Lead-free halide double perovskites (DPs) are emerging as alternate materials for optoelectronic applications. Efforts are on to understand the various mechanisms at play that are operational in influencing the optical and electronic properties of these materials. Transmuting two lead cations by a +1 and +3 cation enables the formation of A_2 B^((I) ) B^((III) ) X_6double perovskites. The luminescence of Cs_2 AgInCl_6can be enhanced upon incorporating a small amount of Al^(3+)or Bi^(3+)in the structure. The PL has been hypothesized to arise as a result of the self-trapped excitonic (STE) emissions. Understanding the structure of the STEs is most important in order to design materials with a handle to tune these properties. Doping of these DPs also results in energy transfer from the host to the dopants given that excited states of the two overlap, enabling the transfer. Further, as in the case of semiconductors, core-shell materials with the proper band alignments can be useful for controlling the optoelectronic properties.