Enhanced photoluminescence of LEuH nanosheets: 2D photonic crystals self-assembled by core-shell SiO 2 @LEuH spheres.

The enhancement in photoluminescence (PL) is a challenge for layered rare-earth hydroxides, which usually have weak PL due to the quenching effect of hydroxyls. In this work, we provide a strategy to enhance the PL behavior by constructing two-dimensional (2D) photonic crystals. The core-shell structured SiO 2 @LEuH spheres were prepared by attaching the positively charged layered europium hydroxide (LEuH) nanosheets onto the negatively charged surfaces of the SiO 2 spheres; the core-shell spheres further formed a monolayered 2D colloidal crystal with the hexagonal lattice on a quartz substrate through an evaporation-induced assembly process. The 2D colloidal crystals exhibited a significantly enhanced photoluminescence at 611 nm related to the 5 D 0 → 7 F 2 transition of Eu 3+ compared with the SiO 2 @LEuH spheres and the LEuH nanosheets dispersed in deionized water. The emission band of Eu 3+ hardly changed in the three samples; therefore, the PL enhancement can be attributed to the emission band located at the short edge of the photonic band-gap of the 2D crystals.