ISSN 10637842, Technical Physics, 2009, Vol. 54, No. 8, pp. 1238–1240. © Pleiades Publishing, Ltd., 2009. Original Russian Text © A.K. Shuaibov, A.A. Heneral, Yu.O. Shpenik, Yu.V. Zhmenyak, I.V. Shevera, R.V. Gritsak, 2009, published in Zhurnal Tekhnicheskoі Fiziki, 2009, Vol. 79, No. 8, pp. 153–155.
SHORT COMMUNICATIONS
Ultraviolet Radiation Sources on (H2O, D2O) Water Vapor A. K. Shuaibova, A. A. Heneralb, Yu. O. Shpenikb, Yu. V. Zhmenyakb, I. V. Sheveraa, and R. V. Gritsaka b
a Uzhgorod National University, Uzhgorod, 88000 Ukraine Institute of Electronic Physics, National Academy of Sciences of Ukraine, Uzhgorod, 88017 Ukraine email:
[email protected];
[email protected]
Received November 18, 2008
Abstract—Emission characteristics of ultraviolet (UV) radiation from water vapor (H2O, D2O, and a mixture of H2O and D2O vapors) excited by pulseperiodic discharges with open electrodes, as well as electrodes out side 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 func tions of pressure and the composition of the He–H2O and He–D2O mixtures, are reported. PACS numbers: 52.80.Hc DOI: 10.1134/S1063784209080258
Not only lasers, but also sources of spontaneous UV–VUV radiation, are being used increasingly widely in ecology, microelectronics, medicine, and so on. The most powerful and effective incoherent emit ters in the UV–VUV spectral range are excimer and exciplex lamps. The main advantage of these emitters over their mercurycontaining predecessors is the absence of mercury in the working medium and more diversified spectral characteristics in the UV–VUV wavelength range. As a rule, mixtures of inert gases and halogen mol ecules are used in exciplex emitters. Apart from exci mer and exciplex lamps, UV–VUV lamps operating on water vapors have become more and more popular since these devices operate in an environmentally friendly and cheap working medium; for this reason, the study of parameters of such lamps is of consider able importance. Water vapors were excited by various types of elec tric discharge for various values of pressure (both high and low) [1–6]. As a rule, a dc glow discharge under a low pressure of water vapor is used. In attaining a high pulse power of UV radiation from water vapors, the application of a barrier discharge and a longitudinal pulseperiodic discharge (PPD) is promising. Here, we consider the results of investigation of emission characteristics of a longitudinal PPD in vapors of H2O, D2O, and their mixtures, as well as a pulseperiodic capacitive discharge in mixtures of helium with water vapors. A PPD with open electrodes was excited in a cylin drical quartz tube with an inner diameter of 1.5 cm and a length of 40 cm. The discharge was excited by a gen erator with resonant recharging of a reservoir capaci tor with a capacitance of 1650 pF; a TGI12000/35
thyratron was used as a switch. The pulse repetition rate was 8 kHz, and the voltage across the rectifier was 2 kV. Water was in a special spout of a gasdischarge tube; water vapor continuously circulated in the dis charge volume under a rated pressure on the order of 150 Pa. A capacitive discharge was initiated in a quartz tube 50 cm in length with an outer diameter of 7 mm. Helium–watervapor mixtures of various composi tions were pumped into the gasdischarge tube from the vacuum gasmixing system. The distance between the electrodes was 18 cm. The anode and cathode were prepared from a nickel foil of width 2 cm; the elec trodes were attached to the outer surface of the gas discharge tube. A capacitive discharge was initiated from the power supply of an LGI505 nitrogen laser. The amplitude of voltage pulses with opposite polarity at the electrodes was 25–40 kV; the pulse frequency was varied in the range 50–500 Hz. The UV emission spectra from the discharges were recorded using an MDR6 monochromator, 1m vac uum monochromator, FEU106 and FEU142 pho tomultiplier, and S199 and LOR04 oscilloscopes. The spectral resolution was 0.2 nm. Figure 1 shows the emission spectrum of a PPD with open electrodes operating on water vapors. The water vapor plasma is characterized by broad bands with peaks at 306, 309, 312, and 314 nm, which can be identified with electronvibrational bands of hydroxyl: OH (X2Π–A2Σ+) (0–0 transition). The replacement of common water by heavy water resulted in doubling of the average power of UV radiation, and the vibra tional–rotational structure of the A X bands was less pronounced.
1238
ULTRAVIOLET RADIATION SOURCES ON (H2O, D2O) WATER VAPOR I, arb. units
1239
I, arb. units (a) H2O
80
80
40 40 0 0
260
280
300
320 λ, nm
(b) D2O
80 Fig. 1. Emission spectrum from a discharge with open electrodes with continuous circulations of water vapor under a pressure on the order of 10 Pa in a wavelength range of 230–325 nm.
