(Y, Gd) BO3: Eu3+ phosphor was produced by a coprecipitation method. The morphology of the particles could be controlled by adjustment of the pH value and the heat-treatment method used. The pH value of the coprecipitation solution was a critical parameter for the luminescent properties of the phosphor. The improved chromaticity in smaller or disk-like particles was attributed to higher lattice distortion, which gives rise to the loss of the inversion symmetry at the site of the Eu3+ ion, thus enhancing the D-5(0) -> F-7(2) transition. (c) 2006 The Electrochemical Society.