Praseodymium sulfate was obtained by the precipitation method and the crystal structure was determined by Rietveld analysis. Pr
2(SO
4)
3 is crystallized in the monoclinic structure, space group
C2/
c, with cell parameters
a = 21.6052 (4),
b = 6.7237 (1) and
c = 6.9777 (1) Å, β = 107.9148 (7)°,
Z = 4,
V = 964.48 (3) Å
3 (
T = 150 °C). The thermal expansion of Pr
2(SO
4)
3 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
2(SO
4)
3 is stable in the temperature range of
T = 30–870 °C. The kinetics of the thermal decomposition process of praseodymium sulfate octahydrate Pr
2(SO
4)
3·8H
2O was studied as well. The vibrational properties of Pr
2(SO
4)
3 were examined by Raman and Fourier-transform infrared absorption spectroscopy methods. The band gap structure of Pr
2(SO
4)
3 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
3+ 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
2(SO
4)
3 belongs to the
3P
0 →
3F
2 transition at 640 nm.
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