White upconversion luminescence in nanocrystalline (Ho,Tm,Yb):KLu(WO4)2 phosphor

Highly crystalline codoped Ho3+,Tm3+,Yb3+ KLu(WO4)(2) monoclinic nanocrystals with the C 2/c space group symmetry were synthesized by the modified Pechini method. Powder X-ray diffraction, transmission electron microscopy, upconversion photoluminescence spectra, and kinetic decay were used to characterize the samples. The nanocrystals belonged to the monoclinic phase, with a crystallite size of 30-70 nm. Under 930 nm laser excitation, red, green and blue upconversion emissions were simultaneously observed, due to the energy transfer from the Yb3+ F-2(5/2) excited level. The decay times of the emitting states were studied at room temperature to describe the photoluminescence dynamics. The influence of excitation power and calcination conditions on CIE chromaticity coordinates were evaluated. ((C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)