The suitability of the three charge transfer co-crystals anthracene with 1,2,4,5-tetracyanobenzene
(A:TCNB), phenazine with 1,2,4,5-tetracyanobenzene (PNZ:TCNB) and acridine with 1,2,4,5-
tetracyanobenzene (Acri:TCNB) as maser gain media was assessed. The ability for NV− centres
in diamond to act as a spin-cold material that can cool a microwave mode at 2872 MHz is also
presented. Through the construction of a homemade transient electron paramagnetic resonance
(trEPR) spectrometer, the triplet EPR signals of all four materials were measured and used to
find their resonant frequencies and solve their triplet spin dynamics. The co-crystals A:TCNB
and PNZ:TCNB were shown by simulation to feasibly support masing at transition frequencies
above 2 GHz, but experiments with A:TCNB could not yet produce masing signals. NV− diamond
on the other hand succeeded as a microwave mode cooler, able to cool the mode from
room temperature down to 188 K and hold that temperature for 10 milliseconds when measured
using a heterodyne receiver setup.