Unconventional Luminescent Centers in Metastable Phases Created by Topochemical Reduction Reactions

Abstract

A low-temperature topochemical reduction strategy is used herein to prepare unconventional phosphors with luminescence covering the biological and/or telecommunications optical windows. This approach is demonstrated by using Bi(III)-doped Y2O3 (Y(2-x)Bi(x)O3) as a model system. Experimental results suggest that topochemical treatment of Y(2-x)Bi(x)O3 using CaH2 creates randomly distributed oxygen vacancies in the matrix, resulting in the change of the oxidation states of Bi to lower oxidation states. The change of the Bi coordination environments from the [BiO6] octahedra in Y(2-x)Bi(x)O3 to the oxygen-deficient [BiO(6-z)] polyhedra in reduced phases leads to a shift of the emission maximum from the visible to the near-infrared region. The generality of this approach was further demonstrated with other phosphors. Our findings suggest that this strategy can be used to explore Bi-doped or other classes of luminescent systems, thus opening up new avenues to develop novel optical materials.

Defective [Bi2O2]2+ Layers Exhibiting Ultrabroad Near‐Infrared Luminescence

“…This can be viewed as the occurrence of subvalent Bi in an undercoordinated geometry. [17] If V 000 Bi2 V O3 V 000 Bi2 defects exist in the Bi 1.95 O 2 layers, the valence state of Bi aroundt he vacancies does not notably change (Figure 4). We also tested the chemical states of Bi atoms using XPS;t he results suggest the absence of Bi metallica toms ( Figure S12 in the Supporting Information).…”

“…[4,30,31] These results indicate the existence of oxygen vacancies in Bi 2.14 Sr 0.75 Ta 2 O 9. Although thermogravimetric analysis in an oxidizing atmosphere can be used for the determination of oxygen stoichiometry in some oxygen-deficient systems, [17,18] it is difficult to apply it to oxygen-and cation-deficient Bi 2. 14 Figure S7 in the Supporting Information).…”

“…Many of today's prominentm aterials, such as high-transition-temperature superconductors, [2,3] solar-drivenp hotocatalysts, [4][5][6][7] photovoltaic materials, [8] metal-organic frame-works, [9][10][11] and ferroelectrics, [12][13][14] are imperfect systems with defect-induced, locally broken periodic structures,i nw hich imperfection plays ap ivotal role in governing, or at least affecting, their physiochemicalproperties. [15][16][17][18][19][20] Materials consisting of as equence of infinitely repeating stacksof[Bi 2 O 2 ] 2 + layers,such as bismuth-based cupratesuperconductors, bismuth oxyhalides, and Aurivillius phases, have attracted intensivea ttention because they exhibit an array of tantalizing properties, such as superconductivity,p hotocatalytic, photoluminescence (PL),a nd ferroelectricity. [4-7, 12-14, 21, 22] In recent years, it has been shownt hat the macroscopic physiochemicalp roperties of these materials are closely linked to their defect states.F or instance, Zeljkovic et al showed that nanoscale spatialv ariations in the pseudogap states in Bi 2 + y Sr 2Ày CaCu 2 O 8 + x are particularly correlated with the presence of apicalo xygen vacancies.…”

Theory‐Guided Defect Tuning through Topochemical Reactions for Accelerated Discovery of UVC Persistent Phosphors

“…Additionally, thermally‐ and light‐stimulated UVC emissions, combined with the thermoluminescence measurements, indicate that a higher concentration of deep traps exist in the reduced sample compared with the as‐synthesized one (Figures S19 and S25–S27, Supporting Information). We underscore that, although topochemical reactions have been employed for tuning the properties of some luminescent materials, for the first time it is used for the optimization of the properties of LPPs.…”

“…Considering that structural defects play a particularly important role in governing the trapping of excited charge carriers and then the afterglow properties, we reasoned that exploring facile chemical routes to defect tuning could offer an efficient way to rationally control and optimize the afterglow properties. Recently, low‐temperature topochemical reactions, involving mild deintercalation of constituent atoms while conserving the original structural features have emerged as a powerful technique to create a large number of metastable phases with unconventional electronic, magnetic, catalytic, and optical properties . Nevertheless, the employment of topochemical reactions for the control and optimization of the properties of LPPs have never been explored.…”