Selective enhancement of green upconversion luminescence of Er–Yb: NaYF4 by surface plasmon resonance of W18O49 nanoflowers and applications in temperature sensing**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474046 and 61775024), the Program for Liaoning Innovation Team in University, China (Grant No. LT2016011), the Science and Technique Foundation of Dalian, China (Grant Nos. 2017RD12 and 2015J12JH201),

Abstract

The W18O49 nanoflowers with a diameter of 500 nm are prepared by a facile hydrothermal method. The Er–Yb: NaYF4 nanoparticles are adsorbed on the petals (the position of the strongest local electric field on W18O49 nanoflowers). With a 976 nm laser diode (LD) as an excitation source, the selectively green upconversion luminescence (UCL) is observed to be enhanced by two orders of magnitude in Er–Yb: NaYF4/W18O49 nanoflowers heterostructures. It suggests that the near infrared (NIR)-excited localized surface plasmon resonance (LSPR) of W18O49 is primarily responsible for the enhanced UCL, which could be partly reabsorbed by the W18O49, thus leading to the selective enhancement of green UCL for the Er–Yb: NaYF4. The fluorescence intensity ratio is investigated as a function of temperature based on the intense green UCL, which indicates that Er–Yb: NaYF4/W18O49 nanoflower heterostructures have good potential for developing into temperature sensors.