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

Abstract

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 R₃ (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 ³P₁ → ¹S₀ transition of Bi³⁺ ions and Eu³⁺-doped La₂MgGeO₆ phosphors to show sharp emission lines that correspond to the characteristic ⁵D₀ → ⁷F_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.