The valence changes of doped samarium and the creation as well as the annihilation of F-centers in the processes of thermostimulated luminescence (TSL) and photostimulated luminescence (PSL) of BaFCl∶Sm crystal have ...The valence changes of doped samarium and the creation as well as the annihilation of F-centers in the processes of thermostimulated luminescence (TSL) and photostimulated luminescence (PSL) of BaFCl∶Sm crystal have been studied. As being irradiated by X-ray,a large number of electron-hole pairs are created in the crystal.Most of the electrons may be trapped at the anion vacancies,producing F-centers.The doped samarium ions,which existed mostly in trivalent state (Sm^(3+)),may capture the holes and convert themselves to tetravalent state.So that part of the incident X-ray energy are stored in this nonequilibrium system.On optical and thermal stimulation the stored energy can be liberated as a characteristic emission of trivalent samarium ion.This emission originates from the recombination of the F-center electrons with tetravalent samarium ions,i.e.the F-center electrons may be excited to the conduction band by optical or thermal stirnulation and then recombine with tetravalent samarium ions.This recombination makes the samarium ions to be in situ reduced to the excited state of Sm^(3+),and gives rise to the characteristic emission of Sm^(3+). On the other hand,during X-irradiation a few electrons can be trapped at the sites of trivalent samarium ions and reduce them to divalent state.But the formation of divalent samarium On X-irradiation is very small as compared with that of F-centers and so their influence on the PSL and TSL can be neglected.展开更多
The formation of color centers in BaFCl:Eu^(2+) crystal is studied in more de- tail and further evidence for FA centers in BaFCl:Eu^(2+)is reported.The creation of color centers in BaFCl:Eu^(2+)may be devided into thr...The formation of color centers in BaFCl:Eu^(2+) crystal is studied in more de- tail and further evidence for FA centers in BaFCl:Eu^(2+)is reported.The creation of color centers in BaFCl:Eu^(2+)may be devided into three stages.Under long time X-irradiation be- yond stage 1,the concentration of FA centers depends linearly on the nth(n=1,2 or 3) power of F center concentration.While under short time X-irradiation within stage 1,the concentration dependence of FA centers on F center is complex.Simple centers are easier to create than complex centers.Possible mechanisms for color centers formation in BaFCl:Eu^(2+) are also proposed and discussed.展开更多
In this paper, we have succesfully prepared the sample of BaFCl: Eu<sup>2+</sup>thin film using the vacuum thermal evaporation method and first studied photostimulated luminescence on BaFCl: Eu<sup>2...In this paper, we have succesfully prepared the sample of BaFCl: Eu<sup>2+</sup>thin film using the vacuum thermal evaporation method and first studied photostimulated luminescence on BaFCl: Eu<sup>2+</sup>thin film.展开更多
High temperature (from room temperature to 773 K) thermoluminescence of BaFCl: Eu2+ is reported. Three new glow peaks have been found to be caused respectively by F2-, F3 - and F4- centers which are the aggregates of ...High temperature (from room temperature to 773 K) thermoluminescence of BaFCl: Eu2+ is reported. Three new glow peaks have been found to be caused respectively by F2-, F3 - and F4- centers which are the aggregates of F centers. Physical parameters characterizing those peaks are present. It is pointed out that the thermoluminescence process in BaFCl:Eu2+ is very complex. Accompanying this process, there occur electron transfers among different centers and dissociation of the aggregates.展开更多
The optical absorption spectra of BaF2-x Clx ：Eu^2＋ after ultraviolet （UV） light excitation were investigated. The differences between the absorption spectra after and before excitation （DAS） were observed. The ...The optical absorption spectra of BaF2-x Clx ：Eu^2＋ after ultraviolet （UV） light excitation were investigated. The differences between the absorption spectra after and before excitation （DAS） were observed. The DAS increase at both the high and the low energy side of F band in BaF2-xClx ： Eu^2 ＋ after 245 nm UV light excitation. The bleach effect of UV light and the absorption of electrons in the valence band may account for the former and the formation of Fa centres （association of F（Cl^-） centres）, whose absorption band matches the HeNe laser better, may explain the latter. In the write-in process, the transfer of electrons is via tunneling, In the readout process, the transfer of electrons captured in F（F^-） and Fa centres is more likely via tunneling, and that of F（Cl^- ） centres is more likely via conduction band.展开更多
