| Summary: | Praseodymium sulfate was obtained by the precipitation method and the crystal structure was determined by Rietveld analysis. Pr<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> is crystallized in the monoclinic structure, space group <i>C</i>2/<i>c</i>, with cell parameters <i>a</i> = 21.6052 (4), <i>b</i> = 6.7237 (1) and <i>c</i> = 6.9777 (1) Å, β = 107.9148 (7)°, <i>Z</i> = 4, <i>V</i> = 964.48 (3) Å<sup>3</sup> (<i>T</i> = 150 °C). The thermal expansion of Pr<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> is strongly anisotropic. As was obtained by XRD measurements, all cell parameters are increased on heating. However, due to a strong increase of the monoclinic angle β, there is a direction of negative thermal expansion. In the argon atmosphere, Pr<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> is stable in the temperature range of <i>T</i> = 30–870 °C. The kinetics of the thermal decomposition process of praseodymium sulfate octahydrate Pr<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>·8H<sub>2</sub>O was studied as well. The vibrational properties of Pr<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> were examined by Raman and Fourier-transform infrared absorption spectroscopy methods. The band gap structure of Pr<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> was evaluated by ab initio calculations, and it was found that the valence band top is dominated by the p electrons of oxygen ions, while the conduction band bottom is formed by the d electrons of Pr<sup>3+</sup> ions. The exact position of ZPL is determined via PL and PLE spectra at 77 K to be at 481 nm, and that enabled a correct assignment of luminescent bands. The maximum luminescent band in Pr<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> belongs to the <sup>3</sup>P<sub>0</sub> → <sup>3</sup>F<sub>2</sub> transition at 640 nm.
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