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New Insight into Phase Formation of MxMg2Al(4+x)Si(5-x)O18:Eu2+ Solid Solution Phosphors and Its Luminescence Properties.

Zhou J, Xia Z, Chen M, Molokeev MS, Liu Q - Sci Rep (2015)

Bottom Line: XRD results revealed that the as-prepared phosphors with different M(+) contents were iso-structural with Mg2Al4Si5O18 phase.The emission peaks of MxMg2Al(4+x)Si(5-x)O18:Eu(2+) (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 MxMg2Al(4+x)Si(5-x)O18:Eu(2+) (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.

View Article: PubMed Central - PubMed

Affiliation: School of Materials Sciences and Technology, China University of Geosciences, Beijing 100083, China.

ABSTRACT
Here we reported the phase formation of MxMg2Al(4+x)Si(5-x)O18:Eu(2+) (M = K, Rb) solid solution phosphors, where M(+) ions were introduced into the void channels of Mg2Al4Si5O18 via Al(3+)/Si(4+) 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 MxMg2Al(4+x)Si(5-x)O18:Eu(2+) (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 MxMg2Al(4+x)Si(5-x)O18:Eu(2+) (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.

No MeSH data available.


XRD patterns of as-prepared KxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) (a) and RbxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) (b). The standard data for Mg2Al4Si5O18 (JCPDS card no. 13-0294) is also shown as a reference.
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f2: XRD patterns of as-prepared KxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) (a) and RbxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) (b). The standard data for Mg2Al4Si5O18 (JCPDS card no. 13-0294) is also shown as a reference.

Mentions: Figure 2a,b shows the typical XRD patterns of the as-prepared KxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) and RbxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) samples, respectively. It can be found that all the diffraction peaks of these two series of samples can be exactly assigned to the corresponding standard data for hexagonal phase of Mg2Al4Si5O18 (JCPDS 13-0294), suggesting that doped M+ ions have been successfully dissolved in the Mg2Al4Si5O18 host lattice. However, once the occupation of the Eu2+ in the Mg2Al4Si5O18 host and MxMg2Al4+xSi5−xO18 host is concerned, there are two different viewpoints, one is that the Eu2+ can enter the void channels, and the other viewpoint think that Eu2+ will replace the cations. Piriou et al. demonstrated that the Eu ion cannot enter the void channels based on the site-selective spectroscopy10. In the present case, it is assumed that Eu2+ (r = 1.17 Å when coordinate number (CN) = 6) ions will occupy the Mg2+ (r = 0. 72 Å when CN = 6) sites, because both the Al3+ (r = 0.39 Å when CN = 4) and Si4+ (r = 0.26 Å when CN = 4) sites are too small to accommodate the Eu2+ ions. In order to further analyze the crystal structure of the as-prepared samples, the Rietveld structural refinement for these samples were performed using TOPAS 4.2 (Bruker AXS TOPAS V4: General profile and structure analysis software for powder diffraction data. – User’s Manual. Bruker AXS, Karlsruhe, Germany. 2008.). Figure S1 (electronic supporting information) demonstrates the observed, calculated, and difference patterns. Based on the Rietveld refinement results, negligible amounts of impurity phases were identified in the samples, and all of these samples exhibit the same crystalline hexagonal crystal system with a space group P6/mcc. The final weighted R factors (Rwp) of the samples were successfully converged at a satisfactory level, and the refined structural parameters of these samples are listed in Table S1. The unit cell parameters and Al3+/Si4+ ratio in tetrahedra become larger with increasing M+ content, which is ascribed to the fact that the M+ were introduced into the void channels. Furthermore, increasing Al3+ concentration results in the expansion of the [(Al/Si)O4] tetrahedra since the average bond length d(Al–O) = 1.618 Å is bigger than the average bond length d(Si–O) = 1.596 Å. In order to further understand the lattice mismatch between the Mg2Al4Si5O18 phase and the MxMg2Al4+xSi5−xO18 (M = K, Rb) phase, Figure S2 gives the lattice variation of the MxMg2Al4+xSi5−xO18 (M = K, Rb) phase compared to the original Mg2Al4Si5O18 phase. When M+ ions are introduced into the void channels of Mg2Al4Si5O18 via the synergistic Al3+/Si4+ substitution, the lattice parameter a for KxMg2Al4+xSi5−xO18:Eu2+ and RbxMg2Al4+xSi5−xO18:Eu2+ series both increased, whereas the lattice parameter c for the two series of samples decreased. Such a different lattice variation will lead to the distortion of the corresponding polyhedra, which will be discussed later.


