Lanthanide pumped

Stelmakh and Tsvirko have also proposed the mechanism [b] for the production of S2 state fluorescence in Mg, Zn, and lanthanide-porphyrins complexes (15), and showed the possibility of another mechanism of pumping by triplet-triplet annihilation (16)(mechanism [a]). The latter process was considered to predominate at relatively low values of the excitation densities. However, the contribution of the mecahnism [C] was not determined experimentally. The experimental results in the present work are summarized as follows ... 

Matrix isolation studies usually permit spectroscopic observation of the species M(CO), M(CO)2,. M(CO) , the coordinatively saturated molecule. In some early studies, species thought to be simple unsaturated carbonyls were in fact carbonyls of metal clusters Mx(CO) a very low concentration of metal in the matrix (e.g., I mol in 104 mol noble gas) has to be used to prevent clustering. All the partially coordinated carbonyls are only matrix species, that is, they only exist when completely isolated from other molecules of their own kind or from CO. The coordinately saturated carbonyls are of more interest in the context of this review. The following new molecules have been reported Au(CO)2 (84a) Ag(CO)3, Cu2(CO)6 (46, 87) Pd(CO)4 (22), Pt(CO)4 (69) Rh2(CO)g, Ir2(CO)g (37) M(CO)6[M = Pr, Nd, Gd, Ho, Yb (100), Ta (24), U (117)]. The Cu, Pd, Pt, Rh, and Ir carbonyls can be obtained by condensing the metal vapors with pure CO at 40 K and then pumping off excess CO to leave a film of the carbonyl. The Cu, Pd, and Pt carbonyls decompose under vacuum temperatures above -100°C, and the Rh and Ir carbonyls dimerize with loss of CO to give M4(CO)12 above -60°C. The gold and silver carbonyls are not stable outside matrix isolation conditions. Unfortunately, the literature is presently unclear about the stability of the Ta and lanthanide hexacarbonyls outside a matrix. 

Because of the optical quality and chemical stability of crystals, the low probability of non radiative processes and the wide transmission range, fluorides are the most appropriate materials for solid state lasers with specific wavelengths. Thus the 4f - 4f line emissions of lanthanide ions have been used in order to obtain infrared laser radiation up to 4.34 fxm and blue or green radiation by up-conversion pumping. Tunable laser operation in the ultraviolet has been demonstrated using the broad 5d 4f emission of Ce3+. Tunable lasers in the UV or IR ranges have also been experimented using Ag+, Pb+, 3d ions. 

Under EOF, solutions of 21 and 75 were pumped through a packed bed containing the polymer-supported lanthanide-Py Box catalyst 76, and the reaction products were analyzed off-line by GC, allowing both the conversion and enantioselectivity of the cyanohydrin to be determined. Compared with standard batch protocols, the use of an EOF-based flow reactor enabled the authors to screen rapidly a series or reaction conditions and additives, while demonstrating excellent recyclability of the catalyst. 

Both f-f and f-d transitions have been used for lanthanide and actinide lasers. The spectroscopic properties of these transitions are compared in Table I. Since the d states have shorter lifetimes, faster pumping as well as higher energies are required for excitation. Possible pumping sources include ultrafast flashlamps, other lasers, electron beams, or synchrotron radiation, with one exception, all lanthanide and actinide lasers have been optically pumped. 

Table IV. Ions used as sensitizers for optically-pumped lanthanide lasers.

Recently - Is- lg cascade laser action was observed for Ho3+ in LiYF4 77). The latter transition is at 3.914 ym and is the longest wavelength lanthanide laser reported to date. By using a 30-ns pump pulse and a high-Q cavity,... 

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. 

Fluorescence Sensitization. The optical pumping efficiency and thereby the prospects for oscillation of several actinides may be improved by codoping with sensitizer ions using schemes similar to those employed for the lanthanides in Table IV. For example, the first excited J states of l)3+, Np3+, and Pu3+ could be sensitized by energy transfer from lanthanide codopants such as Ho3+, Er3+, Tm3+, and Yb3+ as in the "alphabet" Ho3+ scheme (31). Other schemes using actinides include Cf3+-sensitized Bk3+ ( 4- 6), l)3+-sensitized Np3+... 

The field of lathanide lasers is mature but not exhausted. Additional laser schemes and materials will undoubtedly be exploited. There are 1639 free-ion energy levels associated with the 4fn electronic configurations of the thirteen trivalent lanthanides. Yet, of the 192,177 possible transitions between pairs of levels, by mid-1979 only 41 had been used for lasers. It is certain that given suitable pump sources and materials, stimulated emission involving many... 

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