调控Al2O3晶型控制MgAl2O4:Mn4+荧光粉中Mn价态研究

Mn4+激活红光荧光粉是白光半导体发光二极管(wLEDs)领域当前研究热点之一.Mn4+离子2E→4A2跃迁在铝酸盐中的最短发光波长是在MgAl2O4中实现的651nm发光,由于其结构中含有形成四面体或八面体配位的两种阳离子格位(Mg2+/Al3+),易造成所掺杂锰元素存在多种价态(+2/+4/+3等).本研究通过改变...

Valence State Control of Manganese in MgAl2O4:Mn4+ Phosphor by Varying the Al2O3 Crystal Form

Mn⁴⁺ activated red phosphor is one of the current research hot-spots in the field of white light emitting diodes (wLEDs). The shortest emission of Mn^{4+ 2}E→⁴A₂ transition in aluminate is 651 nm realized in MgAl₂O₄, but the doped manganese ions exists in multiple valence states (+2/+4/+3, etc.) due to the fact that there exist two cationic sites (Mg²⁺/Al³⁺) forming tetrahedron or octahedron coordination in the spinel structure. In this study, variation of the Al₂O₃ polymorphs (γ/α ratio) in the starting materials and post-annealing were used to control the doping sites and valence state of manganese ions in the MgAl₂O₄ structure. The results show that a high α/(α+γ) ratio of starting Al₂O₃ favors the formation of Mn²⁺ while a low α/(α+γ) ratio of starting Al₂O₃ favors the formation of Mn⁴⁺ dopant. By using highly active nano-γ-Al₂O₃ as the Al³⁺-bearing source, the occupancy of manganese ions in the Mg²⁺ site and the formation of Mn²⁺ valence state were effectively suppressed. Bright and pure MgAl₂O₄:Mn⁴⁺ phosphors in which only the red luminescence from Mn⁴⁺ was observed in the visible spectral region were successfully prepared via once heat treatment at 1550 ℃ for 5 h in air. The intrinsic reason for the dependence of manganese doping valence state on the Al₂O₃ polymorph lies in that the reactivity of Al₂O₃ determined the sequences of doping reactions and then the doping site/valence of manganese ions in MgAl₂O₄:Mn. All the above data demonstrated that the control of reaction sequences was a new method to regulate the valence state of manganese in aluminate phosphors.