Nonmetallic plasmon induced 500-fold enhancement in the upconversion emission of the UCNPs/WO3−x hybrid

The nonstoichiometric semiconductor tungsten oxide (WO3−x) is proposed to enhance the upconversion luminescence (UCL) of lanthanide doped upconversion nanoparticles (UCNPs) owing to its unique nonmetallic surface plasmon resonance (SPR) in the near-infrared (NIR) region. The UCNPs/WO3−x hybrid was synthesized on the surface of an optical fiber by a simple coating method. With a waveguiding laser excitation of 980 nm, the hybrid exhibits a drastic enhancement of more than 500-fold at 521 nm emission compared to that of UCNPs, which is even higher than those of some metallic plasmonic structures for UCL enhancement. Such great enhancement is attributed to the strong SPR absorption and thermal effect induced by plasmonic WO3−x, which is demonstrated by the UCL behavior studies of the hybrids by varying the SPR intensity of WO3−x. The UCNPs/WO3−x hybrids were found to exhibit a superior performance in temperature sensing with a wide temperature range (306–1354 K) and a high temperature resolution (0.17–1.18 K).