Effect of Al co-doping on the luminescence properties of Nd³⁺-doped TiO₂ thin films

Co-doping Aluminium (Al) with neodymium (Nd) is shown to have a sensitizing effect on the rare earth luminescence in thin film titanium dioxide (TiO₂) host materials. Whilst the Al co-doping has the effect of quenching the direct (resonantly) excited, steady state photoluminescence from Nd³⁺ emitting centers, for indirect (non-resonant) excitation, the emission is enhanced with increasing Al. Time-resolved PL measurements reveal a decrease in both the excitation/de-excitation rates (increases in lifetime) with increasing Al co-doping, confirming the indirect nature of excitation and implying a suppression of non-radiative de-excitation of the Nd³⁺ centers in TiO₂. Suppression of non-radiative processes by Al is considered to be the result of reduced rare earth clustering, which is known to promote de-excitation via energy migration and thus has important implications for improved efficiency infra-red LED materials