Site-selective excitation has been used to simplify complex emission recorded in the visible spectral region for atomic europium isolated in the solid rare gases. In addition to y(8)P resonance fluorescence, excitation of the y(8)P state produces emission from the z(6)P state and the metastable a(10)D state. Very weak emission at 690 nm is tentatively assigned to the J = 9/2 level of the z(10)P state. Eu atoms isolated in the red and blue sites exhibit very different temperature dependence both spectrally and temporally. For the y(8)P state emission the red site atoms exhibit small Stokes shifts and yield radiative lifetimes while the emission from the blue site loses intensity and the temporal profiles shorten dramatically between 10 and 16 K indicating very efficient non-radiative relaxation in this site. An analysis of the Stokes shifts exhibited for the y(8)P state in each site supports the attributions made in a previous publication [O. Byrne and J.G. McCaffrey, J. Chem. Phys. 134, 124501 (2011)] that the smaller blue tetravacancy site has a greater repulsive interaction with the guest. With the exception of the y(8)P state resonance fluorescence, the recorded decay profiles of all the other emissions exhibit multiple components. This behaviour has been attributed to the existence of multiple crystal field levels arising from the splitting of the distinct spin-orbit levels from which emission occurs.
We present an experimental and theoretical study of the absorption and emission spectra of Yb atoms in a solid Ne matrix at a resolution of 0.025 nm. Five absorption bands were identified as due to transitions from the
4f145d06s21S0 ground-state configuration to
4f145d06s6p and
4f135d16s2 configurations. The two lowest-energy bands were assigned to outer-shell transitions to
6s6p3P1 and
1P1 atomic states and displayed the structure of a broad doublet and an asymmetric triplet, respectively. The remaining three higher-frequency bands were assigned to inner-shell transitions to distinct
J=1 states arising from the
4f135d16s2 configuration and were highly structured with narrow linewidths. A classical simulation was performed to identify the stability and symmetry of possible trapping sites in the Ne crystal. It showed that the overarching
1+2 structure of the high-frequency bands could be predominantly ascribed to crystal-field splitting in the axial field of a 10-atom vacancy of
C4v symmetry. Their prominent substructures were shown to be manifestations of phonon sidebands associated with the zero-phonon lines on each crystal-field state. Unprecedented for a metal--rare-gas system, resolution of individual phonon states on an allowed electronic transition was possible under excitation spectroscopy which reflects the semiquantum nature of solid Ne. In contrast to the absorption spectra, emission spectra produced by steady-state excitation into the
1P1 absorption band consisted of simple, unstructured fluorescence bands.
We study the circularly polarized photoluminescence of negatively charged (${\mathrm{NV}}^{\ensuremath{-}}$) and neutral (
NV0) nitrogen-vacancy ensembles and neutral vacancies (
V0) in diamond crystals exposed to magnetic fields of up to 10 T. We determine the orbital and spin Zeeman splitting as well as the energetic ordering of their ground and first-excited states. The spin-triplet and -singlet states of the ${\mathrm{NV}}^{\ensuremath{-}}$ are described by an orbital Zeeman splitting of about 9 $\ensuremath{\mu}\mathrm{eV}/\mathrm{T}$, which corresponds to a positive orbital
g-factor of
gL=0.164 under application of the magnetic field along the (001) and (111) crystallographic directions, respectively. The zero-phonon line (ZPL) of the ${\mathrm{NV}}^{\ensuremath{-}}$ singlet is defined as a transition from the ${}^{1}{E}^{\ensuremath{'}}$ states, which are split by ${g}_{L}{\ensuremath{\mu}}_{\text{B}}B$, to the
1A1 state. The energies of the zero-phonon triplet transitions show a quadratic dependence on intermediate magnetic field strengths, which we attribute to a mixing of excited states with nonzero orbital angular momentum. Moreover, we identify slightly different spin Zeeman splittings in the ground (gs) and excited (es) triplet states, which can be expressed by a deviation between their spin
g-factors: ${g}_{S,\text{es}}={g}_{S,\text{gs}}+\mathrm{\ensuremath{\Delta}}g$ with values of $\mathrm{\ensuremath{\Delta}}g=0.014$ and 0.029 in the (001) and (111) geometries, respectively. The degree of circular polarization of the ${\mathrm{NV}}^{\ensuremath{-}}$ ZPLs depends significantly on the temperature, which is explained by an efficient spin-orbit coupling of the excited states mediated through acoustic phonons. We further demonstrate that the sign of the circular polarization degree is switched under rotation of the diamond crystal. A weak Zeeman splitting similar to $\mathrm{\ensuremath{\Delta}}g{\ensuremath{\mu}}_{\text{B}}B$ measured for the ${\mathrm{NV}}^{\ensuremath{-}}$ ZPLs is also obtained for the
NV0 zero-phonon lines, from which we conclude that the ground state is composed of two optically active states with compensated orbital contributions and opposite spin-1/2 momentum projections. The zero-phonon lines of the
V0 show Zeeman splittings and degrees of the circular polarization with opposite signs. The magnetophotoluminescence data indicate that the electron transition from the
1T2 states to the
1A ground state defines the zero-phonon emission at 1.674 eV, while the $^{1}T_{2}\ensuremath{\rightarrow}^{1}E$ transition is responsible for the zero-phonon line at 1.666 eV. The
1T2 (
1E) states are characterized by an orbital Zeeman splitting with
gL=0.071 (0.128).
