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$\mathrm{Zn}{M}_{2}^{III}{\mathrm{O}}_{4}$ (${M}^{III}=\text{Co}$, Rh, Ir) spinels have been recently identified as promising $p$-type semiconductors for transparent electronics. However, discrepancies exist in the literature regarding their fundamental optoelectronic properties. In this paper, the electronic structures of these spinels are directly investigated using soft/hard x-ray photoelectron and x-ray absorption spectroscopies in conjunction with density functional theory calculations. In contrast to previous results, ${\mathrm{ZnCo}}_{2}{\mathrm{O}}_{4}$ is found to have a small electronic band gap with forbidden optical transitions between the true band edges, allowing for both bipolar doping and high optical transparency. Furthermore, increased $d\ensuremath{-}d$ splitting combined with a concomitant lowering of Zn $s/p$ conduction states is found to result in a ${\mathrm{ZnCo}}_{2}{\mathrm{O}}_{4}\phantom{\rule{0.28em}{0ex}}(\text{ZCO})l{\mathrm{ZnRh}}_{2}{\mathrm{O}}_{4}\phantom{\rule{0.28em}{0ex}}(\text{ZRO})\ensuremath{\approx}{\mathrm{ZnIr}}_{2}{\mathrm{O}}_{4}\phantom{\rule{0.28em}{0ex}}(\text{ZIO})$ band gap trend, finally resolving long-standing discrepancies in the literature.

We present an in-depth first-principles study of the lattice dynamics of the tin sulphides SnS2, Pnma and π-cubic SnS and Sn2S3. An analysis of the harmonic phonon dispersion and vibrational density of states reveals phonon bandgaps between low- and high-frequency modes consisting of Sn and S motion, respectively, and evidences a bond-strength hierarchy in the low-dimensional SnS2, Pnma SnS and Sn2S3 crystals. We model and perform a complete characterisation of the infrared and Raman spectra, including temperature-dependent anharmonic linewidths calculated using many-body perturbation theory. We illustrate how vibrational spectroscopy could be used to identify and characterise phase impurities in tin sulphide samples. The spectral linewidths are used to model the thermal transport, and the calculations indicate that the low-dimensional Sn2S3 has a very low lattice thermal conductivity, potentially giving it superior performance to SnS as a candidate thermoelectric material.