Codoping with Mⁿ⁺ ions (Mⁿ⁺ = Li⁺, Mn²⁺ and Cu²⁺) enhanced the blue and red upconversion (UC) emissions in TiO₂:Yb³⁺/Tm³⁺ nanocrystals under 980 nm excitation. The different effects of Li⁺, Mn²⁺ and Cu²⁺ ions on the phase structures, morphologies and optical characteristics of TiO₂:Yb³⁺/Tm³⁺ were discussed. The minor shifting in the diffraction peaks at 25.2° was observed for TiO₂:Yb³⁺/Tm³⁺/Li⁺, and adding Mn²⁺ ions remained almost the same position of diffraction peaks, while the introduction of Cu²⁺ ions resulted in the shift of the diffraction peaks towards the larger angles. TiO₂:Yb³⁺/Tm³⁺/Li⁺ and TiO₂:Yb³⁺/Tm³⁺/Mn²⁺ nanosheets and the sphere-like TiO₂:Yb³⁺/Tm³⁺/Cu²⁺ were observed. The mechanisms for increased UC emissions caused by adding Li⁺, Mn²⁺ and Cu²⁺ ions were attributed to the tailored local environment around Tm³⁺ ions, efficient energy transition between Mn²⁺-Yb³⁺ dimer and Tm³⁺ ions, and the localized surface plasmon resonance (LSPR) of Cu²⁺ ions, respectively.