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.     

Ultraviolet gas-discharge lamp on iodine molecules

The emission characteristics of a pulsed-periodic UV radiation source are reported. The source excited by a pulsed-periodic capacitive discharge initiated in helium-iodine vapor, neon-iodine vapor, or krypton-iodine vapor mixtures radiates in the spectral range 200–450 nm. It is shown that most of the plasma radiation power concentrates in the integral line of the iodine atom (206.2 nm) and in the D′-A′ band of the iodine molecule with a maximum at 342 nm. The radiation intensity of the lamp is optimized in accordance with the partial pressure of the inert gases. The discharge plasma parameters that are of interest for simulating the process kinetics and the output characteristics of an UV source based on molecular iodine, atomic iodine, and xenon iodide are calculated in helium-iodine vapor and xenon-iodine vapor mixtures.     

Emission properties of a pulsed-periodic barrier discharge initiated in helium-iodine and argon-iodine mixtures

The subject of investigation is the emission properties of a pulsed-periodic barrier discharge initiated by submicrosecond pulses (f = 40–1000 Hz) in He-I₂ and Ar-I₂ mixtures. The investigation is carried out in the spectral range 200–400 nm at a pressure of the working medium of 1–100 kPa and an iodine partial pressure of 130–200 Pa. The dependence of UV emission from the plasma of the barrier discharge at the 342 nm I₂(D′ → A′) band and the iodine atom spectral line at 206.2 nm on the argon and helium partial pressures, excitation pulses repetition rate, and charging voltage of the capacitor of a short high-voltage pulse modulator is optimized. The contribution of the 206.2 nm I* spectral line to the UV emission of the barrier discharge is estimated.     

RF exciplex halogen source of UV radiation on an argon-xenon-chlorine mixture

An exciplex halogen source of UV radiation that is excited by an rf transverse discharge is studied experimentally. The active medium of the source is an Ar-Xe-Cl₂ mixture kept at a low pressure (100–1000 Pa), and its working spectral range is 220–450 nm. The radiation spectrum contains 235 nm XeCl(D-X), 257 nm Cl₂(D′-A′), 306 nm XeCl(B-X), 390 nm XeCl(C-A), and 430 nm XeCl(B-A) lines. The results of optimization of the UV power as a function of the pressure, Ar-Xe-Cl₂ mixture composition, and excitation power are reported.     

Mercury-free emitter pumped by a krypton fluoride molecule pulse-periodic barrier discharge

The characteristics of a pulsed-periodic short-barrier-discharge emitter operating at wavelength λ = 248 nm KrF(X-B) are investigated. The operating mixtures of the UV lamp are low-aggressive krypton-sulfur hexafluoride (SF6) mixtures at a total pressure in the range 1–50 kPa and a SF₆ partial pressure of 0.1–0.4 kPa. The spectral characteristics of the plasma are studied, and the 248 nm KrF(X-B) band luminosity is optimized in terms of the operating mixture composition, pump voltage, and pulse repetition rate. The mean power of UV emission from the lateral surface of the cylindrical lamp is estimated.     

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.     

Electric-discharge He/Xe/I<Subscript>2</Subscript> excimer-halogen UV lamp

The characteristics of a low-size low-pressure UV lamp operating on the atomic iodine resonant line (λ=206 nm) and xenon iodide (λ=253 nm) and dimer iodine (λ=342 nm) bands are investigated. A lamp with an interelectrode distance of 19 cm was pumped by a longitudinal dc glow discharge. The working gas mixtures were He/I₂ and He/Xe/I₂ mixtures with a total pressure of 50–1500 Pa. The output parameters of the electric-discharge excimer-halogen lamp were optimized in terms of the gas mixture pressure and composition and the power deposited in the discharge. It is shown that the total UV power emitted from the entire aperture of the lamp in the spectral range 200–350 nm attains 5–7 W with an efficiency of ≤5%.     

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.     

Short-wavelength emission characteristics of a longitudinal bromine vapor glow discharge in a quartz tube

The output emission characteristics are presented in the spectral range 150–350 nm for a longitudinal bromine vapor glow discharge in a quartz tube (inner diameter 1.4 cm, interelectrode distance 10 cm). Pressure of the working mixtures: P = 0.2–1.0 kPa. The emission spectrum of the lamp based on an He-Br₂ mixture consists of the 163.3 nm and 157.6 nm spectral lines of the bromine atom and a system of molecular bromine bands (170–300 nm). The total power of UV-VUV emission of the lamp based on an He-Br₂ mixture is 5 W max for efficiency <10%. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 816–819, November–December, 2007.     

