Elucidating the Location of Cd²⁺ in Post-synthetically Treated InP Quantum Dots Using Dynamic Nuclear Polarization ³¹P and ¹¹³Cd Solid-State NMR Spectroscopy

Indium phosphide quantum dots (InP QD) are a promising alternative to traditional QD materials that contain toxic heavy elements such as lead and cadmium. However, InP obtained from colloidal synthesis often plagued by poor photoluminescence yields (PL-QYs). In order improve the PL-QY of QD, number post-synthetic treatments have been devised. Recently, it has shown post-synthetically treated with Lewis acid metal divalent cations (M-InP) exhibit enhanced PL-QY; however, molecular structure mechanism behind improved not fully understood. To determine surface M-InP dynamic nuclear polarization surface-enhanced magnetic resonance spectroscopy (DNP SENS) experiments were employed on series magic size clusters Cd ions, cadmium (Cd₃P₂) Cd-treated (Cd–InP QD). With use DNP SENS, we able obtain 1D ³¹P ¹¹³Cd NMR spectra, ¹¹³Cd{³¹P} rotational-echo double-resonance (REDOR) ³¹P{¹¹³Cd} dipolar heteronuclear multiple correlation (D-HMQC) sequence. Changes in chemical shifts after treatment provide indirect evidence some alloys into sub-surface regions particle. DNP-enhanced solid-state spectra suggest most ions coordinated oxygen atoms either carboxylate ligands or phosphate groups. REDOR D-HMQC confirm subset located Cd–InP