Pure Quartz Glass Research Articles

Photocatalytic degradation of methylene blue by anatase TiO2 coating

AbstractPhotocatalytic coatings have the potential to contribute to the purification of water via an advanced oxidation process (AOP). A commonly used method for analyzing the mechanism of the photocatalytic performance of a given reactor type is to document the degradation behavior in a solution containing methylene blue. However, since methylene blue is rather unstable, the degradation results should be viewed critically. In this work, the degradation behavior of a test solution with methylene blue on quartz glass surfaces coated with photocatalytic titanium dioxide (TiO2) of the anatase modification was investigated through a variety of different light sources. The coating was deposited by physical vapor deposition (PVD) with the reactive pulsed DC magnetron sputtering ion plating (MSIP) method described in the study by Desch and Lake, while the quartz glasses were coated with a 100 nm thick TiO2 coating on the outside. The same glasses were used for all experiments with TiO2. In the determination of the degradation rate, additional experiments were performed using pure quartz glass without any coating, which made it possible to examine the influence of different light sources on the degradation rate of methylene blue in general. Three different light sources, namely UV‐A, UV‐C, and simple fluorescent lamps were used in this study. The concentration of methylene blue was recorded by photo spectrometer in 10‐min increments throughout the experiment and the experiments were performed for 24 h in all cases. Our data indicates that the methylene blue test is a poor method because the degradation rate is not clearly differentiable due to the low stability of the test substance. Without including reference testing in the absence of a catalyst, data may be subject to misinterpretation.

Highly sensitive gas pressure sensor utilizing the harmonic vernier effect in parallel FPIs with femtosecond laser processing

This work proposes and prepares a high-sensitive fiber optic gas pressure sensor based on the first harmonic vernier effect (FHVE). It has two parallel Fabry-Perot interferometers (FPI), each made of a single-mode fiber and a small segment of capillary tube fused as a sensing cavity and a reference cavity, and the end face of the sensing cavity is cut into a thin slice with a femtosecond laser pulse to make it sensitive to gas pressure. When the sensing cavity's (FPI1) and reference cavity's (FPI2) free spectral ranges are close to each other, a traditional vernier effect occurs, and the gas pressure sensitivity approaches 58.49 nm/MPa, which is approximately 14.64 times that of the single sensing cavity (FPI1). When the free spectral range of the sensing cavity (FPI1) is roughly twice that of the reference cavity (FPI3), the first harmonic vernier effect is observed. This leads to a significant increase in gas pressure sensitivity, up to 141.80 nm/MPa, which is about 35.45 times higher than what a single sensing cavity (FPI1) would achieve. Furthermore, testing results reveal that the sensor is temperature insensitive, with a low cross-sensitivity of 3.1 × 10−5 MPa/°C for gas pressure to temperature. This device is made of pure quartz glass, has high mechanical strength, a sealed construction, is easy to fabricate, has a high sensitivity of gas pressure, and may be used to monitor pressure in extreme conditions such as offshore oil or underwater operations.

Effect of PyC Inner Coating on Preparation of 3C-SiC Coating on Quartz Glass by Chemical Vapor Reaction

The cubic polycrystal of SiC (3C-SiC) coating on the quartz glass (QG) surface was successfully prepared via a two-step chemical vapor deposition (CVD) by introducing a thin PyC coating as a buffer layer. Through combining the intake system of CVD PyC and CVD SiC, the SiC/PyC composite coating can be in-situ prepared on the QG without halfway in-and-out chamber. The results showed that the SiC/PyC composite coating possesses highly uniform, dense, and continuous features, while the pure SiC coating exhibits many cracks, implying that the internal stress between the SiC coating and the QG can be relieved by adding the PyC buffer coating. The average hardness of the SiC/PyC/QG is measured to be 46.8 GPa, and its calculated modulus is 416.3 GPa by using a nanoindentation technique. Compared to the pure QG, the friction coefficient of the SiC/PyC/QG is slightly increased to 1.47 vs. 1.45. Moreover, the SiC/PyC/QG displays the excellent anti-acid corrosion in the 5%HF and 5%HCl mixed solution with the weight loss of about 33% lower than the pure QG after 8 h acid test at 80°C.

