Luminescence properties, crystal structure and high thermal stable of (Gd_0.85-xLu_x)₂MgTiO₆: Eu³⁺ red phosphors

A series of double perovskite (Gd_0.85-xLu_x)₂MgTiO₆: 0.3Eu³⁺ red phosphors were prepared via a typical high temperature solid-state reaction. XRD and HRTEM exhibits that the phosphors well crystallized as a double perovskite with the space group of P21/n symmetry. The luminescent properties of samples were investigated via excitation and emission spectra. The phosphors emit strong red light and weak orange red light under ultraviolet (UV) and near-UV excitation suggesting that Eu³⁺ ions situated in the sites without inversion symmetry. The UV–vis spectra included a broad host absorption band assigned to O^2--Eu³⁺ and some peaks at 395 nm, 465 nm and 533 nm attributed to the typical f-f transition of Eu³⁺. The CIE chromaticity coordinates of all samples were near to the standard red light, indicating that the (Gd_0.85-xLu_x)₂MgTiO₆: 0.3Eu³⁺ was a potential candidate material for red emitting phosphors. The decay curves matched with the lines fitted by a one exponential decay formula and the decay time increased with increasing Lu³⁺-dopant concentration within x < 0.8. The temperature-dependent emission spectra from 298 K to 473 K were used to evaluate the thermal stability of Gd_0.9Lu_0.8Eu_0.3MgTiO₆ phosphors and the activation energy of Gd_0.9Lu_0.8Eu_0.3MgTiO₆ for ⁵D₀-⁷F₂ transition was calculated to be 0.158eV. The results revealed that the phosphors have the excellent thermal stability and were promising material for applications in LEDs.