HAL Id: jpa-00220106
https://hal.archives-ouvertes.fr/jpa-00220106
Submitted on 1 Jan 1980
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Monochromatic thermoluminescence and models of recombination kinetics in ionic solids
V. Ratnam, R. Gartia, B. Acharya
To cite this version:
V. Ratnam, R. Gartia, B. Acharya. Monochromatic thermoluminescence and models of recombi- nation kinetics in ionic solids. Journal de Physique Colloques, 1980, 41 (C6), pp.C6-269-C6-271.
�10.1051/jphyscol:1980668�. �jpa-00220106�
JOURNAL DE PHYSIQUE Colloque C6, suppldment au no 7 , Tome 41, Juillet 1980, page C6-269
Monochromatic thermoluminescence and models of recombination kinetics in ionic solids
V. V. Ratnam (*), R. K. Gartia (**) and B. S. Acharya (*)
(*) Physics Department, Indian Institute of Technology, Kharagpur, India-721302 (**) Physics Division, J.N.U., Centre, Imphal, India-795003
Rksumk. - L'emission spectrale de thermoluminescence (TL), la decroissance isotherme monochromatique et les resultats de TL monochromatique photostimulee sont utilisQ pour Ctablir la recombinaison cinktique ainsi que la nature des porteurs de charges dans la TL du systkme KC1 :Mn. Ces rksultats soutiennent notre modkle preckdent dans lequel on montre que les di-interstices jouent un r6le intermediaire dans le processus TL.
Abstract. - Thermoluminescence (TL) emission spectra, monochromatic isothermal decay and photostimulated monochromatic TL results are utilized to establish the recombination kinetics as well as the nature of charge carriers in the TL of KC1 : Mn system. These results support our earlier model wherein diinterstitials are shown to play the intermediate role in the TL process.
1 . Introduction. - Thermally stimulated processes are important and one of the convenient methods of investigating the nature of traps and trapping levels in insulating solids. Amongst them thermolumines- cence (TL) is a potentially powerful tool for the understanding of the mechanism of light emission during the thermal stimulation and also for the determination of trapping parameters (thermal acti- vation energy E, frequency factor S or S' no and the order of kinetics). While even to this day there is no unique method of determining the trapping para- meters from experimental TL curves, equally contro- versial is the nature of charge carrier (electron or hole) whose thermal activation initiates TL. As for example thermal activation of F centre electrons in the case of KC1 [I, 2, 31, KBr ,[4, 51 and NaCl [6] is advocated to be the initiating stop for the occurrance of TL. Contrary to this view point thermal activation of holes in the case of KC1 [7,8], KBr [9] and NaCl [lo]
is argued to be the initiating step. Thus it is clear that a unified model is yet to be arrived at to explain the results of TL of alkali halides [I-101.
In order to explain the above controversy recently we have proposed that thermal activation of F centre electron, which destroys a diinterstitial (i.e. a double hole centre) creates a transient single hole centre which being unstable above RT moves to a recombination centre and involves in a luminescent transition [Ill. In the case of crystals containing impurities which trap electrons during irradiation impurities act as the recombination centres. However, in the case of pure crystals recombination of the transient single hole centre with F centre electron is not ruled out.
In this paper we show that TL emission spectra
together with monochromatic isothermal decay can uniquely establish the recombination kinetics.
Secondly by studying the photostimulated mono- chromatic thermoluminescence of Mn emission, not only have we established the nature of charge carrier but also checked the validity of an proposed model [I 11.
2. Experimental. - Several pieces of laboratory grown Mn-doped KC1 crystal of approximate size 8 x 5 x 1 mm3 cleaved from the same bulk were used for study. In all the cases the crystals were given a heat treatment a t 400 O C for 30 min. and then quen- ched to RT (30 OC) before performing the TL expe- riments. The crystals were irradiated by X-rays obtained from a Mo target of a Machlett tube operated at 30 kV and 10 mA. F-stimulation of the X-irradiated crystal was done by the F-light obtained from a fila- ment lamp through a Jarrel-Ash monochromator.
The TL curves were recorded under identical conditions, the crystal being heated at a uniform rate of 44 OC/min. The TL emission was detected by a R-456 Multialkali Photomultiplier tube, the resulting photocurrent amplified by a electrometer amplifier was fed to a MV recorder. The temperature of the sample was recorded on a similar recorder. The emission spectra were scanned by a Jarrel-Ash monochromator in the region of 200 to 800 nm a t a scanning speed of 200 nm/min. Monochromatic TL and monochromatic isothermal decay were recorded by presetting the monochromator at the peak wave- length of the emission band.
3. Results and discussions. - Thermoluminescence of Mn-doped KC1 crystals irradiated with different doses of X-rays starting from3 min. to 30 min. were
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980668
C6-270 V. V. RATNAM, R. K. GARTIA AND B. S. ACHARYA
recorded. In all cases three TL peaks occurred at 95, 135 a t 190OC. This is in agreement with the result reported earlier [I, 21. The TL emission spectra of these peaks show two emission bands at 440 nm and 590 nm. The 440 nm band already observed in TL emission of pure KC1 has been attributed to F centre electron hole recombination [3, 71. The additional band observed at 590 nm in our Mn-doped KC1 can be attributed to Mn-emission. Since irradiation is known to produce Mn', and MnO centres, in general we can write,
where v = ~1590.
