Change in the states of optically excited Rb atoms near sapphire surface
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The changes in the states of excited Rb atoms approaching a single-crystal sapphire surface have been investigated by methods of laser-excitation spectroscopy and luminescence of Rb vapor in a cell with sapphire windows, the gap between which was varied from 250 to 500 nm. Upon resonant excitation of Rb atoms by two semiconductor lasers with powers of 20 and 40 mW, luminescence from optically excited 5D 3/2 and 5D 5/2 states and optically unexcited 6P 1/2 and 6P 3/2 states is observed. It is established that the luminescence intensity from unexcited states is only a few times lower than that from excited states, with allowance for the fact that excited atoms are rapidly and almost completely quenched on the sapphire surface. The found anomalously strong luminescence from optically unexcited 6P J states is explained by their nonradiative occupation near the sapphire surface from optically excited 5P J states, in which atoms fail to reach the sapphire surface because of the repulsion from it. This repulsion is due to the polarization interaction between sapphire and the atoms in the 5P J states near the surface. Nonradiative transition from the 5P J state to the 6P J −1 state is accompanied by excitation of two optical phonons in sapphire.
KeywordsExcited State Luminescence Intensity Optical Phonon Luminescence Line Blue Luminescence
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