Enhanced emission of ultra-small-sized LaF3:RE3+ (RE = Eu, Tb) nanoparticles through 1,2,4,5-benzenetetracarboxylic acid sensitization

Uniform, ultra-small-sized and well-water-dispersible LaF3 nanoparticles doped with trivalent rare earth (RE) ions (Eu3+ or Tb3+) have been synthesized by a simple, low temperature synthesis route. The nanoparticles, with sizes of about 3.2 nm (for those doped with Eu3+) and 3.0 nm (for those doped with Tb3+), are roughly spherical and monodisperse. 1,2,4,5-Benzenetetracarboxylic acid (labeled as BA) as sensitizer has been bonded to the surface of the nanoparticles, which can sensitize the emission of RE3+ in the LaF3 nanoparticles. The BA–LaF3:RE3+ (RE = Eu or Tb) nanoparticles have a broad absorption band in the UV domain, and show enhanced luminescence of RE3+ based on an energy transfer from BA ligands to RE3+ ions (i.e. the so-called "antenna effect"). Due to the dual protection of organic ligands (BA) and inorganic matrices (LaF3), BA–LaF3:RE3+ (RE = Eu or Tb) nanoparticles have longer excited state lifetimes than LaF3:RE3+ (RE = Eu or Tb) nanoparticles as well as lanthanide coordination polymers of BA.