High-energy organic group-induced spectrally pure upconversion emission in novel zirconate-/hafnate-based nanocrystals

Lanthanide ions generally have abundant metastable excited states enabling lanthanide-doped nanocrystals (NCs) to display multipeak emission profiles. We address this issue by presenting a series of novel fluoride-based nanophosphors exhibiting spectrally pure upconversion (UC) red fluorescence upon near-infrared (980 nm) excitation. Single-band deep-red UC luminescence was achieved when a Yb 3+ –Er 3+ ion-pair was incorporated into K 3 MF 7 (M = Zr, Hf). This UC luminescence feature of K 3 MF 7 :Yb 3+ ,Er 3+ (M = Zr, Hf) NCs is independent of the doping levels of Yb 3+ –Er 3+ and the pump power of incident light. High-energy vibrational oscillators on the NCs surfaces are likely to result in a striking increase in the population of the 4 F 9/2 level of Er 3+ , accounting for the spectrally pure luminescence. The composition-optimized nanophosphor presents relatively perfect red monochromaticity.