This work investigates the performance of multi-mode detector crystals which can discriminate between neutron and gamma radiation within the same volume. Knowledge of performance metrics such as intrinsic neutron efficiency and gamma rejection ratio are vital when using such crystals hand held detection systems. As a result, the scatter corrected neutron efficiency to a 252Cf source and the change in the detection efficiency in the presence of an increased gamma field was assessed for the 6 materials (EJ-299, EJ-309, Stilbene, Cs2LiYCl6 (CLYC), P-terphenyl and EJ-270). These materials are of interest as they can detect neutron and gamma radiation and discriminate between them via pulse shape discrimination (PSD). For most detectors, the neutron efficiency was not found to change significantly in the presence of large gamma field. A 30 % increase in counts was observed for crystalline PSD scintillator, CLYC. This was assumed to be due to the different PSD characteristic and higher gamma sensitivity of CLYC. In addition, the absolute detection efficiency was measured for the 6 candidate materials and compared to the FLIR Identifinder 2 NGH. A two orders of magnitude increase was observed for the dual mode detectors compared to the Identifinder 2 thus highlighting the benefit of using larger dual mode detectors in any compact detection system in the future.