Spontaneous Decay of Highly-Charged Fullerene Ions C60Z and C58z

Using isotope-resolved, two sector field mass spectrometric techniques we have identified and investigated quantitatively the energetics and kinetics (in particular the kinetic energy release, KER) of the spontaneous decay reactions C_60-2m^z+ → C_60-2m-p(z-1)+ ₊ C_p⁺ with m = 0 or 1, z ranging from 3 to 6 and p = 2 and 4. The obtained KER results are not compatible with the properties expected for a single-step fissioning reaction as described by the liquid drop model. Therefore the present data had to be interpreted by a different fragmentation mechanism. This novel reaction sequence, termed auto charge transfer (ACT) reaction, is initiated by the statistically driven neutral C₂ (or C₄₎ evaporation followed by an electron transfer process from the receding C₂ (or C₄) fragment to the remaining highly-charged fullerene ion thereby leading finally to the two charged reaction products observed in the exit channel of the decay reaction. Moreover, in the case that a C₂⁺ loss from C₆₀z+ is occurring in the first field-free region we have been able to demonstrate that it is possible to observe in the second field-free region a subsequent C₂ evaporation from the C₅₈(z-1)⁺ fragment ion.     

GROUP TRANSFER AND DIMERIZATION PROCESSES OF C60(CN)2 UNDER ATMOSPHERIC PRESSURE IONIZATION CONDITIONS

Neutral and anionic C₆₀(CN)₂ were investigated with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) mass spectrometry. It was observed that its anions underwent cyano- group and oxygen transfer, and dimerization processes in ESI conditions to form C₆₀(CN)₃H^-, C₆₀(CN)₂(OH₂)^-, [C₆₀(CN)₃H]^-₂, [C₆₀(CN)₂(OH₂)]^-₂ and [(C₆₀)₂(CN)₂(OH)]^-. Meanwhile, neutral C₆₀(CN)₂, for which no signal was observed in ESIMS, showed a base peak corresponding to C₆₀(CN)₂Cl^- in APCIMS spectra with CHCl₃ used as solvent, while only a molecular ion peak corresponding to C₆₀(CN)^-₂ was observed for the toluene solution of neutral C₆₀(CN)₂ in the same conditions. Possible mechanisms for group transfer and dimerization were proposed based on these observations.     

Optical properties and energy transfer among Nd in Nd:Ca2Al2SiO7 crystals for diode pumped lasers

The energy levels of neodymium in the Nd³⁺:Ca₂Al₂SiO₇ (CAS) laser material with gehlenite structure are reported. As the Nd³⁺:Ca₂Al₂SiO₇ compound presents a broad absorption around 806 nm, it is a good candidate for diode pumped laser. The ⁴F_3/2→⁴I_9/2 and ⁴F_3/2→⁴I11/2 emission have been recorded and the fluorescence branching ratios calculated from the Judd-Ofelt analysis are 0.41 and 0.47 respectively. The emission cross section at 1.06 μm (⁴F_3/2→⁴I11/2 transition) is 5 × 10^-20 cm². The decay profiles of the Nd³⁺ emission have been analyzed for several Nd³⁺ concentrations using the kinetic microparameters related to the cross relaxation ( and R₀≈6 Å) and the energy migration probabilities ( ). In the Nd:CAS laser material, the optimal concentration corresponding to the maximum of the fluorescence intensity is determined to be around 2.7 × 10²⁰ Nd³⁺ ions cm^-3. The Nd³⁺-Nd³⁺ interactions are not very strong in this material as the optical concentration value is two times higher than in the Nd:YAG laser material.     

