As seen in Fig. 2b, the low-intensity band at 410 nmis not present with irradiation at 365 nm in the spectrum of theMPs, but it can be observed if 254 nm is used (not shown here).Otherwise, the shapes and band positions in the emission spec-tra are similar for both MPs-containing glasses and the MPs(Fig. 2b) confirming that it is the embedded MPs that show thepersistent luminescence. One can also notice that the emissionband of the MPs is slightly narrower than those of the glassesbecause some of the Eu2+ions diffuse to the glass shell and arein a weakened crystal field. The diffusion of Eu into the glassis confirmed also by the presence of the band located at 410 nmwhich can be related to a decrease in the number of Eu2+ionsin the MP due to the Eu2+diffusion from the MP into the glassand the subsequent weakened energy transfer between ions.