New Phosphor Development And Properties Modification By Non-Equivalent Co-Substitution In LuAG:Ce³⁺

As the new-generation green solid-state lighting source,white-light-emitting diodes(WLEDs)show great competitive advantages,such as small size,high efficiency and long lifetime.With the improvement of the quality of life,high-quality healthy green WLEDs have urgent demand in practical applications.As one of the key materials of WLEDs,phosphors play a major role in determining the color quality.Presently,the commercial WLEDs devices that are fabricated by LuAG:Ce3+ green and(Ca,Sr)AlSiN3:Eu2+ red phosphors with blue chip usually exhibit white light with relatively high rendernng index and low correlated color temperature.But unfortunately,the cavity of cyan component dominating the superhigh CRI(Ra>95)still exists in the 480-520 nm emission region,making them unsuitable for high-quality WLEDs.Therefore,we intend to modify the photoluminescence properties and elucidate the relationship of photoluminescence properties with the local crystal environment of Ce3+ to obtain phosphors for high-quality WLEDs by structural design on LuAG:Ce3+via non-equivalent co-substitution.In addition,we attempt to design and develop novel phosphors considering the crystal characteristics of LuAG:Ce3+.New solid-solution phosphors(Lu2M)Al2(Al2Si)Oi2:Ce3+ and(Lu2M)Ga2(Al2Si)O12:Ce3+(M=Mg,Ca,Sr and Ba)have been achieved via the non-equivalent co-substitution of M2+-Si4+→Lu3+-Al3+ and M2+-Ga3+-Si4+→Lu3+-Al3+-Al3+in LuAG:Ce3+.We investigated the evolution of crystal structure with M2+type.The emission bands show a blue-shift along with the variation of local structure modified by M2+ions,achieving the enhancement of cyan component.Moreover,the thermal stability of phosphors get obviously improved.The optimized phosphor enables to fabricate high-quality WLEDs with Ra more than 95.A local structural evolution model is proposed to investigate the variation of the structural rigidity for the hosts,which reasonably interprets the internal mechanisms for the decrease of Stokes shift and the improvement in thermal stability.It can provide theoretical reference value for the further development of targeted phosphors.Solid-solution phosphors Lu3(MgxAl2-x)(Al3-x、Six)O12:Ce3+(x=0,0.25,0.50,0.75 and 1.00)have been achieved via the non-equivalent co-substitution of Mg2+-Si4+→Al3+-Al3+ in LuAG:Ce3+.Due to the modification of local structure by second-sphere ions,continuously tunable emitting light from green to orange-yellow with spectral broadening are realized successfully in the Lu3(MgxAl2-x)(Al3-xSix)O12:Ce3+ solid solutions.The mechanism on the spectral broadening was carefully investigated by analying the variation of luminescence centers site and local symmetry degree.On the one hand,the single Ce3+ site differentiates into multiple luminescence centers at higher Mg2+-Si4+dopant content,which is ascribed to the compression and expansion of Ce-O bond caused by the formation of Mg-rich and Si-rich sites,respectively.On the other hand,cation-size mismatch in the second-sphere coordination induces the increasing polyhedron distortion of[CeO8],resulting in the degradation of local symmetry.These two factors could comprehensively interpret the spectral broadening of both excitation and emission bands in Lu3(MgxAl2-x)(Al3-xSix)O,2:Ce3+.According to the structural characteristics of garnet,we discuss the experience and design ideas of garnet-type compounds.New phosphors Lu2Mg2Al2SiO12:Ce3+ and Lu2MMg2Al3O9F3:Ce3+(M=Mg and Ca)have been developed by structural design on LuAG:Ce3+ via the co-substitution of Mg2+-Mg2+-Si4+→Lu3+-A13+-A13+ and M2+-Mg2+-F-→+Lu3+-A13+-02-.The crystal structure,luminescence properties and related mechanisms were investigated in detail.The cyan-green phosphor Lu2CaMg2l3O9F3:Ce3+ shows excellent thermal stability.The WLED device adopting the new cyan-green phosphor Lu2CaMg2Al3O9F3:Ce3+ and red phosphor(Ca,Sr)AlSiN3:Eu2+ exhibits a superhigh color rendering(Ra>95)with decreasing loss of cyan component.