Tunable multicolor and white-light upconversion luminescence in Yb3+/Tm3+/Ho3+ tri-doped NaYF4 micro-crystals

NaYF4 micro-crystals with various concentrations of Yb3+/Tm3+/Ho3+ were prepared successfully via a simple and reproducible hydrothermal route using EDTA as the chelating agent. Their phase structure and surface morphology were studied using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD patterns revealed that all the samples were pure hexagonal phase NaYF4. SEM images showed that Yb3+/Tm3+/Ho3+ tri-doped NaYF4 were hexagonal micro-prisms. Upconversion photoluminescence spectra of Yb3+/Tm3+/Ho3+ tri-doped NaYF4 micro-crystals with various dopant concentrations under 980 nm excitation with a 665 mW pump power were studied. Tunable multicolor (purple, purplish blue, yellowish green, green) and white light were achieved by simply adjusting the Ho3+ concentration in 20% Yb3+/1% Tm3+/xHo(3+) tri-doped NaYF4 micro-crystals. Furthermore, white-light emissions could be obtained using different pump powers in 20% Yb3+/1% Tm3+/1% Ho3+ tri-doped NaYF4 micro-crystals at 980nm excitation. The pump power-dependent intensity relationship was studied and relevant energy transfer processes were discussed in detail. The results suggest that Yb3+/Tm3+/Ho3+ tri-doped NaYF4 micro-crystals have potential applications in optoelectronic devices such as photovoltaic, plasma display panel and white-light-emitting diodes. Copyright (C) 2014 John Wiley & Sons, Ltd.