Enhanced photoluminescence of K2Ba(WO4)2:Eu3+ by Cl− co-doping

K2Ba(WO4)2:Eu3+ phosphors were synthesized using solid state reaction method. The effects of Cl− doping on the crystal structure, morphology, and luminescent properties of K2Ba(WO4)2:Eu3+ were investigated. All phosphors exhibit red emission peaking at 615 nm upon 394 nm excitation. The appropriate addition of F−, Cl− and Br− ions in K2Ba(WO4)2:Eu3+ can increases prominently the emission intensity. Unlike the common view, the charge compensation mechanism cannot account for the enhancement of emission intensity. Based on the detail study of the photoluminescence of Cl− doped samples, it can be deduced that the change of the lattice symmetry of Eu3+ sites by the addition of Cl− ions is responsible for the emission enhancement, which results the increase of 5D0 → 7F2 transition probability. It is also interesting that the change of the symmetry at Eu3+ sites is coincident with the crystallinity of the phosphors. Meanwhile, the addition of Cl− decreases the lifetime of Eu3+ luminescence. Compared with the commercial red-emitting phosphor Y2O3:Eu3+, K2Ba(WO4)2:Eu3+, Cl− phosphors show higher luminescent intensity and best color purity. The results suggest the suitability of K2Ba(WO4)2:Eu3+, Cl− phosphors for white LED applications.