Differential Diffusion of Helium Isotopes in Glass, Quantum-tunneling 3He Enrichment, and Portable 3He/4He Monitoring of Mantle Processes

While studying the scientific and engineering aspects of a field-portable 3He/4He ratio detector, we found elevated ratios at comparatively lower temperatures that appear to result from differential diffusion of these isotopes in pure quartz glass. The 3He enrichment relative to 4He in lab air, expressed as the ratio R and normalized to the accepted 3He/4He ratio of 1.40 E-06 (Ra), ranges from peak values of about 200 to 600 in dry static samples. Even at the maximum classical 3He/4He diffusivity ratio of 1.15, the expected R would be only 1.61 E-06. Within a narrow temperature window, the air value in our experimental set up with pure quartz glass can range from about 2.70 to 8.20 E-04, or nearly 1000 times the expected enrichment based upon classical fractionation. When plotted versus temperature, the narrow 3He net partial pressure peak reveals at least three sharper embedded peaks that may be quantized vibrational entrance states in quartz glass which are temperature specific. This discovery has implications for relatively low-energy industrial enrichment of scarce 3He from natural sources on Earth, and for radiogenic and cosmogenic helium dating assumptions in natural glasses. It also has bearing upon designs for field portable 3He/4He ratio detectors aimed at earthquake and volcanic eruption studies, and monitoring of nuclear sites.

Ejector Application for Scavenging of an Aero Engine Bearing Chamber

Oil system architecture in aero engines has remained almost the same for the last 35 years. At least one mechanically-driven oil feed pump is responsible for distributing pressurized oil into the bearing chambers and several scavenge pumps, also mechanically driven, are responsible for evacuating the bearing chambers from the oil and air mixture. Air is used as the sealing medium in bearing chambers and is the dominant medium in terms of volume occupation and expansion phenomena. In order to simplify the oil system architecture, improve the system's reliability with less mechanical parts, and also decrease weight, an ejector system has been designed for scavenging bearing chambers. In Flouros et al. (2013, “Ejector Scavenging of Bearing Chambers. A Numerical and Experimental Investigation,” ASME J. Eng. Gas Turbines Power, 135(8), p. 081602), an ejector system was presented which used aviation oil (MIL-PRF-23699 Std.) as the primary medium. In the course of further development, the original design was modified leading to a much smaller ejector. This ejector was tested in the rig using alternatively pressurized air or pressurized oil as primary medium. Additionally, three in-house developed primary nozzle (jet) designs were introduced and tested. The design of an ejector for application with compressible or incompressible media was supported through the development of an analysis tool. A momentum-based efficiency function is proposed herein and enables comparisons among different operating cases. Finally, ANSYS cfx (ANSYS, 2014, “ANSYS® CFX, Release 14.0,” ANSYS Inc., Canonsburg, PA) was used to carry out the numerical analysis. Similar to the ejector described in Flouros et al. (2013, “Ejector Scavenging of Bearing Chambers. A Numerical and Experimental Investigation,” ASME J. Eng. Gas Turbines Power, 135(8), p. 081602), the new design was also manufactured out of pure quartz glass to enable optical access. Through suitable instrumentation for pressures, temperatures, and air/oil flows, the performance characteristics of the new ejector were assessed and were compared to the analytic and numerical results. This work was partly funded by the German government within the research program Lufo4 (Luftfahrtforschungsprogramm 4/Aeronautical Research Program 4).

Improved Drinking Water Disinfection with UVC-LEDs for Escherichia Coli and Bacillus Subtilis Utilizing Quartz Tubes as Light Guide

A new approach is investigated utilizing light guidance capabilities of optical pure quartz glass in order to maximize drinking water disinfection efficiency with UVC-light-emitting diodes (LEDs). Two experimental setups consisting of soda-lime AR® glass (VWR, Darmstadt, Germany) or HSQ® 100 quartz glass (Heraeus, Wasserburg, Germany) reactors were designed to compare disinfection rates with and without total reflection of UVC radiation along the reactor walls. Each reactor was filled with 9 mL bacteria samples containing either E. coli DSM (Deutsche Sammlung von Mikroorganismen) 498 or B. subtilis DSM 402 strains (concentration 1–3 × 106 colony forming units (CFU)/mL) with and without additional mixing and irradiation periods of 10, 40, and 90 s. Disinfection rates were increased up to 0.95 log10 (E. coli) and 0.75 log10 (B. subtilis) by the light guide approach in stagnant samples. The same experiments with mixing of the samples resulted in an increased disinfection efficiency of 3.07 log10 (E. coli) and 1.59 log10 (B. subtilis). Optical calculations determine that total reflection is achieved with the applied UVC-LED’s viewing angle of 15°. Furthermore measurements show that HSQ® 100 quartz has a transmittance of 92% at 280 nm UVC irradiation compared to the transmittance of soda-lime glass of 2% (1 mm wall thickness).

