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Band-edge emission in CuI single crystals
Journal of Luminescence 29 (1984) 215—221 North-Holland, Amsterdam
215
BAND-EDGE EMISSION IN Cul SINGLE CRYSTALS I.K. VERESHCHAGIN, V.A. NIKITENKO and S.G. STOYUKHIN Institute ofEnergetics, Moscow, U.S.S.R.
Received 17 April 1983
The photoluminescence spectra of Cul single crystals have been studied at T = 4.2 K and at various excitation levels. The emission band of donor—acceptor pairs (DAP) with a maximum at about 4200 A has been shown to possess a complex structure. Theoretical analyses and exciton spectroscopy data make it possible to calculate the ionization energies for the donors and acceptors participating in the formation of DAP, which are equal to = = 0.045—0.065 eV and EA = 0.155—0.170 eV, respectively. The fine structure of emission due to the annihilation of excitons bound on acceptor pairs (band maximum 4075 A) has been detected and calculated. The energy of the longitudinal optical phonon participating in the exciton—phonon interaction (LO — 18.7 meV) has been determined.
I. Infroduction In the region of the fundamental absorption edge, the emission spectrum of Cul single crystals displays a series of narrow bands due to the multiphonon annihilation of free and bound excitons and also to a relatively broad band (with a maximum at 4190—4250 A) which is ascribed to the emission of donor—acceptor pairs (DAP) [1—7].Here the luminescence spectrum of maximum complexity is observed in the case of single crystals grown by the hydrothermal synthesis and investigated at a temperature of 4.2 K [6]. In this paper, we report the heretofore unobserved separation of a complex band of DAP emission, describe a number of novel manifestations of exciton luminescence, and also demonstrate the fact that excitons are related to the defects participating in DAP formation.
2. Experimental To study the photoluminescence of interest, use was made of an ISP-51 spectrograph with the photographic recording of emission, the excitation source being a nitrogen laser (X = 3370 A) and a mercury lamp furnished with an UV-radiation transmitting filter. Chips of Cul single crystals grown by the 0022-2313/84/$03.00 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
216
/
1.K. Vereshchagin et al.
Bond-edge emission in Cu! single crystals
hydrothermal method and displaying a faint orange-red luminescence were examined [4]. Fig. 1 presents a typical photoluminescence spectrum of some Cul single crystals at 4.2 K upon excitation by a mercury lamp (curve 1) or by nitrogen laser radiation (curve 2). It is noteworthy that the complex band with a maximum in the 4190—4250 A range experiences separation into equidistant components having maxima at 4188, 4215 A (I); 4222, 4249, 4276, 4304, 4333, 4362 A (II); 4238, 4263—4265, 4292—4293, 4319—4320, and 4347—4348 A (III). The second series of equidistant bands is particularly pronounced when the level of excitation is low, so that, in view of the data reported in [2—7]and also because of the non-excitonic nature of the series (band halfwidth 0.01 eV) and the energy position of the series, it is feasible to associate the luminescence in question with an electron transfer from the donors to the acceptors in DAP. A good resolution of the bands constituting the equidistant series II provided for the accurate determination of the energy of phonons formed in the process of recombination. The result obtained (18.7 meV) are in good agreement with the energy of LO phonons determined earlier by various techniques [8,9]. LO
~1 LQ
.
1
~ LO.~ I.OT•~LOTLO LO
LO~
I~
*t,J~~~•
100
~~
It
I cx~j 01 I-
~II
20
-~l
~
t~ ,‘
-,
~~O75
~Io~
~j w
H
r
II It
~O5O
II
I
‘-a
~
4125
‘\__
1,r-~-
I
4150
4200
liZ5O
4500
14350
Fig. 1. Photoluminescence spectrum of a Cul single crystal at 4.2 K upon excitation by a mercury lamp (I) and N2-laser (2) radiation.
