White light emission of the single-phase CaWO4:Dy3+ phosphors by simple synthesis and fast heating

Abstract

Tungstates activated by trivalent rare earth ions (R3+) can be used for many optical devices [1]. Nowadays, there is an increasing interest in white phosphors emitting to application in white-light-emitting devices (WLEDs) replacing the conventional fluorescent lamps due its ecofriendliness and tuneable colours. Here we report preparation as well as the spectroscopic properties of the single phase new highly luminescent white emitting of Dy3+ doped into the CaWO4 materials. The materials were prepared by coprecipitation method at room temperature with stoichiometry aqueous solutions of Na2WO4, CaCl2 and DyCl3 (0.1 to 5.0 mol% of the Ca2+ amount). The as-prepared materials were heated for 22 min between 900 – 1000 W in a domestic microwave oven and using Fe3O4 (60 g) susceptor as heating source. The XPD measurements revealed the CaWO4:Dy3+ particles belong to the tetragonal scheelite phase with I41/a (#88) space group. The emission arising mainly from the 4F9/26H15/2 (blue) and 6H13/2 (yellow) transitions are corresponding to the 488 and 575 nm, respectively (Fig.). At lower doping concentrations the broad band (~420 nm) is due to the WO4 group emission. Increasing the RE3+ doping concentration the main emission lines transitions of the Dy3+ are enhanced. After heating, the 1.0 mol% Dy3+ doped material exhibit a better whitish emission due to the simultaneous presence of broad band of the host in blue region and emission lines at longer wavelengths (Fig.). The lifetimes decrease monotonously in function of the Dy3+ concentration which indicates that the energy transfer from host to the Dy3+ becomes more efficient. These results suggest that CaWO4:Dy3+ could act as a white emitting phosphor in solid state-lighting technology.