Photochromic effect and photoconductivity in undoped and doped Bi₁₂SiO₂₀ crystals
Photoinduced phenomena in the sillenite family crystals Bi₁₂MO₂₀ (BMO, with M = Si, Ti, Ge) are studied intensively because these crystals are widely used as functional media in different types of light-modulating devices. So, the study of photoinduced processes and their modification by doping is...
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Інститут фізики конденсованих систем НАН України
2007
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irk-123456789-1183852017-05-31T03:06:47Z Photochromic effect and photoconductivity in undoped and doped Bi₁₂SiO₂₀ crystals Panchenko, T.V. Strelets, K.Yu. Photoinduced phenomena in the sillenite family crystals Bi₁₂MO₂₀ (BMO, with M = Si, Ti, Ge) are studied intensively because these crystals are widely used as functional media in different types of light-modulating devices. So, the study of photoinduced processes and their modification by doping is very important in these applications. At present, the effect of different doping ions on optical and photoelectric properties has been studied on Bi₁₂MO₂₀ (BTO) crystals only [1–5]. It is shown, in particular, that Cu – ions consider- ably increase the photochromic effect (PCE) in the visible range of spectra and decrease PCE in IR [1,6,7]. Mo-ions reduce the relaxation time of photoinduced optical absorption [5,7]. Nevertheless, the PCE mechanisms have not been studied well enough. It seems that unified investigations of PCE and photoconductivity (PC) can provide useful information in solving this problem. In the present paper, the results of investigations of PC and PCE in Bi₁₂MO₂₀ (BSO) crystals doped by Cu-, Ag- and Mo-ions are presented. У спектральному дiапазонi 0.5–3.5 eV дослiдженi стацiонарнi i фотоiндукованi спектри оптичного поглинання i фотопровiдностi, чистих i легованих iонами Cu, Ag i Mo кристалiв Bi₁₂MO₂₀. Спостерiгали вплив легування на фотохромний ефект i iндуковану фотопровiднiсть, отримали температурнi залежностi фотоiндукованого оптичного поглинання i фотопровiдностi. Показана вiдсутнiсть кореляцiї у спектральному розподiлi i у температурнiй залежностi обох ефектiв. 2007 Article Photochromic effect and photoconductivity in undoped and doped Bi₁₂SiO₂₀ crystals / T.V. Panchenko, K.Yu. Strelets // Condensed Matter Physics. — 2007. — Т. 10, № 2(50). — С. 289-292. — Бібліогр.: 8 назв. — англ. 1607-324X PACS: 78.20.-e, 78.40.-q DOI:10.5488/CMP.10.2.289 http://dspace.nbuv.gov.ua/handle/123456789/118385 en Condensed Matter Physics Інститут фізики конденсованих систем НАН України |
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Photoinduced phenomena in the sillenite family crystals Bi₁₂MO₂₀ (BMO, with M = Si, Ti,
Ge) are studied intensively because these crystals are widely used as functional media in different types of light-modulating devices. So, the study of photoinduced processes and their modification by doping is very important in these applications. At present, the effect of different doping ions on optical and photoelectric properties has been studied on Bi₁₂MO₂₀ (BTO) crystals only [1–5]. It is shown, in particular, that Cu – ions consider-
ably increase the photochromic effect (PCE) in the visible range of spectra and decrease PCE in IR [1,6,7]. Mo-ions reduce the relaxation time of photoinduced optical absorption [5,7]. Nevertheless, the PCE mechanisms have not been studied well enough. It seems that unified investigations of PCE and photoconductivity (PC) can provide useful information in solving this problem. In the present paper, the results of investigations of PC and PCE in Bi₁₂MO₂₀ (BSO) crystals doped by Cu-, Ag- and Mo-ions are presented. |
| format |
Article |
| author |
Panchenko, T.V. Strelets, K.Yu. |
| spellingShingle |
Panchenko, T.V. Strelets, K.Yu. Photochromic effect and photoconductivity in undoped and doped Bi₁₂SiO₂₀ crystals Condensed Matter Physics |
| author_facet |
Panchenko, T.V. Strelets, K.Yu. |
| author_sort |
Panchenko, T.V. |
| title |
Photochromic effect and photoconductivity in undoped and doped Bi₁₂SiO₂₀ crystals |
| title_short |
Photochromic effect and photoconductivity in undoped and doped Bi₁₂SiO₂₀ crystals |
| title_full |
Photochromic effect and photoconductivity in undoped and doped Bi₁₂SiO₂₀ crystals |
| title_fullStr |
Photochromic effect and photoconductivity in undoped and doped Bi₁₂SiO₂₀ crystals |
| title_full_unstemmed |
Photochromic effect and photoconductivity in undoped and doped Bi₁₂SiO₂₀ crystals |
| title_sort |
photochromic effect and photoconductivity in undoped and doped bi₁₂sio₂₀ crystals |
| publisher |
Інститут фізики конденсованих систем НАН України |
| publishDate |
2007 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/118385 |
| citation_txt |
Photochromic effect and photoconductivity in undoped and doped Bi₁₂SiO₂₀ crystals / T.V. Panchenko, K.Yu. Strelets // Condensed Matter Physics. — 2007. — Т. 10, № 2(50). — С. 289-292. — Бібліогр.: 8 назв. — англ. |
| series |
Condensed Matter Physics |
| work_keys_str_mv |
AT panchenkotv photochromiceffectandphotoconductivityinundopedanddopedbi12sio20crystals AT streletskyu photochromiceffectandphotoconductivityinundopedanddopedbi12sio20crystals |
| first_indexed |
2025-07-08T13:52:59Z |
| last_indexed |
2025-07-08T13:52:59Z |
| _version_ |
1837087096819417088 |
| fulltext |
Condensed Matter Physics 2007, Vol. 10, No 2(50), pp. 289–292
Photochromic effect and photoconductivity in undoped
and doped Bi12SiO20 crystals
T.V.Panchenko, K.Yu.Strelets
Dnipropetrovs’k National University, 13 Naukova Str., 49050 Dnipropetrovs’k, Ukraine
Received April 13, 2007, in final form May 18, 2007
Stationary and photoinduced spectra of optical absorption and photoconductivity of undoped and doped (by
Cu-, Ag- and Mo-ions) Bi12SiO20 crystals have been investigated in a spectral range of 0.5–3.5 eV. The action
of doping on photochromic effect and induced photoconductivity is determined. The temperature dependence
of photoinduced optical absorption and photoconductivity is observed. The absence of the correlation is shown
between spectral distributions and temperature dependencies of these effects.
