Lasers divalent

Nonradiative energy transfer is very often used in practical applications, such as to enhance the efficiency of phosphors and lasers. A nice example is the commercial phosphor Cas(P04)3 (FCl), which is doubly activated by Sb + and Mn + ions. When the phosphor is singly activated by Mn + ions, it turns out to be very inefficient, due to the weak absorption bands of the divalent manganese ion. However, coactivation with Sb + ions produces a very intense emission from the Mn + ions, because the Sb + ions (the donor centers) efficiently absorb the ultraviolet emission (253.6 nm) of... 

The rare earth (RE) ions most commonly used for applications as phosphors, lasers, and amplifiers are the so-called lanthanide ions. Lanthanide ions are formed by ionization of a nnmber of atoms located in periodic table after lanthanum from the cerium atom (atomic number 58), which has an onter electronic configuration 5s 5p 5d 4f 6s, to the ytterbium atom (atomic number 70), with an outer electronic configuration 5s 5p 4f " 6s. These atoms are nsnally incorporated in crystals as divalent or trivalent cations. In trivalent ions 5d, 6s, and some 4f electrons are removed and so (RE) + ions deal with transitions between electronic energy sublevels of the 4f" electroiuc configuration. Divalent lanthanide ions contain one more f electron (for instance, the Eu + ion has the same electronic configuration as the Gd + ion, the next element in the periodic table) but, at variance with trivalent ions, they tand use to show f d interconfigurational optical transitions. This aspect leads to quite different spectroscopic properties between divalent and trivalent ions, and so we will discuss them separately. 

The luminescence center of divalent europium in fluorite is well known (Haber-land et al. 1934 Tarashchan 1978 Krasilschikova et al. 1986 Barbin et al. 1996). It is clearly seen in laser-induced time-resolved luminescence spectra with a decay time of 600-800 ns (Fig. 4.10a). In several samples the band with a spectrum similar to those of Eu + has a very long decay time and remains even after a delay of several ms. Principally it may be connected with energy migration from a UV emitting center with a long decay time, for example, Gd ". ... 

Platinum porphyrin complexes can be prepared by reaction with PtCl2(PhCN)2. Purification of the final complex is by medium pressure liquid chromatography on alumina. The strongly phosphorescent platinum(II) porphyrin complexes are efficient sensitizers for stilbene isomerization. The quantum yields for the cis to trans process are greater than unity because of a quantum chain process in which the metalloporphyrin serves both as an energy donor and an acceptor.1110 Picosecond laser spectroscopy has been used to obtain time-resolved excited-state spectra of platinum octaethylporphyrin complexes, and to probe the excited-state energy levels.1111 Tetrabenzoporphyrin complexes have been prepared for platinum in both the divalent and tetravalent oxidation states. The divalent complex shows strong phosphorescence at 745 nm.1112... 

A typical example of this is in the preparation of extraordinary divalent carbon intermediates (carbenes) by application of ultrafast laser techniques. Thus, photoexcitement of diphenyldiazomethane (DPDM) to an excited singlet state breaks the C=N bond, releasing diphenvlcarbene (DPC) in a singlet state and ultimately allows its stabilization in the triplet ground state,... 

Fisenthal, K B, et al Divalent Carbon Intermediates. Laser PhotolysisScience, 225. 1439-1445 (1984). 

Because integrins bind extracellular ligands like RGD with the help of divalent cations and hydrogen bonds, it would be interesting to develop a laser-based tech-... 

Because of the instability of the radiation produced divalents, their use in lasers was not desirable, and work on finding methods to prepare materials containing stable divalent lanthanides was stimulated. Reduction techniques were developed for the fused state from which crystals had to be grown and also for the solid state in which the as-grown crystals contained trivalent ions. 

Alkaline-earth fluorides have been the principal hosts for divalent lanthanide lasers. These are relatively soft, optically isotropic materials. Lanthanides enter the alkaline earth sites substitutionally without charge compensation. Because these sites have inversion symmetry, only magnetic-dipole or vibronic transitions are allowed between 4f states. These are weak and the resulting radiative lifetimes are long. In comparison, the radiative lifetimes of 5d->4f transitions, which are parity allowed, are-short. The 4f->5d transitions are broad and thus provide good absorption bands for optical pumping. 

Laser action has been reported for three divalent lanthanides (2J, 34). Figure 6 summarizes the energy levels, transitions, and approximate wavelengths of these lasers. Only crystals have been used as hosts and reduced temperatures were used in all cases. 

Sama/Uum. Divalent Sm laser action has been demonstrated using both d+f and f- f transitions. The former was observed in CaF2 (88, 89). At or below liquid nitrogen temperatures lasing occurs from 708 to 729 nm. For Sm2+ in SrF2, the Dq state is below the lowest 5d band and 5Dq- Fi lasing has the lowest threshold at liquid helium temperatures (90). Samarium laser action was pulsed using xenon flashlamps or a ruby laser for excitation. 

Figure 6. Energy levels and laser transitions for divalent lanthanide ions. Approximate wavelengths of transitions are given in micrometers.

Although most univalent ions are permeable in the gramicidin channel, the channel has some conductance properties that suggest that the permeation process may be more complicated than ion motion down a narrow tube . Channel block by divalent cations is mechanistically complicated (14). Also, when Tl+ ion is present as the sole permeant ion, it is an excellent permeant ion that retains linear behavior to very large transmembrane potentials (15). However, when this ion is present as the minority cation in variable mole fraction solutions of Tl+ and Na+, Tl+ ion severely limits set channel currents (16). Such anomalous behavior can be elucidated if the local velocity of a specific ion (e.g., Tl+ ion) can be determined experimentally. In fact, the laser Doppler scattering technique produces a detectable scatter only with the Tl+ so that ion motions within the gramicidin channels can be differentiated. 

Ryan FM, Ohlmann RC, Murphy J, Mazelsky R, Wagner GR, Warren RW (1970) Optical properties of divalent manganese in calcium fluorophosphate. Phys Rev B 2 2341-2352 Scott MA, Han TPJ, Gallagher HG, Henderon B (1997) Near-infrared laser crystals based on 3cf ions Spectroscopic studies of ions in oxide, melilite and apatite crystals. J Lumin 72-74 260-262 Sears DWG (1980) Thermoluminescence of meteorites Relationships with their K-Ar age and their shock and reheating history. Icarus 44 190-206... 

Wong, C. K. L. and Dominic Chan, T.-W., Cationization Processes in Matrix-assisted Laser Desorption/Ionization Mass Spectrometry Attachment of Divalent and Trivalent Metal Ions, Rapid. Commun. Mass Spectrom., 11, 513, 1997. 

In this paper, the authors present the results of studying of the structural and morphological changes that occur after UV and visible laser irradiation of layered organic-inorganic composites zinc and copper synthesized by laser ablation in liquid. The S5mthesized materials are the second and third group composites. Their structural formulas are as follows (M)2(OH)3X x z X H O and (M)(OH)2X x z x H O, where M - divalent metals (Zn, Cu) and X - intercalated anion - alkyl sulfate where n = 12. 

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