Effect of Covalence and Degree of Cation Order on the Luminous Efficacy of Mn 4+ Luminescence in the Double Perovskites, Ba 2 B TaO 6 ( B = Y, Lu, Sc).

The spectroscopic properties of the Mn 4+ ion are investigated in the series of isostructural double perovskite compounds, Ba 2 B TaO 6 ( B = Y, Lu, Sc). A comparison of these properties highlights the influence of covalent bonding within the perovskite framework and the degree of order between the B 3+ -Ta cations on the energy and intensity of the Mn 4+2 E → 4 A 2 emission transition (R-line). These two parameters of the emission spectrum are of importance for practical application since they determine the phosphor luminous efficacy. The influence of covalent bonding within the corner shared BO 6/2 and TaO 6/2 perovskite framework on the energy of the R-line energy is investigated. From the spectroscopic data, we have derived information on the influence of the degree of order between the B 3+ and Ta 5+ cations on the intensity of the R-line. The lowest energy and the highest intensity of the R-line are found in the double perovskite, Ba 2 ScTaO 6 . The purpose of this work is to propose for first time an explanation of these effects in the considered double perovskites. The obtained results are useful guidelines for practical improvement and tuning of key parameters of phosphors to the desired values.