Selective synthesis of LaF3 and NaLaF4 nanocrystals via lanthanide ion doping†
The capability to selectively obtain expected nanocrystals from a series of possibilities with similar chemical compositions has been a long-term challenge. β-LaF3 and β-NaLaF4 nanocrystals are a kind of host material with excellent physical and chemical stability as well as low phonon energy. Since β-NaLaF4 nanocrystals are difficult to form due to the very strong La3+–F− ionic bond, investigations of the doping effect of different lanthanide ions on the formation of the final product were carried out. The experimental results have indicated that Ce3+ and Pr3+ doping has no obvious effect on the product compared to pure β-LaF3 nanocrystals without doping, and doping of Nd3+, Sm3+, Eu3+, Gd3+, and Tb3+ leads to the formation of pure β-NaLaF4 nanocrystals while doping of Dy3+, Ho3+, Er3+, Tm3+, Yb3+, and Lu3+ only results in a mixture of both. What is more, proper lanthanide ion doping can also help in obtaining enhanced up- and downconversion luminescence. A theoretical model from the nanocrystal growth free energy point of view has been developed to explain the above phenomenon.