多面体共替代对Sr_2(Al_(1–x) Mg_x)(Al_(1–x) Si_(1+x))O_7:Eu~(2+)晶体结构和发光颜色的影响

采用高温固相法合成Sr_(1.98)(Al_(1–x) Mg_x)(Al_(1–x) Si_(1+x))O_7: 2%Eu~(2+)荧光粉完全固溶体,利用X射线衍射、光致发光光谱和光学显微镜进行晶体结构和发光性能的研究. Sr_2Al_2SiO_7和Sr_2MgSi_2O_7同构化合物中包含MgO_4]、SiO_4]和AlO_4]四面体,较大体积的MgO_4]和较小体积的SiO_4],共同替代体积相似的AlO_4],导致(Si/Al)O_4]收缩和(Mg/Al)O_4]膨胀,晶胞参数c减少, a和V增大,使Eu~(2+)周围的环境发生改变,晶体场劈裂程度减小,发射峰位从503 nm蓝移至467 nm,实现发光光谱从绿色(0.2384, 0.3919)到蓝色(0.1342,0.1673)的转变.当x为0时,发射峰的半高宽为120 nm, x从0.25增加到1时,半高宽由89 nm逐渐减小至50 nm,多面体的替代会改变荧光粉的发光性能.

Effect of polyhedral co-substitution on the crystal structure and luminescence color of Sr2(Al1-xMgx)(Al1-xSi1+x)O7: Eu2+

A series of Sr_1.98(Al_1-xMg_x)(Al_1-xSi_1+x)O₇:2%Eu²⁺ phosphors is prepared by the high-temperature solid-state reaction method, the crystal structures and luminescent properties of the prepared phosphors are investigated by measuring the X-ray diffraction, luminescent spectra and optical microscope. The isomorphic compounds of Sr₂Al₂SiO₇ and Sr₂MgSi₂O₇ contain tetrahedra includingMgO₄],SiO₄] andAlO₄]. Although the valences of theMgO₄]^6-,SiO₄]^4- andAlO₄]^5- groups are different, the charge imbalance occurs when theMgO₄]^6- andSiO₄]^4- substitutes ofAlO₄]^5- andAlO₄]^5-, respectively. While the groups are co-substituted, the charge imbalance disappears. And the larger volume ofMgO₄] and the smaller volume ofSiO₄] together replaces the similar volume ofAlO₄], resulting in the decrease of(Si/Al)O₄] and increase of(Mg/Al)O₄]. Moreover, the decrease of unit cell parameters c and the increase of a and V due to the increased replacement of Mg²⁺ (0.57 Å for CN=4) by Al³⁺(0.39 Å for CN=4) and Si⁴⁺ (0.26 Å for CN=4) by Al³⁺ (0.39 Å for CN=4) cause the ambient temperature to change, the crystal field splitting of the Eu²⁺ cation to be weakened, and the emission spectra to be blue-shifted from 503 nm to 467 nm, which are closely related to the local coordination environment of the Eu²⁺, in addition, this reveals that the emission color of this series of phosphors can be tuned from green with color coordinate (0.2384, 0.3919) to blue (0.1342, 0.1673) by adjusting the chemical compositions via theMgO₄]^6- andSiO₄]^4- groups' co-substitution forAlO₄]^5-. The full width at half maximumof emission band is 120 nm when x=0, the photoluminescence emission width decreases monotonically from 89 to 50 nm as x is increased from 0.25 to 1. In other words, the full width at half maximum of emission band exhibits a decreasing trend. The internal quantum efficiency is enhanced with increasing x in Sr_1.98(Al_1-xMg_x)(Al_1-xSi_1+x)O₇:2%Eu²⁺ phosphors. These results verify that the groups' substitutions are enhanced with polyhedron changing in the solid solutions and contribute largely to the luminescence properties of the phosphor.