1K. Vereshchagin et a!. / Band-edge emission in Cul single crystals
217
3. Analysis of the data Let us evaluate the ionization energy of donors and acceptors that form DAP (series II). To do so, it is pertinent to consider a number of parameters necessary for carrying out such an evaluation. Insofar, as the binding energy of free Z12 excitons equals G 0.057 eV [3,10] and the decay of polaritons in the =
lower branch of the dispersion curve at 4.2 K is accompanied by emission at A 4053—4055 A (E. 3.058 eV) [2,3,5,11], the energy gap may be assumed to be Eg 3.115 eV. In order to calculate the binding energy of the hydrogen-like donor ED G(1 ± a) (eV) the knowledge of the ratio of the effective masses of electron and hole, a m~/m~,is essential. This ratio can be assessed using the results of studies of the luminescence H-band (exciton—electron interaction), in which at a reduced exciton mass of ~s 0.27 m0 there were obtained the values 0.31 m0 and m~ 2. 1 m0 [6] and, accordingly, a 0.15. More recent data provide grounds for assuming that p. 0.122 m0 [10], and this value, in compliance with the results obtained in [6], leads to m~ 0.14 m0 and m~ 0.94 m0. The value of a, however, remains equal to 0.15 and, in conformity with the hydrogen-like model, yields ED 0.065 eV. Experimental results [12] point to the value ED 0.045 eV, and therefore, we shall proceed on the assumption that in Cul shallow donors are present with ED 0.045—0.065 eV. Since the first band of the equidistant series II appears due to the phononless emission of distant DAP characterized by the energy of defect interaction of the order ~ 0.02—0.03 eV and taking into consideration the obtained values of Eg, ED and also h~ 2.936 eV, we find that the formation of DAP involves acceptors disposed at a depth of about EA 0.125—0.165 eV from the valence band. On the other hand, inasmuch as the front phononless band 4188 A (I) is distinct from the exciton lines by its adequately significant halfwidth and displays some intensity enhancement with temperature rise to 80 K, it2B6 is reasonable suggestduethat the electron band incapture question, compounds, toappears to free ontobyan analogy acceptor with whichA is a DAP component, and both series I and II are associated with electron capture onto the same acceptor type [13]. In this case, the recombination of free electrons occurs on acceptors with energy EA 0.155 eV. Disregarding, in the present paper, the charge states of the donor partners of acceptors participating in free electron capture, it is feasible to suggest, on the basis of the results obtained, the presence of defects with energy EA 0.155—0.170 eV in Cul single crystals. The presence of such centers should manifest itself in the appearance of an intense band I~of excitons bound on neutral acceptors, the existence of such a band being typical of other copper halides [2,3] which, like Cu!, are p-type conductors. In our opinion, a likely analogue of this band is the complex =
=
=
=
=
=
=
=
=
=
=
=
=
=
218
1. K. Vereshchagin et a!.
/ Band
-
edge emission in Cul single crystals
narrow band with a maximum at 4073—4075 A which invariably accompanies the appearance of equidistant series I and II and as regards its energy level relative to the emission band of free Z12 excitons, corresponds to the peak I~of CuBr single crystals [3]. The binding energy to EA ratio is here in good agreement with the results obtained for other compounds having similar values of a [14]. Let us consider in greater detail the exciton luminescence of crystals. In many specimens with a low resistivity a sharply asymmetric form of the band I~is observed with a fine structure in this long-wave tail (fig. 1, curve 1). At a lower acceptor content, the band J~becomes less intense, more narrow and symmetrical, while at its long-wave wing the fine structure disappears (the DAF emission in such crystals is almost completely absent), as shown in fig. 2. In this case there also occurs a slight blue shift of the band maximum. A similar pattern has of late been observed in some semiconductors doped with an acceptor impurity, e.g., in InP and ZnTe [15,16], and lends itself to a convincing interpretation in terms of the emissive annihilation of excitons bound onto neutral acceptor pairs. Indeed, acceptor concentration growth causes the distance between centres to be comparable with the radius of free excitons, thereby making it necessary to take into consideration the effect of neighbouring acceptors on the localization energy of bound excitons. This
~OTH.~b.
i00
1.0 .~
10
80
A~A 4015
‘1100
14125
4150
Fig. 2. Photoluminescence spectrum of a CuT single crystal at 4.2 K (excitation by UV radiation of a mercury lamp).
