Red or yellow phosphors excited by a blue light-emitting diode (LED) are an efficient source of white light for everyday applications. Melilite type Y2Si3O3N4:Ce3+ is a phosphor that shows intense absorption in the near ultraviolet region and exhibits bright blue emission3 because of this it is a promising blue-emitting phosphor candidate for white LEDs for general illumination or displays. We request 2 days on GEM to collect total scattering data for two 3g samples at room temperature. One sample will be Y2Si3O3N4 and PDF analysis will be used to examine local arrangements of O/N. The second sample will be Ce0.5Y1.5Si3O3N4 where local clustering will be explored. This has important implications for the photoluminescent properties as a coordination environment richer in O and poorer in N leads to a blue shift of the emission spectrum.