Phosphor Microparticles of Controlled Three-Dimensional Shape from Phytoplankton

We demonstrate how the precise three-dimensional (3D) assembly characteristics of biomineralizing micro-organisms may be combined with synthetic chemical processing to generate photoluminescent microparticles with specific 3D shapes and tailored chemistries. Silica-based microshells with a rich variety of controlled shapes are assembled by a type of unicellular algal phytoplankton known as diatoms (Bacillariophyceae). Each of the tens of thousands of diatom species generates a microshell with a particular 3D morphology that can be used as a shape-dictating particle template. In this demonstration, the microshells of Aulacoseira diatoms were converted into -doped -bearing microparticles. The silica-based microshells were first converted into magnesia-based replicas via a gas/solid displacement reaction (the silica of native diatom microshells is not chemically compatible with barium titanate). A conformal, sol-gel-derived coating of europium-doped barium titanate was then applied to the chemically compatible magnesia replicas to yield photoluminescent particles that retained the starting microshell shape. Upon stimulation with (UV) light, the 3D microparticle replicas exhibited a bright red emission associated with the transition of .