3-Dimensional photonic crystal surface enhanced upconversion emission for improved near-infrared photoresponse.

The enhancement of upconversion luminescence of lanthanide-ion doped fluoride upconversion nanoparticles (UCNPs) is particularly important and highly required for their myriad applications in sensing, photoelectronic devices and bio-imaging. In this work, the amplification of luminescence in NaYF4:Yb/Er and NaYF4:Yb/Tm UCNPs in close proximity to the three-dimensional photonic crystal (3D PC) surface for improved near-infrared photoresponse of a carbon nanotube-based phototransistor is reported. The self-assembled opal 3D PCs with polystyrene sphere sizes of 200, 290 and 360 nm that exhibit reflection peaks of 450, 650 and 800 nm respectively were used for upconversion enhancement, and around 30 times enhancement was obtained for NaYF4:Yb/Er and NaYF4:Yb/Tm UCNPs. Time-resolved upconversion emission and 3D PC transmittance-dependent upconversion enhancement reveal that the enhanced absorption and the extraction effects, resulting from the enhanced non-resonant pump excitation field and the strong coherent scattering provided by 3D PCs respectively, are responsible for the large enhancement. As a proof-of-concept experiment, the prepared 3D PC/NaYF4:Yb/Tm UCNP coupled material layer was introduced into the carbon nanotube-based phototransistor. It is shown that the photoresponsivity of the device to near-infrared light was improved by 10 times with respect to the control device with carbon nanotubes only, which reveals the promising applications of this coupled material in photoelectronic devices such as photovoltaics and other types of phototransistors.