1. K. Vereshchagin et a!.
/
Band - edge emission in Cu! single crystals
219
effect results in localization energy growth which proceeds discretely as the distance between the interacting acceptors in the crystal lattice diminishes. An empirical relationship [15,16] (1) ~E(R)=E0exp(—R/R0)3 is the case under consideration, it describes satisfactorily the observed fine structure at E 0 23 meV and R0 16 A. Here the intensity of emission for the given values of R, is determined by the equation [15,16]: I(R)—P(R)z(R), (2) wherein P( R) is the probability of existence of acceptor pairs with the given value R and2NA at a concentration of centers NA: exp(—~i~R3NA) (3) P(R)=477R and Z(R) is the degree of filling of the spherical shell with the radius R,~, —
—
where the radius of a possible mth shell is given by the equation R~, (x~~ x 2 +(Ym _y~)2 +(Zm z 2, (4) 0) z,,~stand for the coordinates 0) and x~,y,,~ and of the m th shell acceptor in fractions of the unit cell (Cu! possesses the sphalerite cubic type cell, the lattice Constant at 4.2 K being a 6.028 A [17]). To obtain a continuous intensity curve, we resort to the relationship =
—
—
=
I~(R)dR Z(Rm)P(Rm) exp
R —
R
m ‘q(Rm) —
2
dR,
(5)
where the broadening parameter ~ was fitted empirically to various R values. ~l0TH.eb.
V
V
~.\
~ ~‘t V
14090
14090
(I
0
14100
Fig. 3. Theoretical (1) and experimental (2) spectrum of emission due to excitons bound on acceptor pairs in Cu! single crystals at 4.2 K.
220
1. K. Vereshchagin et al.
/
Band - edge emission in Cu! single crystals
Fig. 3 shows the calculated (1) and the experimental (2) curve of emission intensity (calculation was carried out for NA 1017 cm3), and the comparison of the curves for m — 8—20 demonstrates the feasibility of the luminescence of excitons bound on acceptor pairs. The concentration of imperfections of the order of 1017~~1018cm3 is likely to be real, thereby altering somewhat the slope of the calculated curve but having no effect upon the fine structure pattern. The value of ~ E( R) counted off the line J~when the formation of acceptor pairs is absent (fig. 2). The asymmetric shape of the observed band in the presence of acceptor pairs can be interpreted in terms of fine structure overlapping and the feasibility of exciton tunnelling between the nearestneighbour states. The 1 1—LO band with a maximum at 4100 A is likewise observed. In the spectral range of DAP emission (series II), particularly in the case of laser excitation, the doublet structure can be observed at 4237, 4239; 4263, 4265 (series III) and 4253, 4255; 4279, 4281; 4307 A (equidistant series IV). The fact that these emission bands are narrow and experience a marked increase in intensity at higher excitation levels indicates their excitonic nature. Under laser excitation there appears an emission band having maxima at 4086, 4087.5 and 4090 A missing in mercury lamp excited spectra. The nature of this emission calls for further investigation, the same being true of the luminescence in the 4109—4114 A region. In the general case, the emission spectrum in the region of the fundamental absorption edge at 4.2 K is highly complex and reflects the exciton—phonon interaction [6], the fine structure of DAP emission, and the presence of excitons localized on acceptor pairs.
Acknowledgements We are indebted to B.V. Novikov for offering us the possibility of carrying out some experiments at the Leningrad State University and also to V.P. Popolitov for growing the Cu! single crystals.
