Doped Silica Glass Research Articles

Synthesis and properties of Er3+-doped silica glass by sol-gel processing with organic complexation

Er3+-doped silica glass (up to 10 wt%) was synthesized by sol-gel processing with the addition of 3-aminopropyl trimethoxysilane (APS) as a complexing reagent. Er3+ ion reacted with the amino groups and, thus, linked to the silica network during the sol preparation. It is anticipated that the motion of Er3+ ions would be restricted, and the formation of Er3+ clusters inhibited. No detectable phase segregation was observed by means of SEM/TEM, regardless the addition of organic complexing reagent and heat-treatment. Nitrogen adsorption analysis indicated that dense glass was obtained after heating at 900–1000 °C for 10 hrs. Although the current experimental results were not conclusive, both fluorescence spectra and magic-angle spin (MAS) nuclear magnetic resonance (NMR) data were indicative that the addition of the complexing reagent APS might result in a homogeneous dispersion of high level Er3+ doping in the resultant gels. After the removal of organic components, however, Er3+ clustering occurs when firing at a high temperature for a long period of time, e.g. at 1000 °C for 10 hrs, due to enhanced Er3+ diffusion.

Up-conversion emission phosphors based on doped silica glass ceramics prepared by sol–gel methods: control of silica glass ceramics containing anatase and rutile crystallites

Using sol–gel methods novel silica based glass ceramics containing TiO2, Er3+ and Yb3+ ions have been prepared. Anatase and rutile crystallites composed of TiO2, Er3+ and Yb3+ ions that segregate in the glasses have been shown to be new yellow emitting up-converting materials. It is demonstrated that by annealing SiO2 glasses containing TiO2, Er3+ and Yb3+ ions, crystals of either the anatase or rutile phases can be grown in the glass (dependent on annealing temperature). Laser Raman spectroscopy is shown to be a useful technique to characterise the crystallographic phases in the pure state, and in these new ceramics. Furthermore, their emission can be excited at a wavelength of 632.8 nm, and the up-converted luminescence in the visible region can be detected and monitored using a Raman spectrometer.

High photoluminescence in erbium-doped chalcogenide thin films

The spectral properties of the chalcogenide glasses As 2S 3 and As 24S 38Se 38-doped with Er 3+ are presented and discussed. Thin films were formed by thermal evaporation and the erbium doping was obtained by subsequent ion implantation. Strong Er 3+ emission at 1.54 μm has been observed. The high refractive index of these chalcogenide glasses lead to Er 3+ emission cross-sections (15×10 −21 cm 2) which are two times higher than for doped silica glass. The lifetime of the Er 3+ metastable 4I 13/2 energy level was measured to be 2.3 ms. This short lifetime is consistent with the high emission cross-section. Furthermore, the very low phonon energies of chalcogenide glasses lead to relatively long lifetimes of the Er 3+ 4I 11/2 pump level, which have been measured to be of the order of 0.25 ms. These spectral properties make this glass a good candidate for applications in the field of integrated optics.

Use of depressed index cladding layers to tailor the chromatic dispersion and birefringence of planar geometry waveguides

We numerically compute the chromatic dispersion and birefringence of a rectangular channel waveguide having a depressed index inner cladding. We assume the materials in the core and outer cladding of the waveguide to be doped silica glasses, whereas we take the inner cladding material to be either a doped silica glass or a polycrystalline fluoride, e.g., CaF/sub 2/ or MgF/sub 2/. Planar lightguide circuits (PLC's) based on such waveguides have application for wavelength or dense wavelength division multiplexing (WDM/ DWDM) in optical fiber transmission systems. Some of the described structures have application in polarization maintaining waveguide devices.

Up-conversion luminescence of a violet color from sol-gel derived Nd3+:SiO2+Al2O3 glasses