Mechanisms of primary long-lived defect production in pure quartz glasses under electron irradiation

Based on an analysis of the dependences of individual absorption band amplitudes in quartz glasses on the electron beam (EB) fluence, mechanisms of primary defect production in KS-4V, KU-1, and Corning 7980 glasses during their prolonged irradiation by EB pulses are determined.

Two-photon absorption in - and -based fibres at a wavelength of

The nonlinear two-photon light absorption coefficients have been measured in an optical fibre with a quartz glass core and in a fibre with a germanosilicate glass core. The two-photon absorption coefficient measured at a wavelength of in the -based fibre multiply exceeds that for the pure quartz glass optical fibre .

Nanostructures formed in pure quartz glass under irradiation in the reactor core

Optical spectroscopy and X-ray diffraction techniques were used for studying nanoscale particles grown in pure SiO2 glass under irradiation with fast neutron fluencies within 6×1016–5·1019 cm−2 and gamma-quanta ~1.8×1020 cm−2 in the reactor core in water. The neutron irradiation results in destroying of the initial α- and β-quartz mesoscopic order of 1.7 and 1.2 nm sizes and growing of cristobalite and tridymite nanocrystals of 16 and 8 nm sizes in the thermal peaks of displacements reapectively. The point defects (oxygen deficient E′s, E'1, E'2 and non-bridging oxygen centers) induced by the γ-irradiation are accumulated in the nanocrystals shell of 0.65–0.85 nm thickness. Interaction of close point defects at the nanocrystal–glass interface causes the splitting of optical absorption bands into the intensive (D~2–4) resonances characteristic for local interband electron transitions, having the width of 10–15 nm close to the nanocrystals' sizes and the energy depending on their structure.

Efficiency of generation of optical centers in KS-4V and KU-1 quartz glasses at neutron and gamma irradiation

Pure quartz glasses of KS-4V and KU-1 types are candidates for optical plasma diagnostic system in ITER. The purpose of experiment was to study the efficiency of defect production in these glasses under irradiation with 60Со γ-quanta (5.7Gy/s) dose range of 102–107Gy and the fission reactor neutrons in the fluency range of 1020–1023n/m2 and gammas simulating the plasma influence. In KU-1 (1000ppm OH) the accumulation kinetics of E′-(5.75eV) and NBO-(1.9eV) centers at γ-doses⩾5×105Gy and neutron fluencies <1021n/m2 is faster, than that in KS-4V glasses (<0.1ppm OH) that is caused by rupture of hydrogen bonds. At fluencies >1021n/m2 the NBO accumulation kinetics is slower in KU-1 than in KS-4B, because highly mobile hydrogen atoms access to the generated NBO centers. In KS-4V irradiated to γ-doses102–5×103Gy a new unstable absorption band at 1.8eV was found, which is caused by the glass synthesis conditions and alkali metal impurities. The transparency at 3.5–6.2eV at fluencies 1020–5×1021n/m2 is higher in KS-4V than KU-1. However at fluencies >1021n/m2 in KS-4V the photoluminescence band at 2.7eV is more intensive and distorts a diagnosed signal. The transparency in 3.5–1.2eV at fluencies >1021n/m2 is higher in KU-1 than KS-4V.

