Fabrication of a core–shell–shell particle with a quarter-wave thick shell and its optical properties

Abstract

A multi-shelled sphere with a quarter-wave thick shell is known to act as a spherical Bragg resonator with a complete photonic band gap and have potential applications in photonics. However, no fabrication techniques have been established. In this work, core–shell–shell particles with quarter-wave thick shells were synthesized by chemical solution processes for the first time. They consist of a Ce³⁺ doped Y₂O₃ nanoparticle core, a SiO₂ first shell, and a Y₂O₃ second shell. The core and the second shell were fabricated by a homogeneous precipitation method and the first shell by a sol–gel method. By carefully optimizing the reaction conditions, the shell thickness was controlled to a quarter optical wavelength for visible (500 nm) light with the standard deviation of thickness of the order of several nanometers. The scattering and photoluminescence spectra of single particles were studied, and they were well reproduced by Mie theory. The results indicate that the luminescence properties of the nanoparticles can be modified by the quarter-wave thick shells. The procedures can be extended for the fabrication of multi-shelled photonic bandgap structures, by simply repeating the SiO₂ and Y₂O₃ coating processes.