Excitation and luminescence line narrowing techniques at temperatures between 1.5 and 5 K are used to study the lowest triplet states of the cyclometalated Rh(III) complex [ Rh( thpy) 2( bpy)] + ( thpyH = 2- thienylpyridine; bpy = 2,2′- bipyridine) doped into a crystalline host and a glass. Crystal excitation spectra reveal two origins C and D separated by 156 cm -1. Their zero field splitting is shown to be less than 1 cm -1. Zeeman spectra of the narrowed excitation and luminescence origin C show an isotropic splitting into 5 lines, and their energy separation depends linearly on the applied field. The 5 lines are a superposition of spectra from three sets of triplets characterized by m s = +1, 0, -1 and a g- factor 2.0±0.1. Using the line intensities, the spin-lattice relaxation rate within the triplet at 4.2 K is estimated to be 160 and 6400 s -1 for fields of 2 and 4 T, respectively.