ON THE USE OF THE THERMAL LENS EFFECT FOR MEASURING ABSOLUTE LUMINESCENCE QUANTUM YIELDS OF TRANSITION-METAL COMPLEXES

The thermal lens effect or thermal blooming of a laser beam passing through an absorbing medium is used to determine the fraction of absorbed laser power which is converted into heat. By this photocaloric method absolute luminescence quantum yields-phi can be evaluated covering the full range of possible phi-values. A check with organic standards for which quantum yields of 1, 0.52 and 0 are reported, supplies values of 0.99, 0.52 and 0.04, respectively. The sample compounds [Ru(bipy)3]X2, X = Cl, ClO4, and bipy = bipyridine, were studied using different concentrations in water and methanol solution at room temperature. The results strongly depend on the counter ion: for the Cl--and (ClO4)--salts quantum yields of phi = 0.31 and 0.79, respectively, are obtained, which may be explained by different polarization conditions. The yields are, on the other hand, independent from the solvents and from the concentration, which was considered ranging from 10(-4) to 2.5 x 10(-5) M. Thermal blooming was also observed from [Ru(bipy)3]Cl2 contained in KBr pellets, measuring al various temperatures.