文摘
The past few years witnessed extensive emergence of short-wavelength upconversion (UC) emission stimulated photoactivation studies. However, low efficiency of multi-photon process greatly limits further applications. Here, ultraviolet (UV) upconversion emissions originated from multi-photon process of Tm3+ were studied with Nd3+-sensitized NaGdF4:Yb, Tm@NaYF4:Nd, Yb core/shell nanoparticles. Crucial factors, including the contents of sensitizers Nd3+, Yb3+ and activator Tm3+, as well as the excitation power density were investigated based on the UV emission. Spectral results showed that high contents of Nd3+ in shell region up to 50% (molar fraction hereafter) and Yb3+ of 10% were essential to mediate the energy transfer via the core/shell interface and facilitate multi-photon UV emissions. Compared with segregated activator and sensitizer, a core/shell strategy with isolated Nd3+ in the shell was important for higher UV emission. Although the upconverting process was initiated with Nd3+→Yb3+, the short-wavelength emissions were intrinsically coming from four- and five-photon process. The optimized nanoparticles were found to be able to manipulate the configuration transition of azobenzene molecules, and it could be promising for near infrared (NIR) triggered optical switches applications.
