The Influence of Pd-Atom Substitution on Au₂₅(SC₈H₉)₁₈ Cluster Photoluminescence

The photoluminescence (PL) of Au 25 (SC 8 H 9 ) 18 and Au 24 Pd(SC 8 H 9 ) 18 was investigated using variable-field magnetic circular photoluminescence (VH-MCPL) spectroscopy. The comparison of low-temperature (4.5 K) PL spectra measured for both nanoclusters revealed an ≈40 meV blueshift of intraband emission upon Pd substitution. Compared to that for the the Au 25 (SC 8 H 9 ) 18 cluster, the degree of circular-polarization for the Au 24 Pd(SC 8 H 9 ) 18 cluster increased for the low energy (<1.65 eV) portion of the PL spectrum, but decreased for the higher energy (>1.65 eV) spectral region. MCPL spectra included three distinct components, underlying the global PL spectrum, for both clusters. Variable-field analysis of each MCPL component revealed an increase in spin–orbit coupling (Landé g-factor) magnitudes for radiative transitions of the Pd-substituted cluster with respect to Au 25 (SC 8 H 9 ) 18 . Variable-temperature (VT) PL spectroscopy yielded reduced integrated global PL intensity and increased electron-vibrational coupling for Au 24 Pd(SC 8 H 9 ) 18, as compared to Au 25 (SC 8 H 9 ) 18 . The results indicate that Pd-substitution for Au in Au 25 (SC 8 H 9 ) 18 results in increased angular momenta for metal–metal intraband transitions; the Landé g-factor for these transitions increased by ≈55% upon substitution, as compared to an approximate 19% increase for ligand-based transitions. The increased angular momentum translates to a 30% increase in electron–phonon coupling constants for intraband transitions, but only a 3% increase for ligand-based transitions. As a result, Pd substitution leads to less efficient metal–metal (intraband) radiative emission for Au 24 Pd (SC 8 H 9 ) 18 than for Au 25 (SC 8 H 9 ) 18 .