabilized by a local excess charge model, and their emissions can be enhanced within lanthanum aluminosilicate glasses by managing the glass structure.

Mechanism of cluster dissolution of Yb-doped high-silica lanthanum aluminosilicate glass: Investigation by spectroscopic and structural characterization

To investigate clusters of Yb ions and the effectiveness of lanthanum co-doping in dispersing and isolating Yb ions in silica glass, Yb-doped high-silica lanthanum aluminosilicate (LAS) glass with compositions Yb2O3Al2O3La2O3SiO2 was prepared by the sol–gel method combined with high temperature sintering. The glass structure and spectroscopic properties of Yb-doped high-silica LAS glass were studied in detail to explore the mechanism of cluster dissolution. 27Al and 29Si solid-state nuclear magnetic resonance (SSNMR) spectra were introduced to study the spatial distribution of the Yb ions in the glass. The spinning sideband patterns of the 27Al and 29Si NMR spectra showed that part of the Yb3+ ions in the vicinity of aluminium atoms transferred to Si ions with increasing La2O3 concentration. The results of two-dimensional hyperfine sublevel correlation (2D-HYSCORE) electron paramagnetic resonance (EPR) spectroscopy led to the conclusion that the vicinity of Yb3+ ions are mostly aluminum atoms for glass doped with Al and aluminum and silicon atoms for glass co-doped with Al and La. It was also found that Yb clusters exist in the form of YbOYb bonds in high-concentration Yb-doped silica glass and that co-doping with La can replace these bonds with YbOLa linkages to reduce the number of Yb3+ pairs. The fluorescence intensity and fluorescence lifetime of Yb increase steadily with increasing La2O3 concentration, which also indicates that the addition of La in silica glass can dissolve the Yb clusters. The results show that co-doping high-silica LAS glasses with La3+ ions is an ideal way to increase Yb solubility and decrease clustering.

Influence of La/Al ratio on the structure and spectroscopy of Tm3+ doped Al2O3[sbnd]La2O3[sbnd]SiO2 glasses

Lanthanum aluminosilicate (LAS) glasses with compositions (Tm2O3)0.8-(Al2O3)12-x (La2O3)x-(SiO2)87.2 (x = 0, 1.2, 4.5 mol%; La/Al = 0, 1/9, 3/5) were prepared via a sol–gel method combined with high temperature sintering. The total amount of Al2O3 and La2O3 was 12 mol%. The effect of the La/Al ratio on the structure and spectroscopic properties of Tm3+ has been studied in detail. The structure of Tm3+ doped LAS glasses was studied via 27Al nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The spinning sideband patterns of the 27Al NMR spectra showed that the population of Tm3+ ions in the vicinity of Al3+ decreased with an increase in the La2O3 concentration. FTIR and Raman spectra suggest that glasses with high La/Al ratios have less interconnected glass networks. The spectroscopic properties of Tm3+ ions were investigated via the Judd–Ofelt method using the measurement of absorption and emission spectra. Both the 1.8 μm fluorescence intensity and the relative intensity of up-conversion emission of Tm3+ ions decrease with an increase in the La/Al ratio. This indicates reduced cross relaxation between Tm3+ ions in glass with a high La/Al ratio. We conclude that the spatial distribution homogeneity of Tm3+ ions in LAS glass improves when the La/Al ratio increases.

Quenching behavior of Sm3+ doped lanthanum aluminosilicate glasses

In this paper we report on the fluorescence quenching behavior of Sm3+ doped lanthanum alumino silicate glasses in dependence of the Sm3+ concentration and chemical composition of the glasses. In general, lanthanum alumino silicate glasses offer relatively low intrinsic Sm3+ fluorescence lifetimes between 2.3 and 2.7ms. Independently on the doping concentration, the lifetime decreases with increasing refractive index and increasing lanthanum concentration of the glasses. For a low doping concentration of 0.1×1020 Sm3+ per cm3 (approx. 0.025mol% Sm2O3) the measured fluorescence lifetimes are very close to the radiative lifetimes which were calculated using the Judd–Ofelt analyses. For higher doping concentrations, such as 1×1020 and 3×1020 Sm3+ per cm3, concentration quenching becomes obvious. For these higher concentrations, the non-radiative relaxation of the excited state can be seen as a mixture of cross-relaxation processes and OH− quenching. Both processes mainly occur at higher concentrations and do not influence the fluorescence decay at low Sm3+ concentrations. By contrast, the maximum phonon energy of the glass network does not affect the radiative relaxation of Sm3+ at all.

