C. Sandmann

Site-selective spectroscopy of Er in GaN

We investigated different Er3+ defect sites found in Er-doped GaN layers by site-selective combined excitation-emission spectroscopy and studied the role of these sites in different direct and multistep excitation schemes. The layers were grown by molecular beam epitaxy and were 200 nm thick. Two majority sites were found along with several minority sites. The sites strongly differ in excitation and energy transfer efficiencies as well as branching ratios during relaxation. For this reason, relative emission intensities from these sites depend strongly on emission and excitation. The sites were identified for several transitions and a comprehensive list of energy levels has been compiled. One of the minority sites appears strongly under ultraviolet excitation above the GaN band gap suggesting that this site is an excellent trap for excitation energy of electron-hole pairs.

Ferroelectric domain imaging by defect-luminescence microscopy

In order to study the role of defects within the domain inversion process in ferroelectric LiNbO3 crystals, we investigated the optical properties of intentionally introduced Er3+ defect complexes across a 180° domain wall produced at room temperature by electric-field poling. Using site-selective excitation-emission spectroscopy for well chosen excitation energies, we found drastic differences in the Er3+ emission, which are due to a rearrangement of the defect complexes. We used these changes in a confocal luminescence microscope to image ferroelectric-domain structures. This powerful imaging method with a 700 nm, 50 ms spatial and temporal resolution can be used to study real-time dynamics of domain walls.

Confocal two photon emission microscopy: A new approach to waveguide imaging

Abstract Based on earlier studies of the interaction effects between Er3+ and Ti4+ ions in Ti:LiNbO3 waveguides we investigated the feasibility of using the Er3+ as a sensitive probe to determine Ti4+-diffusion profiles with high spatial resolution. Using a home-built confocal microscope combined with site-selective optical spectroscopy we tested two different operation modes: (i) Evaluating the emission spectra obtained by one-step excitation with a single laser we obtain high resolution (≈700 nm ) Ti 4+ -concentration images. In particular using the second moments of the spectra, which turn out to be approximately linearly related to the Ti4+-concentration, we obtain very good contrast with essentially no artifacts caused by topology, intensity fluctuations, and Er3+ ion concentration profile. (ii) Measuring the total emission intensity under a specially chosen two step excitation scheme allows to selectively excite regions with a certain Ti4+ concentration. While for (i) a calibration can be done, for (ii) this will be hard due to the multi-site character of the Er3+ in LiNbO3.

Combined Excitation Emission Spectroscopy of Europium ions in GaN and AlGaN films

Site-selective combined excitation emission spectroscopy studies have been performed on Eu-doped GaN and numerous sites have been identified. Relative numbers and broadening of these peaks has been investigated for different growth conditions and for increasing AL content of the Al x Ga 1-x N alloy.

Light Aided Domain Patterning and Rare Earth Emission Based Imaging of Ferroelectric Domains

Trivalent rare earth and transition metal ions in insulating materials have been the topic of extensive investigations over the years due to their application as active ions in solid-state lasers. In lithium niobate (LiNbO3) with its favorable nonlinear and electro-optical properties, Er ions and other rare earth ions have been utilized in integrated optical lasers and optical amplifiers.

In-situ confocal luminescence microscopy study of lithium niobate during domain inversion

In this work we will show that it is possible to probe the Er/sup 3+/ defect in-situ during domain inversion offering the potential to study the spatial extension of the perturbations associated with a moving domain wall and to develop an active feedback system for electron beam or light-induced domain inversion.

Combined excitation emission spectroscopy of Eu-doped GaN

In this contribution we address the first task by applying to the Eu:GaN material system the site-selective technique of combined excitation emission spectroscopy, in which a large number of emission spectra are recorded and a 2D data set of emission intensities as function of excitation and emission intensity is obtained.