Near-infrared emission lanthanide ions

Addition of lanthanide ions to dendrimer solutions showed that (a) the absorption spectrum of the dendrimer is almost unaffected, (b) the fluorescence of the dansyl units is quenched (c) the quenching effect is very large for Nd3+ (Fig. 7) and Eu3+, moderate for Er3+ and Yb3+, small for Tb3+, and very small for Gd3+ (d) in the case of Nd3+ (Fig. 7), Er3+, and Yb3+ quenching of the dansyl fluorescence is accompanied by the sensitized near-infrared emission of the lanthanide ion [42]. 

Wolbers, M.RO., van Veggel, F.C.J.M., SnelUnk-Ruel, B.H.M., et al. (1998) Photophysical studies of m-terphenyl-sensitized visible and near-infrared emission from organic 1 1 lanthanide ion complexes in methanol solutions. Journal of the Chemical Society, Perkin Transactions, 2, 2141. 

VicinelU, V, Ceroni, R, Maestri, M., etal. (2002) Luminescent lanthanide ions hosted in a fluorescent polylysin dendrimer. Antenna-Uke sensitization of visible and near-infrared emission. Journal of the American Chemical Society, 124, 6461. 

Multicolored luminescence is the most attractive property of rare earth-based compounds. Lanthanide ions possess many sharp emission lines that cover the visible and near infrared (NIR) region due fo fhe abundanf fransifions of f-orbital configurations. However, the forbidden f-f fransi-fions induce narrow excitation lines for mosf rare earfh ions. This low absorbency cross-section is the bottleneck in practical application, so host-sensitized emission mode is commonly employed by rare earth phosphors. The vanadate matrix is one of fhe candidafes, which excifes lanthanide ions via charge-transfer energy migration. 

The term upconversion describes an effect [1] related to the emission of anti-Stokes fluorescence in the visible spectral range following excitation of certain (doped) luminophores in the near infrared (NIR). It mainly occurs with rare-earth doped solids, but also with doped transition-metal systems and combinations of both [2, 3], and relies on the sequential absorption of two or more NIR photons by the dopants. Following its discovery [1] it has been extensively studied for bulk materials both theoretically and in context with uses in solid-state lasers, infrared quantum counters, lighting or displays, and physical sensors, for example [4, 5]. Substantial efforts also have been made to prepare nanoscale materials that show more efficient upconversion emission. Meanwhile, numerous protocols are available for making nanoparticles, nanorods, nanoplates, and nanotubes. These include thermal decomposition, co-precipitation, solvothermal synthesis, combustion, and sol-gel processes [6], synthesis in liquid-solid-solutions [7, 8], and ionothermal synthesis [9]. Nanocrystal materials include oxides of zirconium and titanium, the fluorides, oxides, phosphates, oxysulfates, and oxyfluoiides of the trivalent lanthanides (Ln ), and similar compounds that may additionally contain alkaline earth ions. Wang and Liu [6] have recently reviewed the theory of upconversion and the common materials and methods used. 

Although the visible red and green, respectively, emissions from Eu ° and Tb ° complexes are particularly famihar due to their widespread exploitation, " "" they do occur and may be excited by absorption in spectral regions where biological tissues and structures may absorb. Consequently, considerable interest has developed in lanthanide ions which emit in the near-infrared (NIR) region (Nd° being long exploited, in solid state lasers, in particular. 

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