In the present investigation since the TL emission spectra consist of two bands which as we have men- tioned above arise due to two separate recombination processes, monochromatic isothermal decay of the 190 OC TL peak was recorded. The results are shown in figure 1. It is found that in both these cases recom- bination kinetics follow first order. These results establish that 190 OC TL peak which arises due to two distinct recombination processes is due to the thermal activation of charge carriers from one type of trap, retrapping being zero. Now naturally one would ask - What is the nature of the charge car- rier ? As per our equation (1) the obvious answer is that it is a hole.
nary TL data is certainly not adequate, Photostimu- lated TL can provide a way of detecting photoio- nization of centres allowing in some cases the sepa- ration of processes due to electron carriers from those due to hole carriers 1131. Using this technique it has been demonstrated that thermal activation of F centre electrons is the initiating step for the occur- rence of TL in KC1 [I], Ca-doped NaCl[6] and KBr [ 5 ] . However, in these cases we have not identified the emission centre. In the present study since the occur- rance of 590 emission band requires a mobile hole one would naturally conclude that, thermal activation of holes is the initiating step for occurrance of 590 nm emission TL in Mn-doped KCI. In order to check this, photostimulated TL of Mn-doped KC1 for 590 nm emission alone is studied. The monochro- matic TL curve of a 30 min. X-irradiated crystal for monochromator set at 590 nm is shown in figure 2 (Curve 1). As expected it shows all the three TL peaks observed in polychromatic TL curves. Curve 2 (Fig. 2) shows the TL of a crystal irradiated for 30 min. and heated to 160 OC before recording TL.
The result shows that the low temperature TL peaks occurring around 95O and 135 O C are thermally cleaned, leaving the 190 OC TLpeak isolated. However, when an irradiated crystal is heated to 160 OC and cooled down to RT and F-stimulated at RT for 5 min.
the low temperature TL peaks are found to occur again in the TL pattern (Curve 3, Fig. 2). Prolonged
lo3
KCL: Mn
6
+.
I I
0 LO 80 120
TIME IN SECONDS--
Fig. 1. - Monochromatic isothermal decay of the 190 OC TL peak
for 435 nm and 595 nm emissions of X-irradiated KC1 : Mn crystals. ~ i2, - ~ ~~~~~~~~~~~i~ t~ermo~uminescence , curves of 35 kv Irradiation dose 35 kV 10 mA for 30 min. 10 mA R.T. 30 min. X-ray irradiated KC1 :Mn crystals for 590 nm emission. Curve 1) as irradiated; 2) heated to 160 OC after irra- diation and cooled to R.T. for TL run ; 3) same treatment as,for 2
In order to specify the nature of charge carriers but F-stimulated at R.T. for 5 min. ; 4) same as 2 but F-stimulated
giving rise to the observed TL peaks, though ordi- for 15 min.
TEMPERATURE ('~1-
MONOCHROMATIC THERMOLUMINESCENCE AND MODELS OF RECOMBINATION KINETICS C6-271
F-stimulation at RT for 15 min. however destroys However, it is to be remembered that 590 nm emis- the low temperature TL peaks (Curve 4 of figure 2). sion is due to capture of a hole by Mn' centre. Both In this case F-stimulation acts as F-bleaching. This these conclusions fit in to our model wherein we type of behaviour is already found and discussed in have already proposed that thermally activated F the case of KC1 [14]. The present 590 emission photo- centre electrons destroying diinterstitials generate a stimulated TL shows that the 90 and 135 O C TL hole which recombine with Mn' ions to give 590 emis- peaks are due to thermal activation of electrons. sion.
References
[l] GARTIA, R. K., RATNAM, V. V. and MATHUR, B. K., Ind. J.
Phys. 50 (1976) 1009.
[2] JAIN, S. C., MEHENDRU, R. C., Phys. Rev. 140A (1965) 957.
[3] KATZ, I., CHENFOWX, B. and KRISTIANPOLLER, N., Phys.
Status Solidi (a) 12 (1972) 307.
[4] HAGESETH, G. T., Phys. Rev. B 5 (1972) 4060.
[5] GARTIA, R. K., ACHARYA, B. S. and RATNAM, V. V., ((On the role of F centres in the thermoluminescence of KBr s, Crystal Lattice Defects (in press).
[6] GARTIA, R. K., Phys. Status Solidi (a) 37 (1976) 571.
[7] AUSIN, V. and ALVAREZ RIVAS, J. L., J. Phys. C 5 (1972) 82.
[8] AUSIN and ALVAREZ RIVAS, J. L., Phys. Rev. B 6 (1972) 4828.
[9] ANG, F. C. and MYKURA, H., J. Phys. C 10 (1977) 3205.
[lo] LOPEZ, F. J., JAQUE, F., FORT, A. J. and AGULLOW-LOPEZ, F., J . Phys. Chem. Solids 38 (1977) 1101.
[ l l ] GARTIA, R. K. and RATNAM, V. V., J. Phys. Chem. Sol. 40 (1979) 331.
[12] MEHENDRU, R. C. and MITRA, V., J. Phys. Chem. Sol. 30 (1968) 102.
[13] FIBCHI, R. and SCARAMELLI, P., (( Thermoluminescence of Geological Materials D, Ed. P. J. McDougal (Academic Press, New York) 1968 299.
[14] RATNAM, V. V. and GARTIA, R. K., Phys. Status Solidi (a) 27 (1975) 627.
