Spectroscopic diagnostics of barrier-discharge plasma in mixtures of cadmium diiodide vapor with gases

The spectral characteristics of the emission of atmospheric-pressure gas-discharge plasma in mixtures of cadmium diiodide vapor with gases (Ne, Ar, Kr, Xe, and N₂) were investigated along with the time characteristics of the voltage and current. The gas-discharge plasma was produced and excited by a barrier discharge at a repetition rate of sine voltage pulses of up to 140 kHz. The discharge emission was analyzed in the spectral range 200–900 nm with a high resolution (0.05 nm). Radiation from exciplex CdI(B-X) molecules and excimer I₂* molecules was revealed, as well as the atomic lines of cadmium, iodine, and inert gases. In a mixture with xenon, radiation from exciplex molecules XeI(B-X, B-A) was also found. This radiation prevailed in the spectra at mixture temperatures up to 150°C. The further increase of the temperature leads to the prevalence of the CdI(B-X) radiation. It was found that the most intense CdI(B-X) radiation is observed in mixtures CdI₂/Xe(N₂)/Ne. Regularities in the spectral characteristics of the emission of the gas-discharge plasma are discussed.     

Emission characteristics of a discharge iodine vapor plasma in the spectral region of the main absorption maximum of DNA molecules

Radiation of glow and capacitive discharges in inert gas-iodine vapor mixtures is studied in the spectral range 150–210 nm, which coincides with the main absorption maximum of the DNA molecules. Iodine atomic spectral lines at 150.7, 161.8, 170.2, 183.0, and 206.2 nm are observed in the spectra. The emission intensity of the iodine spectral lines is optimized by varying the glow discharge current, capacitive discharge frequency, as well as pressure and composition of the gas mixtures. The glow and capacitive discharges are ignited in cylindrical quartz tubes with interelectrode gaps of 10 and 6 cm. Helium and neon are found to be the most effective buffer gases. The optimum partial pressures of the light inert gases and iodine vapor in the glow discharge are within 0.4–0.6 kPa and 100–150 Pa, respectively. In the capacitive discharge in He(Ne)-I₂ mixtures, the optimum partial helium, neon, and iodine vapor pressures are within 0.8–2.0 kPa, 0.5–1.0 kPa, and ≤ 60 Pa, respectively. It is demonstrated that pulsed bactericidal radiation sources with light pulse lengths of 400–500 ns and continuous radiation sources emitting within the spectral range 150–207 nm can be designed on the basis of low-density iodine vapor plasma.     

Spectral characteristics of a broadband exciplex spontaneous emission source upon mixtures of the cadmium dibromide vapor with gases

The spectral characteristics of radiation from atmospheric-pressure gas-discharge plasma in mixtures of cadmium dibromide vapor with gases (Ne, Ar, Kr, Xe, and N₂), as well as the temporal characteristics of the voltage and current, have been investigated. A barrier discharge at the repetition frequency of sine voltage pulses up to 140 kHz has been used to create the gas-discharge plasma and excite the components of the working mixture. The discharge radiation has been analyzed in the spectral range 200–900 nm with a high resolution (0.05 nm). In the spectra, we have revealed radiation from exciplex molecules CdBr(B → X) and CdBr(C → X), atomic lines of cadmium and inert gases, and, in mixtures with xenon, radiation of exciplex molecules XeBr(B → X, B → A). The XeBr(B → X) radiation prevailed in the spectra at mixture temperatures up to 200°C. The further increase of the temperature resulted in the prevalence of the CdBr(B → X) radiation. The most intense CdBr(B → X) radiation was observed in mixtures of CdBr₂/Xe. When the temperature of the mixture was higher than 250°C, the discharge radiation had a silvery-white color. Regularities in the spectral characteristics of the radiation from the gas-discharge plasma are discussed. The high-frequency atmospheric-pressure barrier discharge in mixtures of cadmium dibromide with gases, excited by sine voltage pulses, can be used in multiwave and broadband excilamps, operating in the UV and visible regions.     

