Glowing synthetic chlorohectorite: The luminescent features of a trioctahedral clay mineral

Clay minerals are versatile materials with numerous industrial applications. Their unique layered structure can act as a host for many optically active species. The synthesis and luminescence properties of chlorohectorite clays are now reported for the first time. The synthesized clays are composed of quasi-circular nanoparticles with diameters around 20–30nm showing blue/green emission and persistent luminescence with a duration of ca. 5s. The luminescence features are associated with titanium impurities in the chlorohectorite structure. It is shown that Ti can act as activator ion even at low concentrations: the XRF and ICP-MS measurements of the chlorohectorite materials indicate a Ti concentration around 60 ppm originating from the precursors. The XPS measurements of the clay materials showed the Ti 2p3/2 signals at 457.8 and 458.9eV associated with Ti3+ and TiIV, respectively. The excitation spectra confirm Ti3+ as the luminescent center in the chlorohectorites through the bands at 287 and 370nm, related to the e−(O2−(2p))→TiIV charge transfer and the electronic transitions from the t2g to eg levels of Ti3+, respectively. The persistent luminescence properties are due to structural defects common for layered silicates.