What Is Beyond Charge Trapping in Semiconductor Nanoparticle Sensitized Dopant Photoluminescence?

A systematic comparison of the Ln3+ [Ln = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb] photoluminescence in doped tin dioxide [Sn(Ln)O2] and doped titanium dioxide [Ti(Ln)O2] nanoparticles shows that the emission efficiency of trivalent lanthanide cations (Ln3+) in an oxide matrix can be improved by change of the cation site symmetry. An analysis of Ln3+ emission quantum yield and asymmetry ratio is used to identify the importance of symmetry breaking around the dopant site for enhancing the Ln3+ emission intensity. These findings identify an important criterion for engineering the luminescence intensity of dopant ions in semiconductor nanoparticle-based luminophores, which goes beyond the primary criterion of engineering the relative positions of the dopant energy levels with respect to the band edges of the host nanoparticle matrix.