Luminescent and structural behaviour of Tb+3 ions doped TiO2 nanoparticles synthesized by facile sol-gel method

Terbium doped titania (Tb–TiO₂) nanoparticles with different concentration of Tb⁺³ ions were synthesized by sol-gel method. The crystallite size of nanoparticles decreased with increasing the Tb⁺³ ions concentration suggesting the inhibition of growth of TiO₂ nanoparticles while the phase of nanoparticles was not affected by doping of Tb⁺³ ions. A marginal red shift in absorption and a decrement in the band gap from ⁓3.18 eV–3.06 eV after doping of Tb⁺³ ions were observed. The radiative transitions of Tb⁺³ ions were observed at 489 nm, 542 nm, 495 nm, and 654 nm corresponding to ⁵D₄-⁷F₆, ⁵D₄-⁷F₅, ⁵D₄-⁷F₄, and ⁵D₄-⁷F₃ transitions respectively in PL spectra. The PL intensity of these transitions first increases and then decreases with increasing Tb⁺³ concentration. The enhancement in PL intensity is due to more Tb⁺³ ions, and further addition of Tb⁺³ ions leads to the cluster formation which results in the loss of PL intensity.