“…The value of R c was calculated to be 12.69 Å (>5 Å), suggesting that the electric multipolar interaction plays a major part in the energy transfer process from Eu 2+ to Mn 2+ ions. Furthermore, to better understand the ET process, the following formula was calculated to judge the type of electric multipolar interaction: 40–42 I S0 / I S ∝ C n /3 where I S0 is the emission intensity of the Na 0.8 Al 11 O 17 :0.20Eu 2+ phosphor, I S is the emission intensity of the Na 0.8 Al 11− y O 17 :0.20Eu 2+ , y Mn 2+ phosphors at the contraction x , C represents the total concentration of Eu 2+ and Mn 2+ ions, and n denotes the type of electric multipolar interaction. The three kinds 6, 8 and 10 of n values corresponded to the dipole–dipole, dipole–quadruple, and quadruple–quadruple interactions, respectively.…”