Optical properties of sol-gel fabricated Mn/SiO2 nanocomposites: Observation of surface plasmon resonance in Mn nanoparticles

Manganese nanoparticles were grown in silica glass and silica film on silicon substrate by annealing of the sol-gel prepared porous silicate matrices doped with manganese nitrate. Annealing of doped porous silicate matrices was performed at various conditions that allowed to obtain the nanocomposite glasses with various content of metallic Mn. TEM of Mn/SiO₂ glass indicates the bimodal size distribution of Mn nanoparticles with mean sizes of 10.5 nm and 21 nm. The absorption and photoluminescence spectra of Mn/SiO₂ glasses were measured. In the absorption spectra at 300 nm (4.13 eV) we observed the band attributed to the surface plasmon resonance in Mn nanoparticles. The spectra proved the creation of Mn²⁺ and Mn³⁺ ions in silica glass as well. The absorption spectra of Mn/SiO₂ glasses annealed in air prove the creation of manganese oxide Mn₂O₃. The measured reflection spectra of Mn/SiO₂ film manifest at 240-310 nm the peculiarity attributed to surface plasmons in Mn nanoparticles.     

Nonlinear photoionization and laser-induced damage in silicate glasses by infrared ultrashort laser pulses

We show that photoionization of wide band gap silicate glasses by infrared ultrashort laser pulses can occur without laser-induced damage. Two glasses are studied, fused silica and a multi-component silicate photo-thermo-refractive (PTR) glass. Experiments are performed by low numerical aperture focusing of ultrashort laser pulses (100 fsec<τ<1.5 psec) at the wavelengths 780 nm, 1430 nm, and 1550 nm. Filaments form inside both glasses and are visibly observable due to intrinsic luminescence. Keldysh’s theory of nonlinear photoionization is used to model the formation of filaments and values of about 10¹³ W cm⁻² for the laser intensity and 10¹⁹ cm⁻³ for the free electron density are estimated for stable filaments to arise. Laser-induced damage is studied by the generation of a third harmonic from an interface created between a damage site and the surrounding glass matrix. It is found that third harmonic generation occurs only after several thousands of laser shots indicating that damage is not a single-shot phenomena. The ability to photoionize PTR glass without damage by ultrashort laser pulses offers a new approach for fabricating diffractive optical elements in photosensitive glass.     

Luminescence centers in silicate and germanate glasses activated by bismuth

Concentration series of silicate and germanate glasses activated by bismuth are studied. It is shown that luminescence in the IR region is controlled by several active centers related to bismuth. Based on a comparison of spectroscopic characteristics of the studied glasses with the data previously obtained for chloride glass, the observed centers were identified as Bi⁺, Bi ₂ ⁴⁺ , and Bi ₅ ³⁺ in germanate glass and Bi⁺, Bi ₂ ⁴⁺ in silicate glass.     

Dy3+掺杂硼硅酸盐玻璃的发光特性

采用高温熔融法制备了Dy3+掺杂硼硅酸盐玻璃,通过测试激发光谱和发射光谱,研究了其光谱性质.研究了玻璃组分及Dy3+掺杂浓度对发射光谱及发光强度的影响,并计算了色坐标,均位于白光区域.通过改变玻璃组分及掺杂浓度,调节黄、蓝发射峰的强度比,在387 nm长紫外光激发下实现了单一基质上有效的白光发射.     

The optical properties of thallium,lead and bismuth in oxide glasses

Absorption, fluorescence, excitation and decay time measurements have been made on a range of glasses containing thallium, lead and bismuth. In calcium phosphate and sodium silicate glasses the bands in both absorption and emission have been assigned to the A band of the Seitz model. For the bismuth doped glasses the A band was always observed in absorption but the emission was very dependent upon glass composition. Configurational coordinate curves have been constructed for Tl⁺ and Pb² in a glass of composition CaO. P₂O₅. Coordinate diagrams are also used to explain the presence or absence of bismuth fluorescence in certain glass compositions. In some borate glasses containing bismuth a brown colouration was observed. This was probably due to particle separation. No A band emission was observed from bismuth in a calcium phosphate glass. Instead there was a faint red emission similar to the cathodoluminescent bands of crystalline calcium phosphates.     

