Due to their unique properties in converting low energy light into higher energy electronic transitions, upconverting nano-materials have garnered considerable interest in bio-imaging, photovoltaic, and opto-electronic applications. In particular, lanthanide-doped upconverting nanoparticles (UCNPs) have demonstrated a host of functionalities due to their nanoscale dimensions and wide range in transition-metal doped compounds. Unlike quantum dots and other single emitters that exhibit luminescence blinking and bleaching, UCNPs undergo upconverting energy processes regardless of material size and provide high photostability in ambient environments. However, while much as been reported on the optical properties of UCNPs, a fundamental understanding of the photo-physics remains unclear, particularly at nanoscale dimensions where surface properties can dominate energy transfer processes. Moreover, the emissive properties of single UNCPs with diameters less than 10nm, ideal for cellular uptake in bio-imaging, are still relatively unknown.Here we report on the luminescence properties of Er3+, Yb3+-doped NaYF4 UCNPs with diameters ranging from 5 � 150 nm. Optical characterization of the luminescence lifetime and spectral emission of UCNPs on a single particle level reveal a strong dependence on UCNP size and surface passivation1, which provides a basis for investigating the enhanced optical properties of single particles coupled with functional architectures. In addition, a quantitative model based on Yb and Er distances inside the NaYF4crystal is presented to explain how over 90% of the total luminescence originates from only a few atomic emitters. Details from this model will be used to describe how significant enhancements in the optical properties of nanoscale upconverting materials based on dopant proximity can be realized.[1] � A.D. Ostrowski, D.J. Gargas, et al ACS Nano 6, 2686, 2012

Scaling down upconverting materials for enhanced light emission

245th National Meeting (2013)

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