10.1021/jp502996t.s004
Mathijs de Jong
Mathijs de
Jong
Andries Meijerink
Andries
Meijerink
Robert
A. Gordon
Robert
A.
Gordon
Zoila Barandiarán
Zoila
Barandiarán
Luis Seijo
Luis
Seijo
Is Bi<sup>2+</sup> Responsible for the Red-Orange Emission of Bismuth-Doped
SrB<sub>4</sub>O<sub>7</sub>?
American Chemical Society
2014
SrB 4O
EPR
Bi concentration
ZPL
Equivalent ab initio calculations
Ab initio calculations
emission
ab initio calculations
XANES
luminescence
2014-05-08 00:00:00
Dataset
https://acs.figshare.com/articles/dataset/Is_Bi_sup_2_sup_Responsible_for_the_Red_Orange_Emission_of_Bismuth_Doped_SrB_sub_4_sub_O_sub_7_sub_/2298904
Red-orange luminescence
from bismuth-doped SrB<sub>4</sub>O<sub>7</sub> has previously been
reported and assigned to 6p-6p transitions of divalent Bi. To provide
support for this assignment and for the stability of this unusual
valence state of Bi, we report here results from low-temperature luminescence
spectroscopy, X-ray absorption near-edge structure (XANES) spectroscopy,
electron paramagnetic resonance (EPR) spectroscopy, and wave function
based ab initio calculations. Low-temperature luminescence spectra
reveal zero-phonon lines (ZPLs) in excitation and emission spectra,
allowing an accurate determination of the energies for the electronic
transitions. The influence of the Bi concentration on the emission
intensity is shown to be small, and only a small increase of the red-orange
emission is observed upon raising the nominal Bi concentration from
0.02% (200 ppm) to 2%. This result indicates that only a very low
concentration of Bi<sup>2+</sup> can be incorporated in SrB<sub>4</sub>O<sub>7</sub>. This observation is supported by EPR experiments,
which do not show a signal that can be assigned to Bi<sup>2+</sup>, and by XANES experiments showing that most Bi is in the trivalent
state. An upper limit of the Bi<sup>2+</sup> concentration is estimated
to be 20 ppm. Ab initio calculations on the (BiO<sub>9</sub>)<sup>16–</sup> cluster embedded in SrB<sub>4</sub>O<sub>7</sub> give energies for excited states that are close to the experimentally
observed energies. Also, the luminescence lifetime for the red-orange
emission (∼12 μs) is consistent with the lifetime for
6p-6p emission calculated for the Bi<sup>2+</sup> emission (3.5 μs).
Equivalent ab initio calculations for Bi<sup>2+</sup> luminescence
are very far from the experimental results, providing independent
evidence and additional support for the interpretation of stable Bi<sup>2+</sup> species being responsible for the red-orange luminescence.
The calculations provide a new interpretation of the third excitation
band, which is not due to a <sup>2</sup>S<sub>1/2</sub> state of the
6s<sup>2</sup>7s configuration of Bi<sup>2+</sup>, as previously assumed,
but is due to a state with important characters of 6s6p<sup>2</sup>–<sup>4</sup>P (63%) and doublets of the 6s6p<sup>2</sup>,
6s<sup>2</sup>6d, and 6s<sup>2</sup>6p configurations; its higher
intensity is due to its character of parity-allowed 6s → 6p
and 6p → 6d excitations.