Comparison of plume expansion in femtosecond laser ablation on oxidized and non-oxidized Sm surfaces

Time development of Sm⁺ and Sm ablation plume produced by the femtosecond laser irradiation has been investigated. The two-dimensional spatial profiles of Sm and Sm⁺ emitted from oxidized and non-oxidized Sm surface were visualized using a planar laser-induced fluorescence method. It was observed that the flow velocity of Sm⁺ is much faster than that of Sm plume in both surfaces. The plumes from the oxidized Sm surface show higher velocity than that from non-oxidized surface, which is originated by the small electric conductivity at the surface. Expansion property observed for Sm⁺ and Sm plume in the oxidized Sm surface ablation implies the formation of the Knundsen layer nearby the surface. Meanwhile, continuous emission of Sm indicates the large contribution of heating effect to emission process at the non-oxidized surface. We conclude that the fsLA process strongly depends on the electric property of the ablated surface and the heating effect contributes to the particle emission process on the conductive material surface.     

Substrate dependence of ion motion in femtosecond laser ablation cloud observed by planar laser-induced fluorescence

We have observed the motion of Sm⁺ ions as well as Sm atoms produced by femtosecond laser ablation of a solidified samarium solution sample on substrates by using a planar laser-induced fluorescence method. Kinetic energies of both Sm⁺ ions and Sm atoms increase as the electrical conductivity of the substrate decreases, which suggests the effect of surface charging. The kinetic energy of Sm⁺ ions is larger than that of Sm atoms for a variety of substrates due to the further electrical acceleration by the surface charge. The knowledge of ion motion will be the key information for the optimization of femtosecond laser simultaneous atomization and ionization of organic and inorganic samples on substrates.     

Crystal field effects on the saturation magnetic moment of Sm3+ ion in ferronagnetic samarium compounds

The effects of cubic crystal fields on the saturation magnetic moment of Sm³⁺ ion in ferromagnetic compounds have been investigated. In samarium compounds with magnetic elements, the exchange fieldH _ex acting on Sm³⁺ ion is taken to be proportional to the sublattice magnetization of the magnetic element, while in compounds with nonmagnetic elementsH _ex is taken to be proportional to the spin average of the Sm³⁺ ion and is determined self-consistently. In both types of compoundsH _ex is assumed to be along [001] direction. The saturation magnetic moment is calculated by taking into account the admixture of excited (J=7/2 andJ=9/2) levels into the ground (J=5/2) level of Sm³⁺ ion by crystal fields and exchange fields. It is shown that depending upon the strength, the crystal fields quench or enhance the magnetic moment from the free ion value, and in some cases force Sm³⁺ ion to behave effectively like an (L+S) ion rather than an (L−S)ion. The crystal fields may have important bearing on the performance of samarium compounds as permanent magnet materials.     

Energy transfer from Sm3+ to Er3+ in zinc phosphate glass

A study of energy transfer from samarium to erbium ions in zinc phosphate glass has been performed for a range of donor (1.0 wt% fixed) and acceptor concentrations ranging from 0.2 wt% to 1.2 wt%. The intensity of emission spectra of Sm³⁺ ions in the presence of Er³⁺ ions shows an overall decrease, thereby suggesting a non radiative energy transfer from Sm³⁺ ions to Er³⁺ ions. The interaction mechanism between the donor and acceptor ions is found to be mainly electric dipole-dipole in nature. The parameters required for the quantitative study of energy transfer e.g. energy transfer efficiencies, transfer probabilities, critical transfer distances have been computed.     

Synthesis and Sm/Sm doping effects on photoluminescence properties of Sr4Al14O25

Complete and partial samarium reduction was achieved under strong reducing atmosphere by solid-state and combustion synthesis of Sr_3.96Sm_0.04Al₁₄O₂₅. Dependence of different fluxing agents on the formation of various strontium aluminates was examined. The samples were investigated by X-ray powder diffraction, temperature dependent luminescence decay and photoluminescence measurements. Excitation with UV radiation resulted in sharp and well resolved emission lines of samarium ions. Distinct temperature behavior for Sm²⁺ and Sm³⁺ were detected in the range of 100-500 K. Estimated emission thermal quenching values (TQ_1/2) for divalent samarium were approximately 270 K while for trivalent state around 660 K. Measured luminescence decay values of Sm²⁺ are substantially lower than for Sm³⁺,≈1.7 and ≈2.7 ms, respectively. The spectral feature of Sm²⁺ emission spectrum indicates that dopant occupies low symmetry site in Sr₄Al₁₄O₂₅ compound.     