References Ill [2] [3] [4] [5] [6]
S. Nikitine, D. Roth and M. Certier, J. Phys. 27 (1966) 329. T. Goto, T. Takahashi and M. Ueta, J. Phys. Soc. Jpn. 24 (1968) 314. M. Ueta, Rev. Roum. Phys. 15 (1970) 369. V.A. Nikitenko, V.!. Popolitov, S.G. Stoyukhin et al., Pisma ZhTF 5 (1979) 1177. V.A. Nikitenko, S.G. Stoyukhin, V.1. Popolitov and Yu.M. Mininson, ZhPS 34 (1981) 435. V.A. Nikitenko, S.G. Stoyukhin, V.!. Popolitov and Yu.M. Mininson, Optika i Spektroskopiya 51(1981) 7.
1. K. Vereshchagin et a!.
/
Band - edge emission in Cu! single crystals
221
[7] 1K. Vereshchagin, V.A. Nikitenko and S.G. Stoyukhin, J. Appl. Spectrosc. (Soviet Union) 36
[8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
(1982) 848. J.E. Potts, R.C. Hanson, CT. Walker and S. Schwab, Solid State Commun. 13 (1973) 389. T. Nanba, K. Haehisu and M. Ikerawa, J. Phys. Soc. Jpn. 50 (1981) 1579. L. Bedikyan, L.A. Ageev and V.K. Miloslavsky, Optika i Spektroskopiya 48 (1980) 518. S. Suga, K. Cho, Y. Niji, J.C. Merle and T. Sauder, Technical Reports of ISSP, A No 981 (1979) 1. ChIn Yu. T. Goto and M. Ueta, J. Phys. Soc. Jpn. 32 (1972) 1971. V.F. Grin, A.v. Lyubchenko, E.A. Salkov and M.K. Sheinkman, FTP 9 (1975) 1507. AM. gtoneham, Theory of Defects in Solids (Clarendon Press, Moscow, Oxford, 1975) Vol. 2. E. Molva and N. Magnea, Phys. Stat. Sol. (b) 102 (1980) 475. P.J. Dean and A.M. White, Solid State Electr. 21(1978)1351. IN. PlendI and L.C. Mansur, AppI. Opt. 11(1972)1194.
215
BAND-EDGE EMISSION IN Cul SINGLE CRYSTALS I.K. VERESHCHAGIN, V.A. NIKITENKO and S.G. STOYUKHIN Institute ofEnergetics, Moscow, U.S.S.R.
Received 17 April 1983
The photoluminescence spectra of Cul single crystals have been studied at T = 4.2 K and at various excitation levels. The emission band of donor—acceptor pairs (DAP) with a maximum at about 4200 A has been shown to possess a complex structure. Theoretical analyses and exciton spectroscopy data make it possible to calculate the ionization energies for the donors and acceptors participating in the formation of DAP, which are equal to = = 0.045—0.065 eV and EA = 0.155—0.170 eV, respectively. The fine structure of emission due to the annihilation of excitons bound on acceptor pairs (band maximum 4075 A) has been detected and calculated. The energy of the longitudinal optical phonon participating in the exciton—phonon interaction (LO — 18.7 meV) has been determined.
I. Infroduction In the region of the fundamental absorption edge, the emission spectrum of Cul single crystals displays a series of narrow bands due to the multiphonon annihilation of free and bound excitons and also to a relatively broad band (with a maximum at 4190—4250 A) which is ascribed to the emission of donor—acceptor pairs (DAP) [1—7].Here the luminescence spectrum of maximum complexity is observed in the case of single crystals grown by the hydrothermal synthesis and investigated at a temperature of 4.2 K [6]. In this paper, we report the heretofore unobserved separation of a complex band of DAP emission, describe a number of novel manifestations of exciton luminescence, and also demonstrate the fact that excitons are related to the defects participating in DAP formation.
2. Experimental To study the photoluminescence of interest, use was made of an ISP-51 spectrograph with the photographic recording of emission, the excitation source being a nitrogen laser (X = 3370 A) and a mercury lamp furnished with an UV-radiation transmitting filter. Chips of Cul single crystals grown by the 0022-2313/84/$03.00 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
216
/
1.K. Vereshchagin et al.
