Multicolor upconversion luminescence of dye-coordinated Er 3+ at the interface of Er 2 O 3 and CaF 2 nanoparticles.

Multicolor upconversion luminescence of Er3+ was successfully enhanced by optimizing the interface in dye-coordinated nanoparticles with a core/shell structure. Red and green upconversion emissions of Er3+ were obtained at the interface of oxide nanoparticles via the intramolecular energy transfer from the coordinating squaraine dye with high light-absorption ability, which was more efficient than emissions through the energy transfer from metal ions such as Yb3+ . Additionally, CaF2 nanoparticles as a core material minimized the energy loss with nonradiative downward relaxations in Er3+ , resulting in the observation of unusual blue upconversion emissions from the upper energy level of Er3+ by nonlaser excitation using a continuous-wave (CW) Xe lamp at an excitation power of 1.2 mW/cm2 .