Na2RE2TeO4(BO3)2 (RE = Y, Dy–Lu): Luminescent and Structural Studies on a Series of Mixed Metal Borotellurates

The first examples of metal borotellurates, namely, Na2RE2TeO4(BO3)2 (RE = Y, Dy–Lu) have been prepared by using solid-state reactions. They possess similar structures and crystallize in space group P21/c (No. 14). These compounds feature a novel [RE2TeO4(BO3)2]2– 3D network structure composed of linear [TeO4(BO3)2]8– anions interconnected by RE3+ ions with the voids of the network filled by the Na+ ions. They exhibit high thermal stability (higher than 800 °C). Results of magnetic measurements on Dy, Ho, and Er compounds indicate that they display weak antiferromagnetic interaction between RE­(III) centers. Luminescent studies show that Na2Er2TeO4(BO3)2 has a strong emission at 1.562 μm with a wide fwhm (70 nm) and moderate lifetime (0.18 ms), whereas Na2Yb2TeO4(BO3)2 has a strong NIR region emission around 1.02 μm. Furthermore, UV–vis-NIR absorption spectra, infrared spectra, and DFT calculations for the Y compound as a representative were also accomplished.