A novel strategy for markedly enhancing the green upconversion emission in Er3+/Yb3+ co-doped VO2

There is a growing interest in developing upconversion nanocrystals at the forefront of promising applications. However, insufficient energy transfer between lanthanide ions still limited the practical application. In this work, a new class of welded-structure upconversion nanoparticles which emits bright green emission upon 980 nm near-infrared (NIR) laser excitation is presented. Importantly, this unique welded-structure arrangement enables the high-efficient energy transfer between different nanocrystals, leading to 65-folds enhancement for green upconversion emission. A continuous wave 980 nm laser is used to reduce interparticle distance followed by structure welding. The experiment findings show that the controlling distance of nanosheets enables readily manipulation the intensity ration of green and red emission, thereby allowing us to achieve the emission color purity tuning from pea green to bright green. And the green and red ratio achieved 11 folds enhancement, leading to a purer green light emission. The result not only provide an upfront experimental design for constructing welded-nanostructures with efficient energy transfer and color purity tunability, but also suggests a new pathway to build high-efficiency upconversion systems. (C) 2019 Elsevier B.V. All rights reserved.