1 research outputs found
Unexpected Roles of Interstitially Doped Lithium in Blue and Green Light Emitting Y<sub>2</sub>O<sub>3</sub>:Bi<sup>3+</sup>: A Combined Experimental and Computational Study
To enhance the photoluminescence
of lanthanide oxide, a clear understanding of its defect chemistry
is necessary. In particular, when yttrium oxide, a widely used phosphor,
undergoes doping, several of its atomic structures may be coupled
with point defects that are difficult to understand through experimental
results alone. Here, we report the strong enhancement of the photoluminescence
(PL) of Y<sub>2</sub>O<sub>3</sub>:Bi<sup>3+</sup> via codoping with
Li<sup>+</sup> ions and suggest a plausible mechanism for that enhancement
using both experimental and computational studies. The codoping of
Li<sup>+</sup> ions into the Y<sub>2</sub>O<sub>3</sub>:Bi<sup>3+</sup> phosphor was found to cause significant changes in its structural
and optical properties. Interestingly, unlike previous reports on
Li<sup>+</sup> codoping with several other phosphors, we found that
Li<sup>+</sup> ions preferentially occupy interstitial sites of the
Y<sub>2</sub>O<sub>3</sub>:Bi<sup>3+</sup> phosphor. Computational
insights based on density functional theory calculations also indicate
that Li<sup>+</sup> is energetically more stable in the interstitial
sites than in the substitutional sites. In addition, interstitially
doped Li<sup>+</sup> was found to favor the vicinity of Bi<sup>3+</sup> by an energy difference of 0.40 eV in comparison to isolated sites.
The calculated DOS showed the formation of a shallow level directly
above the unoccupied 6p orbital of Bi<sup>3+</sup> as the result of
interstitial Li<sup>+</sup> doping, which may be responsible for the
enhanced PL. Although the crystallinity of the host materials increased
with the addition of Li salts, the degree of increase was minimal
when the Li<sup>+</sup> content was low (<1 mol %) where major
PL enhancement was observed. Therefore, we reason that the enhanced
PL mainly results from the shallow levels created by the interstitial
Li<sup>+</sup>