New Insight into Phase Formation of MxMg2Al(4+x)Si(5-x)O18:Eu2+ Solid Solution Phosphors and Its Luminescence Properties.

Zhou J, Xia Z, Chen M, Molokeev MS, Liu Q - Sci Rep (2015)

XRD patterns of as-prepared KxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) (a) and RbxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) (b). The standard data for Mg2Al4Si5O18 (JCPDS card no. 13-0294) is also shown as a reference.
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f2: XRD patterns of as-prepared KxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) (a) and RbxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) (b). The standard data for Mg2Al4Si5O18 (JCPDS card no. 13-0294) is also shown as a reference.
Mentions: Figure 2a,b shows the typical XRD patterns of the as-prepared KxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) and RbxMg2Al4+xSi5−xO18:0.03Eu2+ (x = 0, 0.17, 0.26 and 0.5) samples, respectively. It can be found that all the diffraction peaks of these two series of samples can be exactly assigned to the corresponding standard data for hexagonal phase of Mg2Al4Si5O18 (JCPDS 13-0294), suggesting that doped M+ ions have been successfully dissolved in the Mg2Al4Si5O18 host lattice. However, once the occupation of the Eu2+ in the Mg2Al4Si5O18 host and MxMg2Al4+xSi5−xO18 host is concerned, there are two different viewpoints, one is that the Eu2+ can enter the void channels, and the other viewpoint think that Eu2+ will replace the cations. Piriou et al. demonstrated that the Eu ion cannot enter the void channels based on the site-selective spectroscopy10. In the present case, it is assumed that Eu2+ (r = 1.17 Å when coordinate number (CN) = 6) ions will occupy the Mg2+ (r = 0. 72 Å when CN = 6) sites, because both the Al3+ (r = 0.39 Å when CN = 4) and Si4+ (r = 0.26 Å when CN = 4) sites are too small to accommodate the Eu2+ ions. In order to further analyze the crystal structure of the as-prepared samples, the Rietveld structural refinement for these samples were performed using TOPAS 4.2 (Bruker AXS TOPAS V4: General profile and structure analysis software for powder diffraction data. – User’s Manual. Bruker AXS, Karlsruhe, Germany. 2008.). Figure S1 (electronic supporting information) demonstrates the observed, calculated, and difference patterns. Based on the Rietveld refinement results, negligible amounts of impurity phases were identified in the samples, and all of these samples exhibit the same crystalline hexagonal crystal system with a space group P6/mcc. The final weighted R factors (Rwp) of the samples were successfully converged at a satisfactory level, and the refined structural parameters of these samples are listed in Table S1. The unit cell parameters and Al3+/Si4+ ratio in tetrahedra become larger with increasing M+ content, which is ascribed to the fact that the M+ were introduced into the void channels. Furthermore, increasing Al3+ concentration results in the expansion of the [(Al/Si)O4] tetrahedra since the average bond length d(Al–O) = 1.618 Å is bigger than the average bond length d(Si–O) = 1.596 Å. In order to further understand the lattice mismatch between the Mg2Al4Si5O18 phase and the MxMg2Al4+xSi5−xO18 (M = K, Rb) phase, Figure S2 gives the lattice variation of the MxMg2Al4+xSi5−xO18 (M = K, Rb) phase compared to the original Mg2Al4Si5O18 phase. When M+ ions are introduced into the void channels of Mg2Al4Si5O18 via the synergistic Al3+/Si4+ substitution, the lattice parameter a for KxMg2Al4+xSi5−xO18:Eu2+ and RbxMg2Al4+xSi5−xO18:Eu2+ series both increased, whereas the lattice parameter c for the two series of samples decreased. Such a different lattice variation will lead to the distortion of the corresponding polyhedra, which will be discussed later.

Bottom Line: XRD results revealed that the as-prepared phosphors with different M(+) contents were iso-structural with Mg2Al4Si5O18 phase.The emission peaks of MxMg2Al(4+x)Si(5-x)O18:Eu(2+) (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 MxMg2Al(4+x)Si(5-x)O18:Eu(2+) (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.

View Article: PubMed Central - PubMed

Affiliation: School of Materials Sciences and Technology, China University of Geosciences, Beijing 100083, China.

ABSTRACT
Here we reported the phase formation of MxMg2Al(4+x)Si(5-x)O18:Eu(2+) (M = K, Rb) solid solution phosphors, where M(+) ions were introduced into the void channels of Mg2Al4Si5O18 via Al(3+)/Si(4+) 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 MxMg2Al(4+x)Si(5-x)O18:Eu(2+) (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 MxMg2Al(4+x)Si(5-x)O18:Eu(2+) (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.

No MeSH data available.