高Verdet常数的Tb3+铝硼硅酸盐玻璃

本文研究了一种铝硼硅酸盐基质玻璃,通过加大单位体积的稀土离子浓度,并选择P值大的顺磁性Tb³⁺作为弗尔德常数贡献的主要离子,经反复试验研究,制定合理的熔制工艺,得到性能稳定的透明顺磁旋光玻璃。弗尔德常数V=-0.375/Oe·cm。是目前世界上弗尔德常数较高的磁旋光玻璃。     

Effect of various alkaline-earth metal oxides on the broadband infrared luminescence from bismuth-doped silicate glasses

We report on the effect of various alkaline-earth metal oxides on the broadband infrared luminescence covering 1000-1600 nm wavelength region from bismuth-doped silicate glasses. The full width at half maximum (FWHM) of the infrared luminescence and the fluorescent lifetime is more than 200 nm and 400 μs, respectively. The fluorescent intensity decreases with increasing basicity of host glasses. Besides the broadband infrared luminescence, luminescence centered at 640 nm was also observed, which should be ascribed to Bi²⁺ rather than to the familiar Bi³⁺. We suggest that the infrared luminescence should be assigned to the transition of BiO molecules dispersed in the host glasses.     

Absorption phenomena in multicomponent phosphate glasses with Mn

The absorption and ESR spectra of multicomponent alumino-phosphate glasses doped with manganese (0·2–20 mol %) has been measured and compared with the absorption spectra of manganous and manganic ions in model solutions. The unirradiated glasses show in ultraviolet region increasing absorption below 200 nm with the shoulder at 235 nm and the absorption bands due to manganous oxygen complexes in octahedral symmetry. They are similar to the absorption bands of Mn²⁺ in concentrated H₃PO₄ acid. In irradiated glasses the bands at 200, 235, 275 (only if Mn is present) and a broad band at 540 nm appear. After the annealing at 450 C all radiation-induced bands disappear and the bands at 235 nm is more pronounced. The Mn³⁺ in H₃PO₄ solution exhibit the absorption spectrum with a weak band at 530 nm and a very intense band at 270 nm. It is therefore proposed that both the 540 and 275 nm bands in irradiated glasses can be assigned to octahedral oxygen complexes of Mn³⁺, i.e. to hole centres. The band at 200 nm which is practically independent of the modifiers (Be, Mg, Ca, Sr and Ba) is, therefore, associated with electron centres (electrons trapped in non-bridging oxygen vacancies). It is suggested that the band at 235 nm in irradiated and annealed glasses is associated with irreversible structural changes.The authors wish to express their appreciation to H.Dvoáková for preparing the solutions and E.Linhartová for careful measurements.     

Saturated absorption and nonlinear refraction of silicate glasses doped with silver nanoparticles at 532 nm

The nonlinear optical characteristics of silicate glasses doped with silver nanoparticles are investigated by Z-scan technique using second harmonic radiation of picosecond Nd:YAG laser (=532 nm, =55 ps). The real and imaginary parts of third-order nonlinear susceptibility of silver-contained glasses were measured. It was found that the sign of Im ⁽³⁾was negative due to saturated absorption and the sign of Re ⁽³⁾ was changed from negative (self-defocusing) to positive (self-focusing) with growth of laser radiation intensity. The mechanisms responsible for saturated absorption and nonlinear refraction are discussed.     

Optical properties of sol-gel fabricated Ni/SiO2 glass nanocomposites

Nickel nanoparticles were grown in silica glass by annealing of the sol-gel prepared silicate matrices doped with nickel nitrate. TEM characterization of Ni/SiO₂ glass proves the formation of isolated spherical nickel nanoparticles with mean sizes 6.7 and 20 nm depending on annealing conditions. The absorption and photoluminescence spectra of Ni/SiO₂ glasses were measured. In the absorption spectra, we observed the band related to the surface plasmon resonance (SPR) in Ni nanoparticles. The broadening of SPR was observed with decrease of Ni nanoparticle size. The width of the surface plasmon band decreases 1.5 times at the lowering of temperature from 293 to 2 K because of strong electron-phonon interaction. The spectra proved the creation of nickel oxide NiO clusters and Ni²⁺ ions in silica glass as well.     