Blue, green and 0.8 μm Tm, Ho doped upconversion laser glasses, sensitized by Yb

To obtain efficient upconversion laser glass, the optical properties of Tm³⁺ and Ho³⁺ were investigated in various glasses. Fluoride glass was selected as base glass for upconversion. The efficient upconversion fluorescences corresponding to the ¹G₄→³H₆ and ³H₄→³H₆ transitions of Tm³⁺ and the ⁵S₂→⁵I₈ transition of Ho³⁺ were observed in Yb³⁺-Tm³⁺ and Yb³⁺-Ho³⁺ doped aluminozircofluoride glasses excited at 980 nm. The very stronge blue and green emission light can be observed visually. The upconversion processes observed were two-photon processes for ³F₄→³H₆, ⁵S₂→⁵I₈ transitions and three-photon processes for the ¹G₄→³H₆ transition and can be described by a rate equation model. The energy transfer and energy back-transfer were analyzed in Yb³⁺-Tm³⁺ and Yb³⁺-Ho³⁺ systems. The relationship between emission intensity, pumping intensity and dopant concentrations is described using a rate equation model and shows good agreement with experiments. The dynamics of excited state ( ) is also analyzed with the diffusion-limited model based on Yokota-Tanimoto theory.     

Cr-Tm ion pairs in Gd3Ga5O12 garnet

A study is presented about Cr³⁺→Tm³⁺ energy transfers in Gd₃Ga₅O₁₂ garnet at 10 K. By time-resolved spectroscopy and analysis of decay kinetics we determine the nature of the interaction and we show the existence of chromium-thulium pairs in which the chromium emission wavelength is shifted from 693.6 to 694 nm.     

Enhancement of Er I13/2 population in Y2O3 by energy transfer to Ce

We report measurements of the energy transfer between Er³⁺ and Ce³⁺ in Y₂O₃. The transition between the Er^{3+ 4}I_11/2 and ⁴I_13/2 excited states can be stimulated by energy transfer to Ce³⁺, augmenting the population in the ⁴I_13/2 state at the expense of that in the ⁴I_11/2 state. Experiments were performed on Y₂O₃ planar waveguides doped with 0.2 at.% erbium and 0–0.42 at.% cerium by ion implantation. From measurements of Er³⁺ decay rates as a function of cerium concentration we derive an energy transfer rate constant of 1.3×10⁻¹⁸ cm³/s. The efficiency of the energy transfer amounts to 0.47 at 0.42 at.% cerium. The energy transfer rate constant measured in Y₂O₃ is two times smaller for Er³⁺→Ce³⁺ than that for Er³⁺→Eu³⁺ in the same material.     

A Study of Fullerene Preparation Technique

A new homemade are fullerene generator used in this experiment is reported. The comparation of yields of fullerenes (C₆₀/C₇₀ mixture) was studied by different power supplies (AC and DC), different gaps of two graphite rods and different He pressure between 0.4×10⁴- 2.8×10⁴ Pa. In our experiment, the highest yield up to 13% was achieved, when DC discharge was used and the optimum He pressure was near 0.8×10⁴ - 1.6×10⁴ Pa.

The mixed fullerene was analyzed by electron impact masa spectnun (EIMS). The relative amount af C₆₀ to C₇₀ was 4.2 to 1. After column chromatography aeperation with hexane on alumina, 99.9% Cso was obtained. FTIR and ^1aC-NMR epectrum were ueed to characterize the pure C₆₀ samples.     

Optical properties, fluorescence mechanisms and energy transfer in Tm, Ho and Tm -Ho doped near-infrared laser glasses, sensitized by Yb

The optical properties of the rare elements Tm³⁺, Ho³⁺ and Yb³⁺ were systematically investigated in various glasses. The Tm³⁺ doped aluminozircofluoride glass shows higher quantum efficiency, longer lifetime and stronger fluorescence intensity than Tm³⁺ doped YSGG crystal and other Tm³⁺ doped glasses for the ³H₄ → ³H₆ transition. Similar quantum efficiency, longer lifetime and stronger fluorescence intensity were also found in Ho³⁺ doped aluminozircofluoride glass for the ⁵I₇ → ⁵I₈ transition. The higher quantum efficiencies of Tm³⁺ and Ho³⁺ in aluminozircofluoride glass are due to the longer lifetime and the lower phonon energy. The fluorescence mechanisms and energy transfer in the Yb³⁺ -Tm³⁺ system, Yb³⁺ -Ho³⁺ system and Yb³⁺ - Tm³⁺ -Ho³⁺ system were studied. The very strong fluorescence intensities in the Yb³⁺ -Tm³⁺ system for Tm³⁺ and the Yb³⁺ -Tm³⁺ -Ho³⁺ system for Ho³⁺ which are 1.68 times that of Tm³⁺ doped YSGG crystal and 2.25 times that of Tm³⁺---Ho³⁺ codoped YSGG crystal are attributed to the efficient Yb³⁺ → Tm³⁺, Yb³⁺ → Ho³⁺ and Tm³⁺ → Ho³⁺ energy transfer processes. The fluorescence processes are described by cross relaxations of ²F_5/2 → ³H₅ → ³H₄ → ³H₆ → ²F_7/2 and²F_5/2 → ³H₅ (or ²F_5/2 → ⁵I₆ → ³H₅) → ³H₄ → ⁵I₇ → ⁵I₈ → ³H₆ → ²F_7/2.     