Ejector Scavenging of Bearing Chambers. A Numerical and Experimental Investigation

Oil system architecture in aero engines has remained almost the same for the last 30 years. At least one oil feed pump is responsible for distributing pressurized oil into the bearing chambers, and several scavenge pumps are responsible for evacuating the bearing chambers from the oil and the air mixture. Air is used as the sealing medium in bearing chambers and is the dominant medium in terms of volume occupation and expansion phenomena. In order to simplify the oil system architecture and thus improve the system's reliability with less mechanical parts and also decrease weight, an ejector system has been designed for scavenging bearing chambers. The idea behind the ejector is to use high-pressure oil from the feed pump and use it for feeding the ejector's primary jet. Through the momentum transfer between the pressurized oil at the jet's tip and the two-phase mixture of air and oil from the bearing chamber, the mixture will be discharged into the oil tank. In order to design the ejector for aero engine applications, engine-relevant performance conditions had to be considered. The design was performed using a one-dimensional analysis tool and then considerably refined by using the numerical tool ansys cfx. In a further step, the ejector was manufactured out of pure quartz glass and was tested in a lube rig with a bearing chamber, which has evolved from a real engine application. In the bearing chamber, engine-relevant performance conditions were simulated. Through the provided instrumentation for pressures, temperatures, and air/oil flows, the performance characteristics of the ejector were assessed and were compared to the analytic and numerical results. A high-speed camera was used to record the two-phase flow downstream of the bearing chamber in the scavenge pipe. This work is part of the European Union-funded research program Engine LUBrication System TechnologieS (ELUBSYS) within the 7th EU Frame Programme for Aeronautics and Transport (AAT.2008.4.2.3).

Behavior of absorption bands in pure quartz glasses under electron irradiation

In KS-4V, KU-1, and Corning 7980 glasses, the behavior of six individual absorption bands induced by the electron beam as its fluence F increases to 20 kJ/cm2 are studied. The UV band amplitudes reached a quasi-steady level at F ≈ 4 −5 kJ/cm2 in all glasses.

Nonlinear and electron-beam-induced absorption in pure quartz glasses at the wavelengths of excimer lasers

The two-photon absorption coefficients β at wavelengths 248 and 193nm with pulse widths 80 and 60ns, respectively, have been measured in KS-4V, KU-1, and Corning 7980 glasses. The value of β at 248nm in KS-4V was 0.16cm∕GW, which was about 30% higher than in the other glasses. At a wavelength of 193nm, the value of β virtually coincided at a level of 1.1cm∕GW in all the samples. The coupling factors between the electron-beam (EB)-induced quasi-steady-state optical density at wavelengths 353, 248, and 193nm and the EB power density on the samples were measured for the same glasses, using the radiations of XeF, KrF, and ArF lasers. These factors in KS-4V were 1, 4, and 6cm2∕GW, respectively. The measurement error did not exceed 50%.

Determination of the neutron flux and γ radiation in the core of operating and shut-down reactors using quartz glasses and element monitors

The neutron fluxes and the intensity of γ radiation are measured in 26 channels of a WR-SM reactor and its thermal column. The fast neutron fluxes in the channels are determined using Ni, Fe, Co, Au, and Mn element monitors with different threshold energies, together with a theoretical calculation using the MCNP-4C program. The energy distribution of the neutron flux inside the fuel assembly is obtained for selected channels around the core. The flux of neutrons with energies >1 MeV is in the range (0.5-43).10 12 cm -2 sec -1 , depending on the location of the channel. A linear correlation is discovered between the induced optical absorption at the 215 nm line (E' center) of SiO 2 -BaO glass and the fast neutron flux in the channels. The γ-ray intensity in the thermal channel is estimated for the reactor during operation (∼38.4 Gy/sec) and 24 hours after it is shut down (∼24. 7 Gy/sec ) using the E' centers induced in pure quartz glasses. The observed difference in the efficiency with which oxygen defects are formed during dry and wet irradiation of glass owing to the radiolysis of water must be taken into account when developing radiation technology and during the burial of radioactive waste.

SQUID measurements of remanent magnetisation in refillable 3He spin-filter cells (SFC)

A strong influence of external magnetic fields on the relaxation time constant T 1 of glass cells serving as reservoirs for polarised 3He, observed for various alkali metal-coated cells made of different glass types, was initially associated with the presence of a large number of ferromagnetic clusters on the glass surface. Later experiments showed the presence of the so-called “ T 1 hysteresis” phenomenon with a similar distinctiveness also in uncoated cells made of pure synthetic quartz glass. It suggests that the origin of such a relaxation is a macroscopic magnetisation in the bulk of the cell. We present the results of a multi-SQUID system investigation on magnetised and non-magnetised quartz glass cells, Cs coated as well as bare wall, to be used as neutron spin filters at HMI Berlin. The presence of a macroscopic remanent magnetic moment in the cells after their exposition to external magnetic fields has been experimentally shown. More than 80% of the remanent magnetic moment of the magnetised cells was found to be concentrated in the region of the glass valves. SQUID measurements reveal the existence of some remanent magnetisation in all valve parts and also in the vacuum grease, but most magnetic are the plastic parts and the O-ring. Different valve and sealing types have been compared in order to find the less magnetisable one.

