R. W. G. Syme

Upconversion fluorescence spectroscopy of Er3+ pairs in CsCdBr3 a☆

Using a combination of optical absorption and laser selective excitation, an extensive set of energy levels has been established for the principal Er3+ center in CsCdBr3:Er3+, and Er3+ -vacancy-Er3+ arrangement. The polarized absorption and fluorescence measurements indicate a pair center slightly distorted from the ion positions of the host crystal. This Er3+ pair center exhibits strong upconversion fluorescence, with up to one third the intensity of direct fluorescence, giving an overall visual white emission under CW laser excitation of the 4I15/2 → 4S3/2 transitions in the green. Unusual aspects of the spectra are small pair splitting (about 0.5 cm-1) of the sharper absorption lines and shifts (about 0.3 cm-1) of the fluorescence lines between δ and π polarizations of the incident laser light.

Site‐selective laser spectroscopy of deuterated SrF2:Er3+

Laser selective excitation and optical absorption of deuterated SrF2:0.05% Er3+ crystals have revealed eight Er3+ ion centers involving D− ion charge compensation, nine new Er3+–F− centers not associated with D− ions and several approximately cubic symmetry Er3+ centers. In contrast to the trigonal symmetry of the principal F− center, the dominant arrangements in the D− ion charge compensation case are derived from a tetragonal symmetry center. Detailed spectroscopic results for the new centers are presented. Fluorescence polarization ratios are listed for three centers ( J, B, and G1) present in either SrF2:Er3+ or CaF2:Er3+ and crystal‐field analyses of these, based on assumed trigonal symmetry, are also reported.

Site‐selective spectroscopy of hydrogenic sites in CaF2:Er3+ crystals

Laser selective excitation and optical absorption studies of hydrogenated CaF2:0.05% Er3+ crystals have revealed 16 Er3+ ion sites involving H− or D− ion charge compensation. The relative occurrence of these sites can be controlled over a wide range by varying the duration of the hydrogenation treatment. The hydrogenic nature of these sites is established by the observation of local mode absorption lines in the infrared, Er3+ ion electronic line isotope shifts and associated local mode vibronic lines involving the H− and D− ions. Local mode infrared absorption frequencies of four sites are reported for most rare‐earth ions. Five new Er3+−F− sites were identified in the laser selective excitation study. For 〈100〉 and 〈111〉 oriented crystals the fluorescence spectra of several of the sites exhibit well‐defined polarization which determines their Er3+ ion site symmetries. Symmetry confirmations are also established for the two previously reported single Er3+ ion sites involving fluoride ion compensation. Ele...

Reversible polarized bleaching in hydrogenated rare-earth-doped fluorites.

By using site-selective laser spectroscopy, several sites in hydrogenated and deuterated rare-earth-doped fluorite crystals have been found to exhibit reversible bleaching. The site orientations can be switched between orthogonal directions by corresponding changes in the laser polarization. Such effects are a form of photochemical hole burning and are attributed to laser-induced migration of H(-) or D(-) ions between equivalent interstitial positions adjacent to the rare-earth ion.

Dynamical processes involving local modes for rare earth centers in CaF2

Abstract H - , D - and T - ion local modes play a significant role in dynamical processes involving laser excitation of hydrogenic rare-earth ion centers in CaF 2 and SrF 2 . The hydrogenic varieties of a particular center are found to have substantially reduced fluorescence lifetimes supportive of models for non-radiative decay to lower energy multiplets through the respective local mode phonons. Likewise, upconversion efficiencies are reduced for the hydrogenic single rare-earth ion centers and are found to vary with inter-center separation consistent with a recent model for single ion upconversion involving a weak coupling between nearby equivalent centers. The efficient channelling of the rare-earth ion excitation into the creation of local mode phonons can induce hydrogenic ion migration to produce re-oriented equivalent centers or new photoproduct centers with different excitation wavelengths.

Upconversion fluorescence spectroscopy of Ho3+ dimer pairs in CsCdBr3

Abstract Using a combination of optical absorption and laser selective excitation, an extensive set of energy levels has been established for the principal Ho 3+ center in CsCdBr 3 :Ho 3+ , a Ho 3+ -vacancy-Ho 3+ arrangement. This Ho 3+ pair center exhibits strong upconversion fluorescence under CW laser excitation of the 5 I 8 → 5 S 2 , 5 F 4 transitions in the green and the 5 I 8 → 5 F 5 transitions in the red. A particular feature of the spectrum is the small pair splittings of the sharper transitions, arising from the inter-Ho 3+ ionic coupling. Both the strong upconversion and the small pair splittings parallel features already reported for the principal Er 3+ center in CsCdBr 3 :Er 3+ , and the similarities and differences are high-lighted. The dynamics of the upconversion fluorescence of these Ho 3+ dimer pairs is also presented.

Laser selective excitation of fluorine and hydrogenic charge compensation sites in SrF2:Pr3+

Abstract Two hydrogenic and two fluoride ion sites are identified. Fluorescence lines, local mode vibronics and two near coincidences with argon laser lines are discussed.

Fluorescence lifetimes of Pr3+ centers in mixed CaF2 :SrF2 crystals

Abstract Using polarized laser selective excitation, sets of energy levels have been established for the principal new Pr3+ centers in four mixed alkaline earth fluoride systems: CaF2:Pr3+ containing up to 1% of either SrF2 or BaF2 and SrF2:Pr3+ containing up to 1% of either CaF2 or BaF2. The three principal centers for SrF2 in CaF2:Pr3+ are modified centers derived from the tetragonal C4v symmetry center of the parent crystal: two with an off-axis Sr2+ ion and one with an on-axis Sr2+ ion. Fluorescence lifetimes determined for mixed crystal centers are reported and related to their respective Pr3+ energy level patterns. Some results of high resolution scans of the respective absorption transitions of these centers are also presented.