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

Multicolor upconversion luminescence of Er(3+) was successfully enhanced by optimizing the interface in dye-coordinated nanoparticles with a core/shell structure. Red and green upconversion emissions of Er(3+) 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 Yb(3+). Additionally, CaF(2) nanoparticles as a core material minimized the energy loss with nonradiative downward relaxations in Er(3+), resulting in the observation of unusual blue upconversion emissions from the upper energy level of Er(3+) by nonlaser excitation using a continuous-wave (CW) Xe lamp at an excitation power of 1.2 mW/cm(2).