Spin-Polarized Photoluminescence in Au₂₅ (SC₈ H₉ )₁₈ Monolayer-Protected Clusters

Here, the observation of spin-polarized emission for the Au₂₅ (SC₈ H₉ )₁₈ monolayer-protected cluster (MPC) is reported. Variable-temperature variable-field magnetic circular photoluminescence (VTV $$ -MCPL) measurements are combined with VT-PL spectroscopy to provide state-resolved characterization of the transient electronic structure and spin-polarized electron-hole recombination dynamics of Au₂₅ (SC₈ H₉ )₁₈ . Through analysis of VTV $$ -MCPL measurements, a low energy (1.64 eV) emission peak is assigned to intraband relaxation between core-metal-localized superatom-D to -P orbitals. Two higher energy interband components (1.78 eV, 1.94 eV) are assigned to relaxation from superatom-D orbitals to states localized to the inorganic semirings. For both intraband superatom-based or interband relaxation mechanisms, the extent of spin-polarization, quantified as the degree of circular polarization (DOCP), is determined by state-specific electron-vibration coupling strengths and energy separations of bright and dark electronic fine-structure levels. At low temperatures (<60 K), metal-metal superatom-based intraband transitions dominate the global PL emission. At higher temperatures (>60 K), interband ligand-based emission is dominant. In the low-temperature PL regime, increased sample temperature results in larger global PL intensity. In the high-temperature regime, increased temperature quenches interband radiative recombination. The relative intensity for each PL mechanism is discussed in terms of state-specific electronic-vibrational coupling strengths and related to the total angular momentum, quantified by Landé g-factors.