Long-lived vibrationally excited states are formed by the interaction of hydrogen atoms of thermal energy and their isotopes with nonmetallic surfaces. Heterogeneous chemo-luminescence regarded as the final stage of conversion of energy released during the interaction of hydrogen with the surface into light. Spectral measurements upon excitation of heterogeneous chemo-luminescence are useful for obtaining information on changes in the electronic states of the luminescence centers on the surface.
The researchers, led by professors Yuri Tyurin and Nikolai Nikitenkov at Tomsk Polytechnic University studied the luminescence of zinc sulfide activated by thulium, which excited by free hydrogen atoms. The electronic states of the impurity centers of the thulium ion on the zinc sulfide surface and the interaction of hydrogen with the phosphor surface were studied. Their research work now published in the peer review journal, International Journal of Hydrogen Energy.
The authors carried out research in an automated high-vacuum installation. The free hydrogen atoms were obtained by dissociation of molecular hydrogen in a high-frequency electrodeless plasma discharge. The luminescence spectra of a crystalline phosphor of zinc sulfide activated with thulium were recorded using an optical spectrometer, a multichannel photomultiplier, and a charge-coupled device. The methods of nonstationary luminescence were used to study elementary acts of interaction of hydrogen atoms with the surface.
The research team found that when hydrogen atoms interact with the phosphor surface, a weak luminescence in the thulium ion band of 480 nm is observed at the beginning, which was followed by aa monotonic increase in the luminescence intensity. They noted that the luminescence spectrum of zinc sulfide activated by thulium has peaks at 480 nm, 481.5 nm and at 807.5 nm, which are characteristic for the thulium ion 3+. It was also noted that the peak at 480 nm was significantly brighter compared to the peak at 807.5 nm. The spectra of photoluminescence and luminescence upon excitation by hydrogen atoms practically coincided. This shows that the valences of the thulium ion are the same in the volume and on the surface of the zinc sulfide, since hydrogen atoms that have thermal energy interact only with the first atomic layer of the phosphor. The authors also noted that the appearance and accumulation of vibrationally excited hydrogen molecules on the surface of zinc sulphide generates a transition to nonstationary periodic regimes in fluorescent kinetic curves. Explanation and simulation of such regimes seems relevant for heterogeneous catalytic processes, and for the problems of increasing the stability of the hydrogen maser, managing the growth of crystals and films by layering molecular-beam epitaxy, increase the service life of protective coatings reentry spacecraft and in the formation of structures of the thin film solid oxide fuel elements and others.
It has been experimentally established that the “shutdown” of hydrogen atoms at relatively low temperatures and high fluxes leads to a sharp decrease in the intensity of heterogeneous chemo- luminescence by approximately 10 times. This makes it possible to study the luminescent method of adsorption, desorption, recombination, and dissociation of hydrogen on the surface. The authors noted that the concentration of adsorbed atoms at the stage of the dark pause varied nonmonotonically. The decrease in the intensity of heterogeneous chemiluminescence during the dark pause is associated with the diffusion recombination of hydrogen atoms on the surface
The authors noted that the luminescence centers are excited by nonequilibrium vibrational quanta of the hydrogen bond. The higher the energy of the vibrational quantum and the smaller the energy of the electronic transition, the greater the transition rate. The transition rate increases with increasing dipole moment of the vibrationally excited bond.
Luminescent methods provide a sensitive tool for studying the chemical composition of the surface, the processes of electron energy transfer on the surface, mechanisms of surface degradation. It becomes possible to study elementary acts of gas-solid interaction; the electronic state the centers of luminescence, adsorption and catalysis on the surface, and the dynamic properties of the surface.
Yu. I. Tyurin, N. N. Nikitenkov, T. I. Sigfusson, A. Hashhash, Yaomin Van, N. D. Tolmacheva. Generation of excited electronic states at the nonmetal surface by the hydrogen atoms beam. International Journal of Hydrogen Energy, 42 (2017) 12448-12457.Go To International Journal of Hydrogen Energy