Bond-edge emission in Cu! single crystals
hydrothermal method and displaying a faint orange-red luminescence were examined [4]. Fig. 1 presents a typical photoluminescence spectrum of some Cul single crystals at 4.2 K upon excitation by a mercury lamp (curve 1) or by nitrogen laser radiation (curve 2). It is noteworthy that the complex band with a maximum in the 4190—4250 A range experiences separation into equidistant components having maxima at 4188, 4215 A (I); 4222, 4249, 4276, 4304, 4333, 4362 A (II); 4238, 4263—4265, 4292—4293, 4319—4320, and 4347—4348 A (III). The second series of equidistant bands is particularly pronounced when the level of excitation is low, so that, in view of the data reported in [2—7]and also because of the non-excitonic nature of the series (band halfwidth 0.01 eV) and the energy position of the series, it is feasible to associate the luminescence in question with an electron transfer from the donors to the acceptors in DAP. A good resolution of the bands constituting the equidistant series II provided for the accurate determination of the energy of phonons formed in the process of recombination. The result obtained (18.7 meV) are in good agreement with the energy of LO phonons determined earlier by various techniques [8,9]. LO
~1 LQ
.
1
~ LO.~ I.OT•~LOTLO LO
LO~
I~
*t,J~~~•
100
~~
It
I cx~j 01 I-
~II
20
-~l
~
t~ ,‘
-,
~~O75
~Io~
~j w
H
r
II It
~O5O
II
I
‘-a
~
4125
‘\__
1,r-~-
I
4150
4200
liZ5O
4500
14350
Fig. 1. Photoluminescence spectrum of a Cul single crystal at 4.2 K upon excitation by a mercury lamp (I) and N2-laser (2) radiation.
1K. Vereshchagin et a!. / Band-edge emission in Cul single crystals
217
3. Analysis of the data Let us evaluate the ionization energy of donors and acceptors that form DAP (series II). To do so, it is pertinent to consider a number of parameters necessary for carrying out such an evaluation. Insofar, as the binding energy of free Z12 excitons equals G 0.057 eV [3,10] and the decay of polaritons in the =
lower branch of the dispersion curve at 4.2 K is accompanied by emission at A 4053—4055 A (E. 3.058 eV) [2,3,5,11], the energy gap may be assumed to be Eg 3.115 eV. In order to calculate the binding energy of the hydrogen-like donor ED G(1 ± a) (eV) the knowledge of the ratio of the effective masses of electron and hole, a m~/m~,is essential. This ratio can be assessed using the results of studies of the luminescence H-band (exciton—electron interaction), in which at a reduced exciton mass of ~s 0.27 m0 there were obtained the values 0.31 m0 and m~ 2. 1 m0 [6] and, accordingly, a 0.15. More recent data provide grounds for assuming that p. 0.122 m0 [10], and this value, in compliance with the results obtained in [6], leads to m~ 0.14 m0 and m~ 0.94 m0. The value of a, however, remains equal to 0.15 and, in conformity with the hydrogen-like model, yields ED 0.065 eV. Experimental results [12] point to the value ED 0.045 eV, and therefore, we shall proceed on the assumption that in Cul shallow donors are present with ED 0.045—0.065 eV. Since the first band of the equidistant series II appears due to the phononless emission of distant DAP characterized by the energy of defect interaction of the order ~ 0.02—0.03 eV and taking into consideration the obtained values of Eg, ED and also h~ 2.936 eV, we find that the formation of DAP involves acceptors disposed at a depth of about EA 0.125—0.165 eV from the valence band. On the other hand, inasmuch as the front phononless band 4188 A (I) is distinct from the exciton lines by its adequately significant halfwidth and displays some intensity enhancement with temperature rise to 80 K, it2B6 is reasonable suggestduethat the electron band incapture question, compounds, toappears to free ontobyan analogy acceptor with whichA is a DAP component, and both series I and II are associated with electron capture onto the same acceptor type [13]. In this case, the recombination of free electrons occurs on acceptors with energy EA 0.155 eV. Disregarding, in the present paper, the charge states of the donor partners of acceptors participating in free electron capture, it is feasible to suggest, on the basis of the results obtained, the presence of defects with energy EA 0.155—0.170 eV in Cul single crystals. The presence of such centers should manifest itself in the appearance of an intense band I~of excitons bound on neutral acceptors, the existence of such a band being typical of other copper halides [2,3] which, like Cu!, are p-type conductors. In our opinion, a likely analogue of this band is the complex =
