Control of the two strongest upconversion emission lines in NaYF4:Yb3+, Er3+ nanoparticles is demonstrated by varying the excitation repetition rate. This technique may enable new multiplexed sensing modalities based on multicolor luminescent nanoparticles, currently contemplated for biomedical imaging and diagnostics.
The design and engineering of earth-abundant catalysts that are both cost-effective and highly active for water splitting are crucial challenges in a number of energy conversion and storage technologies. In this direction, herein we report the synthesis of FeO@NiFeO core-shell nanoheterostructures and the characterization of their electrocatalytic performance toward the oxygen evolution reaction (OER). Such nanoparticles (NPs) were produced by a two-step synthesis procedure involving the colloidal synthesis of FeO nanocubes with a defective shell and the posterior diffusion of nickel cations within this defective shell. FeO@NiFeO NPs were subsequently spin-coated over ITO-covered glass and their electrocatalytic activity toward water oxidation in carbonate electrolyte was characterized. FeO@NiFeO catalysts reached current densities above 1 mA/cm with a 410 mV overpotential and Tafel slopes of 48 mV/dec, which is among the best electrocatalytic performances reported in carbonate electrolyte.
In the interest of generating new biomedical sensing techniques as well as improving those that currently exist, a great deal of attention has been given to upconverting lanthanide nanoparticles in recent years. In order to develop these nanoparticles for use in multiplexed and ratiometric sensing techniques, many recent studies have focused on experimental control of their emission wavelengths. Here we describe a new method for controlling the relative intensity of green and red emission bands in NaYF4:Yb3+, Er3+ nanoparticles via control of the excitation pulse repetition rate. Using this method, particles of the same composition may be tuned to produce red and green light in user-defined ratios. We discuss the mechanism behind this control as well as potential applications that could make use of this property, specifically in super resolution imaging techniques.
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