INHIBITORY EFFECTS OF FULLERENE C60 DERIVATIVES ON ENDOTHELIUM-DERIVED RELAXATION IN RABBIT THORACIC AORTA

Inhibitory effects of newly synthesized fullerene C₆₀ derivatives 1 (C₆₀-bis(N,N-dimethylpyrrolidinium iodide)), 2 (C₆₀-proline-N-acetic acid) and 3 (C₆₀-ethylenediamine-N, N'-diacetic acid) on acetylcholine-induced relaxation in endothelium-intact rabbit thoracic aorta precontracted by phenylephrine (10^-6 M) were studied. Fullerene C₆₀ derivative 1 (3 × 10^-6 M), 2 (10^-5 M) and 3 (10^-5 M) reduced the maximum amplitude of the acetylcholine-induced relaxation without significantly changing the pD₂ values obtained from the concentration - response curves. In the presence of fullerene C₆₀ derivative 1 (10^-5 M) the acetylcholine-induced relaxation was eliminated and an acetylcholine-induced contraction was observed. These results suggest that fullerene C₆₀ derivative 1 strongly inhibits endothelium (nitric oxide)-dependent acetylcholine-induced relaxation in thoracic aorta of rabbit.     

The Rectification Studies on the P -Ion Implanted C60/Si Films

N-type doping of the C₆₀ films deposited on Si substrates has been achieved by 80 keV P⁺-ion implantation with doses of 2×10¹⁴ cm^-2 at room temperature. The heterostructures composed of the n-type doped C₆₀ films and n- or p-type Si(111), Si(100) substrates are studied in view of semiconductor heterojunctions. The rectification and other electrical characteristics of the P⁺-ion implanted n-C₆₀/n-(p-)Si heterostructures are disclosed by the current-voltage (I-V) measurements at room temperature. The n-C₆₀/p-Si heterostructures show stronger rectification than n-C₆₀/n-Si heterostructures and Si(111) substrates are found to be more suitable for forming n-C₆₀/Si heterostructures than Si(100) substrates.     

C60 Films Formed by Ionized Cluster Beam Deposition: Structure and Doping by Ion Implantation

C₆₀ films were formed on a variety of substrates by ionized cluster beam (ICB) technique. Their structure was found to depend on the acceleration voltages and substrate. Then the Coo films were implanted by P⁺-ions with doses from 0—2×10¹⁴ ion/cm². The in situ measurement of electrical conductivity revealed an abrupt decrease of three orders in resistance. The temperature coefficient of resistivity of the P⁺-ion implanted C₆₀ film remained in a negative value.     

On the Evaporation of C60 in Vacuum and Inert Gases at Temperatures Between 830 K and 1050 K

The binary diffusion coefficient D_AB of subliming C₆₀ in He, N₂ and Ar gas has been determined at a gas pressure between 5 and 10 kPa. It resulted D_AB/(cm^2/s)=D_o(P_o/P_t(T/T_o)ⁿ as a function of the total pressure P_t of the vapor phase and temperature T. At T_o=273 K and P_o=1.0133×10⁵ P_a, the values D_o = (0.059±0.004) cm²/s, (0.011±0.003) cm²/s, (0.012±0.007) cm²/s, n = 1.77±0.06, 2.02±0.18, 1.77±0.37 were obtained for He, N₂, Ar and (830-1000) K, (800-1020) K, (875-1095) K, respectively. Only 40 wt% of the initial C₆₀ material yielded reliable D_AB where the vapor pressure of C₆₀ followed log₁₀(P/Pa) = -(8976±60)/T/K+(11.05±0.07) for T between 640 and 1055 K.     

