Excited Kr Research Articles

Photoionization pathways and thresholds in generation of Lyman-α radiation by resonant four-wave mixing in Kr-Ar mixture

We develop a set of analytical approximations for the estimation of the combined effect of various photoionization processes involved in the resonant four-wave mixing generation of ns pulsed Lyman-α (L-α) radiation by using 212.556 nm and 820-845 nm laser radiation pulses in Kr-Ar mixture: (i) multi-photon ionization, (ii) step-wise (2+1)-photon ionization via the resonant 2-photon excitation of Kr followed by 1-photon ionization and (iii) laser-induced avalanche ionization produced by generated free electrons. Developed expressions validated by order of magnitude estimations and available experimental data allow us to identify the area for the operation under high input laser intensities avoiding the onset of full-scale discharge, loss of efficiency and inhibition of generated L-α radiation. Calculations made reveal an opportunity for scaling up the output energy of the experimentally generated pulsed L-α radiation without significant enhancement of photoionization.

Excitation Energy Transfer of Metastable Krypton Atoms in Kr–He–Xe Low Pressure Glow Discharge for Mercury-Free Lighting

The discharge of the gas mixture Kr–He–Xe was investigated as a source of vacuum ultraviolet for lighting purposes. The discharge characteristics of the Xe–He–Kr gas mixture were enhanced in comparison to those of Xe and a Xe–He gas mixture. The experimental results were evaluated by the infrared radiation from the positive column. The amount of infrared radiation under optimum conditions displayed higher efficiency than that of the He–Xe gas mixture, which results in the improved efficacy of lamp. This result was due to the emission properties that were improved by the potential energy transferred from the excited Kr to the Xe.

Spatiotemporal behavior of excited Xe*(1s4,1s5) and Kr*(1s5) atoms measured by laser-absorption spectroscopy in unit cell of a plasma display panel with Xe–Kr–Ne ternary gas mixture

We have studied the effects of ternary gas mixtures of Xe(10%)–Kr(20% and 40%)–Ne on the luminous efficiency in ac plasma display panels. Spatiotemporal behaviors of near infrared (IR) emission was measured by an intensified charge-coupled device camera equipped with a narrow bandpass filter and absolute densities of excited Xe* and Kr* atoms in the lowest resonance (1s4) and metastable (1s5) levels were measured by a technique of microscopic laser absorption spectroscopy. We have found interesting features from both emission and absorption experiments, such as longer near-IR emission (0.3–0.4μs) and different temporal behaviors between the excited Kr*(1s5) atoms and Xe*(1s4,1s5) atoms. We have also found that the order of magnitude of the peak density of excited Kr*(1s5) atoms (∼1012cm−3) was ten times smaller than that of Xe*(1s4,1s5) atoms, and that their decay time was remarkably short (∼0.3μs). These results have then been compared with those for a binary gas mixture of Xe(10%)–Ne. At a certain range of the sustain voltage, the production rate of Xe*(1s4,1s5) atoms and the luminous efficiency have turned out to be slightly improved for the ternary gas mixtures, compared to the binary gas mixture.

Production efficiencies of Kr*(1s5,1s4) atoms leading to vacuum-ultraviolet emissions in ac plasma display panels with Kr–Ne binary mixtures measured by laser-absorption spectroscopy

Ne–Kr gas mixtures with high Kr concentrations were applied to ac plasma display panels. Spatiotemporal behaviors of excited Kr atoms in the 1s5 metastable state and the 1s4 resonance state were measured by microscopic laser-absorption spectroscopy in the binary mixtures with Kr concentrations of 20% and 40%. A systematic comparison was done between the characteristics of Ne–Kr-filled panels and those of conventional Ne–Xe panels with the same structure but with lower Xe concentrations of 5% and 10%. For example, the total number of Kr*(1s5) atoms in a unit cell ranged from 7.4×107 to 2.0×108, at the peak was apparently smaller than the value of Xe*(1s5) atoms. However, when the difference in the decay rate of the excited atoms by three-body collision processes is taken into account, the production efficiency of vacuum-ultraviolet (VUV) emission from Kr2* excimers is as large as that from Xe2* excimers in a usual panel since these processes lead directly to the formation of excimers. From the measured density of Kr*(1s4) atoms, it is estimated that the contribution of the atomic resonance line is smaller than the excimer band at those high Kr concentrations. In any case, by summing up those two contributions to the VUV emission, the overall efficiency in the Ne–Kr(40%) panel is estimated to be comparable to that in the Ne–Xe(10%) one.

