Enhanced photoluminescence of LEuH nanosheets: 2D photonic crystals self-assembled by core–shell SiO2@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 SiO2@LEuH spheres were prepared by attaching the positively charged layered europium hydroxide (LEuH) nanosheets onto the negatively charged surfaces of the SiO2 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 5D0 → 7F2 transition of Eu3+ compared with the SiO2@LEuH spheres and the LEuH nanosheets dispersed in deionized water. The emission band of Eu3+ 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.