We report the development of compound dyes which have tunable emission wavelengths, from 520 to 680 nm, and simultaneously tunable excited-state lifetimes, ranging from 50 to 500 mu s. Future work is expected to extend these ranges yet further. The compound dyes are made of a lanthanide donor with a millisecond lifetime, which transfers energy to an acceptor with nanosecond lifetime, the latter made from an organic fluorophore. By varying the distance between the two, energy transfer from donor to acceptor results in a variable donor lifetime and emission, primarily from the acceptor. Emission color of the complex is therefore determined by choice of acceptor, and the lifetime decay of acceptor emission following an excitation pulse is determined by the donor' s lifetime, which feeds the acceptor's delayed emission. By utilizing both the time-domain and wavelength-domain, these probes have the potential for quadratically increasing the number of detectable probes on a single sample.