Light emitting device containing a rare earth complex as luminescent medium

A light emitting device includes a light emitting element (1) and a luminescent medium (2). The luminescent medium (2) contains a rare earth complex wherein a compound represented by the following formula (1) is employed as a ligand :    wherein X and Y are the same or different and are individually O, S or Se; R1, R2, R3 and R4 are the same or different, excluding a situation where R1, R2, R3 and R4 are all the same as each other, and are individually an alkyl or alkoxy group of a linear or branched structure having not more than 20 carbon atoms, a phenyl group, a biphenyl group, a naphthyl group, a heterocyclic group or a substitution product of any of these groups; n is an integer ranging from 2 to 20; and Z and W are the same or different and are individually a hydrogen atom, a deuterium atom, a halogen atom or an alkyl group.