Thermal bleaching of organic laser dyes

Thermal bleaching of organic laser dyes in the temperature range from +20°C to +220°C is investigated.     

Investigating the contribution of recuperated TL to post-IR IRSL signals in a perthitic feldspar

Using a museum specimen of perthitic feldspar, the characteristics of post-IR IRSL production at 200 °C after different prior IR bleaching at 100 °C were investigated. It was found that the post-IR IRSL signal had an isothermal TL contribution that was unexpected following a previous preheat at 320 °C; this is the result of isothermal decay of recuperated TL peaks resulting from photo-transfer that occurred when the previous IRSL signal was measured at a lower temperature. The isothermal TL contribution to the post-IR IRSL signal depends on prior IR bleaching conditions. Since the recuperated TL signal comes from photo-transfer during IRSL production, this signal should also suffer from anomalous fading. Thus, it is suggested that this isothermal TL contribution to the measured post-IR IRSL is removed by the inclusion of an additional step, a cut-heat to 300 °C, in the post-IR IRSL dating protocol.     

Identifying well-bleached quartz using the different bleaching rates of quartz and feldspar luminescence signals

When dating older sedimentary deposits using quartz, there are no unambiguous methods for identifying the presence of incomplete bleaching. Current statistical analysis of dose distributions depends entirely on the assumption that incomplete bleaching and mixing are the main causes of any excess dispersion in the distribution; the only existing way to test this assumption is using independent age control. Here we suggest a new approach to this question, based on the differential bleaching rates of quartz and feldspar luminescence signals. We first present data that confirm the differences in relative bleaching rates of quartz optically stimulated luminescence (OSL) and feldspar luminescence stimulated at 50 °C by infrared light (IR₅₀) and feldspar luminescence stimulated at 290 °C by infrared light after a stimulation at 50 °C (pIRIR₂₉₀), and use recently deposited samples to determine the likely significance of the difficult-to-bleach residual feldspar signals in non-aeolian samples. For a set of mainly Late Pleistocene non-aeolian sediments, large aliquot quartz doses are then used to predict feldspar doses (based on a knowledge of the sample dose rates). The differences between observed and predicted feldspar doses as a function of the quartz dose, combined with a conservative assumption concerning the relative feldspar and quartz residual signals after natural bleaching prior to deposition, are used to identify those samples for which the quartz is very likely to be well bleached (20 out of 24). Two of these apparently well-bleached samples are then examined using single-grain quartz dose distributions; one of these is consistent with the well-bleached hypothesis, and one indicates poor bleaching or a multi-component mixture. However, independent age control makes it clear that the large aliquot data are more likely to be correct. We conclude that a comparison of quartz and feldspar doses provides a useful independent method for identifying well-bleached quartz samples, and that it is unwise to apply statistical models to dose distributions without clear evidence for the physical origins of the distributions.     

An in vitro thermal analysis during different light-activated hydrogen peroxide bleaching

This study measured the critical temperature reaching time and also the variation of temperature in the surface of the cervical region and within the pulp chamber of human teeth submitted to dental bleaching using 35% hydrogen peroxide gel activated by three different light sources. The samples were randomly divided into 3 groups (n = 15), according to the catalyst light source: Halogen Light (HL), High Intensity Diode Laser (DL), and Light Emmited Diode (LED). The results of temperature variation were submitted to the analysis of variance and Tukey test with p < 0.05. The temperature increase (mean value and standard deviation) inside the pulp chamber for the HL group was 6.8 ± 2.8°C; for the DL group was 15.3 ± 8.8°C; and for the LED group was 1.9 ± 1.0°C for. The temperature variation (mean value and standard deviation) on the tooth surface, for the group irradiated with HL was 9.1 ± 2.2°C; for the group irradiated with DL were 25.7 ± 18.9°C; and for the group irradiated with LED were 2.6 ± 1.4°C. The mean temperature increase values were significantly higher for the group irradiated with DL when compared with groups irradiated with HL and LED (p < 0.05). When applying the inferior limits of the interval of confidence of 95%, an application time of 38.7 s was found for HL group, and 4.4 s for DL group. The LED group did not achieve the critical temperatures for pulp or the periodontal, even when irradiated for 360 s. The HL and DL light sources may be used for dental bleaching for a short period of time. The LED source did not heat the target tissues significantly within the parameters used in this study.     