=
=
=
=
=
=
=
=
=
=
=
=
=
218
1. K. Vereshchagin et a!.
/ Band
-
edge emission in Cul single crystals
narrow band with a maximum at 4073—4075 A which invariably accompanies the appearance of equidistant series I and II and as regards its energy level relative to the emission band of free Z12 excitons, corresponds to the peak I~of CuBr single crystals [3]. The binding energy to EA ratio is here in good agreement with the results obtained for other compounds having similar values of a [14]. Let us consider in greater detail the exciton luminescence of crystals. In many specimens with a low resistivity a sharply asymmetric form of the band I~is observed with a fine structure in this long-wave tail (fig. 1, curve 1). At a lower acceptor content, the band J~becomes less intense, more narrow and symmetrical, while at its long-wave wing the fine structure disappears (the DAF emission in such crystals is almost completely absent), as shown in fig. 2. In this case there also occurs a slight blue shift of the band maximum. A similar pattern has of late been observed in some semiconductors doped with an acceptor impurity, e.g., in InP and ZnTe [15,16], and lends itself to a convincing interpretation in terms of the emissive annihilation of excitons bound onto neutral acceptor pairs. Indeed, acceptor concentration growth causes the distance between centres to be comparable with the radius of free excitons, thereby making it necessary to take into consideration the effect of neighbouring acceptors on the localization energy of bound excitons. This
~OTH.~b.
i00
1.0 .~
10
80
A~A 4015
‘1100
14125
4150
Fig. 2. Photoluminescence spectrum of a CuT single crystal at 4.2 K (excitation by UV radiation of a mercury lamp).
1. K. Vereshchagin et a!.
/
Band - edge emission in Cu! single crystals
219
effect results in localization energy growth which proceeds discretely as the distance between the interacting acceptors in the crystal lattice diminishes. An empirical relationship [15,16] (1) ~E(R)=E0exp(—R/R0)3 is the case under consideration, it describes satisfactorily the observed fine structure at E 0 23 meV and R0 16 A. Here the intensity of emission for the given values of R, is determined by the equation [15,16]: I(R)—P(R)z(R), (2) wherein P( R) is the probability of existence of acceptor pairs with the given value R and2NA at a concentration of centers NA: exp(—~i~R3NA) (3) P(R)=477R and Z(R) is the degree of filling of the spherical shell with the radius R,~, —
—
where the radius of a possible mth shell is given by the equation R~, (x~~ x 2 +(Ym _y~)2 +(Zm z 2, (4) 0) z,,~stand for the coordinates 0) and x~,y,,~ and of the m th shell acceptor in fractions of the unit cell (Cu! possesses the sphalerite cubic type cell, the lattice Constant at 4.2 K being a 6.028 A [17]). To obtain a continuous intensity curve, we resort to the relationship =
—
—
=
I~(R)dR Z(Rm)P(Rm) exp
R —
R
m ‘q(Rm) —
2
dR,
(5)
where the broadening parameter ~ was fitted empirically to various R values. ~l0TH.eb.
V
V
~.\
~ ~‘t V
14090
14090
(I
0
14100
Fig. 3. Theoretical (1) and experimental (2) spectrum of emission due to excitons bound on acceptor pairs in Cu! single crystals at 4.2 K.
