Color control and white upconversion luminescence of LaOF:Ln3+ (Ln = Yb, Er, Tm) nanocrystals prepared by the sol-gel Pechini method.

A series of Yb(3+)-Er(3+) and Yb(3+)-Er(3+)-Tm(3+) 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 Yb(3+)-Er(3+)-Tm(3+) codoped LaOF nanocrystals, an ideal white upconversion luminescence with chromaticity coordinates of (0.331, 0.368) is obtained in La0.885Yb0.1Er0.01Tm0.005OF nanocrystals for the first time. The blue, green and red components of the white light come from the (1)G4 → (3)H6 transition of Tm(3+), (2)H11/2/(4)S3/2 → (4)I15/2 transitions of Er(3+) and (4)F9/2 → (4)I15/2 transition of the Er(3+) ions, respectively. The possible physical mechanisms involved in the different upconversion processes were discussed in detail.