Separating and enhancing the green and red emissions of NaYF4:Yb3+/Er3+ by sandwiching them into photonic crystals with different bandgaps†
Rational control of the multiple emission outputs and achieving single-band and strong luminescence of Ln3+ doped upconversion nanoparticles is highly desirable for their applications in sensor and display fields. Here, we designed a sandwich structure to separate and enhance the green and red emission of NaYF4:Yb3+/Er3+ simultaneously and realized pure strong green and red emissions. NaYF4:Yb3+/Er3+ nanocrystals were sandwiched between two layers of photonic crystals, which have bandgaps at 660 nm and 530 nm, respectively. The photonic crystal with a bandgap at 530 nm on top of the NaYF4:Yb3+/Er3+ layer can filter the green emission of NaYF4:Yb3+/Er3+, prohibiting its emission upward, and at the same time, enhancing its emission downward. Similarly, the photonic crystal with a bandgap at 660 nm can prohibit the transmission of the red emission, and at the same time enhance its reflection in the opposite direction. Consequently, enhanced green emission was observed from the bottom of the sandwich structure and enhanced red emission was observed from the top of the sandwich structure. Thus, the green and red emissions of NaYF4:Yb3+/Er3+ were separated and both of them were enhanced. On the other hand, when using a photonic crystal with a bandgap that overlapped with the excitation light of NaYF4:Yb3+/Er3+ nanoparticles, their emissions were all greatly enhanced. Our results suggest that photonic crystals are good candidates to separate and enhance the emissions of Ln3+ doped luminescent materials.
- This article is part of the themed collection: International Year of the Periodic Table : Lanthanides for Precision Therapy and Beyond