Self-assembled peanut-like Ln 3+ (Ln = Tb, Sm, Eu) doped NaLa(Wo 4) 2: Phase control and its relevance to luminescence modification

Ln(3+) (Ln = Tb, Sm, Eu) doped NaLa(WO4)(2) peanuts were successfully self-assembled by a facile EDTA assisted hydrothermal treatment. EDTA played critical roles in the phase and morphology control, which regulated the phase transformation from monoclinic La-2(WO4)(3) flowers to tetrahedral NaLa(WO4)(2) peanuts. La-2(WO4)(3):Tb3+ exhibited two broad excitation bands at 280 and 340 nm, which are related to the normal and perturb sites of WO42-. However, the excitation band for NaLa(WO4)(2):Tb3+ shifted to near ultraviolet region and showed only one broad excitation band originating from perturb sites. Under ultraviolet excitation, La-2(WO4)(3):Tb3+ displayed green light and NaLa(WO4)(2):Tb3+ showed blue green light consisting of WO42- self-activated blue emission and the characteristic Tb3+ emission. It can be clearly seen that the blue emission of WO42- was not sufficiently quenched in NaLa(WO4)(2) as that in La-2(WO4)(3), because the distortions of crystalline lattice for NaLa(WO4)(2) may alter the energy migration processes. When doping with Sm3+ and Eu3+, NaLa(WO4)(2) peanuts exhibited white color emission which may find practical applications in solid state lighting devices.