Influence of silver on the Sm<Superscript>3+</Superscript> luminescence in “Aerosil” silica glasses

The introduction of silver into the samarium-containing silica glasses prepared by the original solgel method leads to the formation of complex optical centers involving samarium ions and simple and/or complex silver ions. These centers are characterized by the effective sensitization of Sm³⁺ luminescence by Ag⁺, (Ag₂)⁺, and (Ag⁺)₂ ions according to the exchange mechanism for, at least, Sm³⁺-Ag⁺ centers. The formation of Sm-Ag centers is accompanied by an increase in the concentration of nonbridging oxygen ions, which prevent the reduction of silver ions by hydrogen. Silver nanoparticles formed in small amounts upon this reduction are effective quenchers of luminescence from the corresponding excited states of Sm³⁺ ions.     

A Tunneling Model for Afterglow Suppression in CsI:Tl,Sm Scintillation Materials

Combined radioluminescence, afterglow and thermoluminescence experiments on single-crystal samples of co-doped CsI:Tl,Sm suggest that samarium electron traps scavenge electrons from thallium traps and that electrons subsequently released by samarium recombine non-radiatively with trapped holes, thus suppressing afterglow. Experiments on single crystals support the inference that electrons tunnel freely between samarium ions and are trapped preferentially as substitutional Sm⁺ near V_KA(Tl⁺) centers where non-radiative recombination is the rate-limiting step. Afterglow in microcolumnar films of CsI:Tl,Sm is enhanced by inhomogeneities which impede tunneling between samarium ions, but is partly suppressed by annealing.     

Hydrogenation of carbon fragments after femtosecond laser ablation of solid C60

We have observed several kinds of hydrocarbon cations after the nanosecond and the femtosecond laser ablation (nsLA and fsLA) of solid C₆₀. The observation indicates that the carbon fragments produced just after laser ablation of the C₆₀ molecule react with the hydrogen atoms and ions coexisting in the ablation plume. In the case of fsLA, clear dependence of the product hydrocarbon species on the ablation laser power has been observed although the dependence is not clearly observed in nsLA. The production of C_nH₅⁺ (n = 8, 10, and 12) is only observed in fsLA suggesting the unique nature of the transient carbon fragments produced by fsLA.     

Analysis of Energy Transfer and Concentration Quenching in Sm3+-Activated Borate GdB3O6 Phosphors by Means of Fluorescence Dynamics

This article reports on the optical properties of Sm³⁺-activated GdB₃O₆ phosphors based on the measurement of their photoluminescence spectra and luminescence decay curves. Energy transfer from Gd³⁺ to Sm³⁺ and the concentration quenching of the Sm³⁺ ion emission are investigated. From the photoluminescence spectra and decay curves, the energy transfer from Gd³⁺ to Sm³⁺ is confirmed. The concentration quenching of the Sm³⁺ ion emission can be ascribed to resonant cross-relaxation. The interaction between the Sm³⁺ ions is derived of the electric dipole–dipole type through fitting the data with the Inokuti-Hirayama model. The critical distances and energy transfer microparameter for the transfer processes are given. The decay curves of Sm³⁺⁴G_5/2 level exhibiting a buildup and decay process also confirm the energy transfer from Gd³⁺ to Sm³⁺ and between Sm³⁺ ions.     

Thermally stimulated desorption of Na<Superscript>+</Superscript> and Cs<Superscript>+</Superscript> ions from a NaAu alloy film grown on Au

The formation of Na⁺ and Cs⁺ ions on and their thermal desorption from the surface of a NaAu alloy film grown on metallic gold are studied. It is shown that thermionic emission from insulator-coated metallic substrates is governed by a sequence of processes, such as diffusion of Na and Cs adatoms into the film, ionization of these atoms at the insulator-metal interface, diffusion of the resulting ions toward the surface, and desorption of the ions. The effect of weak electric fields on ion diffusion and desorption is investigated.     

Energy transfer between Sm and Er in orthophosphate YPO4

The energy transfer between Sm³⁺ and Er³⁺ ions in yttrium orthophosphate is studied. This choice of ions is based on the possibility of quantum cutting processes and the host material is selected according to the position of the 5d bands of the Sm³⁺ ion. The Sm³⁺ and Er³⁺ doped and Sm³⁺, Er³⁺ co-doped YPO₄ have been synthesized. Spectroscopic studies were done in the ultraviolet and vacuum ultraviolet ranges. The energy transfer between Sm³⁺ and Er³⁺ is very efficient but it does not lead to Er³⁺ visible emission. Whatever the excitation wavelength, the emission of co-doped samples mainly occurs in the infrared range.     

