• Structural analysis and phase transformation of Š 4 A 3 $ were studied. • Transformation temperature from Pcc 2 to I 23 was established. • Eu3+ ions addition can influence the crystal-field splitting of both Š 4 A 3 $ phases. • A promising platform to the crystal structure regulation of related phase-change materials was set up. Strontium sulfoaluminate (Sr 4 Al 6 O 12 SO 4 or Š 4 A 3 $) is a polymorph that exists at low and high temperatures and presents a reversible phase-change phenomenon. In this paper, Ga3+ ions are successfully incorporated into Al3+ site of the Š 4 A 3 $ structure, and the phase transformation mechanism from Pcc 2 to I 23 as well as the related influence on the crystal-field splitting of Eu3+ ions of the two phases are studied. Experimental results reveal that the addition of Ga3+ ions facilitates the transformation from Pcc 2 to I 23, and the metastable I 23 phase is successfully reserved at low temperature for Ga3+-doped content above 20 at%. Structural information, DSC, SEM-EDS, and structural disorder in infrared spectra further verify the phenomenon. Moreover, Eu3+ ions emission intensity of c -Š 4 A 3 $ phase in fluorescence spectra is much more intense than that of o -Š 4 A 3 $ phase with a complex spectral distribution. That is to say, the incorporation of Eu3+ ions mainly influences the crystal-field splitting of Pcc 2 and I 23 phases. [ABSTRACT FROM AUTHOR]