Infrared spectroscopy on lead silicate glass

The reflectance spectra of some lead silicate glasses of general formula (PbO)_x(SiO₂)_y have been measured in the infrared frequency range from 50 to 4000 cm^–1. The dispersion and absorption spectra in the range 50–2000 cm^–1 have been calculated from the reflectance data using the Kramers-Kronig relations. The band at 135 cm^–1 is assigned to the stretching vibration of lead-oxygen bonds. The shoulder band of the silicon-oxygen stretching mode at 900 cm^–1 shows a weak coupling of those bonds to the Pb²⁺ modifier. The vibration strength of those bands shows that the number of the Pb²⁺ modifier increases first up approximately to 50 Mol% with the increase of PbO content and then decreases rapidly. It indicates that different PbO content causes different structural forms in lead silicate glasses: The addition of small amounts of PbO to vitreous silica serves to modify the continuous three-dimensional silica network: whereas in those glasses with a high lead content, the influence of the cation, Pb²⁺, appears to lie between that of network former and network modifier. This result is in agreement with the structural model of Worrel and Henshall.     

Laser emission at 1077 nm in Nd3+-doped calcium aluminosilicate glass

Laser emission at 1077 nm (⁴F_3/2⁴I_11/2) was demonstrated in Nd³⁺-doped low silica content calcium aluminosilicate (LSCA) glass under 810-nm pumping by a Ti:sapphire laser. The slope efficiency of the laser emission was found to be 34% with a 20-mW threshold power. The excited-state absorption (ESA) and stimulated emission were measured between 850 and 1520 nm. The results showed two ESA bands from 931 to 1070 nm (⁴F_3/2²D_3/2,²G_9/2,⁴G_11/2,²K_15/2) and from 1160 to 1414 nm (⁴F_3/2,⁴G_9/2⁴G_7/2,²K_13/2). The stimulated emission for the laser transition was found to be 45-nm broad with a peak value of 1.8×10^-20 cm². Thermal and mechanical properties of the LSCA glass were compared to the ED-2 and LHG-8 glasses. While the mechanical properties of the LSCA glass are superior to those of the commercial glasses, its temperature coefficient of optical path length is the highest among the three hosts. PACS 42.60.Pk; 42.70.Ce; 78.66.Jg     

Far infrared sub-nanosecond pulse generation in GaP with a time-synchronized mode-locked double-frequency Nd: Glass laser system

Light pulses of 149 m wavelength and 700 ps duration are generated by non-collinear phase-matched difference frequency mixing of laser pulses at 1053.5 and 1061 nm in a (110) cut GaP crystal. The pump laser pulses are generated in a time-synchronized mode-locked double-frequency Nd:glass laser system consisting of a silicate glass branch and a phosphate glass branch. A photon conversion efficiency of 4 × 10^–6 is achieved. The non-linear susceptibility constant of GaP is determined to be d ₁₄ = (10 ± 1) pm V^–1.     

Luminescent properties of erbium-activated glasses

The spectra, intensity, and duration of trivalent erbium luminescence in a large number of inorganic glasses of various compositions were investigated. The observed absorption and luminescence bands were attributed to transitions between certain^sL_j levels of the Er³⁺ ion. It is shown that in all cases the principal portion of the luminescence yield was associated with the⁴I_13/2 ⁴I_15/2 transition band with _max = 6500 cm^–1. The effects of glass composition, activator concentration, and temperature on the yield and duration of luminescence in the 6500 cm^–1 band were studied. An investigation of the effect of temperature on the structure of this band was used to construct a diagram of the crystalline splitting of the⁴I_13/2 and⁴I_15/2 levels in glass.     

Solid-state NMR study of bioactive binary borosilicate glasses

A series of binary borosilicate glasses prepared by the sol-gel method are shown to be bioactive. Tetraethyl orthosilicate (TEOS) and trimethylborate (TMB) in acidic medium are used to prepare xB₂O₃·(1−x)SiO₂ glass systems for x=0.045-0.167. The formation of a layer of apatite-like mineral on the glass surface becomes apparent after soaking in simulated body fluid for 48 h. We have measured the ¹¹B-¹¹B homonuclear second moments of the borosilicate glasses and inferred that no macroscopic phase separation occurred in our glasses. The ¹¹B chemical shift data also show that the formation of clustered boroxol rings is negligible in our glass system. Although the bioactivity of our borosilicate glasses is less than that of CaO-SiO₂ sol-gel glasses, these simple binary systems could be taken as reference glass systems for the search of new bioactive borosilicate glasses.     

