Enhanced upconversion of NaYF4:Er3+/Yb3+ phosphors prepared via the rapid microwave-assisted hydrothermal route at low temperature: phase and morphology control

Monophasic NaYF4:Er3+/Yb3+ crystals were synthesized via the microwave-assisted hydrothermal route at 180 degrees C. Microwave heating during the hydrothermal process substantially reduces the duration of reaction for the formation of cubic-NaYF4:Er3+/Yb3+ nanocrystals from 6 h to 30 min. As the duration of the reaction increases, cubic-NaYF4:Er3+/Yb3+ nanocrystals are transformed to uniform hexagonal-NaYF4:Er3+/Yb3+ microprisms because of the enhanced reaction kinetics. Bright upconverted emission from the NaYF4:Er3+/Yb3+ crystal, obtained by the efficient two-photon excitation, is related to crystal structure and morphology. The hexagonal microprisms exhibit better upconversion and are employed in security applications. (C) 2016 Optical Society of America