Integrating multiple emission centers for photoluminescence regulation in copper–antimony/bismuth halides

Abstract

Zero-dimensional (0-D) heterometallic halides containing multiple metal–halogen units are emerging optoelectronic materials with diverse photophysical properties. In this work, eight 0-D ionic compounds, including heterometallic halides [(Tp)₃CuX]MX₆ (Tp = protonated thiomorpholine; X = Cl, Br; M = Sb, Bi), monometallic halides (Tp)₃MX₆ (M = Bi when X = Cl; M = Bi, Sb when X = Br), and (Tp)Br have been synthesized. Their structures and photoluminescence have been comparatively studied. Inserting a CuX unit into the three (Tp)⁺ cation moieties of (Tp)₃MX₆ results in the formation of [(Tp)₃CuX]MX₆ with a complex cation of [(Tp)₃CuX]³⁺. The assembly of two distinct metal–halogen units in the heterometallic halide enables charge transfer between the complex cation and anion unit, as verified by DFT calculations, and meanwhile achieves the wide modulation of the luminescent color (green to red region) resulting from the integration of both complex cationic and anionic emission centers in one single lattice of [(Tp)₃CuBr]MBr₆. The luminescence mechanisms of monometallic and heterometallic halides are elucidated by detailed structural and spectral comparisons. Moreover, the compound [(Tp)₃CuBr]SbBr₆ shows significant potential for low-temperature optical temperature sensing applications based on the fluorescence intensity ratio of its dual emissions, with absolute sensitivity (S_a) and relative sensitivity (S_r) values of 0.078 K⁻¹ and 5.38% K⁻¹, respectively. This study not only provides a new strategy for developing heterometallic halide photoluminescence materials, but also offers new ideas for a better understanding of the photophysical mechanism of 0-D heterometallic halides.