40
The average radiation power in a spectral range of 300–325 nm for a discharge current of 0.07 A was 1.5 W for an efficiency of 0.2%. The entire spectral range was conditionally divided into three regions of 25 nm each. Region 250–275 nm is less intense as compared to two other regions. Regions II (275–300 nm) and III (300–325 nm) belong to the A X electron transitions of the water molecule and OH, respectively. In these regions, the bands with principal peaks at 283 nm (1 0 transi tion) for region II and 309 nm (0 0 transition) for region III are most intense. The time characteristics of a longitudinal PPD in water vapors are given in [7]; it was shown that elec tron collisions in a gasdischarge plasma are con trolled by the properties of the UV radiation source under investigation. In this work, the effect of hydro gen isotopes on radiation from a watervapor lamp was investigated in greater detail. Figure 2 shows the emission spectra of (a) common water H2O, (b) heavy water D2O, and (c) their mixture in a spectral range of 250–350 nm. These spectra were recorded in a short spectral range with such an ampli fication that the peak of region III is strongly trimmed. These spectra are compared in Fig. 2. The experimen tal conditions under which the spectra were recorded were as follows: the pulse repetition rate was 8 kHz, the voltage supplied to the electrodes of the lamp was 2 kV, and the average value of the current was 0.07 A. It can be seen that the main features of these spec tra are similar. However, these details of the spectrum shown in Fig. 2b are shifted toward higher values of the wavelength as compared to the spectrum in Fig. 2a. The oscillatory structure is manifested in Fig. 2b less clearly than in Fig. 2a. These features are associated with a larger mass of the heavy water molecule D2O. In TECHNICAL PHYSICS
Vol. 54
No. 8
2009
0
(c) H2O + D2O
80
40
0 250
300
350 λ, nm
Fig. 2. Emission spectra from a pulseperiodic discharge with open electrodes on vapor of (a) H2O, (b) D2O, and (c) H2O + D2O mixture.
addition, the actual spectral intensity in Fig. 2b must be multiplied by two. It follows from Fig. 2c depicting the radiation spec trum for a plasma on the H2O + D2O vapor mixture that a sort of summation of the spectra depicted in Figs. 2a and 2b takes place. This can be useful for some applications of UV sources of spontaneous radiation. The pulseperiodic capacitive discharge on He– H2O mixtures at P(H2O) < 150 Pa and P(He) = 1– 15 kPa was dazzling white in color and uniformly filled the entire electrode gap. The emission spectra in a wavelength range of 250–350 nm are shown in Fig. 2.
1240
SHUAIBOV et al.
ation of the bands corresponding to the hydroxyl mol ecule in a spectral range of 177–200 nm generally decreased. The radiation brightness of these bands for a discharge based on heavy water was 1.5–2.0 times higher was higher than for common water.
I, arb. units 100 (a) 189.5 nm 196.6 nm
187.1 nm 181.0 nm 50
0 180 J, arb. units 100 (b)
190
λ, nm
10
15 PHe, kPa
50
0
5
Fig. 3. (a) Spectrum of UV radiation from a capacitive dis charge plasma on a mixture of helium and water vapors. (b) Dependence of radiation brightness of the 297.7nm band of the OH radical for a plasma on the He–H2O mix ture on the partial pressure of helium at P(H2O) = 130 Pa and an amplitude of the voltage pulse exciting a capacitive discharge of 50 kV.
The spectra corresponding to a shorterwave range are shown in Fig. 3a. The emission spectra of a lamp based on water vapor are characterized by the hydroxyl bands. These are the band at 181.0, 187.1, and 189.1 nm in the spec tral range 175–200 nm. The radiation bands with the peaks in the spectral range 181–190 nm can be ascribed to the hydroxyl molecule OH (C–A) [9, 10]. As the partial pressure of D2O and H2O vapors increases to above 130–150 Pa, the brightness of radi
Figure 3b shows the dependence of the relative brightness corresponding to the radiation band of the hydroxyl molecule with a peak at 297.7 nm on the par tial pressure of helium under the optimal pressure of vapors of H2O and the He–H2O mixture. It follows from Fig. 3b that the optimal pressure of helium is approximately 8 kPa. For a discharge on the He–D2O mixture under a pressure of P(D2O) = 130 Pa, the optimal helium pressure under the same conditions of discharge excitation decreased to 5.2 kPa. The radia tion brightness of the OD radical band was 1.5 times higher than the brightness of the corresponding OH bands. Thus, the emission characteristics of the plasma of vapors of common and heavy water, as well as their mix ture, are studied in a spectral range of 180–350 nm. We analyzed the effect of the isotopic composition of water vapor on the type of emission spectra. It was found that, if common water is replaced by heavy water, the power of radiation from the lamp is approx imately doubled and details of the emission spectrum are shifted towards longer waves. A UV lamp operating on water vapors with an average radiation power of 1.5 W and an efficiency of 0.2% was constructed. REFERENCES 1. M. I. Lomaev, V. S. Skakun, E. A. Skakun, et al., Usp. Fiz. Nauk 173, 201 (2003) [Phys. Usp. 46, 193 (2003)]. 2. A. A. General, Yu. V. Zhmenyak, and Yu. O. Shpenik, in Proceeding of the Conference of Young Sciensists and PostGraduates, Inst. Electron. Fiz. Ukr. Akad. Nauk, Uzhgorod, 2007, p. 97. 3. E. A. Sosnin, M. V. Erofeev, S. M. Avdeev, A. M. Popenko, et al., Kvantovaya Elektron. (Moscow) 36, 981 (2006). 4. A. Ya. Vul’, S. V. Kidalov, V. M. Milenin, et al., Pis’ma Zh. Tekh. Fiz. 25 (1), 10 (1999) [Tech. Phys. Lett. 25, 4 (1999)]. 5. F. Morozov, R. Kruchen, T. Ottenhal, and A. Ulrich, Appl. Phys. Lett. 86, 0115021 (2005). 6. A. K. Shuaibov, I. V. Shevera, and A. A. General, Zh. Prikl. Spektrosk. 73, 831 (2006). 7. A. K. Shuaibov, A. A. General, V. A. Kel’man, and I. V. Shevera, Pis’ma Zh. Tekh. Fiz. 34 (14), 6 (2008) [Tech. Phys. Lett. 34, 588 (2008)].
Translated by N. Wadhwa
TECHNICAL PHYSICS
Vol. 54
No. 8
2009