220
1. K. Vereshchagin et al.
/
Band - edge emission in Cu! single crystals
Fig. 3 shows the calculated (1) and the experimental (2) curve of emission intensity (calculation was carried out for NA 1017 cm3), and the comparison of the curves for m — 8—20 demonstrates the feasibility of the luminescence of excitons bound on acceptor pairs. The concentration of imperfections of the order of 1017~~1018cm3 is likely to be real, thereby altering somewhat the slope of the calculated curve but having no effect upon the fine structure pattern. The value of ~ E( R) counted off the line J~when the formation of acceptor pairs is absent (fig. 2). The asymmetric shape of the observed band in the presence of acceptor pairs can be interpreted in terms of fine structure overlapping and the feasibility of exciton tunnelling between the nearestneighbour states. The 1 1—LO band with a maximum at 4100 A is likewise observed. In the spectral range of DAP emission (series II), particularly in the case of laser excitation, the doublet structure can be observed at 4237, 4239; 4263, 4265 (series III) and 4253, 4255; 4279, 4281; 4307 A (equidistant series IV). The fact that these emission bands are narrow and experience a marked increase in intensity at higher excitation levels indicates their excitonic nature. Under laser excitation there appears an emission band having maxima at 4086, 4087.5 and 4090 A missing in mercury lamp excited spectra. The nature of this emission calls for further investigation, the same being true of the luminescence in the 4109—4114 A region. In the general case, the emission spectrum in the region of the fundamental absorption edge at 4.2 K is highly complex and reflects the exciton—phonon interaction [6], the fine structure of DAP emission, and the presence of excitons localized on acceptor pairs.
Acknowledgements We are indebted to B.V. Novikov for offering us the possibility of carrying out some experiments at the Leningrad State University and also to V.P. Popolitov for growing the Cu! single crystals.
References Ill [2] [3] [4] [5] [6]
S. Nikitine, D. Roth and M. Certier, J. Phys. 27 (1966) 329. T. Goto, T. Takahashi and M. Ueta, J. Phys. Soc. Jpn. 24 (1968) 314. M. Ueta, Rev. Roum. Phys. 15 (1970) 369. V.A. Nikitenko, V.!. Popolitov, S.G. Stoyukhin et al., Pisma ZhTF 5 (1979) 1177. V.A. Nikitenko, S.G. Stoyukhin, V.1. Popolitov and Yu.M. Mininson, ZhPS 34 (1981) 435. V.A. Nikitenko, S.G. Stoyukhin, V.!. Popolitov and Yu.M. Mininson, Optika i Spektroskopiya 51(1981) 7.
1. K. Vereshchagin et a!.
/
Band - edge emission in Cu! single crystals
221
[7] 1K. Vereshchagin, V.A. Nikitenko and S.G. Stoyukhin, J. Appl. Spectrosc. (Soviet Union) 36
[8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
(1982) 848. J.E. Potts, R.C. Hanson, CT. Walker and S. Schwab, Solid State Commun. 13 (1973) 389. T. Nanba, K. Haehisu and M. Ikerawa, J. Phys. Soc. Jpn. 50 (1981) 1579. L. Bedikyan, L.A. Ageev and V.K. Miloslavsky, Optika i Spektroskopiya 48 (1980) 518. S. Suga, K. Cho, Y. Niji, J.C. Merle and T. Sauder, Technical Reports of ISSP, A No 981 (1979) 1. ChIn Yu. T. Goto and M. Ueta, J. Phys. Soc. Jpn. 32 (1972) 1971. V.F. Grin, A.v. Lyubchenko, E.A. Salkov and M.K. Sheinkman, FTP 9 (1975) 1507. AM. gtoneham, Theory of Defects in Solids (Clarendon Press, Moscow, Oxford, 1975) Vol. 2. E. Molva and N. Magnea, Phys. Stat. Sol. (b) 102 (1980) 475. P.J. Dean and A.M. White, Solid State Electr. 21(1978)1351. IN. PlendI and L.C. Mansur, AppI. Opt. 11(1972)1194.