C. Zaldo

OH-related defects in LiNbO3:Mg,M (M = Nd, Cr, Ti, Mn) crystals

Abstract In addition to the 3539 cm −1 OH − stretching vibration related to Mg 2+ OH − complexes, OH − bands at 3522 and 3506 cm −1 were found in MgNd and MgCr doubly doped LiNbO 3 crystals, respectively. These bands, polarized perpendicular to the c -axis, are interpreted as an OH − vibration in an M 3+ OH − Mg 2+ association. In this complex the OH − ion is assumed to be located between the M 3+ and Mg 2+ ions which occupy Nb 5+ and Li + sites, respectively. In Mg 2+ Ti 4+ and Mg 2+ Mn 2+ codoped LiNbO 3 , no OH − band corresponding to that kind of complex was observed. The absorption strength of the OH − ions involved in the M 3+ OH − Mg 2+ association is about 6 × 10 −20 cm 2 ion −1 .

Study of the precipitation behavior of NaCl:Pb and KCl:Pb by optical spectroscopy†☆

Abstract The aggregation and precipitation behavior of lead in NaCl and KCl crystals has been systematically investigated by absorption and luminescence spectroscopy. For NaCl, absorption bands at 265 and 285 nm have been identified which correspond to intermediate stages in the formation of a double band (262–266 nm) associated with PbCl2 precipitates. The kinetics of growth during ageing as well as the thermal annihilation behavior have been obtained for all bands. The emission spectra for excitation at those absorption bands have also been determined. For KCl, absorption bands at 265 and 280 nm develop during ageing at 160 and 200°C and their growth-rate is markedly enhanced by plastic straining. Their emission spectra involve a main band at

Mechanical strengthening and impurity precipitation behaviour for divalent cation-doped alkali halides

550 nm. In contrast to NaCl, no stage has been found where those absorption bands feed into a final band, which could be associated with PbCl2 precipitates.

Optical properties of Cu+ centers in NaCl

The yield stress of NaCl doped with Ca, Sr, Mn, Pb and Cd, KCl doped with Pb, and KBr doped with Sr and Pb, has been investigated as a function of the state of aggregation of the impurity. For all systems the yield-stress remains constant during isothermal annealing treatments if the impurity concentration is below a threshold value dependent on the material. At higher concentrations two opposite behaviours have been found. For systems where a coherent Suzuki phase has been detected (NaCl-Cd and NaCl-Mn) or is expected to occur (KCl-Pb, KBr-Pb and KBr-Sr) a marked softening is observed during annealing. On the other hand, a marked hardening appears for NaCl-Pb, NaCl-Ca and NaCl-Sr, where the stable dihalide phase has been shown to form. Mechanisms responsible for the reported behaviour are proposed and briefly discussed.

INFLUENCE OF PRECIPITATION PROCESSES ON THE OPTICAL SPECTRA OF Pb2+ IN ALKALI HALIDES

Abstract Different aggregation-precipitation states of Cu + have been characterized by absorption bands peaked at 305, 350 and 372–383 nm. The absorption bands at 372–383 nm, observed exclusively in the most doped crystal, have been associated with the Z 12 , Z 3 excitons of CuCl microcrystals incorporated into the NaCl matrix Their positions shift to low energies with increasing concentration, as expected for a decrease in the stress over the precipitate. The Z1 12 , Z 3 exciton bands of CuCl microcrystals precipitated in NaCl can be observed by the optical absorption spectrum without reaching saturation Therefore, this technique could be an alternative method to studies of CuCl thin-film depositions or reflectivity of CuCl single crystals. The red emission band observed at 600 nm is a long-lived emission (τ≅ 29 ms) at variance with the behavior reported for the Cu + emission It is related to energy transfer processes from Cu + to Mn 2+ .

Optical spectroscopy of Pb2+ as a tool to study Ca precipitates in NaCI

Abstract The influence of the aggregation and precipitation processes of lead ions on optical (absorption and luminescence) spectra have been studied for KBr, KI and RbCl. Bands presumably associated with aggregates and precipitates have been identified and compared with those observed for NaCl and KCl. The thermal annihilation behavior of precipitate bands as well as the effect of precipitation on yield-stress have also been determined. As a consequence, a more complete scheme of the influence of aging processes on optical spectra of lead-doped alkali halides has now become available.

PB++ as an optical probe to investigate clustering processes of M++ in alkali halides☆

Abstract A small concentration (6 ppm) of lead has been used as an optical probe to investigate the different precipitated phases formed in the NaCl:Ca system. The experimental results strongly suggest that lead ions become incorporated into CaCl2 precipitates as well as into {111} and {310} Suzuki platelets acting as intermediate stages in the precipitation process. In fact, new optical (absorption and luminescence) bands of Pb++ have been associated with each of those phases: 261–267 nm (absorption) and 290 nm (emission) for CaCl2; 264 (absorption) and 360 nm (emission) for the {310} platelet; 305 nm (emission) for the {111} platelet.

Optical spectra of Pb2+ to monitor the precipitation behavior of NaCl:Cd†

Abstract Pb++ has been used as an optical probe to monitor clustering processes in a number of divalent-cation doped alkali halides. In fact, some new optical bands are observed in as-grown and annealed samples which are presumably associated to Pb++ embedded in to a precipitated phase (dihalide for NaCl : Sr and NaCl:Ca and Suzuki for NaCl:Cd).