Emission characteristics of a high-power glow discharge plasma in a mixture of inert gases with bromine and iodine vapor

The results of an investigation of the UV radiation from the plasma of a dc glow discharge in mixtures of inert gases with bromine and iodine molecules are presented. The current-voltage and spectral characteristics of a longitudinal glow discharge with a power of 10–250 W are studied. The power and the efficiency of the total UV radiation of the plasma, as well as the power of radiation at the spectral line of the iodine atom at 206.2 nm, are optimized as functions of the power deposited into the plasma and the composition of the gas mixture. In active media based on Kr-Br₂ mixtures, the molecular emission of the plasma was represented by bands at 207 (KrBr(B-X)) and 289 nm (Br ₂ ^* ), while, in He-Xe-I₂ mixtures, it was represented by bands at 253 (XeI(B-X)) and 342 nm (I₂).     

Emission characteristics of plasma of a transverse volume discharge in mixtures of helium, argon, and krypton with sulfur hexafluoride

The emission characteristics of the plasma of repetitively pulsed spontaneous UV-VUV radiation sources on the basis of ArF* (193 nm) and KrF* (249 nm) molecules, and the products of decomposition of sulfur hexafluoride molecules pumped by a transverse volume discharge in a mixture of inert gases with sulfur hexafluoride molecules have been investigated. The discharge emission spectra in the range of 190–780 nm at the low-current and high-current stages of the transverse discharge, the time characteristics of the voltage across the electrodes, the pump current, and the emission of excimer molecules and the products of decomposition of sulfur hexafluoride have been studied. It is shown that, in the gas-static operation mode of the radiator at the number of discharge pulses smaller than 10³, the 193-nm ArF* and 249-nm KrF* bands are main in the emission spectrum. Upon further operation of the radiator, a spectral continuum is formed on the basis of sulfur molecular bands in the range 260–550 nm.     

Characteristics of a high-frequency barrier discharge in mixtures of mercury diiodide vapor with gases

The spectral and electric characteristics of atmospheric-pressure high-frequency barrier discharge plasma based on mixtures of mercury diiodide with neon and admixtures of argon, xenon, and nitrogen are analyzed. A repetition rate of sinusoidal voltage pulses of about 100 kHz is used both to produce the gas discharge plasma and to excite the components of the working mixture. The radiation of the discharge in the range 200–900 nm is analyzed with a high resolution. It is found that, in the range 400–900 nm, the system of bands of excimer molecules HgI(B → X) emits 85% of the barrier discharge radiation. It is established that the radiation intensity of HgI(B → X) molecules is maximal in the mixture HgI₂/Xe/Ne = 0.6/10/90 kPa. In this mixture, UV radiation of molecules XeI(B → X) and XeI(B → A) is observed. The regular features of the spectral and electric characteristics of the gas discharge plasma are discussed. An atmospheric-pressure high-frequency barrier discharge in mixtures of mercury diiodide with gases is of interest for use in a selective (Δλ = 438–446 nm) excilamp with a cylindrical working aperture.     

Emission characteristics of a glow discharge in a mixture of heavy inert gases with iodine vapor

The results of a systematic investigation of the emission characteristics of a low-pressure UV excimer-halogen lamp pumped by a longitudinal dc glow discharge are presented. The discharge was initiated in mixtures of heavy inert gases with iodine vapor at a total pressure of 100–2000 Pa and a power deposited into the plasma of 10–100 W. Current-voltage characteristics of the glow discharge and emission spectra of the plasma in the region of 190–360 nm are studied. The radiation intensity at the resonance line of the iodine atom (206.2 nm) and the intensity at the peaks of the XeI(B-X) (253 nm) and I₂(B-X) (342 nm) emission bands are analyzed as functions of the pressure and partial composition of the mixtures of Ar, Kr, and Xe with iodine vapor, as well as the electric power of the glow discharge. The most efficient gas mixtures are determined for an electric-discharge UV iodine vapor lamp with continuous-wave emission and a long service life before a change of the mixture is required.     

