White light emission of the single-phased CaWO4:Tb3+,Eu3+,Dy3+ materials prepared by an environmentally friendly method

Abstract

Trivalent rare earth (RE3+) doped tungstates [WO4]2- host matrix offers possibility to design new photoluminescent materials.1 Nowadays, there is an increasing interest of WLEDs to replace the conventional fluorescent lamps due its environment-friendliness and tuneable colours.2,3 Here we report preparation as well as the spectroscopic properties of the new highly luminescent white emitting materials Tb3+/Eu3+/Dy3+ triply-doped in CaWO4 matrix. The materials were prepared by coprecipitation method at room temperature with stoichiometry aqueous solutions of Na2WO4, CaCl2 and RECl3 (RE3+: Tb, Eu, Dy with 0.5 to 5.0 mol% of the Ca2+ amount). The RE3+ doping concentrations were identical for each rare earth ion in the range from 0.5-5.0 mol%. The XPD measurements revealed the as-prepared CaWO4:xTb3+,xEu3+,xDy3+ (x: 0.5-5.0 mol%) particles belong to the tetragonal scheelite phase with I41/a (#88) space group. The average crystallite sizes are ~11 nm. The white luminescence emission arising mainly from the 5D07F2 (Eu3+), 5D47F5 (Tb3+) and 4F9/26H15/2 (Dy3+) transitions at 614 nm (red), 545 (green) and 488 (blue), respectively (Fig. 1). The emission lifetimes of the 5D0, 5D4 and 4F9/2 emitting levels were and their values are reduced when comparing the ratio from 0.5-5.0 mol% of the RE3+ ions, respectively. The results indicate the presence of energy transfer processes between RE3+. These values could be assigned to non-radiative energy transfer contributions of the Dy3+Tb3+, Dy3+Eu3+ and Tb3+Eu3+ systems due the cross relaxation. The CIE diagram (Fig. 1 right) exhibits emissions whitish colour indicating that these materials could be suitable for solid state lighting technology.