Findings on the decomposition of persistent luminescent (PeL) SrAl₂O₄:Eu²⁺,Dy³⁺ microparticles (MPs) in phosphate glass melt under static condition are reported. PeL phosphate glasses with the composition (50P₂O₅-10Na₂O-40SrO) (in mol%) were prepared by adding the MPs in the glass melt. The decomposition of the MPs occurs during the preparation of the glass and leads to changes in the Eu²⁺ sites and to the formation of Eu³⁺ which decreases the PeL properties of the glasses. The decomposition of the MPs depends on the temperature at which the MPs are added in the melt and also on the time before casting the melts.