Lanthanide Luminescence as a Probe of Nanocrystalline Materials

The sharp lines in the optical spectra of lanthanide ions in solids are sensitive to the local environment surrounding the ion and, therefore, provide a local probe to study new materials. This paper reports the laser spectroscopic characterization of a series of Eu₂O₃ nanocrystals, which serve as a model compound for understanding the spectroscopy of lanthanides in nanocrystalline materials. The optical spectra of Eu₂O₃ particles with diameters of approximately 18 to 4 nm show an increase in inhomogeneous broadening and a transition to a very disordered phase as the particle size decreases. The ⁵D₀ fluorescence transients of the nanocrystals are shorter than in bulk material show no clear trend as a function of particle size but do become single exponential for 6- and 4-nm particles.