New Insight into Phase Formation of MxMg2Al4+xSi5−xO18:Eu2+ Solid Solution Phosphors and Its Luminescence Properties

Abstract

Here we reported the phase formation of MxMg2Al4+xSi5−xO18:Eu2+ (M = K, Rb) solid solution phosphors, where M+ ions were introduced into the void channels of Mg2Al4Si5O18 via Al3+/Si4+ substitution to keep the charge balance. XRD results revealed that the as-prepared phosphors with different M+ contents were iso-structural with Mg2Al4Si5O18 phase. The combined analysis of the Rietveld refinement and high resolution transmission electron microscopy (HRTEM) results proved that M+ ions were surely introduced into the intrinsic channels in Mg2Al4Si5O18. The emission peaks of MxMg2Al4+xSi5−xO18:Eu2+ (M = K, Rb) phosphors with various x values performed a systematic red-shift tendency, which was ascribed to the elongation of [MgO6] octahedra. The temperature stable photoluminescence and internal quantum efficiency (QE) of MxMg2Al4+xSi5−xO18:Eu2+ (M = K, Rb) phosphors were enhanced owing to the filling of M+ in the void channels suggesting a new insight to design the solid solution phosphors with improved photoluminescence properties.

Ca6La4(SiO4)2(PO4)4O2:Eu2+: a novel apatite green-emitting phosphor for near-ultraviolet excited w-LEDs

“…4,17 On the other hand, the PL spectra at different temperatures show a slight blue-shift, which is attributed to thermally-active phonon-assisted tunneling from the excited states of the lowenergy emission band to the excited states of the high-energy emission band. 11,12 As mentioned before, there are two emission centers for the Ca 6 La 4 (SiO 4 ) 2 (PO 4 ) 4 O 2 :Eu 2+ phosphor. The thermal back transfer from lower energy centers to higher energy centers will be promoted at higher temperature.…”

“…Researchers have paid great attention to green-emitting phosphors, for instance the cordierite structure phosphor K 0.5 Mg 1.5 Al 4 Si 5 O 13 :Eu 2+ , 11 the garnet structure phosphors Ca 2 LaZr 2 Ga 3 O 12 :Ce 3+ , 12 Ca 2 YZr 2 Al 3 O 12 :Ce 3+ , 13 and the commercial green phosphor (Ba,Sr)SiO 4 :Eu 2+ . However, there is still room for improvement in some aspects such as wider emission region, better thermal stability and higher quantum efficiency.…”

Tunable photoluminescence of apatite phosphor Ca5.95−xSrxLa4(SiO4)2(PO4)4O2:0.05Eu2+ and its application in light‐emitting diodes

“…It is therefore very clear that the lifetime gradually increases with increasing Sr 2+ ion concentration. Because the phase structures become more consolidated with the substitution of the Ca 2+ ion by the Sr 2+ ion, the decreasing energy‐transfer possibility among the Eu 2+ ions decreases the possible non‐radiative transition and leads to increasing lifetimes . In addition, the two decay components ( τ 1 and τ 2 ) further prove that Eu 2+ occupies two different cation sites …”

“…The good linear fitting indexes (0.99334‐0.99796) imply the continuous evolution of the crystal structure. Due to the substitution of the small Ca 2+ ion by the large Sr 2+ ion, the cell parameters linearly increase; they are proportional to the value of x , indicating that the coordination environment of the cations, which has a direct influence on the luminescence properties, consolidates with increasing x …”

“…The thermal stability shows an increase with increasing x due to the effect of the neighboring cation . The substitution of the Ca 2+ ion by the Sr 2+ ion increases the distances between the Eu 2+ ion and the neighboring cations, resulting in a smaller Columbia force and higher thermal quenching barrier . Therefore, the thermal stability can be improved when the replacement occurs.…”