A novel method for preparing the cathodoluminescent red europium-doped yttrium oxide (Y2O3 :Eu) phosphor using the copolymer microgel of N-isopropylacrylamide (NIPAM) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) is described. An extensive range of spherical particle sizes can be produced by careful manipulation of the experimental conditions. Spherical particle size is shown to be directly controlled by the quantities of copolymer microgel, allowing spherical particles for a given size from 0.1 to 1.3 mm to be produced. The luminescent intensity of the particles related to the particle size is also reported.