Halide perovskite nanocrystals have shown promise in high-performing solar cells and light-emitting diodes (LEDs). Incorporating thallium into these materials could provide additional bandgap tunability. One example of this effect is Cs₂AgTlBr₆, which has a very low bandgap of 0.95 eV. Thallium halide nanocrystals could also prove useful for radiation detectors and near-infrared (NIR) optical components. However, there are only a few examples of nanocrystal syntheses involving thallium.

Brian A. Korgel and colleagues, The University of Texas at Austin, USA, have developed colloidal syntheses of uniform TlBr and Tl₂AgBr₃ nanocrystals. The TlBr synthesis involves the injection of trimethylsilyl bromide (TMSBr) into heated solutions of thallium(III) or thallium(I) acetate in oleylamine, oleic acid, and octadecene. Tl₂AgBr₃ nanocrystals were obtained using an analogous reaction with additional silver(I) acetate.

The team found that the TlBr nanocrystals made with thallium(III) were uniform enough to self-assemble into face-centered cubic (FCC) superlattices. The band gaps of the TlBr and Tl₂AgBr₃ nanocrystals are both 3.1 eV, which is too large for most solar-cell and LED applications; however, the ability to deposit thin films on large-area surfaces might allow a new class of radiation scintillator materials to be developed.

• Synthesis of TlBr and Tl₂AgBr₃ Nanocrystals,
  Timothy Siegler, Tushti Shah, Daniel Houck, Mokshin Suri, Yangning Zhang, Brian A. Korgel,
  ChemNanoMat 2020.
  https://doi.org/10.1002/cnma.202000100