Synthesis and upconversion luminescence of hexagonal-phase NaYF4:Yb, Er3+, phosphors of controlled size and morphology

Green upconversion emission from hexagonal-phase NaYF4:Yb, Er3+ phosphors can be directly observed with the naked eye. Powders with controlled size and morphology can be synthesized in ethanol and show a minimal decrease in luminescence intensity after 24 It (see Figure). The intense upconversion emission suggests good crystallinity of the materials, which may be used in biological labeling.