Site-Isolated Upconversion Nanoparticle Arrays Synthesized in Polyol Nanoreactors

A versatile approach for synthesizing Yb3+- and Er3+-doped NaYF4 upconversion nanoparticle (UCNP) arrays is presented. The nanoparticles are positioned at precisely defined locations through the tip-directed deposition of polyol nanoreactors and subsequent thermal conversion. This method is based on conducting a solution-phase polyol synthesis in nanometer-scale reactors, which provide isolated and confined reaction vessels for the thermal decomposition of a fluoride precursor and the coarsening of fluoride nanoparticles. When the nanoreactors are annealed at 350 °C, the polyol degrades, and the nanoparticles, which exhibit upconversion properties, crystallize. Single nanoparticles are attained in each nanoreactor by tuning the precursor concentration, nanoreactor size, and temperature ramping rate. This strategy enhances the scope of nanostructures that can be synthesized by tip-directed routes and, when combined with massively parallel pen approaches such as polymer pen lithography, provides a generalizable platform for the high-throughput synthesis, screening, and discovery of nanomaterials for photonics and other applications.