Synthesis and Luminescent Properties of Bismuth Titanates Bi1.6HoxTi2O7 – δ and Bi1.6Mg0.1HoxTi2O7 – δ

Abstract

where x = 0, 0.01, 0.05, and 0.1, and Bi 1.5 Ho x Ti 2 O 7 -δ , where x = 0.25 and 0.5, have been synthesized and their structural, optical, and luminescence properties have been studied. As a result of analyzing the data obtained experimentally and the available theoretical data, it is shown that the intrinsic luminescence of the samples is due to the O2p ↔ Bi6p and Bi6s ↔ Bi6p electron transitions and the impurity luminescence is due to the f-f transitions in Ho 3+ and the O2p → Ho 3+ charge transfer.

Photocatalytic Properties of Bi2–xTi2O7–1.5x (x = 0, 0.5) Pyrochlores: Hybrid DFT Calculations and Experimental Study

“…Nanosized powders of the bismuth titanate pyrochlores Bi 1.5 Ti 2 O 6.25 and Bi 2 Ti 2 O 7 were synthesized via the coprecipitation technique as was performed in our previous work for other pyrochlore compositions. , We used Bi­(NO 3 ) 3 ·5H 2 O (99.9%) and Ti­( i -OC 3 H 7 ) 4 (99.9%) as the sources of the elements. The calculated amounts of titanium tetraisopropoxide and bismuth nitrate crystallohydrate were weighed.…”

“…The observed scatter might be caused by different methods of sample synthesis, which affects the size and morphology of particles, and the different techniques of spectroscopic measurement. Moreover, the known tendency of bismuth titanate to form a nonstoichiometric pyrochlore composition − affected the observed characteristics and sometimes the considered titanate compound “Bi 2 Ti 2 O 7 ”, in fact, had a Bi-deficient composition. , The photocatalytic activity of the prepared BTO samples was investigated by the decomposition of organic dyes rhodamine B, ,− , methyl orange, ,,,, and methylene blue , and for water splitting to produce molecular hydrogen. ,, The high photocatalytic activity of BTO in the visible range was found in comparison with anatase, due to the smaller band gap of the pyrochlore resulting in a greater absorption of light.…”

Structural, Optical, Luminescence, and Electrical Properties of Eu/Li- and Eu/Na-Codoped Magnesium Bismuth Niobate Pyrochlores

“…The integral PCL intensity shows the regular growth at the Eu concentration increase in the whole range of the investigated dopant concentrations (Figure c). The usually observed concentration quenching ,,, for doped systems with an increase in the dopant concentration does not appear in this case because of the second phase formation.…”

“…19,20 However, according to the data for the Bi 2−x Eu x Ti 2 O 7 and Bi 1.5−x M x Eu 0.5 Ti 2 O 7 (M = Gd and Y) pyrochlore thin films, the maximum photoluminescence efficiency (PLE) is predetermined by the host band gap energy mainly. 8,9 In our previous work, 21 the weak influence of Mg 2+ substitution in the host on luminescence properties for the Bi 1.6 Ho x Ti 2 O 7−δ and Bi 1.6 Mg 0.1 Ho x Ti 2 O 7−δ pyrochlores was determined. According to works, 22−24 Li + , as well as Bi 3+ , enhances the luminescence properties of the pyrochlores due to modification of the local crystal structure and creation of a charge imbalance compensated by the host material.…”

“…Bismuth-based pyrochlores attract attention due to their dielectric properties, − mixed electronic–ionic conductivity, , photoluminescence properties, − and photocatalytic activity. − These properties proceed with both structural features ( A 2 B 2 O 6 O′) and complex tiered electron structures caused by the 6s 2 lone pair of Bi 3+ . The polarizability created by Bi 3+ , as well as the dopant atom distribution in the bismuth sublattice ( A 2 O′), predetermines the dielectric properties of the ceramics mainly. ,,− In the high-temperature region ( T ≥ 100–200 °C), mixed electronic–ionic conductivity is caused by the structural behavior of the host. − , In the pyrochlores, Bi 3+ promotes high electron mobility due to the cooperative action of the 6s and 6p orbitals, influencing the band structure, and provides the stereochemical activity and, as a result, photocatalytic properties. , In luminescent materials, Bi 3+ usually acts as a sensitizer ion, which changes the local crystal structure and transfers its excitation energy to the rare-earth (RE) ion in the matrix, efficiently increasing the photoluminescence intensity. , However, according to the data for the Bi 2– x Eu x Ti 2 O 7 and Bi 1.5– x M x Eu 0.5 Ti 2 O 7 ( M = Gd and Y) pyrochlore thin films, the maximum photoluminescence efficiency (PLE) is predetermined by the host band gap energy mainly. , In our previous work, the weak influence of Mg 2+ substitution in the host on luminescence properties for the Bi 1.6 Ho x Ti 2 O 7−δ and Bi 1.6 Mg 0.1 Ho x Ti 2 O 7−δ pyrochlores was determined. According to works, − Li + , as well as Bi 3+ , enhances the luminescence properties of the pyrochlores due to modification of the local crystal structure and creation of a charge imbalance compensated by the host material.…”