Solid-state up-conversion lasers are found to be practical alternatives to frequency doubling techniques for the conversion of infrared radiation into visible light. Several applications, such as under-water optical communications and biomedical sensors, await the development of compact, efficient room-temperature devices that can operate at wavelengths not commonly obtainable by conventional laser sources. Such up-conversion lasers are considered as possible solutions to immediate technological problems. Trivalent rare-earth ions doped in different glasses and in certain crystals demonstrate up-conversion emissions in the visible wavelength range. The 4fn electronic level structures of these ions provide many long-lived intermediate levels, which could be populated using infrared radiation. These levels, together with some meta-stable higher lying levels, give rise to strong visible emissions [1]. Over the past few years, up-conversion emission (violet color) from Nd3+ ions has been reported in a variety of glasses based on certain chlorides, fluoroindate, fluorogallate, fluorozirconate, multi-component oxides and heavy metals [2–7]. In all these neodymium glasses, the up-conversion emissions are due to their low vibration frequencies and small phonon energy, and they are all synthesized by conventional melting methods. It is commonly believed that the Nd3+ in silica glasses cannot emit the up-conversion emission. In the literature, some researchers have stated that they did not observe violet up-conversion emission from the Nd3+doped silica glasses [6]. In addition, conventional silica fibers are not efficient in generating up-conversion signals from Nd3+ because of their large phonon frequencies. However, in our present work, we have indeed observed a relatively strong up-conversion emission in violet (399 nm) color upon excitation with a yellow light (580 nm) from Nd3+ : SiO2+Al2O3 glasses prepared by the sol-gel process. This short paper reports, for the first time, up-conversion emission in Nd3+ doped SiO2 based sol-gel glasses. Following the conventional sol-gel process [8], tetraethylorthosilicate (TEOS) was diluted in ethanol (EtOH) and water, with HCl added as a catalyst. The mole ratio of TEOS to EtOH to H2O was 1 : 8 : 8. The solution was allowed to a hydrolyze at 60 ◦C for an hour. Al(NO3)3·9H2O and Nd(NO3)3·6H2O were used as the precursors of Al2O3 and Nd2O3 respectively. They were dissolved in EtOH in separate beakers and then added drop-by-drop into the pre-hydrolyzed TEOS solution. The end solutions were stirred at room temperature in a sealed bottle for a period of one week. Dried gels were thus obtained by removing the cover of the bottle and leaving the gel in the open air for several days. A high temperature treatment was carried out on all these dried gels in an electric furnace at 1000 ◦C for about 12.5 h, and were kept there for about 5 h, and then cooled down to room temperature gradually. Based on our previous results on the laser transition (F3/2→ I11/2) properties at 1064 nm of Nd3+ doped Al3+ co-doped silica [9], we have analyzed three samples for upconversion emissions at various Nd3+ concentrations. The mole ratio of each of the chemicals used was as follows: 100SiO2 : 10AlO1.5 : xNdO1.5 (x = 0.1, 0.5 and 1.0). The up-conversion emission spectra were measured by using a Spex Fluorolog-3 spectrofluorometer, attached with a 1934D3 phosphorimeter. This system employs the Datamax software package for acquiring the spectrum and the decay curve data. The source of excitation was a xenon flash lamp. The measured data pertaining to the luminescence were corrected for the detector. Fig. 1 shows the up-conversion emission spectra of the three samples studied under excitation at 580 nm. An intense violet emission peak at 399 nm has been observed in all these samples. Three additional weaker fluorescent transitions at 342 nm, 372 nm and 452 nm have also been found. Referring to the energy diagram of Fig. 2, the emissions correspond to transitions: D3/2 → I9/2 (∼342 nm), D3/2 → I11/2 and

Temporal soliton switching in a rectangular nonlinear directional coupler

We address the theory of temporal soliton switching in a planar geometry directional coupler constructed from silica and doped silica glass and operating at the central wavelength of 1.55 microm, significant for erbium-doped amplification. We formulate the field in the coupler in terms of the supermodes of the total structure and take account of the two transverse dimensions of the rectangular channels. In the case of the weak coupling between channels consistent with elimination of pulse breakup, the effect of the fields in the outer corner regions of the channels results in a switching intensity that differs significantly from that derived from coupled-mode theory on the basis of a slab model of the coupler.

Er3+ Doped Silica Glass by Sol-Gel Processing with Organic Complexation

ABSTRACTEr3+-doped silica glass (up to 10 wt%) was synthesized by sol-gel processing with the addition of 3- aminopropyl trimethoxysilane (APS) as a complexing agent. Er3+ ions reacted with amino groups and, thus, linked to the silica network during the sol preparation. As a result, the motion of Er3+ ions was restricted and the formation of Er3+ clusters was inhibited. Both fluorescence spectra and magic-angle spinning (MAS) nuclear magnetic resonance (NMR) indicated that the addition of the complexing agent APS resulted in a homogeneous dispersion of high-level Er+3 doping in the resultant gels. After the removal of organic components, however, Er+3 clustering occurs when firing at a high temperature for a long period of time, e.g. at 1000°C for 10 hrs, due to enhanced Er3+ diffusion.

