Molybdenum substitution simultaneously induced band structure modulation and luminescence enhancement in LiLaMg(W, Mo)O6: Eu3+ red-emitting phosphor for near ultraviolet excited white light diodes

Highlights: • Li_1-xLaMgW_1-yMo_yO₆:Eu³⁺ phosphors were firstly synthesized. • Mo⁶⁺ substitution could induce the decrease of band gap. • The excitation band of LiLaMgWO₆:Eu³⁺ phosphor had been extended largely by doping Mo⁶⁺. • Mo⁶⁺ substitution could enhance the red luminescence intensity. • A white light-emitting diode (LED) device was fabricated. In this study, LiLaMgW_1-xMo_xO₆: Eu³⁺ phosphors have been synthesized by high-temperature solid-state reaction method. By changing the WO charge transfer (CT) band through Mo⁶⁺ substitution, the excitation band of obtained phosphors had been widened largely and could match well with the InGaN-based LED chips. The crystal structure, diffuse reflection spectra, photoluminescent properties of the LiLaMgW_1-xMo_xO₆: 0.1Eu³⁺ phosphors were investigated as a function of W/Mo ratio. The red shift of charge transfer band (CTB) was observed with the increase of Mo⁶⁺ concentration. Density functional theory (DFT) were performed to calculate the band structure in order to support the excitation band modulation. Moreover, LiLa_1-yMgW_0.7Mo_0.3O₆:yEu³⁺ phosphors exhibit strong red emission. The excitation, emission spectra, decay dynamics and thermal stability of the phosphors had been measured and investigated in detail. The quenching concentration of Eu³⁺ is up to 20 mol% and the concentration quenching is attributed to the dipole-dipole interaction. Finally, a white-LED device was fabricated by integrating a mixture of optimal red phosphor, commercial green- and blue-emitting phosphors with a near-ultraviolet (UV) InGaN-based LED chip. The results suggest that the Eu³⁺-activated LiLaMgW_0.7Mo_0.3O₆ phosphor is a promising red-emitting phosphor for white-LEDs.