Spin‐Polarized Photoluminescence in Au₂₅(SC₈H₉)₁₈ Monolayer‐Protected Clusters

Abstract

Here, the observation of spin‐polarized emission for the Au25(SC8H9)18 monolayer‐protected cluster (MPC) is reported. Variable‐temperature variable‐field magnetic circular photoluminescence (VTVH⇀‐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(SC8H9)18. Through analysis of VTVH⇀‐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.

Size-Scalable Near-Infrared Photoluminescence in Gold Monolayer Protected Clusters

“…The global PL includes three components in this spectral range, with the most intense emission occurring in the near-infrared, at energies typically less than 1.7 eV. 12 As previously reported, an intensity increase of the near-infrared PL is observed upon increasing sample temperature from 4.5 to 60 K. 11,12 Further temperature increases lead to PL quenching due to phononmediated nonradiative decay. The near-infrared PL is assigned to intraband relaxation between core-localized states.…”

“…10 Metal nanoclusters also exhibit multiple PL emission bands, which have been attributed to metal−metal-based intraband and interband charge transfer recombination. 9,11,12 Nanocluster emission is often spin polarized, with degrees of polarization that depend on cluster composition and emission energy. 12,13 In contrast to plasmonic nanoparticles, the optical properties of nanoclusters are not believed to be size scalable; PL occurs between discrete cluster-specific electronic states.…”

“…9,11,12 Nanocluster emission is often spin polarized, with degrees of polarization that depend on cluster composition and emission energy. 12,13 In contrast to plasmonic nanoparticles, the optical properties of nanoclusters are not believed to be size scalable; PL occurs between discrete cluster-specific electronic states. Here, we provide the firstknown description of size-scalable PL properties for a series of gold nanoclusters that include Au 20 (SC 8 H 9 ) 15 -diglyme, Au 25 (SC 8 H 9 ) 18 , and Au 38 (SC 12 H 25 ) 24 .…”

“…18,19 Recently, the photoluminescence mechanism for the charge-neutral Au 25 (SC 8 H 9 ) 18 MPC was characterized by using variable-temperature variable field magnetic circular photoluminescence (VTV ⎯ ⇀ H -MCPL) spectroscopy. 12,20 Three PL channels were resolved and assigned through analysis of VTV ⎯ ⇀ H -MCPL and VT-PL methods. A near-infrared PL component was assigned to intraband radiative relaxation involving superatomic states of the metal core.…”

Atomic-Level Structure Determines Electron–Phonon Scattering Rates in 2-D Polar Metal Heterostructures

“…10 However, upon subnanometer 3-D spatial confinement, metal nanoclusters exhibit complex dynamics that include wavelength-dependent electron−phonon coupling strengths. 4,11,12 Therefore, the exploration of metals in the sub-to-few nanometer range may impact energy management materials.…”