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Determination of the absolute quantum efficiency of the luminescence of Xe2Cl* in Cl2–Xe mixtures

This content has been downloaded from IOPscience. Please scroll down to see the full text. 1987 Sov. J. Quantum Electron. 17 884 (http://iopscience.iop.org/0049-1748/17/7/A12) View the table of contents for this issue, or go to the journal homepage for more

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ization bands (λρ < 102 nm) for the purpose of pumping. It is interesting to consider also the possibility of using primary excitation of xenon for the transfer to other "laseractive" states of atoms and molecules. In the case of a high efficiency of the reaction mechanism the upper active level can receive up to ~12(172/A,)% of the stored energy, where At is the luminescence wavelength in nanometers. This can be achieved in Cl2-Xe mixtures. When chlorine is excited in the transparency band of xenon (—137 nm) at xenon pressures £ 1 atm, then in media of this kind we can expect effective formation of the triatomic excimer Xe 2 Cl*(/i ; = 490 + 45 nm), as described in Ref. 11: Cla

hv

Cl

XeCl* i i t

(2)

Xe2Cl*.

When pumping is provided by radiation from an open discharge, Xe 2 Cl* can exhibit lasing.13 However, it is known that excited atomic xenon interacts strongly with molecular chlorine: Xe*+Cl2->- XeCl*+Cl,

(3)

and the rate constant is 7.6χ 10~ 10 cmVsec (Ref. 14). As already established, the relaxation channel in xenon passes through the atomic states iPl/2- Therefore, even for [Cl 2 ] s; 1017 c m " 3 the "atomic reservoir" is emptied mainly in XeCl* and then in Xe2Cl*. Therefore, in the case of a mixture of the Cl2:Xe = 1:250 composition ( ρ = 1 atm) the

absorption of practically every photon of wavelength shorter than ~ 150 nm produces the Xe2Cl* trimer. 'B. L. Borovich and V. S. Zuev. Zh. Eksp. Teor. Fiz. 58, 1794 (1970) [Sov. Phys. JETP31, (1970)]. Shardanand, J. Quant. Spectrosc. Radiat. Transfer 8, 1373 (1968). 3 B. L. Borovich, V. S. Zuev, V. A. Katulin, L. D. Mikheev, F. A. Nikolaev, O. Yu. Nosach, and V. B. Rozanov, High-Current Light-Emitting .Discharges and Optically Pumped Gas Lasers [in Russian], VINITI, Moscow (1978). 4 M. A. Tsikulin and E. G. Popov, Radiative Properties of Shock Waves in Gases [in Russian], Nauka, Moscow (1977). 5 B. L. Borovich, V. S. Zuev, and D. B. Stavrovskii (Stavrovsky), J. Quant. Spectrosc. Radiat. Transfer 13, 1241 (1973). 6 B. L. Borovich, V. S. Zuev, and D. B. Stavrovskii, Kvantovaya Electron. (Moscow) 1,2048(1974) [Sov. J. Quantum Electron. 4,1138 (1975)]. 7 R. Brodmann, G. Zimmerer, and U. Hahn, Chem. Phys. Lett. 41, 160 (1976). 8 R. Brodmann and G. Zimmerer, J. Phys. Β 10, 3395 (1977). 9 H. D. Wenck, S. S. Hasnain, M. M. Nikitin, K. Sommer, G. Zimmerer, and D. Haaks, Chem. Phys. Lett. 66, 138 (1979). 10 T. D. Bonifield, F. H. K. Rambow, G. K. Walters, M. V. McCusker, D. C. Lorents, and R. A. Gutcheck, J. Chem. Phys. 72, 2914 (1980). 1 'V. S. Zuev, A. V. Kanaev, and L. D. Mikheev, Kvantovaya Elektron. (Moscow) 11,354 (1984) [Sov. J. Quantum Electron. 14,242 (1984) ]. I2 D. C. Lorents, Physica Β + C (Utrecht) 82, 19 (1976). 13 N. G. Basov, V. S. Zuev, A. V. Kanaev, and L. D. Mikheev, Kvantovaya Elektron. (Moscow) 12, 1954 (1985) [Sov. J. Quantum Electron. 15, 1289 (1985)]. 14 K. Y. Tang, D. C. Lorents, R. L. Sharpless, D. L. Huestis, D. Helms, D. Durrett, and G. K. Walters, Program and Abstracts of Papers presented at Thirty-Third Annual Gaseous Electronics Conf., Norman, Okla. 1980, publ. by University of Oklahoma, Norman, Okla. (1980), p. 57. 2

Translated by A. Tybulewicz

Determination of the absolute quantum efficiency of the luminescence of Xe2CI* in CI2-Xe mixtures V. S. Zuev, A. V. Kanaev, and L. D. Mikheev P. N. Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow

(Submitted October 24, 1986) Kvantovaya Elektron. (Moscow) 14, 1397-1398 (July 1987) The composition dependences of the absolute quantum efficiency of the luminescence of the Xe 2 Cl* trimer, emitting in the blue-green part of the spectrum, were determined for Cl 2 -Xe mixtures excited at the wavelength of 137.2 nm. A high (up to 100%) efficiency of trimer formation observed under optical excitation conditions makes media of this kind promising for laser applications. The present paper reports a continuation of an earlier determination1 of the quantum efficiency of the luminescence of mixtures Cl 2 with Xe, Kr, and Ar subjected to continuous excitation with vacuum ultraviolet radiation from a spectrosopic source. Visible and ultraviolet luminescence of Cl?*, Cl*, KrCl*. and XeCl* was reported in Ref. 1. The present study is concerned with the luminescence of the Xe2Cl* trimer in the visible range. The method used to determine the quantum efficiency 884

Sov. J. Quantum Electron. 17 (7), July 1987

of the luminescence, described in Ref. 1, was based on the constancy of this efficiency over a range of pump and luminescence wavelengths. In the present experiments we replaced an FEU-19A photomultiplier with an FEU-38 model with the sensitivity range extended to 800 nm. Both photomultipliers were constructed in the same way, so that there was no need for any significant modification of the apparatus. The photomultiplier current was amplified in a dc amplifier and recorded

0049-1748/87/070884-02S04.10

© 1987 American Institute of Physics

884

Xe,Cl· --U- 2Xe + Cl - Λν ( ~490 nm), k

i

Xe2Cl* + CI 2 —>• 2Xe + Cl + Cl s .

FIG. 1. Dependence of the quantum efficiency of the Xe,Cl* luminescence on the chlorine pressure at pXc = 2 atm.

with a V7-21 digital voltmeter. A ZhS-11 filter placed behind a cell containing the investigated gas removed radiation of wavelengths shorter than 400 nm and transmitted ~ 90% of the Xe 2 Cl* band at its maximum. A hydrogen lamp emitting at 137.2 nm was used as the excitation source of Cl 2 -Xe mixtures. The spectral width of the monochromator slit was 1.6 nm. In these experiments we used high-purity (~99.99%) xenon. Chlorine was purified additionally by removal of the volatile components by repeated vacuum pumping at liquid nitrogen temperature; the heavy components were removed by freezing at — 100 °C. The cell and the gas admission system were passivated with fluorine before the experiments. The dependences of the quantum efficiency γ of the XeCl* luminescence on the chlorine pressure at a xenon pressure of 2 atm and on the xenon pressure at a chlorine pressure of 0.4 Torr were determined in two series of experiments (Figs. 1 and 2). In agreement with the earlier data,' it was found that at xenon pressures in excess of 1 atm practically the whole of XeCl* reacted to triple collisions. The resultant Xe2Cl* trimers either emitted the observed luminescence or were quenched by chlorine: XeCl·

r

2Xe

Xe.Cl* I-Xe,

0,75 0.5

2

V(Xe2Cl*)-=v(XeCl*)ftT,[Xe] /(l + fc,T2[Cl2l

(1)

where r, is the radiative lifetime of XeCl* and 38 3 jtr, = 1.6xlO- cm (Ref. 1). Figure 2 shows the theoretical curve plotted on the basis of Eq. (1) using the constants taken from Ref. 1. The experimental points fit well this curve. Hence, we can conclude that the three-body reaction of recombination of XeCl* with xenon is not branched and its only product is the Xe2Cl* trimer. Moreover, there is no significant quenching of the trimer of xenon. Since, as indicated by the experimental results, the quenching of Xe2Cl* by xenon at pXe = 2 atm is not detectable against its quenching by chlorine at ρ = 0.5 Torr, it follows that the constant of the reaction Xe2Cl* + Xe

3Xe + Cl

should be much less than 7 x 1 0 1 4 cmVsec. This is in agreement with the results of earlier investigations, particularly with Ref. 2, where the measured value of k'q is 6 x 10~ 15 cmVsec. These results are a demonstration of a high (approaching 100% of some of the mixtures) efficiency of photochemical excitation of Xe2Cl*. Lasing of Xe2Cl* as a result of optical pumping3 therefore sounds promising.

'V. S. Zuev, A. V. Kanaev, and L. D. Mikheev, Kvantovaya Elektron. (Moscow) 11, 354 (1984) [Sov. J. Quantum Electron. 14,242 (1984) ]. H. P. Grieneisen, Xue-Jing Hu and K. L. Kompa, Chem. Phys. Lett. 82, 421 (1981). 3 N. G. Basov, V. S. Zuev, A. V. Kanaev, and L. D. Mikheev, Kvantovaya Elektron. (Moscow) 12, 1954 (1985) [Sov. J. Quantum Electron. 15, 1289 (1985)]. 2

0,15 300

600

900

A». Torr

FIG. 2. Dependence of the quantum efficiency of the Xe 2 Cl* luminescence on the xenon pressure aXpa% = 0.5 Torr.

885

Therefore, the experimental points plotted using the coordinates \/γ and [Cl 2 ] should fit a straight line, the slope of 17 3 which (Fig. 1) corresponded to fc9r2=;3.34x 10~ cm . Hence, assuming that r 2 = 185 nsec (Ref. 2), we found that 10 λ,-Ι.δχΙΟ" cmVsec. The solution of the rate equations in the steady-state approximation gives the following expression for γ{ Xe2Cl*) (see Ref. 1):

Sov. J. Quantum Electron. 17 (7), July 1987

Translated by A. Tybulewicz

Zuev era/.

885