Photoluminescence of Cu+-doped silica glass prepared by MeV ion implantation

2 MeV Cu+ ions were implanted in silica glass at doses from 1×1015 to 1×1017 ions/cm2. Cu+-ion implanted silica glass followed by heat treatment showed photoluminescence due to monovalent copper ions. The photoluminescence intensity was the highest at a dose of 1×1016 Cu+ ions/cm2 in the present implantation condition. It was deduced that co-implantation of oxygen ions stabilizes the monovalent copper ions in silica glass.

Optical properties of Pr3+ doped silica gel glasses obtained by sol–gel method

Thermally densified silica glasses doped with Pr3+ ions were prepared by sol–gel method. Three procedures of synthesis are described. Absorption, emission and excitation spectra of Pr3+ doped silica glasses obtained by sol–gel method are reported. We found on the basis of now presented results and those earlier reported that intensities of the absorption bands of Pr3+ change with concentration nonlinearly, especially in the range of 3H4→3P2; 3P0 and 1D2 transitions. This phenomenon could be caused by clustering, which leads to cooperative interactions. On the basis of the absorption spectra measurement, the energy level diagram was prepared which helps in the explanation of the emission properties of glasses synthesized by different techniques. The luminescence spectra were dependent on excitation wavelength. The spectra excited in high UV range exhibited, except emission in the red range corresponding to the 1D2→3H4 transition, a broad band emission with characteristic holes at the envelope corresponding to the 3P2, (3P1, 1I6) and 3P0 terms. Nature of this broad band emission is discussed. The observed holes result from reabsorption processes, which are controlled by concentration of active ions. Mechanism of their occurrence remains unknown. No emission from 3P0 level was observed for some kind of glasses, for another one the emission from 1D2 and 3P0 levels was detected.

270 nm absorption and 432 nm luminescence bands in doped silica glasses

We describe the spectroscopic properties associated with the occurrence of a 270 nm band giving rise to a blue luminescence at 432 nm and its dependence on the chemical composition in doped silica glasses. The luminescence life-time is found at around 75 μs. The associated defect is related to Ge doping.

Preparation and optical properties of solid solution semiconductor (Zn x Cd1−x S) doped silica glasses

Semiconductor(Zn\-\%x\%Cd 1-x S) doped silica glasses were prepared by Sol_Gel process and \%in situ\% growth technique. The structure of the materials was characterized by X_ray diffraction technique, the particle size of semiconductor crystallites from X_ray patterns was estimated less than 10 nm. From absorption spectra, it is obtained that the absorption edges shifted to short wavelength diraction when Zn contents increased, and the absorption edge can be adjusted from 2.46 eV to 2.96 eV by controlling Zn contents. The third_order nonlinear optical susceptibility was studied at 532 nm with 8 ns pulse laser by degenerate four wave mixing (DFWM) technique.

Spectroscopic properties of erbium doped silica glasses obtained by sol-gel method

The spectroscopic properties of erbium doped silica glasses obtained by sol-gel technology have been investigated. The emission properties of Er3+ ion are discussed on a basis of the absorption and emission spectra. The transmission and emission characteristics of Er doped silica fibers are presented. The efficient emission in the mid-ir region (at 1.55 μm) was observed. It has been found that, for the high concentration (1000 ppm) Er doped fiber, the 1.55 μm emission was completely quenched. Instead of this emission, the efficient green anti-Stokes emission (after laser diode pumping at 980 nm) was observed.

Mn 2+ electron paramagnetic resonance study of a sodium borosilicate glass prepared by the sol-gel method

Sodium borosilicate glasses were prepared by the sol-gel method and doped with a paramagnetic manganese probe. X-band electron paramagnetic resonance (EPR) experiments, carried out on powdered samples, showed that even for molar ratios higher than 10%, manganese can be inserted in the glass. EPR results obtained on different doped silica glasses showed that the ability of Mn 2+ to be inserted in the glassy network is connected with the presence of alkali species. The bulk location of the probe was confirmed by 29Si nuclear magnetic resonance investigations. EPR results indicated that manganese is located in distorted sites in an octahedral silica environment.

EXAFS study on metal cluster doped silica glass obtained by ion implantation procedures

Metal-doped glasses were prepared by double ion implantation (Ag+Cu and Au+Cu) in silica glass. X-ray absorption spectroscopy was used to study the different oxidation states of the dopant metals and the possible formation of metal or alloy clusters. We present an investigation on co-implanted silica glass at the Cu K, Ag K and Au L III edges. The local atomic order around each dopant was determined. In particular, no evidence of metal alloying was found. Cu is mainly bound to O atoms of the glass, Ag mainly forms pure metallic clusters and Au is present as small metallic particles and isolated atoms.