Radiation sensors based on optical fiber

The spectroscopic parameters of especially pure quartz glass fabricated by the sol-gel process is investigated. When the glass samples are irradiated with gamma radiation, absorption bands are formed at 4.85, 2.05, and 1.75 eV. The absorption intensity in the band at 4.85 eV is proportional to the absorbed dose of gamma radiation. A schematic diagonal is proposed for an optical-fiber sensor with a sensitive element fabricated from sol-gel quartz glass. © 2004 Optical Society of America

Metal Transport and Deposition in Hydrothermal Veins Revealed by 213nm UV Laser Ablation Microanalysis of Single Fluid Inclusions

213nm UV laser ablation provides a powerful and cost-effective new method for the chemical microanalysis of individual fluid inclusions. The instrument offers significantly improved energy absorption in many geological materials compared to 266nm UV lasers resulting in improved ablation characteristics. The laser is not strongly absorbed by either air or commonly used optical material, permitting relatively easy delivery and control of the beam. Ablation of multielement standard solutions in pure quartz glass capillaries was found to be an effective method for external calibration of instrument sensitivity. Internal calibration for calculation of absolute element concentrations in inclusion fluids was carried out using chloride concentration estimated from microthermometric data. Using this approach, analyses of groups of cogenetic primary and secondary inclusions using a 30 element analyte menu gave typical relative standard deviations for absolute element concentrations of around 20 percent for alkali and alkali earth elements and 20 to 50 percent for metals, comparable with those obtained by 193nm Excimer laser ablation. Results for Ca are consistent with independent estimates made from microthermometric measurements and a range of other elements are in reasonable agreement with previously published bulk chemical analyses. Overall, the data give good charge balance, within 5 percent. The technique was used to test the hypothesis that the metal content of hydrothermal ore deposits is primarily controlled by the metal content of the mineralizing solutions rather than selective precipitation mechanisms. We studied Pb(-Zn) mineralized ‘crosscourse’ veins from Southwest England that are known to have formed from low temperature brines expelled from Permo-Triassic red-bed basins adjacent to the Cornubian peninsula, probably during the Triassic. These fluids are comparable with the solutions that formed Mississippi Valley-type Pb-Zn deposits. Analyses of primary fluid inclusions across growth-zoned quartz crystals from one of these veins indicate the orefluids at an early stage of vein growth are relatively Pb-rich (up to 295 ppm Pb, up to 86 ppm Zn; Pb/Zn = 1.3-16.1) and display marked temporal variations in chemistry. Gradual increases in K, Ca, Sr, Ba and Zn are observed across a significant (∼10 mm) interval of quartz growth. These increases are interpreted to reflect mineral dissolution-precipitation reactions occurring within the fracture system exploited by the fluids after being expelled from the basin source area. Superimposed on this trend are comparatively short time-scale (∼1 mm of quartz growth) chemical excursions characterized by decreases in the concentrations of Cl, K, Ca, Ba, Sr, Pb and Zn of up to two orders of magnitude. These excursions are believed to be due to local, volumetrically significant, mineral precipitation events and indicate the operation of processes that result in the simultaneous supersaturation of a number of phases. It is suggested that initial galena precipitation (>98% Pb loss from solution) was due to reduction as oxidized fluids encountered the first strongly reducing lithology on their flow path out of the basin source region. Several later dilution events were caused by fluid mixing and are inferred to have caused the co-precipitation of sulfides (galena, sphalerite; up to 98% loss of metals from solution) with sulfates (anhydrite, barite; up to 91% Ca and 97% Ba loss from solution) and/or silicates (K-mica; up to 96% loss of K from solution). However, at only one stage is galena (±anhydrite, K-mica) observed in the sample studied suggesting that fluid inclusions may commonly trap depleted fluids after mineral precipitation has already occurred some distance upstream, rather than reflecting precipitation events in their immediate vicinity. The primary ore-forming fluid in this case study contained elevated Pb and Zn and, at least initially, displayed a higher Pb/Zn ratio than predicted for fluids saturated with respect to both sphalerite and galena. Therefore, we suggest that the Pb-rich tenor of the vein deposit is primarily controlled by the metal content of the ore fluids, which is ultimately a function of the geochemistry of the basin source. In this example, the source area is dominated by oxidized terrestrial clastic rocks. Reactions within the aquifer and selective precipitation mechanisms at the site of ore formation also appear to have modified fluid geochemistry but played a second order role in controlling the metal budget of the mineral deposit formed.

