Spontaneous emisssion of phonons and spectral line widths of some rare earth ions in crystals

Neil B. Manson, Matthew J. Sellars, Peter Fisk +1 more

4fn ⇒ 4fn transitions of trivalent rare earth ions doped in crystals frequently give sharp spectral lines. The transitions associated with the higher levels of a multiplet can be relatively sharp, 10-1000 GHz, where the width is determined by the decay rate of the levels by spontaneous phonon emission to lower levels. The transitions and their linewidth can be determined using conventional absorption or excitation techniques. On the other hand the transitions associated with the meta-stable lower levels typically give much sharper features with linewidths of 1 - 100 GHz and the widths are determined by the inhomogeneities of the crystal field. These inhomogeneous linewdths can be obtained by conventional spectroscopic techniques but the homogeneous linewidth requires more innovative techniques such as optical holeburning or photon echoes. The time domain photon echo measurements do not requiring a high resolution source and have frequently been used to establish that the homogeneous linewidth of such transitions. The lines can be very narrow down to the kHz regime [1,2]. Should complimentary measurements be attempted in the frequency domain utilising holeburning a special frequency stabilised lasers is required and one has been developed in association with the current work [3].

Lidia Smentek

Nikolay T. Timofeev, Е. Б. Свешникова

John G. Bartholomew, Karmel de Oliveira Lima, Alban Ferrier +1 more

We identify the physical mechanisms responsible for the optical homogeneous broadening in Eu 3+:Y 2 O 3 nanoparticles to determine whether rare-earth crystals can be miniaturized to volumes less than λ 3 while preserving their appeal for quantum technology hardware. By studying how the homogeneous line width depends on temperature, applied magnetic field, and measurement time scale, the dominant broadening interactions for various temperature ranges above 3 K were characterized. Below 3 K the homogeneous line width is dominated by an interaction not observed in bulk crystal studies. These measurements demonstrate that broadening due to size-dependent phonon interactions is not a significant contributor to the homogeneous line width, which contrasts previous studies in rare-earth ion nanocrystals. Importantly, the results provide strong evidence that for the 400 nm diameter nanoparticles under study the minimum line width achieved (45 ± 1 kHz at 1.3 K) is not fundamentally limited. In addition, we highlight that the expected broadening caused by electric field fluctuations arising from surface charges is comparable to the observed broadening. Under the assumption that such Stark broadening is a significant contribution to the homogeneous line width, several strategies for reducing this line width to below 10 kHz are discussed. Furthermore, it is demonstrated that the Eu 3+ hyperfine state lifetime is sufficiently long to preserve spectral features for time scales up to 1 s. These results allow integrated rare-earth ion quantum optics to be pursued at a submicron scale and, hence, open up directions for greater scaling of rare-earth quantum technology.

W.F. Krupke

USM ADMIN

Effects of the electron-phonon interaction for rare earth ions (RE) in crystals are multi-phonon relaxation, vibronic bands, band broadening depending on temperature or non-resonant energy transfer assisted by phonons. Since the Stark splitting for RE ions are of the order of lattice phonon energy, it could arise and other related effects, especially in the approximation of quasi-resonant processes. If the distance between two Stark levels is close to the region of resonance phonon spectrum, then electron-phonon interaction creates mixed vibronic states, which causes changes in the optical spectral lines (widening, asymmetry, splitting or displacement). The modeling of interaction of the electron-phonon resonance for RE ion Yb3+ in three different laser crystals is the purpose of this paper. Keywords: electron-phonon interaction, rare earth ions, adaptive application.