Selective enhancement of green upconversion luminescence of Er–Yb: NaYF 4 by surface plasmon resonance of W 18 O 49 nanoflowers and applications in temperature sensing

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.