Academic literature on the topic 'Pink afterglow'

CaTiO3:Pr3+ was prepared by high temperature solid state reaction and measured by SEM, XRD, excitation and emission spectra. The samples obtained possessed orthorhombic crystal structure of CaTiO3, belonging to Pbnm space group. Excitation spectra of the samples were broad band, their peaks and shoulder peaks were located at about 335nm, 379nm respectively. Emission spectra were single narrow band, emission peaks were located at about 602nm, corresponding to emission of 1D2→3H4 of Pr3+ion. The addition of Eu3+and Dy3+ as co-activator led phosphorescent intensity to greatly enhance, the addition of AgNO3 as ion compensator made the samples material pink and vibrant.

The study of plasmas generated in pure nitrogen and their afterglows are a subject of many hundreds works bringing a lot of information about the kinetic processes and energy transfer reactions. The effect of nitrogen pink afterglow has a specific position among the other kinds of discharges and post-discharges. The post-discharge, and especially the pink afterglow, is extremely sensitive to the presence of various impurities and experimental conditions (total gas pressure in a discharge tube, temperature, etc.) because of their significant influence on all kinetic processes. That is the reason, why it is so important to study this processes. The DC flowing afterglow (generated using the hollow molybdenum electrodes in the distance of 12 cm, power ± 290 W) was used for the experimental part of this work. The discharge was created in Pyrex discharge tube at different concentration ratio of nitrogen and argon. The total gas presure was in range from 500 Pa to 5000 Pa. The emission spectra of post-discharge were recorded by TRIAX 550 spectrometer with CCD detector in the range of 320-780 nm. The vibrational populations at individual vibrational levels were calculated using the emission bands of the first (N2 (B 3g) N2 (A 3u+)) and the second (N2 (C 3u) N2 (B 3g)) positive and the first negative (N2+ (B 2u+) N2+ (X 2g+) nitrogen spectral systems. The dependencies of intensity on decay time and relative vibrational populations on argon concentration and pressure were obtained. The pink afterglow was very sharp in pure nitrogen at low pressure. With the increasing total pressure it was shifted to the later decay times and it was visible for longer time, too. The same effect was observed with the increase of argon concentration in the gas mixture. At the highest argon concentrations, especially at lower pressure, the effect of pink afterglow dissapeared. The knowledge of these processes can give the solution of all kinetic reactions in plasma and this can be used in plasma chemistry and for development of new technologies. This will be a subject of further intensive studies.

Dissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico.
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Neste trabalho foram determinadas as condições experimentais necessárias para a geração do regime de pós-descarga denominado de "pink afterglow" numa descarga D.C. de N2 em fluxo. Fortes emissões oriundas dos 1o sistema negativo e 1o e 2o sistemas positivos do nitrogênio foram detectadas na região de pós-descarga até distâncias superiores a 15 cm a partir do final da descarga. Um modelo cinético para a formação das espécies radiativas responsáveis pelas emissões foi proposto para o regime de "pink afterglow". Constatou-se que, fundamentalmente são os processos vibracionais os precursores da excitação dos estados eletrônicos (B3Pg, v), (C3Pu, v) e da ionização na "pink", a qual apresenta dois mecanismos de geração distintos pela temperatura vibracional e tempo de residência das espécies. No intuito se estudar a possibilidade da tratamentos de nitretação e carbonitretação de aço no regime de "pink afterglow", introduziu-se CH4 na região de pós-descarga. Constatou-se que traços deste gás são suficientes para inibir os principais mecanismos da "pink" destruindo sua emissão. Neste caso, evidencia-se uma significativa produção de radicais CN pela forte emissão do sistema violeta do CN. Resultados preliminares sobre tratamentos de nitretação e carbonitretação em pós-descargas de N2-CH4 em regime de "pink afterglow"são apresentados.

The aim of this master thesis is a study of nitrogen post-discharge by mercury vapours titration. The nitrogen post-discharge is investigated for many years theoretically as well as for a practical use. The object of this master thesis is a study of kinetic processes ongoing at titrations of mercury vapours during the nitrogen post-discharge at different pressures and applied powers. All experimental data were obtained from an optical emission spectroscopy of nitrogen post-discharge. DC discharge in flowing regime was chosen for measurements. The first part of experiments was carried out at the constant discharge current (100 mA), voltage (1300 V) and wall temperature (300 K). The total gas pressure was varied in range of 500-3000 Pa at nitrogen flow in range of 0.12-0.68 l/min. Nitrogen flow values were arranged to obtain constant nitrogen flow velocity for all gas pressures. The second set of experiments studied power dependencies. The current was varied in the range of 50-200 mA for constant voltage 1300 V. The total gas pressure in this case was 1000 Pa. Mercury vapours were introduced into the system by titration tube at different post-discharge time. The nitrogen pink afterglow effect was well visible at all experimental conditions. This effect corresponds to the maximum intensity of light emission, which expresses as considerable growth of characteristic pink radiation in the post-discharge time. Optical emission spectra of post-discharge were taken in the range of 320-780 nm. Besides three nitrogen spectral systems (first and second positive and first negative), the mercury line at 254 nm was recorded in the second order spectrum at 508 nm under these conditions if mercury was added. This spectral line is excited under post-discharge conditions by collisionally induced resonance energy transfer from nitrogen highly vibrationally excited ground state metastables and it opens an unique technique for their monitoring. The dependence of relative intensities on decay time for mercury spectral line and selected nitrogen spectral systems at different titration positions were measured. The relative intensities of nitrogen bands decrease with increasing of mercury line relative intensity for all total gas pressures. The pink afterglow phenomenon shifts to the later decay times with the increasing of total gas pressure. In the case of experiments at different power, it can be seen that with decreasing power mercury spectral line intensity decreases in post-discharge time. The first detailed tests of the unique detection for highly excited of nitrogen metastables were completed. However this master thesis is concentrated on the basic research which supports better indication of kinetic processes and reactions leading to transformation of excitation energy, this new knowledge should be applied in future also in technologies based on the long-lived metastable induced reactions.