Energy relaxation and quenching processes of doped rare-gas clusters with a shell-like geometric structure

Energy relaxation processes of photo-excited Kr50¯ clusters covered with a shell of Ar atoms (up to 40), which are embedded inside large Ne7500¯ clusters are investigated with energy resolved fluorescence spectroscopy. In the energy range of the characteristic Ne cluster absorption (16.5–18 eV) a strong energy transfer to the embedded Kr cluster is observed, which results in the desorption of electronically excited Kr* atoms. Kr* atoms move through the Ne cluster, desorb and emit visible and near-infrared light in the vacuum (5p→5s). By coating the Kr clusters with Ar atoms, the Kr lines disappear and 4p→4s transitions of Ar* become dominant. Additionally, new emission bands occur, which are assigned to transitions of perturbed atomic Kr 5p-states inside Ne clusters. Due to the interaction of electronically excited Kr* atoms with neutral Ar atoms in the surrounding shell, several excited Kr states namely 5p [1/2]0 and 5p [3/2]2 decay nonradiatively. This is in agreement with the well-known “energy-gap law.” The results give experimental evidence that clusters with a multishell structure can be prepared by a sequential pick-up technique. This allows the preparation of Kr clusters embedded inside Ne clusters and coated with a shell of Ar atoms. Such clusters cannot be prepared with conventional coexpansion techniques.

Surface diffusion of metastable krypton atoms on krypton-doped solid argon

Besides desorption and surface trapping of selectively excited Kr atoms at the surface of Kr-doped Ar crystals, a new relaxation mechanism has been observed. It includes surface diffusion of long-living atomic-type surface centers and guest-molecule formation at the surface. It has been analyzed with time- and spectrally-resolved luminescence measurements. The results are interpreted with a model based on two-dimensional diffusion controlled reactions with an initial random distribution of guest atoms at the surface. We obtained an activation energy of 6meV for thermally activated diffusion which is in good agreement with the lateral potential wells of the excited Kr atom on top of an Ar surface.

Desorption of atoms and excimers upon self-trapping of excitons in rare gas solids

On the basis of one-electron Hartree-Fock approximation, the extended-ion method has been used to investigate desorption induced by the formation and trapping of two types of excitons on and near the three different faces ((100), (110), (111)) for solid Ne and Kr. Excited Ne atom, Ne excimer and Kr excimer can be ejected upon self-trapping of excitons on and near the surface, while excited Kr atom cannot. After desorption, the excited atom and excimer will decay radiatively, the luminescence energies are in fair agreement with the experiment. For the excimer, the radiative decay terminates at the strongly repulsive ground state, this repulsive energy is converted into kinetic energy of two atoms constituting the excimer, resulting in the desorption of ground state atom. It is also observed that a localized hole on the surface and below is efficiently converted into a molecule-ion R 2 + without leading to any desorption, showing that exciton-lattice interaction plays a key role in the process of desorption. The ejected direction is basically along the normal to the surface for the excited particle, but for the ground state atom, it does not show a preferential direction of desorption.

Absorption spectra of excited Kr 84 states between 1.5 and 1.58 μm and their use for absolute frequency locking

We have shown to our knowledge for the first time the absorption spectrum of Kr between 1500 and 1580 nm via the opto-galvanic effect and we measured the stability of a laser locked to the absorption line of Kr 1s/sup 2/-2p/sup 8/ at 1547.825 nm. The noise of the Galvatron signal as a function of the current through the bulb was carried out. Additionally it was shown to our knowledge for the first time that is it possible to lock more than one laser simultaneously at different wavelengths to one Galvatron tube.

Measurements of circular polarization correlations following excitation of Ar and Kr by electron impact

We report measurements of the circular polarization correlation parameterP3 for the excitation of the 4s′[1/2]j=1 state in Ar by 40 eV electrons and for the excitation of the Kr 5s[3/2]J=1 state by 30 eV electrons at electron scattering angles up to 50°. The measured Ar data are compared to predictions of a distorted wave Born approximation (DWBA). The agreement is in general not very good with theory predictingP3 values considerably larger than the measured values in the regime of small scattering angles. In Kr, where the measured data are compared to theoretical predictions from a DWBA, a first-order many-body theory (FOMBT) and a relativistic distorted wave theory (RDW), the level of agreement between experiment and theory is somewhat better. The measuredP3 parameters in conjunction with the previously measured linear coherence parametersP1 undP2 under the same scattering conditions yield the total polarizationPtot+ which is a measure for the level of coherence in the excitation process. In both cases studied here, we found values of eliminatePtot+ that were consistent with a fully coherent excitation process.