Spectral characteristics of the emission from a barrier discharge plasma based on an Ar–H2O mixture in the UV spectral region

We present the results of a study of a barrier-discharge plasma in an Ar–H₂O mixture in the UV region of the spectrum (200–500 nm). The saturated water vapor pressure was varied over the range 2.0–2.5 kPa. A comparative study of the spectral characteristics of the plasma based on water vapor and the Ar–H₂O mixture showed that the intensity of the emission of the A → X band of the OH^● radical increases three-fold in the mixture of water with argon.     

Optical characteristics of the plasma of a transverse volume discharge in Cl2 and He/Cl2 mixtures

Results are presented from a study of UV and VUV emission from the plasma of a transverse volume discharge in chlorine and a He/Cl₂ mixture. In the wavelength range Δλ=140–300 nm, the Cl₂(D′-A′) band with an edge at 258 nm and the Cl ₂ ^* band with edge at λ=195 nm are found to be dominant. It is shown that, in the pressure range [Cl₂]=0.1–2.0 kPa, the intensity of emission with λ≤195 nm is higher than the intensity of the Cl₂(D′-A′) band. At [Cl₂]≥2 kPa, emission in the 258-nm band is dominant.     

Multiwave excimer lamps using XeF/XeCl/KrF/KrCl molecules

Results are presented of an investigation of the spectral and temporal characteristics of an electricdischarge excimer lamp emitting simultaneously on the 351 nm XeF, 308 nm XeCl, 249 nm KrF, and 222 nm KrCl transitions. The He/Kr/Xe/SF₆/HCl working mixtures were excited in a transverse discharge with ultraviolet spark preionization at a total pressure of 25–100 kPa. In order to obtain the same brightness the concentration ratio [Kr]/[Xe] for the excimer molecular transitions was 8/0.8 kPa, and that for the halogen-containing molecules was [SF₆]/[HCl][=[0.06–0.12]/[0.08–0.16] kPa. The duration of the radiation pulses for the excimer molecular transitions at atmospheric pressure was 100–200 ns and when the total mixture pressure was reduced to 250 kPa, this was doubled or trebled. The service life of the spontaneous radiation for B-X transitions in excimer molecules was 10⁵ pulses. Zh. Tekh. Fiz. 68, 64–67 (December 1998)     

Investigation of scaling laws as applied to the gas discharge in the case of a barrier-discharge-excited Kr/CCl<Subscript>4</Subscript> mixture

The electrical and luminescent characteristics of a barrier-discharge lamp filled with a Kr/CCl₄ (150: 1) mixture are experimentally studied versus the value of pd, which varies in the range (7.6–14) × 10³ Pa cm. When simulating the gas discharge using similarity parameters, the following relationships are fulfilled: for pd = const (p is the pressure, d is the interelectrode distance), the pulse duration and the mean current density are τ _j ∼ 1/p and 〈j〉 ∼ p; the surface charge density on the electrodes, σ ∼ const; the duration of the UV radiation pulse and the efficiency of UV radiation due to a KrCl* (222 nm) exciplex, τ_rad ∼ 1/p and η ∼ p ². The maximal radiation efficiency achieved in the experiments is about 13%. Deviations from the similarity laws for the gas discharge are related to the filamentary form of the observed discharge. Qualitative analysis indicates that similarity laws may be fulfilled for such a form of discharge as well but locally, within a single filament.     

Ultraviolet radiation sources on (H2O,D2O) water vapor

Emission characteristics of ultraviolet (UV) radiation from water vapor (H₂O, D₂O, and a mixture of H₂O and D₂O vapors) excited by pulse-periodic discharges with open electrodes, as well as electrodes outside the discharge tube (capacitive discharge), are presented. Radiation is studied in a spectral range of 175–350 nm. The emission characteristics of a UV radiation source based on vapors of ordinary and “heavy” water, as well as the results of optimization of brightness of radiation bands from the OH and OD radicals as functions of pressure and the composition of the He-H₂O and He-D₂O mixtures, are reported.     

On the effect of ultraviolet radiation on water vapor absorption of submillimeter waves

The submillimeter absorption spectra of pure water vapor and a water vapor + dry air mixture are experimentally studied under the conditions of illumination of the gas sample by ultraviolet (UV) radiation. The measurements were carried out by a vacuum echelette spectrometer in the wave number range 21.5–56 cm⁻¹ with spectral resolution 0.4–0.9 cm⁻¹, using a DRT-375 mercury-vapor discharge lamp as the source of UV radiation. In contrast to the results of similar experiments performed by other researchers, the data presented here demonstrate the absence of a noticeable effect of the UV radiation on the absorption spectra of the gas samples used. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 5, pp. 581–587, May, 1998.     