NTCR behavior of Sm-substituted barium zirconium titanate nanocrystalline solid solution

Ceramic solid solution of nanocrystalline barium zirconium titanate in the form of Ba(Zr_0.52Ti_0.48)O₃ substituted by samarium (Sm³⁺) was prepared using the conventional solid state reaction method. The phase assemblage analyzed by the X-ray diffraction technique was fitted for cubic-crystal-symmetry. The change in the grain size depicted the influence of Sm³⁺ ions on the microstructure. The electrical behavior was studied in the temperature range from 323 to 773 K. The sintered samples exhibited a negative temperature coefficient of resistance (NTCR) and superior semiconducting behavior above 513 K. Addition of Sm³⁺ increased the room temperature resistivity of Ba(Zr_0.52Ti_0.48)O₃ solid solution. The results obtained from the thermoelectric power measurement confirm electrons as the majority charge carriers.     

Effect of CdS nanoparticles on fluorescence from Sm doped SiO2 glass

Sm³⁺ doped CdS nanoparticles have been prepared by sol-gel method. The effect of annealing temperatures and doping concentrations of CdS on the photoluminescence spectra of Sm³⁺ were studied. From the measurement of its optical absorption, three phenomenological Judd-Ofelt intensity parameters (Ω₂, Ω₄, and Ω₆) have been computed and used to parameterize the radiative properties. The influences of CdS on Sm³⁺ ions were studied by fluorescence spectroscopy. The fluorescence spectra revealed that the emission intensity of samarium increased considerably in the presence of CdS nanoparticles. The evaluation of radiative properties of Sm³⁺ containing CdS showed that the ⁴G_5/2→⁶H_7/2 transition in silica matrix had the potential to be a laser transition.     

Photoluminescence properties of samarium-doped TiO2 semiconductor nanocrystalline powders

In this work, the luminescence properties of samarium ions-doped titanium dioxide prepared by the sol-gel process were studied. A strong orange red emission (⁴G_5/2−⁶H_7/2 (orange) and ⁴G_5/2-⁶H_9/2 (red)) ascribed to the electron transitions in 4f⁵ configuration of Sm³⁺ ions was observed upon excitation into TiO₂ host. The energy transfer from TiO₂ to Sm³⁺ was verified and the relevant mechanism was discussed. In addition, the impacts of metal ion codopants upon the TiO₂:Sm³⁺ luminescence properties were studied. The results indicated that the central excitation band shifted to blue in the bismuth-codoped materials (0.5-4% in molar ratio), while it shifted to red in the zirconium-codoped materials. Such materials may find applications in white light-emission diode (LED) and tunable solid lasers.     

Crystal field and exchange interactions in the SmFe3(BO3)4 multiferroic

The optical spectra of oriented SmFe₃(BO₃)₄ single crystals are studied in the region of the f-f transitions in the Sm³⁺ ion by Fourier spectroscopy. The energies, the symmetry properties, and the exchange splittings of the Stark sublevels of the ground and 17 excited multiplets of the Sm³⁺ ion in a crystal field of symmetry D ₃ are determined from the measured temperature dependences of polarized-radiation absorption spectra. The parameters of the crystal field acting on samarium ions and the parameters of the exchange interaction between Sm³⁺ and Fe³⁺ ions are found. The anisotropy of the effective exchange interaction is shown to be substantially stronger than the magnetic anisotropy, due to a strong crystal-field-induced mixing of the ground and excited multiplets.     

An experimental and quantum mechanical study on luminescence properties of SM(β-Nbm)3·(Pd)

A new ternary samarium complex Sm(β-NBM)₃·(PD) has been synthesized by the reaction of SmCl₃·⁶H₂O with β-naphthoylbenzoylmethane (β-HNBM) and 1,10-phenanthroline-5,6-dione (PD) in stoichiometry. The new samarium complex obtained was characterized by elemental analysis, ¹H NMR, and FT-IR spectroscopy. The absorption and emission of this complex were systematically investigated. Photoluminescence studies indicated that the energy absorbed by the organic ligands was efficiently transferred to the central Sm³⁺ ions and the complex showed intensely and characteristically orange emission due to the ⁴G_5/2→⁶H_j transitions of the central Sm³⁺ ions. The energy levels (HOMO and LUMO) of the ligands and the complex were further confirmed by computer simulation and cyclic voltammetry, respectively. All the results suggested that the synthesized Sm(β-NBM)₃·(PD) would have the potential application for organic light-emitting diodes.     

