Nano Lett. 14, 101–106 (2014)

Upconversion photoluminescence (UPL) — a process through which several infrared photons combine to generate one ultraviolet–visible photon — promises to improve the performance of solar cells by harnessing the infrared part of the solar spectrum. In biological imaging applications it would also enhance the detection of the infrared signal that arises from deep biological tissue, which is currently limited by the poor efficiency of photodetectors in this wavelength range. However, to become a technological reality the intrinsic limitation of UPL, namely, the poor conversion efficiency of infrared photons into ultraviolet–visible photons, needs to be addressed. Sun and co-workers now propose a path to overcome this stumbling block. Through the enhancement of the local electric field by surface plasmon polaritons on nanopatterned gold substrates, the authors obtain a significant amplification of both the absorption of infrared radiation and the energy transfer between the ytterbium ions and erbium dopants in doped lanthanide nanocrystals that coat the substrate. Their findings constitute an important step towards achieving more efficient access to the infrared region.