The XRD patterns of the pure and 1.5% doped samples are shown in Figs. 2 and 3, respectively. The samples are still single crystals and doping the NDs host crystal does not effect on its single crystal properties. For using, the crystal in optical systems single crystals is more applicable than polycrystalline. As seen in figures, the important planes (200) and (400), in doped crystal, are not shifted and they are parallel.
In crystal growth mechanism, it is very important to distribute the impurity in based crystal uniformly. It is simple in cases of ionic additives because in the melt state, ionic bonding are broken and external ions can sit easily instead of original ions of the crystal lattice. In this research as it is clear, ND particles have a complete structure, so observing their placement in host environment that has considerably different structure can be helpful for modification of crystal growth methods. Pieces of KCl with different amounts of ND crystal were cut randomly and observed by ESEM. The ESEM images of the sample are shown in the Figs. 4–6. Figure 4 depicts KCl + 0.5% ND sample. In the figure, we can see a nearly smooth distribution of the NDs inside the host crystal. The ND cluster size varies between 133 to 421 nm. Figure 5 shows KCl + 1.0% ND sample. The distribution of the NDs is not smooth as the KCl + 0.5% ND sample and the ND cluster size changes between 53.4 to 107 nm. In the Fig. 6, we have a smooth distribution of the NDs with a size range from 295 to 502 nm. It has observed a little agglomeration of ND particles that is natural, because surface adhesionin ND particles is strong and they tend to stick together.
The results of the etching analysis are shown in Figs. 7–10. Based on mentioned figures, the surface dislocation of the samples are collected in the Table 1.
Table 1
KCl Samples Dislocation Surface Densities
Dislocation Surface Density(cm-2) | Crystal |
105 ×3.0 | KCl (Pure) |
105 ×4.5 | KCl + 0.5% ND |
105 ×6.0 | KCl + 1.0% ND |
105 ×8.8 | KCl + 1.5% ND |
The KCl crystal is transparent in the IR range. Therefore, this crystal can be utilized as an optical window for the lasers working in the IR range (for example CO2 laser). The FTIR analysis was done on the KCl + 1.5 % ND sample. The selected sample had the most ND impurity and the effect of the impurity on its transparency was more than other samples. Figure 11 shows the FTIR transmission spectrum for the KCl + 1.5 % ND sample. As it can be seen, the transmission is ~ 87.4%. This transmission shows the sample is nearly transparent in the IR range. Before, utilizing of the KCl crystal as a laser window had a limitation due to damaging the crystal by beam collision. One way to solve the problem was the crystal coating in order to increase the hardness and the crystal’s lifetime. Unfortunately, that way was not economic. Considering the results of the harness analysis and the FTIR spectrum shows ND doping into the KCl crystal is the better method to overcome the problem.
The samples (pure KCl, KCl + 0.5% ND, KCl + 1% ND and KCl + 1.5% ND) were irradiated by gamma 60Co source with 10, 80 and 300 Gy as well as 1kGy doses, separately. After irradiation, the colour of the samples changed to violet. Then, by TL reader the sample were characterized. The results are collected in Figs. 12–15.
The results are compared with the thermoluminesence curve of LiF:Mg,Ti reference dosimeter (known commercially as TLD100). Its significant dosimeteric peaks occur in temperature range between 160–260° C. For all samples the TL intensity of the ND doped KCl is stronger than pure crystal. In the Fig. 16, we can see the under curve area for the KCl + 0.5% ND sample is the greatest one. Therefore, in 10Gy irradiation dose, the best sample is the KCl + 0.5% ND sample. Its TL significant peaks occur on 160 and 240 ° C the operation temperature range is 100–300° C. In the Fig. 17 (80 Gy irradiation), the KCl + 0.5% ND sample has the best quality for TL and its significant peak appears on 180° C and the operation temperature range is 100–260° C. Again, in the operation temperature range between 100–200° C, the KCl + 0.5% ND sample shows the best quality in comparison with the other samples (Fig. 18). The significant peak occurs on 180° C. In the Fig. 19, the best TL quality belongs to KCl + 1% ND sample. Its operation temperature range and significant peak are 100–250 ° C and 160° C, respectively. As a result, for low irradiation doses 0.5% ND impurity and for high doses 1% ND impurity are proper for TL dosimetery.