High-Resolution Optical Line Width Measurements as a Material Characterization Tool

Abstract

We present a case study on Eu 3+ -doped Y 2 O 3 transparent ceramics in which high-resolution laser spectroscopy is used as a material characterization tool. By comparing the results from coherent and incoherent optical spectroscopy with other characterization methods, we show that optical techniques can deliver supplementary information about the local environment of the activator ions in materials. Thus, high-resolution spectroscopy may be of interest for the investigation of a wider range of rare earth doped optical materials beyond materials studied for quantum information technology. The refinement of optical spectroscopy for the study of narrow optical transitions in rare earth ion single crystals has demonstrated that these techniques are extremely sensitive tools for probing the local environment of the rare earth ion. These techniques, such as photon echo experiments, have been important in developing materials for quantum information technology and spectral filtering applications. Here, we apply these techniques to transparent ceramic samples and compare the results with information gained from conventional material characterization techniques. Our present study demonstrates the high sensitivity of laser spectroscopic methods to microstructural strain and the presence of defects. In particular, the sensitivity is sufficient to detect small changes introduced by different thermal treatments in nominally equivalent materials. The results of our work show that it is possible to relate highresolution optical measurements to defects and microstructural strain.

Dephasing mechanisms of optical transitions in rare-earth-doped transparent ceramics

“…The greatest level of broadening out of all the samples was observed in the samples with post-HIP annealing and without ZrO 2 : eff < 25 kHz. This result is correlated with the fact that in such samples the highest defect concentration of F + centers and O − 2 ions has been observed [33]. Therefore, we tentatively assign the rapid broadening to an interaction with these defect center spins.…”

“…8(2) 6200 1.8 (4) previous finding that F + and O − 2 centers are present in these samples [33], we relate the linear temperature dependence of the homogeneous linewidth in the low-temperature region and thus, the dynamic disorder to these centers.…”

“…From previous electron paramagnetic resonance (EPR) and (thermally stimulated) luminescence studies [33] it is known that, depending on the synthesis conditions, different defect centers are present. In samples without post-HIP annealing the presence of F centers (two electrons on an oxygen vacancy) is suggested based on the presence of a thermoluminescence glow peak and short-lived luminescence.…”

“…In samples with post-HIP annealing, the F-center signal disappears but there are significant signals arising from the presence of F + centers and O − 2 ions, respectively. Optical experiments were carried out on the 7 F0 → 5 D0 transition (580.88 nm in vacuum), which has an inhomogeneous linewidth of about 20 GHz in the samples without additives and about 100 GHz in the ones with additives [33]. Homogeneous linewidths were measured by photon echo experiments.…”

“…Further investigations are needed to fully understand this broadening mechanism, but given previous materials analysis of these transparent ceramics [33] it is likely that the temperature dependence is related to the fluctuations of defect centers. One further measurement that could provide additional information is to apply rf or microwave fields that are resonant with one of the known defects during the photon echo sequence [53].…”