Fluorescence enhancement mechanism in phosphor CaAl12O19:Mn4+ modified with alkali-chloride

CaMAl_12-xO₁₉:xMn⁴⁺ (M is one or more of K⁺, Na⁺, Li⁺) materials were prepared by a combustion method in air atmosphere. The Mn concentration, the influence of one or more alkali-chloride on luminescence properties, crystal phases and surface morphology of the samples were investigated. The fluorescence intensity of CaAl_11.98O₁₉:0.02Mn⁴⁺ modified by combining three kinds of alkali-chloride can be enhanced by three times. Blue shift of CaMAl_12-xO₁₉:xMn⁴⁺ luminescence is explained from the point of view of enhancing electron cloud deformation after doping. Alkali metal ions were beneficial to form hexagonal CaAl₁₂O₁₉ while there was certain inhibition to other peak strengths. The mechanism is the coexistence of alkali-chloride replacing Al³⁺ or Ca²⁺ instead of Mn²⁺ based on the difference of cation radius, this would increase the luminous centre of Mn⁴⁺ and provide charge compensation at the same time. The size of red phosphors was 5-10 μm, which is useful for light emitting diode applications.