Quantum yields of luminescent lanthanide chelates and far-red dyes measured by resonance energy transfer

Luminescent lanthanide chelates have unusual spectroscopic characteristics that make them valuable alternative probes to conventional organic fluoroph ores. However, fundamental parameters such as their quantum yield, and radi ative and nonradiative decay rates have been difficult or impossible to mea sure. We have developed a simple and robust method based on resonance energ y transfer to accurately measure these parameters. In addition, the excitat ion/emission process in lanthanide chelates involves several steps, and we are able to quantify each step. These include excitation of an organic ante nna, transfer of energy from the antenna to lanthanide, and then Ianthanide emission. Overall, the parameters show that Ianthanide chelates can be eff icient long-lived emitters, making them sensitive detection reagents and ex cellent donors in resonance energy transfer. The method is also shown to be applicable to photophysical characterization of red-emitting dyes, which a re difficult to characterize by conventional means.