Nanoparticles lanthanide fluoride

Nunez NO, Ocana M (2007) An ionic liquid based synthesis method for uniform luminescent lanthanide fluoride nanoparticles. Nanotechnology 18 455606... 

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. 

Coprecipifation is perceived as the most convenient approach to produce UCNPs with an ultrasmall size (sub-10 nm, Figure 5a and b) and narrow size distribution. In a typical synthesis procedure, lanthanide salt solutions are quickly injected into a fluoride solution under vigorous stirring, and NaLnF4 or LnF3 nanoparticles will be obtained... 

Vetrone F. and J. A. Capobianco, Lanthanide-doped fluoride nanoparticles luminescence, upconversion, and biological applications, Int. J. Nanotechnol, 5, 1306-1339 (2008). 

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