Annealing studies of irradiation effects in vitreous silica

Abstract

This paper describes a series of annealing experiments devoted to the study of the thermal behaviour of B₂ and E' centres produced by heavy-ion irradiations in v-SiO₂. Thermal bleaching of the B₂ component is shown to be complete and irreversible at relatively low temperatures (?500°C). On the other hand, bleaching of E' in the same range is reversible and the corresponding absorption band can be entirely recovered in subsequent electron irradiations, suggesting the existence of a stable precursor defect for this centre. By alternating isochronal annealing cycles with electron re-irradiations, the annealing of such defects was investigated up to 1000°C, taking care to compare the behaviour of the heavy-ion damaged material with that of undamaged material. The results seem to suggest a structural difference between pre-existing E' precursors of normal SiO₂ and those produced in excess by displacing radiation, the latter being characterized by a distinct process of destruction with an activation energy Q ?0.6 eV.     

Establishing an ultrasound-assisted activated peroxide system for efficient and sustainable scouring-bleaching of cotton/spandex fabric

This study presents a high-efficient and cost-effective ultrasound-assisted strategy for one-bath one-step scouring and bleaching of cotton/spandex fabric using sodium percarbonate (SPC) and tetraacetylenediamine (TAED) couple. SPC plays both roles of pH regulator and H₂O₂ donor to initiate the peracetic acid (PAA) release from TAED. The significance and interaction effects of operating parameters (TAED concentration, temperature and time) on the WI (Whiteness Index) of fabrics were investigated through a central composite design. The bleaching mechanism was studied by exploring the relationship between WI and PAA and hydroxyl radical (HO·) concentrations. The mechanical and dyeing performances of treated fabrics were also evaluated. Results show that temperature exerted a significant impact on WI followed by TAED concentration and time. The PAA concentration decreased and HO· concentration increased upon the temperature rise. Both PAA and HO· were significant to upgrade WI and ultrasound was effective in enhancing their bleaching efficiency. The fabric treated only with 15 mmol/L TAED and 10 mmol/L SPC at 40 °C for 40 min under ultrasound could achieve a WI of 68.6 (43% higher than greige fabric), which was almost equivalent to that of the fabric treated at 60 °C without ultrasound. This verifies the contribution of ultrasound technology in reducing bleaching temperature for energy-saving purpose. Moreover, the treated fabric displayed less than 5% tensile strength loss, having a marginal impact on the apparel performance. The wettability of fabric was greatly improved leading to a good dyeing performance. Encouraging results demonstrate the high efficiency of the ultrasound-assisted pre-treatment process of cotton/spandex fabric, which contributes to the sustainable production of textiles.     

Ultrasonic pilot-scale reactor for enzymatic bleaching of cotton fabrics

The potential of ultrasound-assisted technology has been demonstrated by several laboratory scale studies. However, their successful industrial scaling-up is still a challenge due to the limited pilot and commercial sonochemical reactors. In this work, a pilot reactor for laccase-hydrogen peroxide cotton bleaching assisted by ultrasound was scaled-up. For this purpose, an existing dyeing machine was transformed and adapted by including piezoelectric ultrasonic devices. Laboratory experiments demonstrated that both low frequency, high power (22 kHz, 2100 W) and high frequency, low power ultrasounds (850 kHz, 400 W) were required to achieve satisfactory results. Standard half (4 g/L H₂O₂ at 90 °C for 60 min) and optical (8 g/L H₂O₂ at 103 °C for 40 min) cotton bleaching processes were used as references. Two sequential stages were established for cotton bleaching: (1) laccase pretreatment assisted by high frequency ultrasound (850 kHz, 400 W) and (2) bleaching using high power ultrasound (22 kHz, 2100 W). When compared with conventional methods, combined laccase-hydrogen peroxide cotton bleaching with ultrasound energy improved the whitening effectiveness. Subsequently, less energy (temperature) and chemicals (hydrogen peroxide) were needed for cotton bleaching thus resulting in costs reduction. This technology allowed the combination of enzyme and hydrogen peroxide treatment in a continuous process. The developed pilot-scale reactor offers an enhancement of the cotton bleaching process with lower environmental impact as well as a better performance of further finishing operations.     