Judd–Ofelt analysis of Sm3+-doped lanthanum-aluminosilicate glasses

In this paper we report on the Judd–Ofelt analysis of Sm3+-doped lanthanum aluminosilicate glasses. The Judd–Ofelt calculations were done using two different least-squares fitting procedures (absolute and normalized) and two different cavity models (virtual and empty cavity model). It is shown that the absolute least-squares fitting procedure for the reported glasses yields physically more reliable results for the radiative lifetimes and branching ratios of the 4G(4)5/2 emission of Sm3+ than the normalized fitting method. The Ω2 parameters decrease with increasing lanthanum concentration of the glasses indicating an effect of the glass structure (network connectivity) on hypersensitive transitions in Sm3+. For the Ω4 and Ω6 parameters a clear correlation to the glass composition was not found.

Super broadband near-infrared emission and energy transfer in Bi–Er co-doped lanthanum aluminosilicate glasses

The Bi–Er co-doped lanthanum aluminosilicate glasses, which exhibited a broadband near-infrared emission, were developed and observed in using the optical absorption and photoluminescence spectra. A super broadband near-infrared emission extending from 1.0 to 1.8μm with a full-width at half-maximum of 450nm which covered the whole O, E, S, C and L bands, was observed in Bi–Er co-doped samples under 808nm excitation, as a result of the overlap of the Bi-related emission band (1270nm) and the emission from Er3+4I13/2→4I15/2 transition (1545nm). This report will discuss about a possible mechanism for energy transfer between Bi-related centers and Er3+ ion.

Near-infrared broadband luminescence and energy transfer in Bi–Tm–Er co-doped lanthanum aluminosilicate glasses

The Bi–Tm–Er co-doped SiO2–Al2O3–La2O3 (SAL) glasses, which exhibited a broadband near-infrared (NIR) emission, were investigated by the optical absorption and photoluminescence spectra. A super broadband NIR emission extending from 0.95 to 1.6μm with a full-width at half-maximum (FWHM) of 430nm which covered the whole O, E, S, C and L bands, was observed in Bi–Tm–Er co-doped samples under 808nm excitation, as a result of the overlap of the Bi-related emission band (centered at 1270nm) and the emission from Tm3+3H4→3F4 transition (1450nm) as well as Er3+4I13/2→4I15/2 transition (1545nm). In addition, a super broadband emission with amplitude relatively flat from 0.95 to 2.1μm has been observed. The possible energy transfer between Bi-related centers, Tm3+ ions and Er3+ ions was proposed.

Dependence of spectroscopic properties on doping content and temperature of bismuth-doped lanthanum aluminosilicate glass

The effects of bismuth doping content and temperature on the absorption property and near-infrared (NIR) luminescence of Bi-doped La2O3-Al2O3-SiO2 (LAS) glasses are presented. The emission intensity reaches the maximum when the Bi2O3 content in 3.0Bi-LAS is 1.83%. The emission spectra reach their peaks at 1 190 and 1 117 nm, with full-width at half-maximum (FWHM) values of 330 and 228 nm under 500 and 700-nm excitations, respectively. As the Bi2O3 content increases, the peak wavelengths and FWHMs of emission bands increase, but their lifetimes decrease. The lifetime of 2.0Bi-LAS is 460 ?s at 9 K, and is almost temperature independent until 350 K. The NIR emission of Bi in the system has strong resistance to thermal quenching from 9 to 350 K.

Structural characterization of lanthanum aluminosilicate glasses by 29Si solid-state NMR

We investigate the network structures of La Si Al O glasses by 29Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR). Their compositions span most of the glass-forming region of the ternary La 2O 3 Al 2O 3 SiO 2 system at 1600 °C. The 29Si NMR resonances narrow and become progressively deshielded when Al substitutes for Si in the network, as well as for increasing La-content of the glass, which leads to network depolymerization. We compare experimental and calculated center of gravities of the 29Si NMR peaks, the latter generated from different simplified models for the distributions of Al and Si as well as bridging oxygen (BO) and non-bridging oxygen (NBO) atoms over the networks. The data do not permit accurate quantifications and may only be interpreted in limiting scenarios. However, they indicate that both distributions are essentially randomized, implying a clear deviation of the Al/Si ordering from that according to a Loewenstein Al-avoidance, coupled with a nearly uniform partitioning of the NBO atoms between Al and Si tetrahedra.