Ozone Reaction with C70 and C60 Fullerenes: The Effect of Temperature on the Reaction Kinetics

It has been confirmed that the effect of temperature on the rate constants (k) of ozone reaction with C₇₀ and C₆₀ fullerenes follows the Arrhenius law. The experimental values of activation energy (E_a) and pre-exponential factor (A), like as those of other simple alkenes, are in the order of 2.4-2.6 kcal mol^-1 and (1.2-1.8) × 10⁷ L mol^-1 sec^-1, respectively. They are practically equal for the both fullerenes. It has also been found that the value of the rate constant k of C₇₀ fullerene ozonolysis is higher in comparison to the respective k-value of C₆₀.     

Solubility of Fullerenes C60 and C70 in Seven Normal Alcohols and Their Deduced Solubility in Water

The solubilities of C₆₀ and C₇₀ at 25°C in seven normal alcohols obey the relationship InY = a + bX + cX², where Y is solubility and X is the Hildebrand solubility parameter of the solvent. Extrapolation to the solubility parameter of water yields solubilities in water of 1.3'10^-11 (C₆₀) and 1.3'10^-10(C₇₀) ng/ml with an uncertainty of one order of magnitude.     

RADIATION CHEMICAL AND PHOTOPHYSICAL PROPERTIES OF C60(C4H8SO3Na)n IN AQUEOUS SOLUTION: A LASER FLASH PHOTOLYSIS AND PULSE RADIOLYSIS STUDY

Optical absorption studies on aqueous solutions of C₆₀(C₄H₈SO₃Na)_n (n = 4-6) revealed deviation from the Beer-Lambert law in the 250-350 nm region, which is assigned to the formation of solute aggregates at concentrations higher than 1 × 10^-3 mol dm^-3. Dynamic light scattering experiments showed aggregates with an average size of ∼100 nm. The solute has a broad weak fluorescence emission (ϕ_f = 1.8 × 10^-3) in the 450-650 nm region, which remained independent of solute concentration. The broad transient absorption band in the 450-900 nm region (ε₆₆₀ = 2170 dm³ mol^-1 cm^-1), which formed immediately on laser flash photolysis (λ_ex = 355 nm, 35 ps), is assigned to singlet-singlet transition. It decays to a triplet excited state whose absorption is observed to depend strongly on solute concentration. In dilute solutions, an absorption band with λ_max = 590 nm is seen, and at high solute concentration a broad absorption in the 500-900 nm region is observed. The e_aq^- reacts with the solute with a bimolecular rate constant of 1.7 × 10⁸ dm³ mol^-1 s^-1 and forms weak broad absorption bands at 440, 540, 620, 870, 940, and 1020 nm. Isopropanol radicals also react with the solute with a bimolecular rate constant of 2.3 × 10⁸ dm³ mol^-1 s^-1 with the formation of a transient optical absorption spectrum similar to that observed on reaction with e_aq^- and assigned to a solute radical anion. The ^•H and ^-OH radicals react with bimolecular rate constants of 3.2 × 10⁹ and 4.4 × 10⁹ dm³ mol^-1 s^-1, respectively, and form transient absorption bands at 440, 510, and 660 nm. Based on electron transfer studies with suitable electron donor/acceptor substrates, the ranges of the reduction and oxidation potentials of the solute an estimated.     

Laser Photolysis Study on Mechanism and Efficiency of Electron Transfer Between Fullerenes (C60 and C70) and Tetraselenafulvalenes

Efficient electron-transfer reactions from three kind of tetraselenafulvalenes (TSeF's) to photoexcited triplet state of C₆₀ or C₇₀ in polar solvents have been confirmed by transient absorption spectroscopy observing the decay of ³C₆₀*/³C₇₀* and rise of C₆₀^-•/C₇₀^-•. Growth of single crystal seems to be stimulated by laser irradiation of the solution containing C₆₀ and bis(ethylenedithio)tetraselena-fulvalene (BEDT-TSeF), in which C₆₀^-• was effectively formed.     

