Visible light emission upon near-infrared excitation in a transparent solution of nanocrystalline β-NaGdF4: Yb3+, Er3+

High quality nanocrystals of hexagonal β-NaGdF4 codoped with Yb3+ and Er3+ were synthesized by controlled precipitation in high boiling organic solvents and characterized by XRD and TEM. The particles of roughly spherical shape and a size of about 30 nm can be transparently dissolved in DMSO. Visible by eye green and red upconversion emission is observed upon near-infrared excitation at 10 233 cm−1 (977 nm) with a laser power density of 2 kW cm−2.