Caracterização micrográfica de próteses dentais de alumina infiltrada com vidro de lantânio e sua correlação com a resistência à flexão por três pontos

Estudou-se a infiltração (em diferentes condições) do vidro de lantânio em alumina parcialmente sinterizada e a sua relação com a resistência à flexão. As barras de In-Ceram Alumina, fraturadas em flexão por 3 pontos, foram lixadas, polidas e caracterizadas por microscopias ótica e eletrônica de varredura (MEV). Foram usadas 10 barras para cada condição operacional. Resultados: (a) A MEV confirma que os núcleos de barras In-Ceram Alumina (sinterizados a 1120ºC durante 2h) infiltrados a 1100ºC durante 6h contém menos vidro de lantânio do que aqueles das barras infiltradas durante 6h a 1110ºC; (b) A micrografia ótica confirma que os núcleos de barras In-Ceram Alumina (sinterizada a 1120ºC durante 2h) infiltrada durante 6h (ou 2h) nas temperaturas de 1100ºC, 1100ºC, 1120ºC e 1130ºC não se diferem notavelmente; (c) A MEV mostra que a microestrutura interna de barras In-Ceram Alumina infiltradas com vidro de lantânio a 1120ºC e 1130ºC é complexa.

Caracterização micrográfica de barras de ZTA infiltradas com vidro de lantânio e sua correlação com resistência à flexão por três pontos

Após a sua fratura em ensaio de flexão por três pontos, barras de In-Ceram®ZTA foram lixadas e polidas e , por microscopia eletrônica de varredura (MEV), foram avaliadas as quantidades relativas de fases que elas continham. Foram usadas 10 barras de 25,0 mm x 4 mm para cada uma das seguintes espessuras: 1,0 mm, 2,0 mm e 3,0 mm. Resultados: (a) Barras de In-Ceram®ZTA de 3mm de espessura não conseguem alcançar uma completa infiltração de vidro de alumino-silicato de lantânio até o seu núcleo, nas condições operacionais recomendadas pelo fabricante (b) A MEV com elétrons retro-espalhados é de fato uma técnica adequada para o estudo da infiltração do vidro de lantânio em barras In-Ceram®ZTA.

Spectroscopic Properties of Er3+‐Doped Na2O–La2O3–Al2O3–SiO2 Glasses

Er3+‐doped sodium lanthanum aluminosilicate glasses with compositions of (90−x)(0.7SiO2·0.3Al2O3)·xNa2O·8.2La2O3· 0.6Er2O3·0.2Yb2O3·1Sb2O3 (in mol%) (x= 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ωt (t= 2, 4, 6) decreases with increasing Na2O. Ω2 decreases rapidly with increasing Na2O while Ω4 and Ω6 decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na2O. Fluorescence spectra of the 4I13/2 to 4I15/2 transition have been measured and the change with Na2O content is discussed. It is found that the full width at half‐maximum decreases with increasing Na2O.

Correlation between Thermal Expansion Coefficients of La<sub>2</sub>O<sub>3</sub>-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> Glasses and Strength of the Glass Infiltrated Alumina for all Ceramic Crown

16 different lanthanum-aluminosilicate glasses were prepared to evaluate the effect of alkalis (Na2O, K2O) and alkaline earths (MgO, CaO) on thermal expansion coefficients (CTEs) of the glasses. Analysis was performed with an aid of the Taguchi method and orthogonal arrays to elucidate four factor interactions between 4 two-level factors using two level L16(215) orthogonal arrays. The observed CTEs were in the range of 6.29×10-6 C-1 to 8.22×10-6 C-1. The addition of alkalis was more influential to CTE of the glass than that of alkaline earth, however, co-addition of the mixed alkalis was detrimental to CTEs of the glasses due to the crystallization caused by the mixed alkali effect. However, the highest strength of the glass infiltrated alumina composite was observed at a CTE of 6.4×10-6 C-1 due to the compressive stress caused by the thermal mismatch, indicating that CTE difference between the glass and the alumina should be above 1.0×10-6 C-1.