J.K. Krebs

Photo bleaching in Sm2+ selectively doped epitaxial CaF2 films

Abstract We present a study on the bleaching properties of Sm 2+ doped epitaxial CaF 2 films. Previously, the Sm 2+ emission in these films has been found to bleach partially under optical excitation. For a detailed investigation of the bleaching mechanism, single crystal CaF 2 films were grown on Si(111) surfaces by molecular beam epitaxy (MBE) and were selectively doped with Sm 2+ ions at various distances from the semiconductor/insulator interface. A correlation between the bleaching rate and the distance from the insulator-semiconductor interface could not been found. In addition, we find that the bleaching rate depends linearly on the intensity of the optical excitation and that the shape of the emission line is not altered during the bleaching process. Our results are discussed in the framework of photoionization due to excited-state absorption, tunneling of excited electrons into the semiconductor substrate, and the role of lattice defects.

Optical spectroscopy of trivalent chromium in sol-gel lithium niobate

We report on the characterization of sol-gel derived lithium niobate via trivalent chromium probe ions, a study that is motivated by recent reports on the synthesis of high quality sol-gel lithium niobate (LiNbO3). In order to assess the quality of sol-gel derived LiNbO3, we incorporate Cr3+ during the hydrolysis stage of the sol-gel process. A comparison of the Cr3+ emission and photoexcitation data on both sol-gel and melt-grown LiNbO3 shows that the sol-gel derived material is highly stoichiometric.

Selective control of excitation pathways of upconverted fluorescent states using a broadband laser and a spectral mask

We present a new technique to study materials’ response to broadband, optical excitation using upconversion through excited state absorption. We use the broadband spectrum from an ultrafast laser coupled to a spectral shaper to manipulate our excitation bandwidth and selectively control which transitions occur in the ground state and excited state absorptions. By analyzing the effects of spectral shaping of the excitation laser on the emission yield of fluorescent light, we can test models of the electron population densities and transition probabilities to recover electron energy-level-specific information about the system being studied. Here, we apply this technique to Y2O3:Er3+.