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). © 2005 Elsevier B.V. All rights reserved.