Design and energy transfer mechanism for single-phased Gd2MgTiO6: Bi3+, Eu3+ tunable white light-emitting phosphors

In recent years, numerous efforts have been made to develop single-phased white light-emitting phosphors for the near-UV region to solve problems of color reabsorption and ratio regulation between different phosphors. In this work, we have designed Bi3+- and Eu3+-codoped single-phased Gd2MgTiO6 phosphors to achieve tunable white light emission based on multi-luminescence center energy transfer. The structural analysis showed that all the samples were crystallized as a monoclinic double perovskite with the P21/n symmetry space group (No. 14), with HRTEM images showing clear lattice fringes between the lattice planes. The single Bi3+-doped Gd2MgTiO6 sample exhibits two obvious emission peaks at 417 and 508 nm, which correspond to a characteristic 3P1 → 1S0 transition for the Bi3+ ions under near-UV excitation due to two types of Bi3+ emission centers, with their relative emission intensity depending closely on the value of the excitation wavelength. In this case, a suitable choice of excitation wavelength can achieve tunable emission for Gd2MgTiO6: Bi3+ between blue and green. Eu3+ is codoped into Gd2MgTiO6 as a red emission component and shows sharp emission lines that correspond to the characteristic 5D0 → 7FJ (J = 1, 2, 3, and 4) transitions of Eu3+ ions. Energy transfer in Gd2MgTiO6: Bi3+, Eu3+ has been confirmed by the electric dipole–dipole (d–d) interaction from Bi3+ to Eu3+. Our experiments show that it is straightforward to create tunable white light emission by adjusting the excitation scheme and Eu3+ concentration. Moreover, a schematic for the energy transfer mechanism and simplified spectral levels based on Bi3+ and Eu3+ ions has also been established.