Optical Detection of NQR: Crystal Field and Matrix Effects on Halogenated Organic Molecules

Electron spin polarization or alignment achieved in the excited triplet state of organic molecules can be transferred into nuclear spin polarization (alignment) during an optical pumping cycle. Due to this effect, quadrupole resonance (NQR) investigations of nuclei with concentrations of 10-5 molar are possible in the electronic singlet ground and excited triplet state in one and the same experiment by the applied optical pumping cycle. By this conventional NMR sensitivity is enhanced by several orders of magnitude, enabling investigations of defect site structures in molecular crystals.