A series of Yb³⁺–Er³⁺ and Yb³⁺–Er³⁺–Tm³⁺ codoped LaOF nanocrystals were synthesized via a modified sol–gel Pechini method. The phases and morphologies as well as the luminescence properties of the as-prepared samples were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and upconversion luminescence (UCL) spectra, respectively. Under 980 nm near infrared (NIR) excitation, the UCL properties and the corresponding luminescent colors of the samples could be precisely modulated by changing the annealing temperatures, the dopant concentrations and the pump densities. By regulating the intensities of blue, green and red emissions in Yb³⁺–Er³⁺–Tm³⁺ codoped LaOF nanocrystals, an ideal white upconversion luminescence with chromaticity coordinates of (0.331, 0.368) is obtained in La_0.885Yb_0.1Er_0.01Tm_0.005OF nanocrystals for the first time. The blue, green and red components of the white light come from the ¹G₄ → ³H₆ transition of Tm³⁺, ²H_11/2/⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ and ⁴F_9/2 → ⁴I_15/2 transition of the Er³⁺ ions, respectively. The possible physical mechanisms involved in the different upconversion processes were discussed in detail.