Time-resolved OSL studies on BeO ceramics

Time-Resolved Optically Stimulated Luminescence (TR-OSL) from BeO ceramics was investigated using a blue laser (445 nm) as stimulation light source. It was observed that, at relatively low dose levels (up to ∼25 Gy) the TR-OSL decay curve can be approximated with a single exponential decay function with a lifetime of ∼26 μs at room temperature. Beyond 25 Gy a new decay component with a lifetime of a ∼2 μs was observed in addition to the ∼26 μs component. Thermal stability, radiation dose response, optical bleaching, measurement temperature dependence of the components of the TR-OSL signal were investigated in detail. As result of these studies, a new OSL component which becomes unstable after 150 °C was observed. OSL decay rate of this component was found to be higher than the one which becomes unstable after 300 °C. In order to obtain information about the temperature dependence of the luminescence efficiency, luminescence emission lifetime was determined in the temperature range from 30 to 130 °C with 10 °C steps. Using the temperature dependence of the lifetime, thermal quenching energy was determined to be around 0.56 eV for the 26 μs component. For the ∼2 μs component an enhancement in the component intensity was observed pointing to a thermally assisted process with activation energy of 0.15 eV.     

Vacuum annealing effects in lithium niobate

A series of undoped LiNbO₃ crystals have been subjected to heat treatments in a reducing atmosphere, i.e., a vacuum. Electron spin resonance spectra of Fe³⁺ and Mn²⁺ ions, infrared absorption of OH^- molecules, and optical absorption peaking near 500 nm were observed to change as a function of annealing temperature. After reduction above 700°C, subsequent optical bleaching near 77 K significantly enhanced a Nb⁴⁺ electron spin resonance spectrum.     

Comparison of the properties of various optically stimulated luminescence signals from potassium feldspar

Various optically stimulated luminescence signals from K-feldspar have been used to determine the equivalent doses of sediment samples. Understanding the properties of these optical signals is critical to evaluate their applicability and limitations to optical dating. In this paper, some properties of IRSL, post-IR OSL and post-IR IRSL signals (detected in the UV region using U-340 filters) from a museum sample of K-feldspar were investigated by analyzing the relationships between optical and TL signals, and the effect of optical bleaching and heating on optical signals. The trap parameters of the different optical signals were calculated using the pulse annealing method. The results show that this sample exhibits two regenerated TL peaks at ～140 and ～330 °C. Corresponding to the low temperature TL peak, the OSL and post-IR OSL signals appear to be more associated with lower temperature TL than the IRSL signal measured at 50 °C. Corresponding to the high temperature TL peak, the post-IR IRSL signals mainly originate from the more thermally stable traps associated with the high temperature TL, compared with the IRSL and post-IR OSL signals. However, the post-IR IRSL_225 °C signal is shown to be hard to be bleached by blue light and simulated sunlight, compared with the IRSL_50 °C and low temperature post-IR IRSL signals. The implication for optical dating is that the elevated temperature post-IR IRSL signals can be preferentially applied over other signals from K-feldspar, but it is desirable that the effectiveness of the pre-depositional zeroing of these signals is assessed.     

Absorption and thermal glow of x-irradiated NaCl:Sr

Experiments were carried out to seek correlation between colour centre absorption and thermoluminescence of strontium-doped sodium chloride crystals. The results obtained suggest that the thermal glow at 410°K results from the thermal bleaching of Z₂ centres.     

Optical detection of organic hydrides with platinum-loaded tungsten trioxide

Tungsten trioxide powder with loading 0.1 wt% platinum (Pt/WO₃) was prepared for optical detection of organic hydrides such as cyclohexane, decalin by impregnation with PtCl₆^2? and subsequent calcination in air at 500 °C. The scanning electron microscopic observation of Pt/WO₃ shows that the Pt particles with mean diameters of 80–100 nm were on the surface of the WO₃ powder. The Pt/WO₃ showed coloration for 13% cyclohexane at higher 100 °C and for 1.3% cyclohexane at 200 °C. The in-situ XRD results of the Pt/WO₃ in coloring/bleaching change indicate that the coloring of Pt/WO₃ was caused by transformation of WO₃ to tungsten bronze. The analysis of reacted gas demonstrates that Pt on WO₃ produces only hydrogen and benzene through dehydrogenation of cyclohexane over 100 °C. It was founded that the Pt/WO₃ has potential of optical detection of organic hydrides by heating at higher 100 °C.     

