Unravelling the 6sp ← 6s absorption spectra of Bi(III) complexes

We report a spectroscopic and computational study that investigates the absorption spectra of Bi(III) complexes, which often show an absorption band in the UV region (∼270-350 nm) due to 6sp ← 6s transitions. We investigated the spectra of three simple complexes, [BiCl5]2-, [BiCl6]3- and [Bi(DMSO)8]3+, which show absorption maxima at 334, 326 and 279 nm due to 3P1 ← 1S0 transitions. Theoretical calculations based on quasi-degenerate N-electron valence perturbation theory to second order (QD-NEVPT2) provide an accurate description of the absorption spectra when employing CAS(2,9) wave functions. We next investigated the absorption spectra of the [Bi(NOTA)] complex (H3NOTA = 1,4,7-triazacyclononane-1,4,7-triacetic acid), which forms ternary complexes [Bi(NOTA)X]- (X = Cl, Br or I) in the presence of excess halide in aqueous solutions. Halide binding has an important impact on the position of the 3P1 ← 1S0 transition, which shifts progressively to longer wavelengths from 282 nm ([Bi(NOTA)]) to 298 nm (X = Cl), 305 nm (X = Br) and 325 nm (X = I). Subsequent QD-NEVPT2 calculations indicate that this effect is related to the progressive stabilization of the spin-orbit free states associated with the 6s16p1 configuration on increasing the covalent character of the metal-ligand(s) bonds, rather than with significant differences in spin-orbit coupling (SOC). These studies provide valuable insight into the coordination chemistry of Bi(III), an ion with increasing interest in targeted alpha therapy due to the possible application of bismuth isotopes bismuth-212 (212Bi, t1/2 = 60.6 min) and bismuth-213 (213Bi, t1/2 = 45.6 min).

Controllable solute-diffusion gel-growth of BCHT: an effective approach towards large functional material single crystal synthesis

An underutilized, but highly advantageous, method of growing functional-single-crystals, the gel-growth technique, is highlighted. Large nonlinear optical crystals, BCHT, were grown and their dehydration phase-transformation to β-BTC were studied.

Solution-Processed Bi2S3 Photoresistor Film To Mitigate a Trade-off between Morphology and Electronic Properties

Bismuth sulfide (Bi₂S₃) is an attractive 2D layered, visible-light-absorbing semiconductor composed of nontoxic, abundant elements. Improving the quality of a Bi₂S₃ film for device applications while maintaining its intrinsic electronic properties is a challenge, as conventional film fabrication processes require a trade-off due to the uncontrolled nucleation and growth steps. We report a novel procedure for Bi₂S₃ film formation involving spin-coating of a precursor solution of bismuth acetate and thiourea, followed by crystallization under diluted H₂S gas. This two-step process produced a large-grained (<400 nm), smooth (surface roughness = 1.7 nm), and highly pure Bi₂S₃ film with a layer-stacked structure on a substrate. Most importantly, the film exhibited a moderate Hall effect electron mobility (∼7 cm² V^-1 s^-1) and excellent performance as a photoresistor with improved photoconductance and on-off ratio compared with those prepared by conventional methods. Our approach provides a versatile route for the development of metal sulfide semiconductors for optoelectronic devices.