UV laser induced desorption of CsI and RbI ion clusters

Experimental results of laser sputtering of cesium and rubidium iodide secondary ions are presented. A TOF mass spectrometer, operating in linear mode, continuous extraction for positive or negative ions, was used for the analysis of (CsI)_nCs⁺, (CsI)_nI⁻, (RbI)_nRb⁺ and (RbI)_nI⁻ ion emission as a function of the laser irradiance. Experimental data show that the cluster ion emission yields decrease exponentially with n, for all the laser irradiances applied. Theoretical analysis of the clusters structure was performed using density functional theory at the B3LYP/LACV3P level, for the positive and negative cluster series. A quasi-equilibrium evolution of the clusters is proposed to extract a parameter characteristic of the cluster recombination process: the effective temperature. The hypothesis of the atomic species’ recombination (during the expansion of a high density highly ionized cloud) leading to cluster formation is confirmed to some extent in a second set of experiments: the UV laser ablation of a mixed and non-mixed cesium iodide and potassium bromide targets. These experiments show that the emission yields contain contributions from both the recombination process and from the sample stoichiometry, even for high laser irradiances.     

Dynamics of ablation plasma induced by a femtosecond laser pulse in electric fields

Direct observations of ablation plasma dynamics in electric field is presented. A time-resolved spatial profile of the ablation plasma induced by femtosecond laser ablation (fsLA) with high fluence is visualized using a planar-laser-induced fluorescence (P-LIF) method. The external electric field is produced by installing a mesh electrode at 6 mm from a Samarium solid target. The Sm ion plasma created by the fsLA showed collective motion regardless of the external electric field, until they reached close to the electrode. When the accelerating and decelerating field was applied, the ions almost disappeared behind the electrode from the field of view. The observations are understood utilizing a SIMION simulation with a conceivable potential gradient caused by Debye shield effect, which is that the ablation plasma keeps the same potential as the target voltage and follows electric potential gradient near the mesh electrode. It is also revealed that this effect degrades time-of-flight resolution at high fluence irradiation. This work gives a new direction for further developments of a fsLA time-of-flight spectrometer.     

Time-of-flight investigation of the intensity dependence of laser-desorbed positive ions from SrF2

The intensity dependence of the total and specific yields of positive ions desorbed from SrF₂ under 193 nm and 308 nm excimer-laser irradiation has been investigated by the time-of-flight method. The following positive ion species have been detected: F⁺, Sr⁺, Sr⁺⁺, SrF⁺⁺ and SrF ₂ ⁺ . The Sr⁺ and SrF⁺ emission yields are found to increase as E ⁿ, where E represents the laser energy per pulse. The exponent n is related to defect-initiated neutral particle emission and gas-phase ionization. The influence of surface damage on this power dependence is investigated. The F⁺ emission yield showed a quite different behaviour compared to that of the Sr⁺ and SrF⁺ emission. At both wavelengths the total positive ion emission yields saturate at a certain laser energy. In the saturation regime the SrF⁺ emission vanishes and alternative emission of F⁺ and Sr⁺ was observed at both wavelengths, but the total emission yield in the saturation regime (F⁺ + Sr⁺) remained constant. A Scanning Electron Microscope (SEM) was used to investigate the damage spots after laser irradiation for thermal effects.     

The effect of charge compensation by means of Na+ ions on the luminescence behavior of Sm3+-doped CaAl4O7 phosphor

Results of structural and spectroscopic measurements of Sm³⁺ doped calcium aluminates: Ca_1?xSm_xAl₄O₇ and Ca_1?2xSm_xNa_xAl₄O₇ (x=0.0005, 0.002, 0.01, 0.02, 0.03, 0.05) obtained by the modified Pechini method are presented. All samples yield intense orange–red emission under violet excitation (404.5 nm). Narrow bands corresponding to characteristic f–f intraconfigurational transition of Sm³⁺ in excitation and emission spectra were observed. The influences of the concentration of Sm³⁺ as well as charge compensation by co-doping with Na⁺ ions on the luminescent properties of the phosphor were investigated. Detailed analysis of the emission spectra of Sm³⁺ doped and Sm³⁺,Na⁺ co-doped CaAl₄O₇ powders proved that activator ions substitute Ca²⁺ in the host. Co-doping with Na⁺ ions enhanced greatly the intensity of the luminescence. Concentration dependencies of the intensity of luminescence and its decay kinetics proved the emission quenching at higher dopant contents due to cross-relaxation processes between Sm³⁺ ions. Fitting of the ⁴G_5/2 state fluorescence decay to the Inokuti–Hirayama model indicated dipole–dipole interaction as the dominant mechanism of the cross-relaxation processes.