Upconversion Luminescent NaYbF4: Er3+, Tm3+ Nanoparticles: Spectrally Pure and Intense near Infrared to near Infrared Emission

NaYbF4: Yb3+, Tm3+ nanoparticles (UCNPs) capped with oleic acid (OA) have been synthesized via high-temperature solvent reaction. The optimization sample of NaYb0.96Er0.02Tm0.02F4 nanoparticles possess spectral purity (the S-nw value is bigger than 0.7) and intense near infrared to near infrared (NIR-to-NIR) upconversion luminescence (UCL) (the power of laser is as low as 3.8 W), which makes them ideal and promising platforms for high contrast bioimaging.