Studies of the thermal dissolution process of the Suzuki phase of the Eu²⁺ion in KBr single crystals by analysis of photoacoustic signals

Abstract

An experimental investigation of the thermal behaviour of the dissolution process of the Suzuki phase (SP) by continuous heating (1 °C min−1) of KBr:Eu2+ crystals is reported in this work. The thermal profiles were determined by the correlation functions between subsequent photoacoustic (PA) signals registered during the dissolution process. The behaviour of the thermal profile is directly related to the absorption coefficient of the Eu2+ ion in precipitated states that are present in the crystal. The PA signal is detected as a consequence of the non-radiative processes that take place after the excitation of the low-energy band of the Eu2+ ion by means of a focused laser pulse at 355 nm. The results obtained by this method are compared with those simultaneously obtained by the photoluminescence (PL) technique. The samples were heated from room temperature to 205 °C. The PA signal and PL spectrum were obtained every 6 °C. The temperature range of the SP dissolution process was from 77 to 115 °C. These results are in agreement with those obtained by the PL technique and with the data reported in the literature.

Thermal dissolution of Eu2+ Suzuki phase nanostructures in KBr crystals monitored by pulsed photoacoustic and photoluminescence techniques

“…Single crystals of europium-doped KBr were grown by the Czochralski method under a controlled atmosphere of dry argon. The experimental details and photoacoustic signal analysis are similar to those describes in a previous paper [7].…”

“…On the other hand, recent experimental work on the relation between the optical absorption coefficient and precipitated states detected by photoacoustic technique [6] has been carried out and it was shown that these measurements could be used as an alternative technique to investigate precipitation processes of impurity-doped alkali halides [7]. The precipitate size increases with an increase of the impurity concentration and with a decrease in the crystal cooling rate.…”

Study of NaCl:Mn2+ nanostructures in the Suzuki phase by optical spectroscopy and atomic force microscopy

“…Therefore, the NS starts dissolving at 80 1C and at 120 1C it has disintegrated. In the region labeled X, the last values are zero due to the extinction of the excitation peak, indicating that the NS have been destroyed [28,29]. As a consequence of the thermal dissolution of the NS in SP, the peak wavelength is shifted to 233 nm until the band disappears at 120 1C.…”

“…In general the alkali halide single crystals doped with divalent impurities tend inevitably to form precipitates/aggregates, and depending on the thermal treatment applied, they can form the SP [26,[27][28][29][30], in particular, for NaCl: Mn 2 þ in as-grown samples or samples stored for a long time at room temperature (RT) or around 120 1C. An SP structure consists of a three-dimensional periodic arrangement formed by a divalent cation and its corresponding second nearest monovalent cation vacancy.…”

NaCl(001) surfaces nanostructured by Suzuki precipitates: a scanning force microscopy study

“…However, also other metal impurity cations such as Mn 2+ [13,14], [16]- [19], [36], [40]- [42], [45]- [50], Mg 2+ [1,21,36,41,42], Fe 2+ [15,17,19,36,41,42,51], Ni 2+ [42,52], Co 2+ [53], Sr 2+ [42,54] and Pb 2+ [42,55] have been the subject of many investigations and discussions. In fact, the host lattice need not necessarily be NaCl: the Suzuki phase may exist also in NaBr (Mn 2+ [50]), KCl (Sm 2+ [57], Pb 2+ [58] and Eu 2+ [56,59]), KBr (Mn 2+ [60] and Eu 2+ [59,61,62]), LiF (Mg 2+ [11,63]) and AgCl (Pb 2+ [64]) and even in oxides (MgO:Mn 4+ [31], [65]- [67], NiO:Mn 4+ [67] and CuO:Pb 4+ [32,68]). Suzuki phases including two types of metal impurity cations have even been studied ...…”