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Register a new userPossible centers of broadband near-IR luminescence in bismuth-doped solids: $Bi^{+}$, Bi$_5^{3+}$, and Bi$_4^0$
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Subvalent bismuth centers (interstitial $Bi^{+}$ ion, Bi$_5^{3+}$ cluster ion, and Bi$_4^0$ cluster) are examined as possible centers of broadband near-IR luminescence in bismuth-doped solids on the grounds of quantum-chemical modeling and experimental data.
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Experimental and computer-modeling studies of spectral properties of crystalline AgCl doped with metal bismuth or bismuth chloride are performed. Broad near-IR luminescence band in the 0.8--1.2mkm range with time dependence described by two exponential components corresponding to the lifetimes of 1.5 and 10.3mks is excited mainly by 0.39--0.44mkm radiation. Computer modeling of probable Bi-related centers in AgCl lattice is performed. On the basis of experimental and calculation data a conclusion is drawn that the IR luminescence can be caused by Bi^+ ion centers substituted for Ag^+ ions.
A comparative first-principles study of possible bismuth-related centers in TlCl and CsI crystals is performed and the results of computer modeling are compared with the experimental data. The calculated spectral properties of the bismuth centers suggest that the IR luminescence observed in TlCl:Bi is most likely caused by Bi--Vac(Cl) centers (Bi^+ ion in thallium site and a negatively charged chlorine vacancy in the nearest anion site). On the contrary, Bi^+ substitutional ions and Bi_2^+ dimers are most likely responsible for the IR luminescence observed in CsI:Bi.
Experimental and theoretical studies of spectral properties of chalcogenide Ge-S and As-Ge-S glasses and fibers are performed. A broad infrared (IR) luminescence band which covers the 1.2-2.3~$mu$m range with a lifetime about 6~$mu$s is discovered. Similar luminescence is also present in optical fibers drawn from these glasses. Arsenic addition to Ge-S glass significantly enhances both its resistance to crystallization and the intensity of the luminescence. Computer modeling of Bi-related centers shows that interstitial Bi$^+$ ions adjacent to negatively charged S vacancies are most likely responsible for the IR luminescence.
Recent progress in the field of topological states of matter(1,2) has largely been initiated by the discovery of bismuth and antimony chalcogenide bulk topological insulators (TIs)(3-6), followed by closely related ternary compounds(7-16) and predictions of several weak TIs(17-19). However, both the conceptual richness of Z$_2$ classification of TIs as well as their structural and compositional diversity are far from being fully exploited. Here, a new Z$_2$ topological insulator is theoretically predicted and experimentally confirmed in the $beta$-phase of quasi-one-dimensional bismuth iodide Bi$_4$I$_4$. The electronic structure of $beta$-Bi$_4$I$_4$, characterized by Z$_2$ invariants (1;110), is in proximity of both the weak TI phase (0;001) and the trivial insulator phase (0;000). Our angle-resolved photoemission spectroscopy measurements on the (001) surface reveal a highly anisotropic band-crossing feature located at the point of the surface Brillouin zone and showing no dispersion with the photon energy, thus being fully consistent with the theoretical prediction.
First-principle study of bismuth-related oxygen-deficient centers ($=$Bi$cdots$Ge$equiv$, $=$Bi$cdots$Si$equiv$, and $=$Bi$cdots$Bi$=$ oxygen vacancies) in Bi$_2$O$_3$-GeO$_2$, Bi$_2$O$_3$-SiO$_2$, Bi$_2$O$_3$-Al$_2$O$_3$-GeO$_2$, and Bi$_2$O$_3$-Al$_2$O$_3$-SiO$_2$ hosts is performed. A comparison of calculated spectral properties of the centers with the experimental data on luminescence emission and excitation spectra suggests that luminescence in the 1.2-1.3 $mu$m and 1.8-3.0 $mu$m ranges in Bi$_2$O$_3$-GeO$_2$ glasses and crystals is likely caused by $=$Bi$cdots$Ge$equiv$ and $=$Bi$cdots$Bi$=$ centers, respectively, and the luminescence near 1.1 $mu$m in Bi$_2$O$_3$-Al$_2$O$_3$-GeO$_2$ glasses and crystals may be caused by $=$Bi$cdots$Ge$equiv$ center with (AlO$_4$)$^-$ center in the second coordination shell of Ge atom.
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