A perfect nonabsorbing microsphere with higher refractive index than the surrounding medium is a good optical microcavity.Inside such a sphere

which has a diameter of a few microns

there are a discrete number of resonant optical modes.The spontaneous emission cross-sections at the microcavity resonance photon energies are larger than the bulk spontaneous emission cross-sections because of the modified photon density of states of the microcavity.In the conventional study on microsphere

the luminescent molecules are inside the microspheres.In this paper

we report the fluorescent resonances of a dye solution outside a micrometer-sized

nonluminescent

spherical particle.Oxazine 1 was dissolved in distilled water

and its concentration was adjusted to 10

-3

mol/l.TiBa glass microspheres(refractive index～1.88

diameter=20～50μm)were dispersed in the aqueous solution of oxazine 1.One drop of the solution was put on a glass plate

and placed on a microscope stage at room temperature.The experimental apparatus is micro-Raman spectrometer(RENISHAW System 2000).The laser beam at wavelength of 633nm was introduced into an optical microscope and focused into a～5μm spot by an objective lens(20x

numerical aperture 0.4).The laser beam was irradiated on the edge of the microsphere

so that the oxazine 1 aqueous solution just outside of the microsphere was excited.Emission from the microsphere was collected by the same objective lens

and the spectra were observed by the spectrometer(with CCD).