Component resolved OSL dose response and sensitization of various sedimentary quartz samples

The structure of the linearly modulated optically stimulated luminescence (LM-OSL) signal was studied for four sedimentary quartz samples, collected from different sites around Istanbul, Turkey. Applying a computerized deconvolution analysis to the LM-OSL curves, at least six individual components of first-order kinetics were identified and photoionization cross-section of each component was evaluated. The OSL dose–response curve of each component for each quartz sample was obtained, showing a remarkable differentiation from component to component. The behavior of a highly dosed sample to successive LM-OSL measurements was also studied showing a stable recuperation signal in the position of the “slow” and “medium” components and high resistance to OSL bleaching of the “slow” component. The individual sensitivity of each component as a function of the activation temperature was obtained. The sensitivity of each component was normalized over the respective sensitivity of the glow-peak at 110 °C of quartz in order to investigate the ability of the 110 °C glow-peak to act as a correction factor for all components of the LM-OSL curves examined.     

The effect of power bleaching actived by several light sources on enamel microhardness

The purpose of this study was to evaluate the influence of different light sources for in-office bleaching on surface microhardness of human enamel. One hundred and five blocks of third molars were distributed among seven groups. The facial enamel surface of each block was polished and baseline Knoop microhardness of enamel was assessed with a load of 25 g for 5 s. Subsequently, the enamel was treated with 35% hydrogen peroxide bleaching agent and photo-activated with halogen light (group A) during 38 s, LED (group B) during 360 s, and high intensity diode laser (group C) during 4 s. The groups D (38 s), E (360 s), and F (4 s) were treated with the bleaching agent without photo-activated. The control (group G) was only kept in saliva without any treatment. Microhardness was reassessed after 1 day of the bleaching treatment, and after 7 and 21 days storage in artificial saliva. The mean percentage and standard deviation of microhardness in Knoop Hardness Number were: A 97.8 ± 13.1 KHN; B 95.5 ± 12.7 KHN; C 84.2 ± 13.6 KHN; D 128.6 ± 20.5 KHN; E 133.9 ± 14.2 KHN; F 123.9 ± 14.2 KHN; G 129.8 ± 18.8 KHN. Statistical analysis (p < 0.05; Tukey test) showed that microhardness percentage values were significantly lower in the groups irradiated with light when compared with the non-irradiated groups. Furthermore, the non-irradiated groups showed that saliva was able to enhance the microhardness during the measurement times. The enamel microhardness was decreased when light sources were used during the bleaching process and the artificial saliva was able to increase microhardness when no light was used.     

Investigating the thermally transferred optically stimulated luminescence source trap in fired geological quartz

The pre-dosed thermoluminescence (TL) emission of quartz has been found to be useful in retrospective dosimetry and archaeometry. Though the pre-dosed optically stimulated luminescence (OSL) and TL emissions have been reported to be similar, the former has been found to be un-reliable for the equivalent dose estimation. As this measurement protocol involves thermal heating at around 400 °C, the work reported in this paper investigated the influence of this heating on the OSL using fired specimens from various regions. The results suggested that the discrepancy in the behaviour of two emissions is caused by the presence of the thermally transferred optically stimulated luminescence (TT-OSL) induced by thermal-activation involved in the pre-dose treatment. This transferred signal was observed to be very significant in the case of samples containing a prominent higher-temperature TL peak at ∼375 °C. The characterization of this signal based on (i) the nature of the glow curves, (ii) thermal-annealing of the OSL trap, (iii) observation of the TT-OSL, (iv) bleaching of the source trap and (v) the correlation between TL and OSL seems to suggest that the trap corresponding to this TL peak is the source trap in the TT-OSL emission mechanism.     

Sonochemical and hydrodynamic cavitation reactors for laccase/hydrogen peroxide cotton bleaching

The main goal of this work is to develop a novel and environmental-friendly technology for cotton bleaching with reduced processing costs. This work exploits a combined laccase–hydrogen peroxide process assisted by ultrasound. For this purpose, specific reactors were studied, namely ultrasonic power generator type K8 (850 kHz) and ultrasonic bath equipment Ultrasonic cleaner USC600TH (45 kHz). The optimal operating conditions for bleaching were chosen considering the highest levels of hydroxyl radical production and the lowest energy input. The capacity to produce hydroxyl radicals by hydrodynamic cavitation was also assessed in two homogenizers, EmulsiFlex®-C3 and APV-2000. Laccase nanoemulsions were produced by high pressure homogenization using BSA (bovine serum albumin) as emulsifier. The bleaching efficiency of these formulations was tested and the results showed higher whiteness values when compared to free laccase. The combination of laccase–hydrogen peroxide process with ultrasound energy produced higher whiteness levels than those obtained by conventional methods. The amount of hydrogen peroxide was reduced 50% as well as the energy consumption in terms of temperature (reduction of 40 °C) and operating time (reduction of 90 min).     

