Selective enhancement of green upconversion luminescence of Er-Yb: NaYF₄ by surface plasmon resonance of W₁₈O₄₉ 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.