Spectral characteristics of a barrier discharge in cadmium dihalide vapor-inert gas mixtures

Spectral characteristics of a barrier-discharge plasma produced in atmospheric-pressure mixtures of cadmium diiodide and cadmium dibromide vapors with neon, krypton, and xenon at a repetition rate of sine voltage pulses up to 130 kHz are studied. The emission from the discharge is studied within the spectral range 200–900 nm with a resolution of 0.05 nm. Emission of exciplex molecules CdI(B → X) and CdBr(C, B → X), and cadmium and inert gas atoms is revealed, as well as emission of exciplex molecules XeI(B → X, A) and XeBr(B → X, A) in xenon-containing mixtures. The emission of xenon halides prevails in the spectra at a mixture temperature up to 200°C. With a further temperature increase, the emission of cadmium halides becomes dominating. It is ascertained that the most intense emissions of CdI(B → X) and CdI₂/CdBr₂/Xe/Kr and CdBr(B → X) molecules are observed, respectively, in CdI₂/CdBr₂/Xe/Kr and CdI₂/CdBr₂/Xe mixtures. The cadmium dihalide-inert gas mixtures are of interest for the use as a radiating gas in a multiwavelength and broadband excilamp emitting in the UV and visible spectral ranges.     

Optical characteristics of the steady-state plasma of a longitudinal discharge in a He/CFC-12 mixture

The emission from the plasma of a contracted longitudinal dc discharge in a He/CF₂Cl₂ mixture in the wavelength range 130–300 nm is investigated. It is shown that the discharge plasma emits within the range 150–260 nm. The emission consists mainly of the broad bands of Cl₂ molecules and single-charged chlorine ions. The pressure and composition of the working mixtures, the discharge current, and the time during which the emitter can operate on a single gas fill are optimized to attain the best characteristics of UV and VUV radiation. The results obtained are of interest for developing a steady-state source of VUV and UV radiation to be applied in microelectronics, photochemistry, and medicine.     

Emissivity of the pulsed capacitive discharge in helium-iodine and neon-iodine mixtures

The emission parameters of a pulsed capacitive discharge initiated in helium-iodine and neon-iodine mixtures are reported. The discharge plasma emits at wavelengths of 183.0 and 206.2 nm, which correspond to iodine atom spectral lines. The capacitive discharge is initiated in a cylindrical quartz tube with an electrode distance of 10 cm. The discharge radiation is optimized in exciting pulse repetition rate and helium and neon pressures in He(Ne)-I₂ mixtures. The optimal pressures of helium, neon, and iodine vapor fall into the ranges 0.8–2.0 kPa, 0.5–1.0 Pa, and ≤60 Pa, respectively.     

Output characteristics and parameters of the plasma from a gas-discharge low-pressure ultraviolet source using helium-iodine and xenon-iodine mixtures

The output characteristics and parameters of the plasma of a powerful gas-discharge source of UV radiation are studied. The UV source uses He-I₂ and Xe-I₂ mixtures and is excited by a longitudinal glow discharge. The pressure of the gas mixtures is varied from 100 to 1500 Pa, and the discharge power falls into the range 15–250 W. The source (lamp) emits in the spectral interval 200–390 nm, which covers the spectral line of the iodine atom at 206.2 nm, the spectral band of XeI(B-X) with a maximum at 253 nm, and the spectral band of with a maximum at 342 nm. For He(Xe)-I₂ mixtures at a pressure of 800–1000 Pa (this pressure range is near-optimal according to our experimental data), the electron energy distribution functions and the electron kinetic coefficients as functions of parameter E/N (E is the electric field strength, and N is the particle concentration in the discharge) are calculated. The calculated plasma parameters are used in the qualitative analysis of key electronic processes in the plasma of an exciplex halogen UV source and will be subsequently employed in numerical simulation of the process kinetics and output characteristics of a UV source based on helium-iodine or xenon-iodine mixtures.     

