Photoluminescence investigation of europium-doped alumina, titania and indium sol–gel-derived films in porous anodic alumina

Photoluminescence (PL) properties of Eu-doped xerogel films fabricated on porous anodic alumina (PAA) and flat substrates are analysed with respect to the xerogel content (TiO2, Al2O3, In2O3) and excitation wavelength. A strong enhancement of Eu-related emission in the broad UV range of the excitation has been found for the three xerogel systems. However, the enhancement factor is not simple to interpret, it possesses rather a complex nature. We have proposed that the increase of PL intensity is composed of two components. The first component is associated with an improvement of the energy transfer from the host xerogel matrix to lanthanide ions. The second one is evoked by multiple scattering of exciting light in the pore channels. This additional path of the excitation and energy transfer improves essentially the PL of lanthanide ions. Moreover, in periodic matrix of PAA the emission of lanthanide is redistributed by angle contributing into PL enhancement.