Band gap tailoring of Nd3+-doped TiO2 nanoparticles

Undoped and ${\mathrm{Nd}}^{\text{3+}}$ -doped ${\mathrm{TiO}}_2$ nanoparticles were synthesized by chemical vapor deposition in order to tailor the band gap of ${\mathrm{TiO}}_2.$ The doping reduced the band gap. The band gap was measured by ultraviolet-visible light absorption experiments and by near-edge x-ray absorption fine structure. The maximum band gap reduction was 0.55 eV for 1.5 at. % Nd-doped ${\mathrm{TiO}}_2$ nanoparticles. Density functional theory calculations using the generalized gradient approximation with the linearized augmented plane wave method were used to interpret the band gap narrowing. The band gap narrowing was primarily attributed to the substitutional ${\mathrm{Nd}}^{\text{3+}}$ ions which introduced electron states into the band gap of ${\mathrm{TiO}}_2$ to form the new lowest unoccupied molecular orbital.