Visible and near-infrared upconversion photoluminescence in lanthanide-doped KLu₃F₁₀ nanoparticles

Upconversion (UC) photoluminescent nanocrystals of Ln³⁺-doped KLu₃F₁₀ have been synthesized via a facile and environmentally-friendly hydrothermal route. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectroscopy were employed to characterize the samples. Visible and near-infrared (NIR) UC photoluminescence emissions were achieved with KLu₃F₁₀ samples co-doped with Yb³⁺/Er³⁺, Yb³⁺/Ho³⁺ and Yb³⁺/Tm³⁺. More importantly, the emission intensity could be greatly enhanced by introducing CTAB as a surfactant, while it drastically decreased with the addition of OA. Meanwhile, it was found that the tunable color of the UC photoluminescence could be realized by introducing CTAB and OA. The achievement of red and NIR UC photoluminescence indicates that the Ln³⁺-doped KLu₃F₁₀ nanocrystals could provide potential applications in in vivo and in vitro optical bioimaging.