Structure and photoluminescence of TiO2 nanocrystals doped and co-doped with N and rare earths (Y3+, Pr3+)

Highlights: ► We studied singly and co-doped N, Y and Pr:TiO2 nanoparticles. ► A mixed anatase-brookite phase with average dimension lower than 10 nm was revealed. ► The nature of defects in the TiO2 structures depends on the doping elements. ► Bulk and surface defects are related to nitrogen in the TiO2 matrix. ► Y3+ ion acts as a surface stabilizer, Pr3+ generates surface recombination centers. -- Abstract: The structural and optical properties of sol–gel synthesized TiO2 nanoparticles doped and co-doped with N and rare earth ions (Y3+ and Pr3+) are presented. Crystal structures, phase composition, and crystallite sizes are analyzed by powder X-ray diffraction and Raman spectroscopy. The analysis of intragap excited photoluminescence indicates the formation of radiative recombinations related to different defect centers in the TiO2 structure, generated by the presence of doping elements. In particular we assign the formation of bulk and surface defects to the presence of nitrogen in the TiO2 matrix, whereas we observe different effects on the defective TiO2 structure related to the two rare earths: the presence of Y3+ ion acts as a stabilizer of the TiO2 surface whereas the presence of Pr3+ generates surface recombination centers