Preparation and Optical Properties of Sb2S3 Microcrystallite Doped Silica Glasses by the Sol-Gel Process

The sol-gel process has been applied to the preparation of nano-size Sb2S3 crystallite doped silica glasses and thin films. Silica glasses containing 1–1.5 wt% Sb2S3 are prepared by hydrolysis of complex solution of Si(OC2H5)4, SbCl3 and SC(NH2)2, and subsequent heat treatment. The nano-size crystallite in the matrix is observed by means of TEM. The transmission spectra of the films show that the transmission valley shifts toward longer wavelengths with increasing heat treatment time and temperature. Second harmonic generation (SHG) has been observed in the glasses illuminated with intense 1.06 μm and frequency-doubled laser beams from mode-locked Nd:YAG laser.

The Preparation of Quantum-dot CdS Doped Silica Glass by the Improved Sol-gel Process

The Preparation of Quantum-dot CdS Doped Silica Glass by the Improved Sol-gel Process

Pr 3+ activated silica phosphor glasses by sol-gel method

Pr 3+-doped silica glasses were prepared using acid hydrolyzed tetraethyl orthosilicate (TEOS). Thermal analysis and linear shrinkage of the pure and doped gels indicate that the Pr 3+ ion modifies the structure of the gel. The absorption peak positions of Pr 3+ ions in silica change with Al codoping. Fluorescence of Pr-doped gels shows some interesting behavior and changed considerably with the addition of Al 3+.

Fabrication and characterisation of neodymium-doped silica glass by sol-gel process

Neodymium-doped silica glass possesses many properties ideal for high-power laser applications. These include low thermal expansion coefficient, high temperature stability, and low nonlinear index of refraction. For the first time, the sol-gel process has been successfully employed to prepare highly doped neodymia silica glass, up to 5wt% Nd for homogeneous dopant distribution. The optical characteristics of the silica glass and its in-process gel, including the UV/VIS absorption spectra, infrared absorption spectra, fluorescence emission spectrum and the fluorescence lifetime, are measured and analyzed. The structure of the sample is also characterized by means of XRD and SEM. A porous gel is observed to have formed when the heat treatment temperature reaches 300oC. Wavelength shifts in the absorption peak corresponding to the 4I9/2 to 4F5/2 transition have been observed during the densification process and for different Nd weight contents. The FTIR spectra have shown that high temperature heat treatment can greatly reduce the amount of OH groups and organic residue in the silica. We have also shown that a high OH content contributes to weak fluorescence intensity and short fluorescence lifetimes.

Structural evolution and fluorescence properties of Tb 3+-doped silica xerogels in the gel to glass conversion

The Tb 3+-doped silica glasses were prepared by a sol-gel process with appropriate heat treatment. The structural changes during the gel to glass transition of Tb 3+-doped silica xerogels and the effect on fluorescence properties of Tb 3+ were studied in this paper. The results show that the doped silica glasses may be obtained after the xerogels are heat-treated at 800 °C for 24 h. During heat treatment at 400 °C, the residual organic molecules and most of the absorbed water molecules in silica xerogels are removed, and the SiO 4 tetrahedral structural network forms and strengthens gradually with decreasing number of silanol (SiOH) groups. The fluorescence intensity of Tb 3+ ions increases remarkably when the doped xerogel is heat-treated in the range 300–500 °C, and increases slowly above 500 °C(up to 800 °C). This observation leads to a conclusion that the radiative transitions of Tb 3+ ion in the aqueous gels are quenched strongly by the high-frequency vibrations of OH groups from the coordinated water rather than physically absorbed water. The inhomogeneity in the site state of Tb 3+ ions increases with rise in temperature of heat treatment, which broadens the emission bands of Tb 3+ ions doped in silica glasses. Moreover, there will also be an additional interaction owing to the influence of the ligand field of the glasses, which makes the emission bands shift to red and produces Stark splitting of the Tb 3+ ion energy levels.

A study of the structural evolution of the sol-gel derived Sm3+-doped silica glass

Abstract Sm3+-doped silica gels have been prepared by a sol-gel process using tetraethyl orthosilicate, H2O, HCl and Sm(NO3)3 · 6H2O. The structural evolution and densification behaviour of the gels during thermal treatment have been monitored by physical property measurements, visible-NIR, IR and fluorescence spectroscopy. The gels show a continuous densification and strengthening of the silica network with increasing heat-treatment temperatures (60–100 °C). The fluorescence intensity ratio of the 4G 5 2 → 6H 9 2 to 4G 5 2 → 6H 5 2 transition has been used to study the change of Sm3+ environment during gel-glass conversion. Samarium passes through three different environments at different heat-treatment temperatures during gel to glass conversion.