A planar XeCl-exilamp pumped by a low-pressure glow discharge

The energy characteristics of an XeCl exciplex lamp with planar construction pumped by a low-pressure gas discharge are investigated experimentally. When a discharge gap of width 2 cm and a Xe-Cl₂ mixture were used, average radiation powers up to 20 mW were obtained in the wavelength interval 200–380 nm at efficiencies of ∼0.4%. In this case the total efficiency of radiation into an angle of 4π exceeded 4%. It is shown that increasing the working pressure and using low discharge currents can lead to “point” radiation sources. Zh. Tekh. Fiz. 67, 43–46 (December 1997)     

Optical characteristics and plasma parameters of a blue-green exciplex lamp

The optical characteristics and plasma parameters of an exciplex lamp radiating in the blue-green spectral range are studied. A plasma is generated by an atmospheric-pressure barrier discharge initiated in a quaternary mixture including mercury dibromide, sulfur hexafluoride, nitrogen, and helium. It is shown that the exciplex lamp can radiate at an elevated repetition rate of pump pulses (1–12 kHz) under the conditions of mixture self-heating. A tradeoff between the radiation power and nitrogen partial pressure is found. The mean specific radiation power in the blue-green range at a level of 480 mW/cm³ is achieved at partial vapor pressures of mercury dibromide, sulfur hexafluoride, nitrogen, and helium of 0.70, 0.07, 4.00, and 117.20 kPa, respectively. The plasma parameters, namely, the electron energy distribution function; concentration, temperature, and mean energy of electrons; transport properties; and rate constants of elastic and inelastic electron scattering by the working mixture components are determined as functions of ratio E/N (where E is the electric field strength and N is the total concentration of mercury dibromide, sulfur hexafluoride, and nitrogen molecules and helium atoms). It is found that mercury monobromide molecules and also excited and higher energy states take part in the population of exciplex molecules HgBr* (B²Σ₁^2/+ states) in the course of quenching these exciplexes by sulfur hexafluoride and nitrogen molecules.     

Preparation and optical properties of sol–gel neodymium-doped germania/γ-glycidoxypropyltrimethoxysilane organic–inorganic hybrid thin films

Germania/γ-glycidoxypropyltrimethoxysilane organic–inorganic hybrid spin-coating thin films doped with neodymium ions are prepared by a sol–gel technique and a spin-coating process. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane mixed with germanium isopropoxide are used as matrix precursors. Thermal gravimetric analysis, UV–visible spectroscopy, and Fourier transform infrared spectroscopy are used to study the structural and optical properties of the hybrid thin films. The results indicate that films that are crack-free and have a high transparency in the visible and near-infrared range can be obtained; a strong UV absorption region at short wavelength ∼200 nm, accompanied with a shoulder peaked at ∼240 nm, due to the neutral oxygen monovacancy defects, is also identified. Upconversion emission properties of the transparent dried gel and the thin films heated at different heat treatment temperatures and doped with different neodymium ion concentrations are studied; a relatively strong room-temperature yellow to violet upconversion emission at 397 nm (⁴ D _3/2→⁴ I _13/2) is observed under a xenon lamp excitation with yellow light at the wavelength of 580 nm (⁴ I _9/2→⁴ G _5/2). The effect of Nd³⁺ doping concentration and heat treatment temperature on upconversion emission of the thin films is also studied. The mechanism of the upconversion is proposed. PACS 81.05.Kf; 81.20.Fw; 78.55.Hx     

Source of far and vacuum ultraviolet radiation based on a transverse high-frequency discharge

We present the results of an investigation of a short-wavelength radiation source (Δλ = 130–350 nm) with excitation by a transverse high-frequency (f = 1.76 MHz) discharge based on a mixture of argon and chlorine (p = 100–500 Pa). We have studied the spectral characteristics of the plasma, the oscilloscope traces of the voltage, the current and emission of the discharge, the dependence of the power of the emission on the electrical power of the discharge, and also the pressure and partial composition of the Ar/Cl₂ mixture. The UV-VUV source emits in a system of broadened and overlapping ArCl(B/X), Cl₂(D′/A′), and Cl**₂ molecular bands. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 648–651, September–October, 2007.     

Efficiency of the barrier-discharge UV Xe: SF6 lamp

The efficiency of the barrier-discharge UV lamp filled with a Xe/SF₆ = 50: 1 mixture is studied as a function of the pressure in the mixture (ranging from 40 to 180 Torr) and electrode distance (3–11 mm). It is shown that, if the product pd is constant, the power of the discharge and the intensity of the UV radiation (354 nm) decrease with increasing pressure and shrinking the electrode gap. The maximal efficiency of the lamp (6–8%) is reached in the pressure range 30–50 Torr.