The aim of this thesis is diagnose post-discharge nitrogen plasma with optical emission spectroscopy. There is long interest of investigated of nitrogen post-discharge plasma and study how to use it in theory as well as in practice. All results were measured with method of optical emission spectroscopy of post-discharge plasma. Discharge was generated by direct-current voltage generator with flowing regime. In this thesis was used for different series of experiments. First experiment was performed with adding water vapour into argon plasma. Measuring was processed at constant current 140 mA, voltage 1.5 V and pressure 1 000 Pa. It was changed flow rate and for each individual flow rate was measured in range 1–25 cm from end of active discharge. Second experiment was with adding nitrogen into argon plasma. Measuring was processed at constant current 140 mA, voltage 1.5 V and pressure 1 000 Pa. We were changing flow rate of nitrogen (0,2 sccm, 0,4 sccm and 0,8 sccm). For each individual flow rate was same experiment with changing distance from active discharge. Third experiment was about adding mercury vapour into nitrogen post-discharge. Measuring was processed at constant current 120 mA, voltage 3.5 V and pressure 1 000 Pa. Measuring was performed with two configuration: with diaphragm and without it. Last experiment was about adding air into argon plasma. Measuring was processed at constant current 140 mA, voltage 1.0 V and pressure 1 000 Pa. Temperature of outer face of tube was measured by thermocouple and infrared thermometer, was measured for last two experiments (argon – air and nitrogen). During experiments with pure nitrogen was visible phenomenon called pink afterglow which is manifested by noticeable increase pink coloration. Optical emission spectrums post-discharge was take at various range of wavelength. At argon with water vapour was 280–600 nm and at adding nitrogen into argon was at range 320–500 nm. At added mercury vapour into nitrogen was 320–600 nm. For experiment argon – air was wavelength range 320–600 nm. From results of experiments were designed dependencies of calculated intensity from measured spectra on distance from active discharge. Also were constructed dependencies of measured temperature on distance from active discharge.

Presented thesis gives results obtained during the spectroscopic observations of post –discharges of the pure nitrogen plasma with small oxygen admixture and in the nitrogen – argon mixture and the effect of the pink afterglow in it. The DC discharge in the flowing regime has been used for the plasma generation. The decaying plasma was study by optical emission spectroscopy, mainly in the range of 300–800 nm. The first positive, second positive, first negative nitrogen spectral system and NO spectral systems were observed in measured spectra. The band head intensities of these bands have been studied in the dependencies on experimental conditions. Simultaneously, the relative vibrational populations on the given nitrogen states have been calculated. Two discharge tubes made from different materials (PYREX glass and QUARTZ glass) were used in the case of nitrogen plasma containing low oxygen traces (up to 0.2 %). These experiments have been carried out at two wall temperatures for the determination of the temperature effect on the post-discharge. The discharge tube around the observation point was kept at the ambient temperature (300 K) or it was cooled down to 77 K by liquid nitrogen vapor. The total gas pressure of 1 000 Pa and the discharge current of 200 mA were conserved for all these experiments. The relative populations of electronic states were calculated in the dependence on the post-discharge time. The dependencies on oxygen concentration were given, too. The results showed no simple dependence of vibrational populations on oxygen concentration. Generally, slight increase of neutral nitrogen states populations was observed with the increase of oxygen concentration. These observations were well visible due to the intensity of nitrogen pink afterglow effect that was well visible at all oxygen concentrations. The pink afterglow maximal intensity was reached at about 5–10 ms at the wall temperature of 300 K in the PYREX tube. The molecular ion emission was strongly quenched by the oxygen and as this was dominant process for the pink afterglow emission the pink afterglow effect disappears at oxygen concentration of about 2000 ppm. The temperature and wall material influences were observed, too. The post-discharge in nitrogen argon mixtures was studied only in the PYREX tube at the ambient wall temperature of 300 K. The power dissipated in an active discharge was constant of 290 kW. The experimental studies had two new parameters – total gas pressure (500 Pa – 5 000 Pa) and the argon concentrations that were varied in the range of 0–83 %. Also in this case the dependencies of relative intensities of the bands given above were obtained and further the relative populations of electronic states as a function of decay time, total gas pressure and on argon concentration were obtained. The pink afterglow effect was observed at all applied discharge powers and total gas pressures. At the highest argon concentrations, especially at lower pressure, the pink afterglow effect disappeared. The presented experimental work is one of the hugest sets of experiments in the nitrogen with oxygen traces and in nitrogen-argon mixtures. These data can be used as a very good fundament for the further studies using wide numeric modeling of the post-discharge kinetic processes.