| Summary: | Organic–inorganic halocuprates based on monovalent copper are promising luminescent compounds for optoelectronic applications; however, their relaxation processes in the excited electronic state are severely underexplored. In this contribution, we prepare thin films of bis(tetraethylammonium) di-µ-bromo-dibromodicuprate(I) [N(C<sub>2</sub>H<sub>5</sub>)<sub>4</sub>]<sub>2</sub>[Cu<sub>2</sub>Br<sub>4</sub>], abbreviated (TEA)<sub>2</sub>Cu<sub>2</sub>Br<sub>4</sub>, which features a “molecular salt” structure containing discrete [Cu<sub>2</sub>Br<sub>4</sub>]<sup>2−</sup> anions. This compound, which has an absorption peak at 283 nm, displays a blue, strongly Stokes-shifted emission with a peak at 467 nm. Transient photoluminescence (PL) experiments using broadband emission detection and time-correlated single-photon counting (TCSPC) both find an excited-state lifetime of 57 μs at 296 K. UV–Vis transient absorption experiments at 296 K covering time scales from femto- to microseconds provide evidence for the formation of the T<sub>1</sub> state through intersystem crossing from S<sub>1</sub> with a time constant of 184 ps. The triplet state subsequently decays to S<sub>0</sub> predominantly by phosphorescence. In addition, the time constants for carrier–optical phonon scattering (1.8 ps) and acoustic phonon relaxation (8.3 ns and 465 ns) of (TEA)<sub>2</sub>Cu<sub>2</sub>Br<sub>4</sub> are provided.
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