Laser ions actinides

Table II lists all types of transitions. lanthanide and actinide laser ions and...

Table II. Electronic transitions and and actinide lasers. ions used for lanthanide...

Most of the solid-state lasers employ as active material crystals or glasses doped with rare-earth or actinide ions, because these ions exhibit a large number of relatively sharp fluorescent lines, covering the whole visible and near-infrared spectrum 380) search for new laser materials and investigations of the characteristics of laser emission at different temperatures of the active material and with various pump sources have improved knowledge about the solid state spectra and radiationless transitions in laser media 38i). 

Thus it was not observed until lasers were invented. In principal, one-photon and two-photon excitation follow different selection rules. For example, the inner shell one-photon transitions in transition metal, rare earth, and actinide ions are formally forbidden by the parity selection rule. These ions have d- or/-shells and transitions within them are either even to even (d d) or odd to odd (f /). The electric dipole transition operator is equal to zero. 

R. Stumpe, J. I. Kim, W. Schrepp, H. Walther, Speciation of Actinide Ions in Aqueous Solution by Laser-induced Pulsed Spectrophotoacoustic Spectroscopy, Appl. Phys. B 34, 203 (1984)... 

Prior to the advent of the laser, photo-induced reactions sat, for the most part, in the chemical background. Photochemists of that time typically gave little thought to actinide elements other than uranium which was known for years to be a very excellent chemical actinometer when present as the uranyl ion. The expertise and specialized equipment required in the handling of the other actinides, coupled with their very limited supply,served to discourage photochemists from fundamental investigations of these elements. As a result, no report of actinide photochemistry (save that of uranium) is to be found in the open literature prior to 1969. 

Possible sensitizers for lanthanide and actinide ions include other lanthanide and actinide ions, other transition group ions, and molecular complexes. These may be present either as added impurities or as a component of the host. Of the many sensitization schemes reported, some offer only marginal improvement. The most efficient crystal laser is "alphabet" holmium Ho3+ sensitized by Er +, Tm3+, and Yb +... 

The prospects for actinide lasers, based on available spectroscopic data, is definitely more limited. Although there are a few prospects for visible lasers, the presence of low-lying 6d and electron transfer states can cause intense excited-state absorption, thus limiting oscillation principally to the infrared. Strong ion-host interactions increase the probabilities for radiative and nonradiative transitions and must be carefully considered with respect to the overall operation and efficiency of any practical system. 

In view of the ease and success of lasing lanthanide ions, only some compelling reason such as the requirement of a specific wavelength would warrant development of some of the actinide lasing schemes discussed. Perhaps additional spectroscopy will reveal advantages of using actinide ions in other valence states and hosts for efficient laser action. 

Achieving laser action is a result of a favorable combination of many spectroscopic properties of an ion in a given host. The ability to predict and demonstrate stimulated emission is therefore a powerful confirmation of our understanding of the spectroscopy of lanthanide and actinide ions and a motivation for further study of these ions. 

Ionization potentials of 6.1941(5) eV for uranium i and 6.2657(6) eV for neptunium ) have been derived from observed Rydberg series using laser techniques and the method described above. These are the most accurate ionization potentials available for actinide elements. Series converging to the first excited state and to the ground state of the ion were observed for both elements. In the case of neptunium, the presence of two series converging to limits 24 cm - - apart (see Fig. 6) helps to confirm the unpublished value. ) for the interval between the two lowest levels of neptunium. 

Actinides have particular spectroscopic properties which are characterized primarily by the / - / transitions within the partially filled 5f shell [42] and thus by a number of relatively weak but very sharp absorption bands. The optical spectra of actinides are characteristic for their oxidation states, and to a lesser degree dependent upon the chemical environment of the ion [43]. Thus spectroscopic investigation provides information on the oxidation state of an actinide element [42] and also serves to characterize the chemical states, such as hydrolysis products [44], various complexes [37, 45, 46] and colloids [29, 40]. Hence, laser-induced photoacoustic spectroscopy (LPAS) with its high sensitivity can be conveniently used for the speciation of aqueous actinides in very dilute concentrations [17-28]. 

This blockage of the process can often be avoided for elements with more than one valence electron, by tuning the ionization laser to an auto-ionizing state, which decays rapidly within its lifetime of far less than 1 ns into an ion and a free electron. This is particularly effective for lanthanide and actinide elements, which have a high density of auto-ionizing states near the... 

Conventional optical absorption spectrometry has detection limits of between 0.01 and 1 mM for the actinides. Highly sensitive spectroscopic methods have been developed, based on powerful laser light sources. Time resolved laser fluorescence spectroscopy (TRLFS), based on the combined measurement of relaxation time and fluorescence wavelength, is capable of speciating Cm(III) down to 10 mol/L but is restricted to fluorescent species like U(VI) and Cm(III). Spectroscopic methods based on the detection of nonradiative relaxation are the laser-induced photoacoustic spectroscopy (LPAS) and the laser-induced thermal leasing spectroscopy (LTLS). Like conventional absorption spectroscopic methods, these newly developed methods are capable of characterizing oxidation and complexation states of actinide ions but with higher sensitivity. 

Rare earths have found their widest application in optically-pumped solid-state lasers. Of the different transition metal ion groups which fluoresce in solids and which are thereby candidates for stimulated emission, the rare earths predominate. Ions used for crystalline lasers are listed in fig. 35.1 together with the number of crystal hosts which have been employed for each ion through 1975. Of the approximately 200 crystalline lasers reported, all are based upon rare earths except for a few iron group ions and one actinide ion. 

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