Preparation of strontium aluminate: Eu2+ and Dy3+ persistent luminescent materials based on recycling alum sludge

Abstract Eu2+ and Dy3+ doped strontium aluminate persistent luminescent materials are prepared by solid state reaction using alumina obtained from the alum sludge [1]. Three group compositions; Sr (NO3)2 with alumina (calcined at 1100 °C, ESA1), SrO with alumina (calcined at 1400 °C, ESA2) and Sr(NO3)2 with alumina (calcined at 1400 °C, ESA3) doped with Eu3+: Dy3+ ions in different molar ratios (1 Eu3+: 2Dy3+, 1.5 Eu3+: 1.5Dy3+, 2Eu3+:1Dy3+ and 2.5Eu3+: 0.5 Dy3+) were prepared. The samples were fired under different under active carbon at 1250 °C. Surface morphology, crystalline structure, Photoluminescence measurements and the decay characteristic were characterized by SEM, XRD, and the photoluminescence spectrometers, respectively. The effect of the firing temperature at 1250 °C was also determined by apparent porosity and bulk density measurements. The results indicated that the main composition of the samples fired under active carbon powder was strontium aluminate with a very small amount of secondary phases. The results showed that the samples fired under active carbon had good phosphorescence properties and good decay time. A broad band UV-excited luminescence of the SrAl2O4:Eu2+, Dy3+ phosphorescent pigments was observed at λmax = 517 nm due to transitions from 4f6, 5d1 to 4f7 configuration of the emission center (Eu2+ ions). Photoluminescence spectra for ESA1 group show higher intensity than that of ESA2 and ESA3 groups. The difference in the behavior of the photoluminescence spectra for the three groups can be attributed to (i) different synthesis methods and (ii) the presence of different mixed phases (major SrAl2O4 and secondary phases).