The double M-effect induced by noble gases activated with negative ions

The M-effect (monochromatization-effect) is a powerful tool which can give high intensity monochromatic spectra with a certain wavelength depending on the type of used gas mixtures to generate plasma state. The effect consists in the emission of a single spectral line of plasmas ignited in certain gas mixtures. The main condition to obtain the M effect is the presence of an electropositive and an electronegative gas mixture. For example, in the case of Ne+H₂ monochrome radiation was obtained, the wavelength of Ne being 585.3 nm (1s²–2p⁵). In this paper we prove the general character of this effect, i.e. if the optical emission spectra reduced to nearly one line can be observed also in other gas mixture discharges, for example in the case of one electronegative gas and two electropositive gases. Different other mixtures, as Xe+Ne+H₂ and Xe+Ar+H₂ have been studied. In all these cases, the M-effect appeared without doubt.     

Optical characteristics of plasma of I*<Subscript>2</Subscript>, Cl*<Subscript>2</Subscript>, Br*<Subscript>2</Subscript> halogen dimer barrier-discharge excilamps

Barrier-discharge excilamps operating in homonuclear chlorine, bromine, and iodine and their mixtures with inert gases have been studied. The spectral and energy characteristics of the barrier-discharge plasma have been obtained. The conditions have been determined at which the band D′ → A′ predominates in the spectra of molecules I*₂ (342 nm), Cl*₂ (257.8 nm), and Br*₂ (291 nm). The efficiencies of I₂, Cl₂, and Br₂ excilamps were found to be 1.6, 2, and 3.8%.     

Emission characteristics of plasma based on xenon–rubidium bromide mixture

Luminescence spectra of a longitudinal pulse-periodic discharge in xenon mixture with rubidium bromide vapors (Xe–RbBr) are studied experimentally at low pressures. The conditions leading to the appearance of intense bands of ultraviolet radiation of exciplex XeBr* molecules in the spectral interval between 200 and 400 nm are found. The highest yield of UV radiation of XeBr* molecules is achieved when the temperature of discharge-tube walls is equal to 750°C. A maximum power of UV radiation from the entire plasma volume as high as 4.8 W is obtained.     

Radiative characteristics and kinetics of processes in low-pressure gas-discharge lamps based on a mixture of helium and iodine vapors

The UV radiation of glow- and capacitive-discharge lamps based on mixtures of inert gases with iodine vapors are optimized in the spectral range of 175–360 nm, in which working helium-iodine mixtures of different compositions are used. The most intense spectral lines in the bactericidal region of the spectrum were the atomic lines of iodine (183.0, 206.2 nm), and in the region of 320–360 nm, emission of the spectral band of an iodine molecule prevailed with a maximum at λ = 342 nm. For a capacitive lamp with a casing opaque in the spectral range λ < 250 nm, the main part of the plasma emission power is concentrated in the A′-D′ band of an iodine molecule with a maximum at 342 nm. The emission brightness of this lamp is optimized in iodine molecule transitions depending on the partial helium pressure. We present the results of simulating the kinetics of processes in a glow-discharge plasma in mixtures of He, Xe, and iodine vapors. We establish the dependence of the main part of the emission intensity of the 206.2 nm spectral line of an iodine atom and the 342 nm band of an iodine molecule on the helium pressure in a glow-discharge lamp operating on a He-I₂ mixture.     

Formation of monochlorides of heavy inert gases in a high-frequency transverse discharge plasma

Emission characteristics of a high-frequency transverse discharge plasma in mixtures of argon and xenon with chlorine molecules are presented. It is shown that the discharge in xenon-chlorine mixtures is a source of broadband radiation in the spectral region 220–450 nm, while in argon-chlorine mixtures, it emits in the region 150–270 nm. Double mixtures with a partial pressure of inert gases ranging within 300–400 Pa and a chlorine partial pressure of 30-40 Pa are found to be optimal. The mean output discharge power ranges within 15–50 W.     

