In the plasma-laser star model for QSOs (Varshni, 1973a, 1973b, 1974a, 1974b) the line 4686 Å very likely arises due to laser action in the n=4 to 3 transition in He II. Extensive calculations of population densities in hydrogenic ion plasmas are carried out for a grid of ne (electron density), Te (electron temperature) and n(1) (density of the groundstate atoms) values on the basis of the collisional-radiative model (Bates, Kingston and McWhirter: 1962 Proc.Roy.Soc., A267, 297, Drawin: 1969 Zs.Physik, 225, 470). The region in which the population inversion is most intense for 4686 Å is identified and the bearing of the result on the atmospheres of the quasars 3C 48, 4C 09.31, PKS 2059+034 and 4C 37.43 and also of Of stars is discussed.