Broad color tuning and Eu3+-related photo-emission enhancement via controllable energy transfer in the La2MgGeO6:Eu3+,Bi3+ phosphor

Recently, how to employ a feasible strategy to design novel phosphors with color-tuning properties and enhanced photoemission has become a hot research subject. Herein, we report a series of UV-converted Eu3+, Bi3+-doped La2MgGeO6 phosphors, which enable broad color tuning and Eu3+-related fluorescence enhancement simultaneously. Structural analysis shows that all samples crystallize in a trigonal structure with the space group R-3 (no. 146), and Eu3+ and Bi3+ ions tend to substitute La3+ ions rather than Mg2+ and Ge4+ ions. Photoluminescence (PL) results show that excitation in the UV spectral region (e. g., 248 nm, 292 nm, and 393 nm) enables the Bi3+-doped La2MgGeO6 phosphors to exhibit a single blue emission band (i. e., 412 nm) that corresponds to the characteristic P-3(1)-> S-1(0) transition of Bi3+ ions and Eu3+-doped La2MgGeO6 phosphors to show sharp emission lines that correspond to the characteristic D-5(0)-> F-7(J) (J = 1, 2, 3, and 4) transitions of Eu3+ ions. In addition, we studied the energy transfer mechanism from Bi3+ to Eu3+ ions, and on the basis of the PL results and theoretical evaluations, we revealed that this energy transfer process occurred via a dipole-quadrupole (d-q) interaction and could enhance Eu3+-related fluorescence intensity and thus led to color tuning from blue to red upon excitation at 298 nm. To illustrate our experimental PL observations more clearly, a mechanistic profile based on the energy transfer and simplified spectral energy levels of Bi3+ and Eu3+ ions is also established. This study not only adds a new member into the family of UV-converted tunable phosphors, but also provides new insights into the discovery of more single-phase phosphors with simultaneous PL enhancement and emission color tuning for UV-converted wLEDs using the energy transfer interaction.