Nd3+-doped TiO2 nanocrystals: Structural changes, excited-state dynamics, and luminescence defects

Highlights: • Effect of Nd on the structural and optical properties of TiO₂ NCs. • The temperature and Nd addition change the TiO₂ phase from anatase to brookite. • Raman spectroscopy shows an increase of brookite phase on the Nd:TiO₂ NCs. • Photoluminescence dynamics confirms that the Nd ions are in two environments in the sample. The structural and optical properties of the TiO₂ nanocrystals (NCs) samples pure and doped with Nd³⁺ ions were studied as a function of temperature. These properties were studied by using the Raman spectroscopy, steady-state and time-resolved photoluminescence. A structural transformation is observed by a systematic study as a function of the temperature from room temperature. The results show that the introduction of Nd³⁺ ions and the increase of temperature induces a phase transformation from anatase to brookite. As a result, the intrinsic defects states of TiO₂ NCs decrease and consequently the PL intensity of the ⁴F_3/2 level of Nd³⁺ ions increases. The photoluminescence decay kinetics also shows that Nd³⁺ ions are located in two different environments of TiO₂ NCs: the brookite and anatase phase.