We present the Stark energy sublevels of Nd3+ ions in GaN grown by plasma-assisted molecular beam epitaxy as determined by luminescence spectra. We correlate the photoluminescence spectra with transitions from the F43/2 excited state to the I49/2, I411/2, and I413/2 multiplets of the Nd3+ ion for above and below bandgap excitation, with the strongest emission occurring at 1.12 eV (1106 nm). We determine a splitting of the F43/2 excited state to be 4.1 meV. From photoluminescence excitation spectra, we also identify the Stark sublevels of the upper states F45/2, H29/2, F47/2, S43/2, G27/2, and G45/2. Photoluminescence excitation spectra reveal an optimal excitation energy of 1.48 eV (836 nm). Site-selective spectroscopy studies using combined excitation-emission spectroscopy with confocal microscopy indicate enhanced substantial doping at the Ga site.
The increased solubility and uniform dispersal of branched azobenzene chromophores over their monomeric analogues have been shown to improve the electrooptic performance of high glass transition temperature (T g ) blended polymers. We report here the application of these branched chromophores as guest nonlinear optical molecules in the plasticized low-T g photoconducting host polymer poly(vinylcarbazole) and demonstrate the presence of orientationally enhanced photorefractive index gratings. When compared with their monomeric analogues, branched chromophores were compatible over a broader range of concentrations and resulted in higher quality optical films; these films have retained their optical clarity for 1 year. A new branched electrooptic chromophore with r 33 of 14 pm/V at 1550 nm was synthesized and exhibited photorefractive two-beam coupling over a range of applied fields, including a net two-beam coupling amplification coefficient of 6.4 cm -1 at 780 nm.
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