Article pubs.acs.org/IC
β‑RE1−xBixB3O6 (RE = Sm, Eu, Gd, Tb, Dy, Ho, Er, Y): Bi3+ Substitution Induced Formation of Metastable Rare Earth Borates at Ambient Pressure Xiaorui Sun, Ruirui Yang, Rixiang Song, Song Leng, Pengfei Jiang, Wenliang Gao, Rihong Cong,* and Tao Yang* College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, People’s Republic of China S Supporting Information *
ABSTRACT: There emerge great interests in the syntheses of metastable polyborates; however, most are involved with the high-pressure technique. A facile method to synthesize metastable rare earth borates at ambient pressure is eagerly required for the large-scale production and property investigation. Here we demonstrate the critical role of Bi3+ substitutions in the stabilization of metastable β-REB3O6 (RE = Sm, Eu, Gd, Tb, Dy, Ho, Er, and Y) at ambient pressure, where the Bi3+-to-RE3+ substitutions would efficiently reduce the synthetic temperatures to 735−820 °C, well below the upper limit of thermodynamically stable window (840−980 °C). Partial solid solutions of β-RE1−xBixB3O6 were prepared, and the ranges of the solution were also studied experimentally. The thermal behaviors of β-RE0.8Bi0.2B3O6 were investigated by differential thermal analyses and powder X-ray diffraction, and they were divided into two categories; that is, β-RE0.8Bi0.2B3O6 (RE = Sm, Eu, Gd) transfers to α-RE0.8Bi0.2B3O6 with further increasing the temperature to 950 °C, while β-RE0.8Bi0.2B3O6 (RE = Tb, Dy, Ho, Er, and Y) decomposes into hexagonal REBO3 and B2O3. In particular, the allowed concentration of Bi3+ in β-Gd1−xBixB3O6 was 0.10 ≤ x ≤ 0.25, and these samples show bright blue emissions under UV excitation, which suggests the high efficiency of light absorption and high potential as phosphors with further doping of other activators.
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(RE = Dy, Ho),31,32 α-RE2B4O9 (RE = Sm−Ho),33,34 β-RE2B4O9 (RE = Dy, Gd),35,36 and RE3B5O12 (RE = Er−Lu).37 The great success by applying high pressure to borate system benefits from the flexible coordination behaviors for boron as BO3, BO4, and their diverse combinations. The disadvantage is also obvious that the realization of high-pressure synthesis usually requires a small and sealed vessel; thus, the resultant sample is in a small quantity, and sometimes comprises a high level of structural defects. Our idea is to exploit the similarity between bismuth and RE cations in structural chemistry to realize the high-pressure polymorph of RE borates under ambient pressure. This is inspired by the successful preparation of δ-Bi1−xRExB3O6 (RE = La, Ce, Pr, Nd and 0.01 ≤ x ≤ 0.15) under ambient pressure,38 while the host δ-BiB3O6 was originally synthesized by highpressure/high-temperature method.39 Under ambient pressure, δ-BiB3O6 was supposed to be thermodynamically stable at a relatively low temperature (
