UNIVERSAL METHOD FOR EXCITING THE LUMINESCENCE OF MOLECULES ISOLATED IN SOLID XENON E. B. GORDON Institute of Problems of Chemical Physics,, Russia ; V. D. SIZOV and V. I. MATYUSHENKO Institute of Energy Problems of Chemical Physics, Chernogolovka, Russia Ohio 2006

The molecules isolated in solid matrices are reliably protected from any external perturbers including useful ones. Only light seems to be able to induce a luminescence inside transparent matrix, provided the molecules possess intensive absorption bands. Meanwhile the matrices of rare gases are transparent for excess electrons as well - the path length in condensed Xe – many meters - electron mobility and losses – better than that in silver

Could the electrons embedded into solid excite the matrix and the impurity in it as they do that in a gas electric discharge?

The electric discharge in a solid is impossible for several reasons

Sporadically developed current of high energy electrons in bulk solid Xe Bright emission  dark background is due to practically closed camera aperture

The electric discharge in a solid is impossible for several reasons Sporadically developed current of high energy electrons in bulk solid Xe Bright emission  dark background is due to practically closed camera aperture The same without “discharge” Xe sample – the tablet of 3.5 mm height and 26 mm in diameter

Two kinds of luminescence VUV (172 nm) – Xe 2 exciton emission visible – from impurities though their density is less than 1 ppb, why it is so bright?

The Comparison of Inelastic Processes Probabilities for Beams and Drift Motion The real electron pathway exceeds the sample thickness in times Beam or ray Drift motion

Conclusion Many substances are soluble in liquid Xe in amounts of 1 ppb or more. Being isolated in solid Xe with spacing about 3,000 Å they may be subjected to high (up to 8 eV ) energy electrons to induce their electroluminescence and to study plasmo-chemical reactions at low temperature and in conditions of reliable isolation of both reagents and products.

The milestones I. Prediction 1. E. B. Gordon, O. S. Rzhevskii and V. V. Khmelenko, Quant.Electr.,1994, 21, E. B. Gordon, V. V. Khmelenko and O. S. Rzhevskii, Chem.Phys.Lett., 1994, 217, 605. II. The observation of exciton emission under electron drift through LXe 1. A.S.Schussler, J.Burghorn, P.Wyder, B.I.Lembrikov, R.Baptist, Appl.Phys.Lett, 2000, 77, 2786 III. The prove of multiple exciton formation under under electron drift through SXe. Achieving the electron multiplication. 1. A. Usenko, G. Frossati and E. B. Gordon, Phys.Rev.Lett., 2003, 90, E. B. Gordon, G. Frossati and A. Usenko, J.Exp.Theor.Phys., 2003, 96, 846.

Electron energy Crystal depth molecular exciton ion h 2 h 3 h 1 excited atom electron Three bands of emission (Xe) atomic – 8.4 eV ionic – 8.0 eV exciton – 7.4 eV Multiple exciton formation Any ionization !!!

1. Positive feedback – VUV photons from Xe crystal 2. Electron avalanche – in low density gas Gas multiplicator gain coefficient ~ 10 3 Efficiency of photoelectron emission from Zn ~ VUV emission yield per electron drifted through Xe crystal – 10 – 100 Idea of the “discharge” design

Electron drift through Solid Xe (current in a gas gap) Regeneration peak  Termination of positive feedback  d = 1 mm T = 110K d = 2 mm T = 77K

Far from the practice Necessity of a laser application For given crystal some limiting electron charge exists compensating the field in the sample – after some (short) time you should remelt the solid “Discharge” At high current the drifting electrons are bleaching out the trapped electrons How to trigger?

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Set up 1. Oil free pumping – turbomolecular + scroll pumps 2. Absence of any plastics and soldering even by silver (due to flux presence), HV valves, sapphire, glass, and ceramics as materials 3. Embedded system of xenon deep ( ) purification

Cryostat 77 – 150K Controller of the pressure in LN2 bath Controller of cooling power determined by N2 gas outflow from a cryostat inner part 4 pairs of sapphire windows Keeps cell’s temperature constant within 1K during several hours

Embedded system of xenon deep ( ) purification (electrospark technique) Electro spark sputtering of blade-shaped titanium cathode. Cavitations accompanied spark promotes the liquid mixing. Хе contamination removal down to 0.2 ppb proceeds in in scm volume in a few hours

Sapphire 3-electrode cell

Discharge through solid Xe Total view

Discharge through solid Xe Total view U ga = 2.4 kV; U cg = 100 – 200V Discharge !!!

Discharge through solid Xe Total view U ga = 2.4 kV; U cg = 100 – 200V Discharge U ga = 2.4 kV; U cg < 100V Spark !!!

Discharge through solid Xe Total view U ga = 2.4 kV; U cg = 100 – 200V Discharge U ga = 2.4 kV; U cg < 100V Spark U ga = 2.4 kV; U cg > 200V Glow !!!

“Spark” is rather short Four successive sparks followed by the regeneration “discharge” peaks with “time-of-drift” duration

The current is similar to emission but more smooth

Thanks to Russian Foundation for Basic Research

Discharge emission The oscillation rise time is equal to the time of an electron drift through the sample of solid Xe

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