Luminescence efficiency of upconversion – Quantification of size, particle architecture and dopant concentration effects for different excitation power densities

Lanthanide-based upconversion nanoparticles (UCNPs)like hexagonal beta-NaYF4 UCNPs doped with Yb3+ and Er3+, which efficiently convert 976 nm light to ultraviolet, visible, and near infrared photons, offer new strategies for luminescence-based sensing and imaging. The properties of their upconversion (UC) luminescence (UCL) are, however, strongly influenced by particle size, concentration and spatial arrangement of dopant ions, surface chemistry, microenvironment, and excitation power density (P). We present here comprehensive studies of the influence of UCNP size and particle architecture for Yb3+ and Er3+ co-doped NaYF4 nanoparticles and energy transfer processes in these materials, which underline the importance of quantitative luminescence measurements for mechanistic insights and the determination of application-relevant matrix- and P-dependent optimum dopand concentrations.