Exciton-induced desorption and surface-type luminescence of Kr atoms from Kr-doped solid Ar

Selective excitation of Kr atoms at the surface of solid Ar with synchrotron radiation stimulates the desorption of excited Kr atoms (e.g., Kr 3P 1) as well as the luminescence of Kr-type surface centers at hv = 9.998 eV( 3P 1) and at hv = 9.881 eV( 3 P 2) . The high-resolution luminescence spectra and the yield curves of the radiative decay channels have been measured. They are interpreted taking into consideration ab initio KrAr pair potentials. A general correlation between the desorption mechanism and the energetic position of the vacuum level is established for pure (Ne, Ar, Kr, Xe) and doped rare gas solids.

Superthermal component in an effusive beam of metastable krypton: Evidence of Kr2+ dissociative recombination.

A superthermal component in a metastable ${\mathrm{Kr}}^{+}$ krypton beam produced in a Kr gas discharge has been observed and studied. Evidence is presented that this fast component is due to dissociative recombination of ${\mathrm{Kr}}_{2}^{+}$, and that the excited Kr direct products of this reaction are predominantly in the 5s states. An effective method (time of flight) for studying the product states of dissociative recombination reactions is thus demonstrated.

Luminescence of rare gas atoms in rare gas matrices: The case of Kr in an Ar matrix

The luminescence spectra of 4p 55s,s′ Kr atoms in an Ar matrix were investigated. The combination of selective optical excitation with synchrotron radiation and high-resolution luminescence analysis, together with sample preparation at T = 30 K and low Kr concentrations (0.3%–0.001%) enabled the spectroscopic detection of Kr atoms at there lattice sites in the bulk of the matrix. Moreover, a surface site and desorption of excited Kr atoms were observed. The single-configuration-coordinate model was applied to the spectra of the most prominent site. The Huang-Rhys factors are S = 41.7 for 3P 1 centers, and S = 38.0 for 1P 1 centers. In both cases, a value of 4.8 meV was obtained for the vibrational quantum.

A photoion–photoelectron coincidence study of Kr and Xe dimers

The photoion–photoelectron coincidence (PIPECO) spectra for Kr+2 and Xe+2 in the wavelength regions of 825–970 and 900–1030 Å, respectively, have been measured at different nozzle temperatures and stagnation pressures (P0). The ionization energies (IE) for Kr2 and Xe2 to Kr+2[I(1/2)u] and Xe+2[I(1/2)u] determined by the PIPECO spectra are in excellent agreement with the results of previous photoionization experiments. The PIPECO measurements for Kr+2 and Xe+2 also provide lower limits for the IEs of Kr2 and Xe2 to Kr+2[II(1/2)u] and Xe+2[II(1/2)u]. The PIPECO spectra for Kr+2 and Xe+2 display strong autoionization structures similar to those resolved in the corresponding photoionization efficiency spectra, indicating that a significant fraction of autoionizing electrons are slow electrons with near zero kinetic energies. The extreme weakness of the Kr+2[II(1/2)u] and Xe+2[II(1/2)u] PIPECO bands observed at low P0 support the conclusion that excited Kr+2[II(1/2)u] and Xe+2[II(1/2)u] ions are dissociative with dissociation lifetimes shorter than 68 and 85 μs, respectively. These values are in accord with the calculated radiative lifetimes for the II(1/2)u→I(1/2)g transitions in Kr+2 and Xe+2. The intensities for the II(1/2)u PIPECO bands relative to the I(1/2)u and I(3/2)g PIPECO bands for Kr+2 and Xe+2 are found to increase as P0 is increased, an observation attributed to the formation of Kr+2 and Xe+2 from fragmentation of excited Kr+n and Xe+n ions produced in the photoionization of Krn and Xen, n≥3. The fragmentation of excited Kr+n and Xe+n , n≥3, ions have the effect of lowering the appearance energies for the Kr+2[II(1/2)u] and Xe+2[II(1/2)u] PIPECO bands.

Optical excitation spectra of rare-gas atoms physisorbed on metal surfaces

Numerical computations are presented for the optical excitation spectra of neutral rare-gas atoms physisorbed on various metal surfaces. At low coverage and when the damping of the surface plasmons is much greater than the effective radiative damping, the occasional disappearance of the spectral lines of the optical absorption is due to a cancellation process, which occurs between the frequency profiles arising from two nearby excited states of the adsorbed atom. The red (blue) shifted peak of the symmetric mode of the higher (lower) excited state and the blue (red) shifted peak of the antisymmetric mode of the lower (higher) excited state of the atom cancel each other out provided that the frequency profiles of their lineshapes nearly coincide. Results of numerical calculations indicate that at low coverage the peaks of excited Xe on Ti and Au and excited Kr on Mg, in addition to those of Xe on Al and Kr on Au, vanish; this is compatible with the experimental observations. Predictions have been made for the adsorption spectra as a function of the distance from the atom to the surface of excited Xe and Kr, which are physisorbed on the surfaces of W, Ni, and Rh, respectively.