Radiation of the Plasma of a Transverse Discharge in a Helium–Krypton–Elegas Mixture

We carried out a spectroscopic investigation of the degradation of the active medium of a pulsed-periodic KrF emitter based on a He/Kr/SF₆ mixture (P = 10–150 kPa) with pumping by a transverse volumetric discharge. The plasma radiation spectra in the range 200–620 nm at different stages of degradation of the working mixture and the dynamics of the radiation of inert gases as well as of the products of decomposition of SF₆ molecules in the plasma are studied. It is shown that since the number of discharge pulses is 10⁴, rather effective formation of excited sulfur molecules is observed which decompose with emission in the spectral range 260–550 nm. This can be employed for developing a wideband lamp based on the system of KrF(B–X; D–X), S₂(B–X), and S₂(f–a) bands.     

Emission spectra of working mixtures of a HgBr/HgCl excimer lamp

A study of emission spectra of a gas-discharge plasma produced in a HgBr/HgCl excimer lamp, which is filled with multicomponent working mixtures at atmospheric pressure (HgBr₂ and HgCl₂ with additions of molecular nitrogen and xenon), are reported. A gas-discharge plasma was produced by high-frequency (pulses ～100 ns long with a repetition rate of up to 2000 Hz) barrier and surface discharges, which took place simultaneously. Emission of HgBr* and HgCl* excimer molecules, the second positive system of molecular oxygen, and helium and xenon lines in the UV, visible, and IR spectral regions was observed. The strongest emission of HgBr* and HgCl* molecules (the emission intensities were in the ratio 10:1) was observed in the HgBr₂: HgCl₂: N₂: He mixture. Regularities in spectral and integrated characteristics of gas-discharge plasma emission are discussed.     

Luminescence of XeCl* and XeBr* exciplex molecules initiated by a longitudinal pulsed discharge in a three-component mixture of Xe with CsCl and CsBr vapors

The excitation of simultaneous luminescence of XeCl* and XeBr* exciplex molecules in a longitudinal pulsed-periodic discharge has been studied. To generate exciplex molecules, a three-component mixture of xenon with cesium bromide and chloride vapors was used. Spectral, energetic, and pulse-temporal characteristics of the discharge have been investigated, and the dependences of the UV luminescence yield on the composition and excitation conditions of the mixture have been studied. The average specific power of the discharge UV radiation in the Xe-CsBr-CsCl mixture has been determined to be 0.25 W/cm³, which corresponds to the total efficiency value ～0.7%. Also, mechanisms by which exciplex molecules are formed in a low-pressure vapor-gas mixture of the inert gas with halogenides of alkali metals have been considered.     

Wide-band exciplex halogen lamps operating on inert gas mixtures with chlorine and Freon-12 molecules

The results of analysis of the spectral characteristics of short-wave radiation sources operating on transitions in argon, krypton, and xenon monohalogenides, as well as chlorine molecules, excited by a longitudinal low-pressure glow discharge are considered. Radiation emitted by ArCl^*, KrCl^*, XeCl^*, Cl ₂ ^** , and Cl ₂ ^* molecules in a spectral range of 170–350 nm is optimized using complex working mixtures of Ar-Kr-(Xe)-Cl₂ in the lamps. The average radiation power of the lamps ranges from 1 to 10 W for an efficiency of ≤25%. Optimization of wide-band lamps on transitions in chlorine molecules and the decay products of Freon-12 molecules (CF₂Cl₂) is carried out on mixtures of helium with chlorine and Freon-12 molecules. This makes it possible to develop lamps emitting in a spectral range of 140–270 nm and containing no costly inert gases (Xe or Kr) in their working mixtures. Exciplex halogen lamps with a wide-band emission spectrum in the VUV-UV range can be used in spectrometers as radiation sources in experiments with absorption and in high-energy chemistry, ecology, and medicine.