Optical properties of multicomponent oxide glasses and glass fibers

AbstractWe experimentally studied the optical properties of multicomponent oxide glasses that contain metallic components, such as potassium and sodium, and their glass fibers. The Rayleigh scattering coefficients of glasses such as Na2O‐B2O3‐SiO2 (NBS), K2O‐MgO‐SiO2 (KMS), K2O‐Na2O‐MgO‐SiO2 (KNMS) are smaller than that of pure quartz glass. In particular, the Rayleigh scattering coefficient of KNMS glass was significantly lower at 38% of the value for pure quartz glass. This is believed to be the result of suppressing the composition fluctuations of KNMS glass by the mixed alkali effect. Furthermore, we studied the absorption properties of OH group impurities included in multicomponent oxide glasses. In particular, we fabricated NAS glass fibers that substituted the OH group impurity with an OD group (deuterium) by the double crucible method and verified a loss reduction of about 800 dB/km at the 1.55‐µm wavelength. Through these studies, we clearly showed that the absorption losses of the OH group that hydrogen bonds to nonbridging oxygen clearly affected the increase in the 1.55‐µm band loss in multicomponent oxide glass fibers. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(12): 21–35, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10128

Determination of trace elements in quartz glass by use of LINA-Spark-ICP-MS as a new method for bulk analysis of solid samples.

The determination of trace elements in pure quartz glass samples has been performed by coupling an ICP quadrupole mass spectrometer with the LINA-Spark-Atomizer, an IR laser ablation system dedicated to direct bulk and surface analysis of solid samples. Linear calibration curves were obtained for nine elements (Na, Al, Ca, Ti, Cr, Mn, Zr, Ba, and Pb) in the ng g(-1) range with detection limits of less than 10 ng g(-1) for Ca, Cr, Mn, Zr, Ba, and Pb and in the range of 120-220 ng g(-1) for Na, Al, and Ti. The distance between the laser focal point and the sample surface has a significant influence on signal intensity and precision, both of which can be improved by a factor of approximately two by focusing the laser 15 mm behind the sample surface. Aerosol moistening reduced the standard deviation of the signal intensity by a factor of 2-4. Signal instability, which resulted from different ablation rates or variations in the transmission of the mass spectrometer, were compensated by use of the simultaneously measured SiAr+ ion as an internal standard. Under these conditions precision was usually better than 5% RSD. The results were compared with those obtained by use of a commercial LA-ICP-MS system. With this instrumentation linear calibration curves were achieved for three elements only (Al, Ti, and Pb), showing that LA-ICP-MS is less appropriate for bulk analysis in the ng g(-1) range.

Cathodoluminescence Microcharacterization of the Irradiation Sensitive Defect Structure of Amorphous Silicon Dioxide

Cathodoluminescence (CL) Microscopy (imaging) and Spectroscopy in a Scanning Electron Microscope enables high spatial resolution, high sensitivity detection of defect centers in materials. Cathodoluminescence microanalysis has been used to investigate the irradiation sensitive defect structure of Types I, II, III and IV amorphous silicon dioxide SiO2 (quartz and silica glasses). The CL experiments were performed in a JEOL JSM 35C SEM equipped with Oxford Instruments liquid N and liquid He cryogenic stages, and an Oxford Instruments MonoCL cathodoluminescence imaging and spectral analysis system. The observed CL emissions, were excited with a stationary electron beam at normal incidence and corrected for total instrument response. The corrected CL spectra were fitted with a multiparameter Gaussian function using a non linear least squares curve fitting algorithm and were identified with particular defect structures. The CL emission from high quality pure amorphous silica and quartz glasses is dominated by intrinsic processes (associated with the host lattice). See Table 1.