文摘The valence changes of doped samarium and the creation as well as the annihilation of F-centers in the processes of thermostimulated luminescence (TSL) and photostimulated luminescence (PSL) of BaFCl∶Sm crystal have been studied. As being irradiated by X-ray,a large number of electron-hole pairs are created in the crystal.Most of the electrons may be trapped at the anion vacancies,producing F-centers.The doped samarium ions,which existed mostly in trivalent state (Sm^(3+)),may capture the holes and convert themselves to tetravalent state.So that part of the incident X-ray energy are stored in this nonequilibrium system.On optical and thermal stimulation the stored energy can be liberated as a characteristic emission of trivalent samarium ion.This emission originates from the recombination of the F-center electrons with tetravalent samarium ions,i.e.the F-center electrons may be excited to the conduction band by optical or thermal stirnulation and then recombine with tetravalent samarium ions.This recombination makes the samarium ions to be in situ reduced to the excited state of Sm^(3+),and gives rise to the characteristic emission of Sm^(3+). On the other hand,during X-irradiation a few electrons can be trapped at the sites of trivalent samarium ions and reduce them to divalent state.But the formation of divalent samarium On X-irradiation is very small as compared with that of F-centers and so their influence on the PSL and TSL can be neglected.
文摘The formation of color centers in BaFCl:Eu^(2+) crystal is studied in more de- tail and further evidence for FA centers in BaFCl:Eu^(2+)is reported.The creation of color centers in BaFCl:Eu^(2+)may be devided into three stages.Under long time X-irradiation be- yond stage 1,the concentration of FA centers depends linearly on the nth(n=1,2 or 3) power of F center concentration.While under short time X-irradiation within stage 1,the concentration dependence of FA centers on F center is complex.Simple centers are easier to create than complex centers.Possible mechanisms for color centers formation in BaFCl:Eu^(2+) are also proposed and discussed.
基金Project Supported by the National Science Foundation of China.
文摘In this paper, we have succesfully prepared the sample of BaFCl: Eu<sup>2+</sup>thin film using the vacuum thermal evaporation method and first studied photostimulated luminescence on BaFCl: Eu<sup>2+</sup>thin film.
基金Project supported by the National Natural Science Foundation of China.
文摘High temperature (from room temperature to 773 K) thermoluminescence of BaFCl: Eu2+ is reported. Three new glow peaks have been found to be caused respectively by F2-, F3 - and F4- centers which are the aggregates of F centers. Physical parameters characterizing those peaks are present. It is pointed out that the thermoluminescence process in BaFCl:Eu2+ is very complex. Accompanying this process, there occur electron transfers among different centers and dissociation of the aggregates.
文摘The optical absorption spectra of BaF2-x Clx ：Eu^2＋ after ultraviolet （UV） light excitation were investigated. The differences between the absorption spectra after and before excitation （DAS） were observed. The DAS increase at both the high and the low energy side of F band in BaF2-xClx ： Eu^2 ＋ after 245 nm UV light excitation. The bleach effect of UV light and the absorption of electrons in the valence band may account for the former and the formation of Fa centres （association of F（Cl^-） centres）, whose absorption band matches the HeNe laser better, may explain the latter. In the write-in process, the transfer of electrons is via tunneling, In the readout process, the transfer of electrons captured in F（F^-） and Fa centres is more likely via tunneling, and that of F（Cl^- ） centres is more likely via conduction band.
