Influence of structural distortions upon photoluminescence properties of Eu3+ and Tb3+ activated Na3Ln(BO3)2 (Ln=Y, Gd) borates

The comparative study of the structure and photoluminescence (PL) properties of the Eu3+ and Tb3+ activated Na3Ln(BO3)2, with Ln=Y, Gd, showed the important role of the host lattice structure upon PL. Higher emission intensities of Eu3+ and Tb3+ are observed for Na3Gd(BO3)2 than for Na3Y(BO3)2, through direct Eu3+ excitation at 395 nm for Eu3+ doped borates, and through Gd3+ excitation around 280 nm for Tb3+ doped borates. This higher performance for Na3Gd(BO3)2 is due to the less regular environment of Eu3+ (Tb3+) in the Gd sites than in the Y sites and to energy transfer from Gd3+ to Eu3+(Tb3+). The smaller critical concentration in Na3Ln1−xTbx(BO3)2 observed for Ln=Gd, x=0.5, compared to x=0.6 for Ln=Y, is explained by shorter Ln–Ln distances (4.11 Å for Gd–Gd vs. 4.59 Å for Y–Y). Both Na3Y0.4Tb0.6(BO3)2 and Na3Gd0.5Tb0.5(BO3)2 show intense green emission under UV excitation.