Optical absorption spectra are reported for the 4115/2 "-9"4113/2, 4111/2, 4F9/2, 4S3/2, ~Hlx/2, 4F7/2, 4F5/2, 4F3/2, ~Gg/~ and 4Gn/2 transition regions of Er a+ in the cubic Cs~NaErCI6 system. These spectra, obtained under variable temperature conditions (2.6K to 300 K), are analysed on the basis of a crystal field model in which the Er a+ ions are assumed to reside at sites of exact octahedral (Oh) symmetry. This crystal field model is used to calculate energy levels and to calculate the magnetic dipole strengths and intensities of crystal field transition origin lines. Vibronically-induced electric dipole strengths are also calculated using a model in which the ErCI63-clusters are treated as isolated chromophoric units (uncoupled to the lattice). This latter model allows calculation of electric dipole intensities for the vibronic lines associated with the v3(t2u), v4(tlu) and v~(t~u) vibrational modes of the ErCI~ 3-cluster (the so-called moiety modes). Detailed analysis of the spectra leads to the location and assignment of all crystal field levels split out of the 4123/~, 4In~z, 4F9/~, 4Sa/2, ~Hn/2, 4F~/z, 4F5/~, 4Fa/2, 2G9/2 and 4G21/2 intermediate-coupling states, and of the three lowest-lying crystal field levels split out of the 4125/2 ground state. The best fit between the calculated and observed crystal field energy level schemes was achieved using the values of crystal field coefficients BoO) = 1608 cm -2 and B0 (6) = -195 cm -1 (defined according to the unit-tensor formalism). The most intense transitions were observed (and calculated) to be 41~512 -+4Glt/z > 4Ila12 > 2H21/z. The 4125/3 -'."4Ila/z transition region is entirely dominated by intense magnetic dipole origin lines, whereas nearly all of the intensity in the 4125/2-+4Gn/2 and ~Hn/2 transition regions is found in vibronic lines associated with the v6(85-90cm-2), v4(107-114cm -t) and v3(245-260 cm -2) ErCl~ 3-moiety modes.

Optical excitation and emission spectra are reported for the Cs2NaErCl6 system under variable-temperature (8.5–298 K) conditions. Detailed line assignments are made for the 4I15/2←4S3/2 and 4I15/2←4F9/2 high-resolution emission spectra, and all five crystal-field levels split out of the 4I15/2 ground multiplet are located. These results combined with our previously reported absorption results provide the locations of 35 crystal-field levels spanning 11 multiplets of the Er3+ ion in Cs2NaErCl6. Energy level calculations based on a nine-parameter 4f-electron Hamiltonian operating within the 4f11 configuration of Er3+ give results in good agreement with experiment. Excitation spectra for 4I15/2←4S3/2 emission are reported at several temperatures over the 340–540 nm spectral region. Emission spectra excited by near-ultraviolet radiation (centered at 383 nm) are reported over the 405–725 nm spectral region for sample temperatures ranging from 8.5 to 298 K. All but one of the seven multiplet-to-multiplet emission bands observed in this region decrease in intensity as the sample temperature is increased. The 4I13/2←4G11/2 emission exhibits an increase in intensity with increasing temperature.

Luminescence and power-gated spectral holeburning studies have been performed on Eu-doped MgS nanoparticles. These particles are atomically tailored to produce and control the relative concentration of Eu(2+) and Eu(3+), which is necessary for power-gated holeburning. The spectral holes are permanent at low temperatures. Optical studies show that the electron-phonon coupling is stronger in nanoparticles than in thin films or microparticles of the same material. This is the reason for inherently broader spectral holes in nanoparticles as compared to microparticle or thin-film samples. Temperature broadening of spectral holes in nanoparticles follows a T(2.4) behavior, a faster rate than thin films or microparticles. This behavior can be attributed to the glassy nature of the particles produced.