Spectroscopic and crystal field analysis of absorption and photoluminescence properties of red phosphor CaAl12O19:Mn4+ modified by MgO

The spectroscopic properties of a series of red phosphors with general composition of CaAl12O19:yMn(4+) and (Ca1-xAl12O19, xMgO):yMn(4+) (x = 0-1, y = 0.001-1.5%) synthesized by a modified solid state method in air have been investigated in detail. Addition of MgO is necessary for Mn4+ charge compensation and leads to the formation of separate crystal phases of Al2O3 and MgAl2O4, which was confirmed by the XRD studies. Enhancement of Mn4+ luminescence with increasing content of MgO was observed and a mechanism for explanation of this phenomenon is suggested. For an analysis of the crystal phases and luminescent efficiency of the phosphors in the prepared series, crystal field calculations of the Mn4+ energy levels have been performed. This theoretical approach allowed for assigning the observed excitation and emission spectra. Red shift of the Mn4+ luminescence with increasing concentration of Mg ions is explained from the point of view of enhanced nephelauxetic effect after doping. (C) 2010 Elsevier B.V. All rights reserved.