Ion Formation and Fragmentation in Gas-Phase Fast-Atom Bombardment Mass Spectrometry of C60

The observation of multiply-charged ions C₆₀^Z+ (z=1-4) and fragment ions (C₆₀ - C_2n)^z+ (z=1-4, n=1-12) has been reported using a new ionization/ collision technique, called gas-phase fast-atom bombardment with a high-energy (8 keV) helium beam.     

Anomalous elastic properties of RF-sputtered amorphous TeO2+x thin film for temperature-stable SAW device applications

The anomalous elastic properties of TeO_2+x thin films deposited by rf diode sputtering on substrates at room temperature have been studied. The deposited films are amorphous, and IR spectroscopy reveals the formation of Te-O bond. X-ray photoelectron spectroscopy confirms the variation in the stoichiometry of TeO_2+x film from x = 0 to 1 with an increase in the oxygen percentage in processing gas composition. The elastic parameters of the films in comparison to the reported values for TeO_2+x single crystal are found to be low. However, the temperature coefficients of elastic parameters of all deposited films exhibit anomalous behavior showing positive values for TC(C₁₁) in the range (32.0 to 600.0) x 10^-40 C^-1 and TC(C¹¹) = (35.0 to 645.5) x 10^-4degC^-1 against the negative values TC(Cn) = -2.7 x 10^-4degC^-1 and TC(C₁₁) = -0.73 x 10^-4degC^-1 reported for TeO₂ single crystal. The variation in the elastic parameters and their temperature coefficients is correlated with the change in the three-dimensional network of Te-O bonding. The anomalous elastic properties of the TeO_2+x films grown in 100% O₂ are useful for potential application in the design of temperature stable surface acoustic wave devices.     

Evaluation of the capabilities of several ions to sensitize Nd in the laser material LNA (La0.9Nd0.1MgAl11O19)

In the hexaaluminate laser material La_0.9Nd_0.1MgAl₁₁O₁₉ also known as LMA:Nd the Nd³⁺ fluorescence can be enhanced by codoping the matrix with rare-earth (REⁿ⁺) or transition metal (TM^m+) ions. A large number of potential donor ions D (D = Mn²⁺, Dy³⁺, Tb³⁺, Eu²⁺, Eu³⁺ and Ti³⁺) are studied in the hexaaluminate host. The D→Nd³⁺ energy transfer, t he, luminescent efficiency as well as the back-transfer strongly depend on the overlap of the D emission and Nd³⁺ absorption, the concentration of the two ions and their localization in the crystal host. In this paper the optical properties — absorption and emission — of the D and Nd³⁺ ions as well as the D→Nd³⁺ interactions are considered using a Forster-Dexter's approach, to compare the capabilities of the different donors in the Nd³⁺-doped hexaaluminate host. The C_DNd and R₀ parameters are estimated in each case, and the results discussed in terms of the localization of the donor ions, their absorption and emission as well as their lifetime properties.     

Yb to Er energy transfer and rate-equations formalism in the eye safe laser material Yb:Er:Ca2Al2SiO7

Rate equations formalism is used to predict the population ratio of the Er^{3+ 4}I_13/2 levels involved in the 1.55 μm laser transition in the Yb:Er:CAS laser materials. An effective Yb → Er energy transfer, favourable to the Er³⁺ 1.55 μm laser emission, is demonstrated in this laser host. Indeed, the Yb → Er transfer and the Er → Yb back transfer rates are calculated to be 6 x 10⁻¹⁶ and 0.45 x 10⁻¹⁶ cm³ s⁻¹, respectively. Attempts of codoping the system with Nd³⁺, Eu³⁺ and Ce³⁺ have been realised in order to increase the population of the Er^{3+ 4}I_13/2 laser emitting level. Best results are obtained with Ce³⁺ ion since in the sample containing 6 x 10²⁰ Ce³⁺/cm³, the Er^{3+ 4}I_11/2 level lifetime is divided by a factor of 3 while the Er^{3+ 4}I_13/2 fluorescence lifetime remains unaffected. On the contrary, codoping with Nd³⁺ or Eu³⁺ ions simultaneously decreases the Er^{3+ 4}I_11/2 and ⁴I_13/2 kinetics parameters. The role of the other parameters such as Yb/Er concentrations ratios is also discussed.