INFLUENCE OF IMPURITIES ON THE LUMINESCENCE QUANTUM EFFICIENCY OF THELAMP PHOSPHOR (CE, GD, TB)MGB5O10

The influence of impurities on the luminescence quantum efficiency of Ce0.2Gd0.6Tb0.2MgB5O10 has been studied. Low concentrations of Pr3+, N d3+, Dy3+, Ho3+, and Er3+ do not compete efficiently with Gd3+ and Tb3 + for the excitation energy on the Ce3+ ions. However, the luminescenc e efficiency of Ce3+ is strongly decreased by Sm3+ and Eu3+ due to an electron transfer process. The luminescence efficiency of Ce3+ is also decreased by Cr2+, Mn2+, Fe2+, and Ni2+ due to energy transfer to the se ions. In the case of Cr3+ the luminescence efficiency of Ce3+ is qu enched due to competitive absorption. The luminescence efficiency of G d3+ is strongly decreased by Cr2+, Mn2+, and Fe2+ due to energy transf er to these ions. The excitation energy migrates over the Gd3+ ions. T herefore, low concentrations of impurities have a considerable effect on the luminescence efficiency of Gd3+. Since there is no energy migra tion over the Tb3+ ions, small concentrations of impurities have a lim ited effect on the luminescence efficiency of Tb3+.