New phosphors synthesised by ion exchange of a metakaolin-based geopolymer

A geopolymer prepared from dehydroxylated kaolinite-type clay was used as a host for trivalent rare earth ions to produce new photoluminescent materials. Sm3+ and Eu3+ ions were individually incorporated into the geopolymer host by ion exchange, partially replacing the charge-balancing K+ ions. The resulting materials were characterised by XRD, SEM/EDS, 27Al and 29Si MAS NMR and PIXE, and their luminescence behaviour was determined by photoluminescence spectroscopy. In addition to the characteristic photoluminescence of the Sm3+ and Eu3+ ions, the geopolymer host exhibited broad-band photoluminescence peaking at 440 nm under 372 nm excitation. The use of the clay-based geopolymer host permitted a higher concentration of rare earth ions to be incorporated compared with a previously reported chemosynthetic aluminosilicate inorganic polymer host, resulting in rare earth photoluminescence of increased intensity. A further advantage of the clay-based geopolymer phosphor is its ease of synthesis and cost-effectiveness compared with the chemosynthetic aluminosilicate inorganic polymer host.