In support of the continuing quest of combining i.r. detectors and silicon electronics on a single substrate, an experimental survey was made of doping candidates for use in the 2–2.7 and 3–5 μm i.r. spectral ranges. The elements beryllium, copper, zinc, nickel, thulium and ytterbium were explored for applicability. Measured spectral response curves and the dependence of detectivity on temperature are presented and compared, where applicable, with theory. Various useful attributes of some of these dopants (Si:Cu, Si:Zn) including higher operational temperatures as well as the observed limitations are discussed and critiqued against the Si:In, Si:S and Si:Tl detectors previously investigated for the 3–5 μm range.