Optically active defects suspended in an inert solid are an interesting system for sensing and magnetometry at the nanometer scale, in addition to being a potential source of high-density, identical quantum emitters for quantum information. Beyond their response to external fields, the optical absorption and emission spectra also reflect information about the host matrix, which is critical to understand for either application. For the particular system of thulium atoms implanted in solid argon, high resolution laser spectroscopy reveals narrow ensemble linewidths of the 1140 nm f to f ground state spin-orbit transition, which is split due to crystal field effects and hyperfine coupling. Pump-probe spectroscopy is used to identify crystal field levels in at least two stable trapping sites, and the crystal field is determined to be nearly axial in both sites. Strong selection rules indicate that this transition becomes magnetic-electric in the argon host, most likely due to dielectric effects. In the presence of mT magnetic fields, Zeeman shifts are resolvable by laser fluorescence, allowing crystal axis selective polarized spectroscopy. These results show that all-optical detection schemes for DC magnetic fields are already possible with thulium-doped argon, and point towards more informed strategies for monitoring and improving crystal growth and annealing.
Optically active defects in solid-state systems have many applications in quantum information and sensing. However, unlike free atoms, which have fixed optical transition frequencies, the inhomogeneous broadening of the transitions in solid-state environments limit their use as identical scatterers for such applications. Here we show that crystals of argon and neon prepared in a closed-cycle cryostat doped with thulium atoms at cryogenic temperatures are an exception. High resolution absorption and emission spectroscopy show that the 1140 nm magnetic dipole transition is split into multiple components. The origin of this splitting is likely a combination of different classes of trapping sites, crystal field effects within each site, and hyperfine interactions. The individual lines have ensemble widths as small as
0.6GHz, which temperature dependence and pump-probe spectroscopy indicate is likely a homogeneous effect, suggesting inhomogeneity is well below the GHz scale.
We report the first observation of anticrossings in solid-state laser spectroscopy. Measurements are performed on the 6105-\AA{} zero-phonon transition $^{3}H_{4}({\ensuremath{\Gamma}}_{1})\ensuremath{\leftrightarrow}^{1}D_{2}({\ensuremath{\Gamma}}_{1})$ of
Pr3+ in a YAl
O3 crystal at 2\ifmmode^\circ\else\textdegree\fi{} K where both ground- and excited-state anticrossings appear. A perturbation theory of the anticrossing signal is derived from the wave equations of motion for a three-level quantum system subject to a static interaction
V between two neighboring levels (1 and 2) while a laser field resonantly excites the inhomogeneously broadened $2\ensuremath{\leftrightarrow}3$ transition. Ground- and excited-state gyromagnetic ratios ${\ensuremath{\gamma}}_{i}(i=X,Y,Z)$ and the interactions
V are obtained by fitting the observed anticrossings to a diagonalized hyperfine-spin Hamiltonian for
141Pr3+ which includes second-order ligand field corrections in terms containing the electron orbital angular momentum. Under certain conditions, one anticrossing signal develops into a strongly modulated oscillation with a period of \ensuremath{\sim} 20 G, an unexpected feature which appears to be a nonlinear optical coherence effect. The influence of anticrossing state mixing on optical free-induction-decay observations is also discussed.