Analysis of Quantum Dot Fluorescence Coupled with a Microsphere Resonator

The emission spectrum of CdSe/ZnS quantum dots adhering to the surface of a microsphere resonator is measured and discussed. Only certain peaks are observed, and the order numbers of the modes (l=5 to 7) of the observed peaks are different from those previously reported (l=1 and 2). [Nano Lett. 1 (2001) 399]. A detailed analysis is presented using the cavity mode efficiency , which is a function of surface roughness, the absorption coefficient of the quantum dots, and mode parameters. The difference between the observed order number modes is explained to be due to the ratio of the rate of absorption by the quantum dots to that of the leakage rates of the modes. The surface roughness of a quantum-dot-coated microsphere and the absorption coefficient of the quantum dots on the sphere are estimated in the analysis.