Micro-spherical MAl2O4: Eu2+ (M=Ca; Sr) phosphors: fast sol-gel route to monodisperse size distribution and monoclinic lattice structure to high efficiency

A propylene oxide (PO)-driven fast sol-gel route followed with a post high temperature calcination were utilized to synthesize Ca x Sr 1- x Al 2 O 4 : Eu 2+ cationic solid solution phosphors with micro-spherical morphologies and improved internal quantum efficiencies. The polyethylene oxide (PEO) was also employed to induce the phase separation of Ca x Sr 1- x Al 2 O 4 : Eu 2+ precursors to get monodispersed spherical morphologies in the sol-gel system. Benefit from uniform copolymerization of each chemical components and pyrolysis of organic matter, Ca, Sr, Al and O were homogenously distributed in the produced Ca x Sr 1- x Al 2 O 4 : Eu 2+ cage like microspheres. It helps to efficiently trap incident light and to improve the PL efficiencies. By changing the ratio of Ca/Sr, infinite solid solution polycrystalline phosphors, Ca x Sr 1- x Al 2 O 4 : Eu 2+ microspheres with x  = 0~1, can be obtained and their PL emission can be gradually tuned from green to white to blue. Micro-spherical SrAl 2 O 4 : Eu 2+ , Ca x Sr 1- x Al 2 O 4 : Eu 2+ and CaAl 2 O 4 : Eu 2+ phosphors exhibited internal quantum efficiencies as high as 71.1, 35.3~45.9 and 75.3%, respectively. Graphical abstract