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The intensity of luminescence of piperidinium tetrakis (1,3-diphenyl-1,3-propanediono) Tb (III) in EPA is enhanced when the phenyl groups are deuterated. This luminescence has been measured as a function of temperature and the enhancement appears to be a constant over the temperature range studied. Similar studies when carried out with piperidinium tetrakis (1,3-diphenyl-1,3-propanediono) Eu (III) with deuterated phenyl groups did not lead to any appreciable enhancement over that of the undeuterated complex. Similar results were obtained with deuterated and undeuterated tris dibenzoylmethides of Eu (III) and Tb (III). Increased ion emission was observed with the deuterated Tb complex but not with the deuterated Eu complex. An explanation for the temperature dependence as well as the difference observed between the terbium and europium complexes is offered.