Time-resolved population measurements of excited Kr atoms in a KrCl excimer laser

The temporal behavior of excited state (3P2, 3P1) of Kr atoms in a discharge-pumped KrCl excimer laser has been studied using the hook method and the sidelight method with nanosecond time resolution. On the basis of these experimental results, the mechanism of the formation of KrCl* excimer is also discussed.

Resonance Auger decay after selective excitation of Kr 3d states by synchrotron radiation.

The ${M}_{4}$,5NN normal and resonance Auger spectra of Kr have been measured using different photon energies to ionize or excite the 3d levels. Excitation of the 3d electrons to the 3${d}^{9}$4${s}^{2}$4${p}^{6}$5p resonance states results in decay with a 5p spectator or participator electron. The spectra are analyzed by comparing them with the calculated profiles. The calculations take into account the presence of a spectator electron, and the correlation effects in the case of a 4s hole state.

Multiple photoionization from 3p excitation of Kr and 4p excitation of Xe

The photoionization cross sections for multiply charged ions produced by 3p excitation of Kr and 4p excitation of Xe have been obtained by means of a time-of-flight mass spectrometer and synchrotron radiation. It is found that the main formation of doubly to quadruply charged ions in both Kr and Xe is caused from the each initialp-hole state through a Coster-Kronig transition followed by Auger or double Auger processes. The formation of singly charged ions in these excitation energy regions is caused by direct photoionization from outermost shell electrons in both Kr and Xe. Triply charged ions are prominently produced among the multiply charged ions. The quadruple photoionization cross sections show clearly the structures due to the Rydberg series, 3p−1nl of Kr and 4p−1nl of Xe. Their main structures were assigned to the 3p−1nd series in Kr and the 4p−1nd series in Xe.

Multiple photoionisation of the rare gases in the XUV region

The photoionisation cross sections for multiple ionisation produced by 2p-shell excitation of Ar, 3d-shell excitation of Kr, 4d-shell excitation of Xe and the two-electron excitation, 4d-15p-1nln'l', of Xe have been obtained by means of a time-of-flight mass spectrometer and synchrotron radiation. The formation of Ar+ is prominent in the 2p-1ns and 2p-1nd states of the Rydberg series and Ar2+ is dominant above the L-shell ionisation threshold. The post-collision interaction effect is discussed for photoionisation of Ar in connection with the structure above the L-shell ionisation threshold. Doubly charged ions of Kr and Xe are produced dominantly not only above the 3d- and 4d-shell ionisation thresholds but also through the 3d-1np and 4d-1np states of the Rydberg series, respectively. The formation of these doubly charged ions for Kr and Xe is considered to be due to the Auger process.

Near-threshold electron impact excitation of Kr

Absolute differential cross sections and energy dependences for excitation of each of the four 4p55s states of Kr are measured within the first 4 eV of threshold using a crossed-beam electron impact spectrometer which has been modified to achieve controlled transmission of low-energy (100 meV-4 eV) scattered electrons. These are the first absolute measurements of near threshold to be reported for any heavy noble gas. The observed large differences in the relative magnitudes of the cross sections are interpreted in terms of the angular momenta of the Kr+ ion core (4p5) and the entire electron configuration. A resonance is found to be most prominent in the excitation functions of states having the same core angular momentum as that of resonance itself, indicating that the rearrangement involved in the decay of a temporary negative ion generally involves only the outer electrons.

Excitation of Kr and Xe in collisions with Ar +

The excitation of Kr and Xe in with Ar + ions has been studied by monitoring the resulting luminescence. Energetic collisions of Ar + with Kr and Xe excite the 116.5 and 123.6 nm Kr(I) lines and the 129.6 and 147.0 nm Xe(I) lines respectively. Apparent cross sections and kinetic energy onsets for collisional excitalition in bimolecular ion -atom collisions in the laboratory energy range of 5–100 eV are reported. The results are compared with those reported for other symmetric and asymmetric ion-atom collisions among the rare gases. Possible reaction mechanism and the criteria that may be applied to predict the relative importance of reaction pathways in ion-atom collisions are also discussed.