Fig. 5 shows the composition maps of SEM/EDXA imagesshowing the main elements (P, Na, Ca, Sr and Al) in the CaOglass with x = 3. Fig. 6 gives the line profiles showing the elemen-tal distribution along the diameter of a microparticle embeddedin the CaO glass. Figs. 7 and 8 show similar data for the SrO glasswith x = 3. In both glasses, the composition of the glass matrixis in accordance with the theoretical one within the accuracyof the measurements. Micro-scale particles can be seen in bothimages. The average size of the MPs according to the imageswas 60–100 m. According to the composition analysis, the MPin the CaO glass contains only Al2O3and SrO homogeneouslydistributed (Figs. 5 and 6). The elemental analysis suggests thatthe MPs maintain their compositional integrity confirming theSr4Al14O25composition. It is noteworthy that the outermostlayer of the particles at the interface of the CaO glass seemsto contain slightly more Al and less Sr than the inner parts.The MPs are surrounded by a thin layer which is rich in Ca(Figs. 5 and 6). The matrix in the CaO glass is free of SrO andAl2O3. In contrast, Al2O3seems to diffuse from the MPs intothe SrO glass matrix (Figs. 7 and 8). The MPs in the SrO glassexhibit a homogeneous distribution of Al2O3and SrO over ca.40 m in the inner part surrounded by a thick Al2O3layer at theglass interface. As the optically active Eu2+ion is too large tosubstitute for Al3+,21we suspect the Al-rich layer to be Eu2+-free. Moreover, the MPs size (and most probably the volume ofthe emitting particles) decreases due to the diffusion.