Coordination environment evolution of Eu3+ during the dehydration and re-crystallization processes of Sm1-xEu x[B9O13(OH)4]·H2O by photoluminescent characteristics

作者：Yi X.; Cong R.; Yue M.; Chai Y.; Jiang P.; Gao W.; Yang T.^*

来源：Dalton Transactions, 2013, 42(46): 16318-16327.

There are limited photoluminescence (PL) studies for rare earth borates with crystalline water molecules, which are usually supposed to have low PL efficiency because the vibrations of H2O or -OH may lead to emission quenching. We investigated the PL properties of Sm1-xEu x[B9O13(OH)4]·H2O (x = 0-1.00) and their dehydrated products α-Sm1-xEu xB5O9. There is no quenching effect in those studied polyborates because the large borate ionic groups isolate the Eu 3+ activators very well. Sm3+ and Eu3+ are basically separated luminescent activators. Comparatively, Sm3+ shows a very small emission intensity, which can be almost ignored, therefore our interest is focused on the Eu3+ luminescence. By TG-DSC and powder XRD experiments, we defined three weight-loss steps for Eu[B9O 13(OH)4]·H2O and a re-crystallization process to α-EuB5O9, during which luminescent spectra of Eu3+ are recorded. It shows an interesting variety and therefore is a good medium to understand the coordination environment evolution of Eu3+, even for the intermediate amorphous phase. In fact, the coordination symmetry of Eu3+ in the amorphous state is the lowest. The high efficiency of the f-f transitions and large R/O value (3.8) imply this amorphous phase is potentially a good red-emitting UV-LED phosphor. Anhydrous α-EuB5O9 shows the highest luminescent efficiency excited by Eu3+ CT transition. In addition, α-Sm 1-xEuxB5O9 was synthesized by a sol-gel method directly for the first time, and α-EuB5O 9 shows superior PL properties due to its better crystallinity. A lot of hydrated polyborates with crystalline water molecules remain unexplored and our study shows their potential as good phosphors.