Color-fading reaction mechanisms of TiO₂-coated photoluminescent materials

This paper presented underlying methylene blue (MB) color-fading mechanisms by photoluminescence-photocatalysis (PL-PC) reaction with PL materials coated with titanium dioxide (TiO₂). The color fading mechanism means the photocatalytic degradation of organic dye by the coated TiO₂photocatalyst. The photocatalyst is activated by photoluminescent material. For PL materials, SrAl₂O₄:Eu²⁺,Dy³⁺(SAOED) and water resistant SAOED were selected for its long-lasting after-glow characteristics and well-known PL effect. All the tests were performed on a solution basis. The TiO₂coating played an important role in the subsequent MB color-fading reactions as revealed by a comparative study performed in dark and white light conditions. The presented results also revealed that the MB color-fading reaction involves two major mechanisms. The first mechanism is adsorption by the hydrolysis product of SAOED, that is, Al(OH)₃. The second is photocatalytic degradation by the TiO₂coating layer activated by the photoluminescent light. These results revealed color-fading mechanisms by PL-PC, which have potential for mechanochromic sensing characteristics since the tested materials are known to have mechanoluminescence properties.