Micrometric Zn1.8Mn0.2SiO4 phosphor powders prepared by spray pyrolysis have been annealed between 900 and 1200 degrees C under ambient air atmosphere to investigate their luminescence properties, Two original gas-solid fluidization processes have been tested in order to limit sintering phenomena, and the post-treated products have been compared with those annealed using a conventional process in crucible. The crystallinity, the size distribution, the outer morphology and the luminescence properties of powders before and after treatment have been analysed. Massive sintering phenomena occur in crucible from 1000 degrees C, whereas the original granulometry and spherical morphology are preserved till 1100 degrees C in fluidized bed. The luminescence efficiencies are comparable for the three processes and shown to be maximal after annealing at 1200 degrees C. It has been established that residual ZnO and manganese ions at oxidation state higher than 2+, still present after treatment at 1100 degrees C, are detrimental to good luminescence efficiency. Both disappear from samples post-treated at 1200 degrees C. (C) 2007 Elsevier Ltd. All rights reserved.