Behavior of Volatile Elements in the Graphite Furnace in the Presence of Silver as Matrix Modifier

The effect of silver, as an aqueous solution of AgNO₃, on the pretreatment and atomization behaviour of As, Cd, Bi, Hg, Pb, Sb, Se, Sn and Tl during electrothermal atomic absorption spectrometry has been investigated. The presence of silver in the graphite furnace leads to thermal stabilisation of all investigated volatile elements to allow higher pyrolysis temperatures. The maximum, loss‐free, pretreatment temperatures (°C) in the presence of 100 µg Ag by atomization from the wall or from a platform are respectively: As (1500°C, –); Cd (800°C, 800°C); Bi (700°C, 700°C); Hg (250°C, –); Pb (600°C, 900°C); Sb (1200°C, 1200°C); Se (1400°C, 1400°C); Sn (1100°C, 1100°C) and Tl (1000°C, 1100°C). Also, silver facilitates a relatively low atomization temperature (°C) from the wall for Cd (1300°C), Bi (1700°C), Pb (1400°C), Se (1900°C) and Tl (1400°C). In addition, silver enhances the measurement sensitivity by a factor of 1.2–1.8.     

The interpretation of quartz optically stimulated luminescence equivalent dose versus time plots

Numerical modelling has shown that the form of the quartz OSL shine plateau (hereafter ‘D_e(t)-plot’) is influenced by the effects of phototransferred TL in the ∼110°C region. It is suggested also that the presence of multiple OSL components (as described by Bailey, Smith and Rhodes, 1997. Partial bleaching and the decay form characteristics of quartz OSL. Radiat. Meas., 27, 123–136; Bailey, 1998. The form of the optically stimulated luminescence signal of quartz: implications of dating. Unpublished PhD thesis, University of London) affects the form of the D_e(t)-plot. Laboratory measurements of a fully reset and artificially dosed sample yielded non-flat D_e(t)-plots, the deviation being greater for the larger of the two simulated palaeodoses, in accordance with theoretical predictions. It is suggested that the so-called ‘shine plateau’ test is of limited use in assessing the bleaching history of quartz sediments.     

Hot electron studies of lattice damage created in silicon by implantation of 2.8 MeV protons

Abstract

In this paper we report the results of a study of the annealing properties of the ionized defect density associated with the damage created in the silicon lattice by implantation of 2.8 MeV protons at room temperature. In particular, the annealing of damage created by implanting to a level of 4.43 × 10¹² protons/cm² is reported. The resulting isochronal annealing curve covered the temperature range from 70°C to 460°C. Two major annealing stages are discussed, one a broad stage between 70°C to 200°C and the other an abrupt annealing stage between 440°C to 460°C. Between the temperature range 200°C to 440°C the number of ionized defects remained relatively constant. Above 460°C no detectable effects of the proton implantation remained.     

Adsorption of oxygen on Ag(110) studied by high resolution ELS and TPD

Adsorption of oxygen on Ag(110) has been studied by high resolution electron energy loss spectroscopy (ELS) and temperature programmed desorption (TPD) in the temperature range from ? 160°C to 310°C. At ? 160°C oxygen is absorbed as a diatomic species. The low vibrational frequency of the O-O stretch vibration is explained in terms of charge transfer from the metal into the π¹ antibonding orbital and donation from the π bonding orbital to the metal. A tentative model is presented, according to which the molecule is adsorbed in the grooves of the (110) surface with its axis parallel to the surface. It is explicitly shown that this diatomic species is the precursor for dissociative adsorption of oxygen at temperatures above ? 100°C. Upon dissociation part of the diatomic species is desorbed. Between ? 100°C and + 310°C a single type of adsorbed atomic oxygen is observed which is desorbed at 310°C. Above 150°C adsorbed atomic oxygen also diffuses to subsurface sites. Below 450°C subsurface oxygen neither desorbs nor diffuses into the bulk, although it does exchange with adsorbed atomic oxygen at a temperature below 310°C. Therefore, both forms of atomic oxygen coexist at temperatures at which ethylene epoxidation occurs.