Laser active F-aggregate colour centres in LiF monocrystals doped by divalent impurity cations

Abstract

F-aggregate colour centres in LiF crystals with divalent impurities (M = Ni, Co, Be, Mg) are investigated by optical and thermally stimulated depolarization current (TSDC) spectroscopy methods. The F+2 centres accumulation in the LiF:M2+ crystals is similar to the F+2 centres accumulation in undoped LiF. Accumulation of F+2-like colour centres was observed only in the LiF:Mg2+ crystals at the first stage of low temperature irradiation with radiation doses exceeding 107 R. F+2-like centres are not formed in LiF with Ni, Be and Co impurity ions. The difference between the properties of the magnesium on one hand and the nickel, beryllium or cobalt doped crystals on the other is discussed in terms of the Hayes-Nickols mechanism with extra anion vacancy generation in the case of the LiF:Mg2+ crystal. The absence of the mechanism in LiF:Ni2+ and LiF:Be2+ is connected to the reduction of the impurity Ni2+ and Be2+ ion valence state and in LiF:Co2+ to the small concentration of single Co2+V-c dipoles as a result of extensive dipole aggregation. The destruction of the F+2 and F+2-like centres takes place in LiF:Mg2+ crystals at the second stage of aggregation, at which other F-aggregated centres are formed, with the impurity-vacancy (IV) dipoles included in their composition. The two-band structure of the TSDC curve of irradiated LiF:Mg2+, with relaxation parameters close to those of single IV dipole reorientation bands, is in accordance with the above mechanism of aggregation. The creation mechanisms and models of laser active colour centres (F+2-like and F3Mg2+V-c `red' colour centres) are discussed.

Synthesis and luminescence properties of nanocrystalline LiF:Mg,Cu,P phosphor

“…This may perturb the localized metastable energy levels formed due to the impurity ions. However, it is not easy to understand the role of each type of the impurities on the TL output in the present more complex case (nanoparticles of different shapes) when it has not yet been understood properly in single or microcrystalline phosphor [31,32].…”

TSDC spectroscopy of relaxational and interfacial phenomena

“…A variety of natural minerals, such as amethyst [94], sapphire [95], stilbite [96], calcite, dolomite, quartz [97], clays [98], mordenites [99,100], cretaceous strata [101], and synthetic solids, such as ceramics doped with CuO, FeO and TiO 2 [102], silicas, silicates and other compounds with silica [103][104][105][106], different crystals [107][108][109][110][111][112] and polycrystalline structures [113,114], disordered materials [115], thin films [116][117][118][119][120][121], ferrites [122], metal fluorides [123][124][125][126][127][128][129] and solid solutions based on fluorides [130][131][132][133][134][135], was investigated by the TSDC method.…”

Thermal transformation of colour centres in LiF crystals with given content of oxygen, hydroxyl and metal ions

“…The current understanding of the role of traces of impurities in CCs-related phenomena of LiF crystals is mainly based on the study of OA and PL bands of samples annealed at different temperatures. In this regard, the main results of the present investigation on some LiF crystals are summarized as follows: (i) different efficiencies of host defect formation and the appearance of new spectral bands in consequence of impurity effect were observed; (ii) on the basis of OA and PL measurements, the bleaching temperatures of F 3 + , F 2 , and F centres have been assigned to be: near 250, 450 and below 600 °C, respectively, comparing to previous values [3]; (iii) other defect centres with 540 and 670 nm emissions, possibly associated with metal impurities, are still existing in the range of temperatures up to 300-450 °C; (iv) CCs increasing in number with increasing cation impurities, irradiation doses, and annealing temperatures in the region 200-450 °C, represents a strong evidence for the presence of Mg impurities, and is also related to F 2 + -like centres [10][11][12]. These results have been obtained as a first qualitative analysis of the experimental data, and correlations between impurities and CCs have been discovered.…”