Morphology evolution, energy transfer and multicolor luminescence of lanthanide-doped Ba2LaF7 nanocrystals via a one-step hydrothermal synthesis

Abstract

Lanthanide-doped Ba₂LaF₇ nanocrystals were successfully synthesized via a one-step hydrothermal method. The phase, size and shape of the lanthanide-doped Ba₂LaF₇ nanocrystals were systematically investigated by controlling the fluorine source, additive, lanthanide doping, synthesis method and temperature. Regular hexagonal Ba₂LaF₇ nanocrystals with a side length of 60 nm were obtained by using NaBF₄ as the fluorine source. A variety of lanthanide ions (Ho³⁺, Er³⁺, Tm³⁺, Dy³⁺, Eu³⁺, Tb³⁺, Ce³⁺, and Sm³⁺) was successfully doped into the Ba₂LaF₇ host, which showed abundant luminescent colors due to the intrinsic emission of the lanthanide ions. Because of the emission spectrum of Tb³⁺ (⁵D₄ → ⁷F_j) having obvious overlap with the Eu³⁺ excitation spectrum (⁷F_0,1 → ⁵D_0,1,2), the excited state energy of Tb³⁺ can be transferred to Eu³⁺. Under ultraviolet excitation, the energy transfer from Tb³⁺ to Eu³⁺ in the Ba₂LaF₇ matrix occurs mainly via the dipole–quadrupole mechanism. The regulation of luminescent color was achieved from green to warm yellow to yellow orange and finally to red by changing the doping concentration of Eu³⁺ ions from 0.1% to 7%, respectively. The obtained Ba₂LaF₇:Ln³⁺ nanocrystals have potential application in multicolor lighting and displays.