Glynn D. Jones

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.

Persistent spectral hole burning due to deuteron tunneling in SrF(2):Pr(3+):D(-).

We report the observation of persistent spectral hole burning due to a mechanism that is new to inorganic materials, i.e., light-induced deuteron (or proton) tunneling. Measurements were made on (3)H(4) ? (1)D(2) transitions of SrF(2):Pr(3+) centers having two D(-) ions as near neighbors. The spectral holes exhibit hyperfine structure dominated by very large (~100-MHz) pseudoquadrupole splittings in the singlet ground state.

Site-selective laser spectroscopy of 4fn–4fn−15d transitions in CaF2:Pr3+ with F−, D−, H−, Li+, or Na+ charge compensation

Site-selective luminescence spectroscopy of the 4f2−4f5d(fd) transition is reported for six different Pr3+ sites in CaF2:Pr3+. In addition to the naturally occurring distantly charge-compensated cubic site and the locally charge-compensated Pr3+–F− site, charge compensating ions (H−, D−, Li+, and Na+) were added to create four other types of sites. In the fd luminescence spectra fine structure (zero-phonon lines and vibronic lines) is observed. The positions of zero-phonon lines and vibrational frequencies vary for these different Pr3+ sites. For the H− and D− charge-compensated site the lowest 4f5d level is shifted to some 3000 cm−1 lower energy compared to the cubic site. This is attributed to a higher degree of covalency and a larger crystal-field splitting. Contrary to previous results for Ce3+–H− and Ce3+–D−, only a small (close to zero) isotope shift is observed. In the fd emission spectra, the 4f5d–1I6, 3PJ transitions are used to reveal marked differences between sites which allows their identific...

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.

Hyperfine patterns of infrared absorption lines of Ho3+ C4v centres in CaF2

Hyperfine structure is observed on several infrared transitions to the 5I7 and 5I6 multiplets of the Ho3+ C4v centre in CaF2. Particularly complex and detailed hyperfine structures are observed for transitions to the Y3 level of the 5I7 multiplet, which include the appearance of ΔIz ≠ 0 transitions. The hyperfine lines of this level are satisfactorily accounted for by strong mixing of close-lying levels of this multiplet by the perpendicular hyperfine interaction, which leads to relaxation of the ΔIz = 0 selection rule and a redistribution of the hyperfine intensities over many transitions. An excellent correspondence is found between the measured and simulated spectra.

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.

Na+, Li+ and cubic centres in rare-earth-doped CaF2 and SrF2

Abstract Co-doping of rare-earth (R3+)-doped CaF2 and SrF2 with LiF, NaF or KF enhances the concentration of single R3+ centres of cubic symmetry. C2v centre are also produced in which the R3+ ions are charge-compensated by Li+, Na+ or K+ ions located in the nearest-neighbour Ca2+ or Sr2+ sites in the 〈1 1 0〉 direction. Infrared-absorption studies have been carried out for many R3+ co-doped crystals. The infrared-absorption lines of the cubic centres appear as magnetic-dipole allowed transitions and Zeeman measurements confirm their cubic symmetry. Absorption lines of the Li+ and Na+ centres occur within 10 cm −1 of the cubic-centre lines and shift in going from Li+ to Na+ indicating different placements of these ions in the 〈1 1 0〉 position.

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.