Luminescent rare earth compounds

The impetus for the development of synthesis and characterization of complexes of lanthanides with organic nitrogen donor ligands is due to the search for more efficient luminescent rare earth compounds. One of the difficulties is the risk of precipitating lanthanide hydroxides in the process of synthesis of lanthanide complexes with organic amines. In the early stages, lanthanide complexes of heterocyclic bases of low basicities were prepared in aqueous alcoholic media [224], In the synthesis section it was appropriately pointed out the need for the anhydrous conditions and involved procedures for the preparation of lanthanide complexes of ligands of non-ionizable nature. Some representative complexes of both aliphatic and aromatic amines are listed in Table 4.19. 

It has long been recognized that luminescence can potentially provide an equally sensitive detection method where the obvious drawbacks and problems associated with the radioactive substances do not arise. Using luminescent rare earth compounds not only eliminates these problems but also offers several advantages over the fluorescent organic dyes currently used in substitution of radioisotopes. 

In conclusion, recent research progress on the photofunctional rare earth materials based on ionic liquids has been summarized, which mainly consist of two important classes one is the rare earth compounds dispersed or dissolved in ionic liquids, even including the rare earth compounds of ionic liquids with exact crystal structures the other is the photofunctional rare earth hybrid materials using ionic liquids both as the chemical linkers and host. However, some problems still exist in the field of photofunctional rare earth materials based on ionic liquids. The first problem is the controlled preparation and fabrication of thin film materials of ionic gels based on luminescent rare earth compounds, which is important and necessary for the further applications in optical devices. The second problem is luminescent enhancement and functional integration of the photofunctional rare earth materials based on ionic liquids. Here it is worth pointing out that it is important to develop visible-excitation lanthanide hybrid system and obtain white luminescence through multicomponent assembly of rare earth species and ionic liquids. 

Non-metallic rare-earth compounds studied under high pressure. In almost all cases the energy level shifts as a function of pressure have been determined. The second column gives details concerning the measurements and evaluations made. In particular the following abbreviations are used L Luminescence-, A Absorption-, E Excitation-, S Site-selective spectroscopy, O Other methods, EPC Electron-Phonon Coupling, Int Intensities, LT Lifetime, CFP Crystal-Field Parameters, FIP Free-Ion Parameters, IP Intrinsic Parameters, ET Energy Transfer... 

Vogler, A. Kunkely, H. Luminescent metal complexes diversity of excited states. In Transition Metal and Rare Earth Compounds Excited States, Transition, Interactions I, Vol. 213 Yersin, H., Ed. Springer Berlin, 2001 pp 143-182. 

Mudring, A.-V, Babai, A., Arenz, S., Giernoth, R., Binnemans, K., Driesen, K. and Nockemann, R, Strong luminescence of rare earth compounds in ionic liquids luminescent properties of lanthanide(III) iodides in the ionic liquid l-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, J. Alloys Compd. 418, 204-208 (2006). 

Lanthanum oxyhalides including LaOF doped with luminescent rare-earth ions were studied as phosphors for potential applications in the earlier times [82]. Crystal structures and optical or luminescent properties of rare-earth oxyfluoride compounds were extensively investigated in the 1990s [81-87]. Usually, rare-earth doped oxyfluoride materials are synthesized by heat treatments of rare-earth fluorides in the air [88] or mixtures of rare-earth oxides and NH4F in N2 atmosphere [89]. 

Emission due to excited state energy transfer has been reported in layered low dimensional rare earth complexes such as uranyl phosphates [50],cryptates [51] and platinum tetracyanides [52, 53]. The luminescence properties of the low dimensional rare earth compounds of the type RE[M(CN)2]3 where RE = Eu, Dy, Gd " and M = Au, Ag are also interesting in this regard. We recently reported [16] that efficient excited state energy transfer from the Au(CN)2 and Ag(CN)j ions to Eu " enhances the luminescence observed from the rare earth ion. A similar result is obtained from other rare earth salts [17]. In some cases vibronic structure appears in the luminescence spectrum. 

The exceptions to the rule that rare earth hosts are best for rare earth activators are special cases. For example, some anions such as sulfide yield compounds in combination with non-rare earth cations (e.g. Zn) which show higher luminescent efficiency than with rare earths. Additionally, divalent rare earth activators like Eu " " substitute readily for non-rare earth divalent cations. 

A study was made by Freeman and co-workers (93) of the effect of deuterium on the luminescence decay times of solvated rare earth chlorides. Hutchison and Mangum (94) and Robinson (95) had previously shown that there is a substantial increase in the mean triplet-state lifetimes of aromatic organic compounds when the hydrogen is replaced by deuterium. Robinson... 

Bunzli, J.-C.G., 2005. Rare earth luminescent centers in organic and biochemical compounds. In Liu, G.K., Jacquier, B. (Eds.), Spectroscopic Properties of Rare Earths in Optical Materials. Springer Verlag, Berlin, pp. 462 199 (chapter 11). 

The merocyanine form of numerous BIPS compounds in solution complex with many transition and rare-earth metal ions. The complexation between 6-nitro-8-methoxyBIPS and several ions was studied by spectrophotometric, luminescent, stopped-flow, and nanosecond laser flash photolysis techniques. The absorption maximum of the dye, 580 nm, is shifted to the 480-500 nm region, and the relatively weak fluorescence shows a similar hypsochromic shift. The kinetics of the complexation involved a fast reaction between the components, followed by a slow equilibrium of the complex to its most stable isomer. The photoreactions of the complexes include formation of a short-lived triplet state (lifetime about 2 x 10 5 s,... 

The luminescence of various chelated compounds of the rare earths is very promising because their spectral and luminescent properties help to solve a number of theoretical and applied problems. Luminescence spectra of europium complexes with selenophene /3-diketones have been studied as a function of the ligand structure. Of the spectra obtained, m-picolinoyl-2-acetoselenophene and di-selenoylmethane look most promising for obtaining induced radiation.136... 

Of various rare earth 2-selenenoylacetone chelates luminescence was found only in the europium compounds. Physicochemical properties and IR spectra of 2-selenenoylacetonates of rare earths (except cerium and promethium) give information regarding the structure of these complexes as a function of the metal. 

---