A method for making phosphor ink is provided which uses ultrasonic vibrations to remove surface defect layers from phosphor particles and to quickly and uniformly disperse the phosphor particles throughout a slurry. Propagation of low frequency vibration through the slurry generates cavitation, causing distortion and then removal of the surface defect layer, and propagation of high frequency vibration through the slurry causes the particles to be dispersed quickly and uniformly throughout the slurry. In this manner, a quantity of light generated in the phosphor and corresponding luminance of a PDP is increased.