Structural study of Mg‐bearing sodosilicate glasses by Raman spectroscopy

The presence of magnesium in glasses of geological, medical, and technological interests influences their physicochemical and durability properties. However, the understanding of the role of magnesium is dependent on the combined knowledge of the structural environment of magnesium in the glass or melt and of the silicate network connectivity of the studied systems. In this article, we present a Raman spectroscopic study of the network connectivity of 10 ternary silicate glasses in the system Na₂O MgO SiO₂ and one Mg‐free binary silicate glass Na₂O SiO₂. Results obtained at constant polymerization suggest the existence of various Qⁿ units according to the nature of the modifying cation. As polymerization decreases for Na₂O MgO αSiO₂ glasses (labeled as NMSα with α decreasing from 10 to 2), the band associated with Si O Si bending in fully polymerized region disappears being gradually replaced by a band attributed to Si O Si bending in region containing mainly Q² and Q³ species. For highly polymerized glasses (NMS10‐NMS4), the coexistence of these two bands suggests the presence of two interconnected networks. Concomitantly, the signal associated with Q³ species first increases. For a further decrease of the polymerization, the high wavenumber part of the signal associated with Q³ species decreases, while the intensity of the high wavenumber part of the band related to Q² species increases. This result strongly suggests that magnesium charge‐balances preferentially Q² species rather than Q³ species. Copyright © 2010 John Wiley & Sons, Ltd.     

Environmental effects on initiation and propagation of surface defects on silicate glasses: scratch and fracture toughness study

The glass composition and surrounding environment can play an important role in the initiation and propagation of surface defects, which affect the practical strength of glass. We have studied how the environment and glass composition affect the tribological and indentation properties of multicomponent silicate glasses. Soda lime silica and aluminosilicate glasses were studied to compare the effects of the alkali ion and glass network type on surface defect formation. Although both glasses contained leachable sodium ions, the surface wear of soda lime glass decreased with increasing humidity while sodium aluminosilicate glass had an observable increase in surface wear. This indicated that sodium ion and water activity on/in glass surfaces vary depending on the glass network structure. The exchange of Na⁺ with K⁺ in aluminosilicate glass increased the elastic modulus, hardness, and resistance to fracture substantially; however, it did not improve the surface scratch resistance in humid environments. This suggested that the improved fracture toughness for the K-exchanged aluminosilicate glass is mainly due to the improved bulk properties; surface wear can readily take place regardless of Na/K-exchange.     

Formation of embedded patterns in glasses using femtosecond irradiation

Channel formation in glasses is demonstrated and discussed. Photosensitive glass (Foturan) was microstructured using femtosecond irradiation at 800 nm and 400 nm wavelengths, with subsequent thermal annealing, and HF etching of a lithium-silicate phase formed by exposure-annealing. It was found that there is a significant difference in the volume of lithium-silicate when the exposure was made with and without optical breakdown. Channels with a minimum cross section of approximately 10 m were achieved.In silicate glasses, the optically induced dielectric breakdown was used for the recording of channel patterns. The highest wet etching rate in a HF based solution was observed when the irradiance corresponded to the 2.5–3.0 thresholds of dielectric breakdown and the adjacent pulses were overlapping by more than 50% of the diameter of the focussed beam. Under these conditions, the formation of a void inside the glass was confirmed by optical observation of single shot damage under a microscope. The mechanism of selective wet etching in silicate glasses is discussed in terms of the stress corrosion effect, which explains crack propagation in glasses via the reaction of stretched Si–O–Si bonds at the tip of a crack with water, resulting in SiOH formation. It is shown that intra-connection of voxels was the key factor to achieve etching of high aspect ratio patterns in silica glass. PACS 42.70.Ce; 81.05.Kf; 82.50.Pt; 87.80.Mj     

Spectroscopical splitting of Cu ion energy levels in magnesium lead fluoro silicate glasses

Homogeneous 40.0 MgO-(10-x) PbF₂-50.0 SiO₂: x CuO glasses were prepared using melt-quenching technique under controlled conditions. Spectroscopic studies (UV-vis absorption, ESR, FT-IR) are carried out for these glasses. One broad characteristic visible absorption band is observed around 700-850 nm in these glasses, the optical band gap decreases as the content of the CuO increases in the glass network up to 0.7 mol % then reversal trend is observed. ESR spectra of all these glasses show resonance peaks characteristic of Cu²⁺ ions and hyperfine splitting is resolved with increasing the CuO content in the glass network. From the observed ESR spectra, the spin-Hamiltonian parameters have been evaluated and indicate that Cu²⁺ ions have octahedral coordination with a strong tetragonal distortion in these glasses. By correlating ESR and optical absorption data, the molecular orbital coefficients have been evaluated. FT-IR spectra give important information about the nature of bonds in the glass matrix. The density of the glasses is also measured and is found to decrease with the increase CuO contents in the glass matrix. The physical parameters along with spectroscopic parameters are measured.