Cryogenic thermometer employing molecular luminescence

A cryogenic thermometer using molecular luminescence determines temperature. A sensor material is used which is capable of emitting radiant energy from a spin multiplet when excited, the excited state being characterized by a large zero field splitting (ZFS), and in which two of the sublevels split by the ZFS are radiative in the visible or near infrared region and are optically resolvable from each other. Spin-lattice relaxation rates between the sublevels are much larger than the sublevel decay rates to other states in order that their populations remain close to thermal equilibrium during optical pumping. The relative intensity of the two bands of radiation is determined and the temperature calculated therefrom. Xanthione (XS) dissolved in n-hexane may be used as a sensor material in the optimum range of 3 to 10K, with estimated precision varying between 0.4 mK and 3.0 mK within this range. Other disclosed sensor materials should allow extension of the optimal range to about 20K on the ...