Key words: photochromic effect, optical absorption, photoconductivity, sillenite crystals
PACS: 78.20.-e, 78.40.-q
1. Introduction
Photoinduced phenomena in the sillenite family crystals Bi12MO20 (BMO, with M = Si, Ti,
Ge) are studied intensively because these crystals are widely used as functional media in different
types of light-modulating devices. So, the study of photoinduced processes and their modification
by doping is very important in these applications.
At present, the effect of different doping ions on optical and photoelectric properties has been
studied on Bi12TiO20 (BTO) crystals only [1–5]. It is shown, in particular, that Cu – ions consider-
ably increase the photochromic effect (PCE) in the visible range of spectra and decrease PCE in IR
[1,6,7]. Mo-ions reduce the relaxation time of photoinduced optical absorption [5,7]. Nevertheless,
the PCE mechanisms have not been studied well enough. It seems that unified investigations of
PCE and photoconductivity (PC) can provide useful information in solving this problem. In the
present paper, the results of investigations of PC and PCE in Bi12SiO20 (BSO) crystals doped by
Cu-, Ag- and Mo-ions are presented.
2. Experiments
Nominally undoped and doped BSO crystals were grown using the Czochralski method. Dopants
(Cu-, Ag- and Mo- ions) were introduced in the starting materials in an oxide form. The con-
tent of Ag, Mo and Cu in BSO crystals constitutes 0.1, 0.1 and 0.3 mass %, respectively. Opti-
cal absorption (α0(hν), αPI(hν)) and photoconductivity (∆σP
0 (hν) = σP
0 (hν) − σT
0 ,∆σPI(hν) =
σPI(hν) − σT) spectra have been studied where σT
0 (ν) – dark conductivity, (α0(hν), σP
0 (hν)) and
(αPI(hν), σPI(hν)) – optical absorption and photoconductivity spectra before and after the blue
light illumination corresponding to stationary and excited state of the crystals. Induced absorp-
tion ∆αPI(hν) = αPI(hν) − α0(hν) and induced (additional) photoconductivity (IPC) spectra
∆∗σPI(hν) = ∆σPI(hν) − ∆σP
0 (hν) characterizing PCE and IPC have been analyzed.
Optical transmission spectra t(hν) were obtained using Specord M 40, Specord NIR 61 and Cary
– 5E spectrophotometers. Measurements were carried out on polished plane-parallel (001)-cuts with
0.03–5 mm thickness. Absorption spectra α(hν) were calculated according to [6]. Photoconductivity
spectra were measured by means of the monochromator SPM-2 using the techniques of synchronous
detection. Ag-electrodes were obtained by Ag-paste firing. All measurements were carried out at
c© T.V.Panchenko, K.Yu.Strelets 289
T.V.Panchenko, K.Yu.Strelets
T = 80 K. PCE and IPC were excited using 600 W halogen lamp. To return from the excited to
the initial stationary state, the samples were slowly heated up to 800 K and then cooled down to
80 K during 24 hours.
3. Results and discussion
The common picture of the effect of Ag-, Cu-, Mo- ions on the absorption and photoconductivity
spectra is given in (figure 1). Stationary spectra α0(hν) show new structural bands of absorption
(with respect to undoped BSO) in near IR (BSO:Ag, BSO:Cu) and blue-green range (BSO:Mo)
(figure 1a). But stationary photoconductivity spectra ∆σPI
0 (hν) show small changes. There should
be noted a substantial decrease of photosensitivity (with respect to BSO) in the BSO:Cu crystals
in the whole spectral range (figure 1b).
Figure 1. Spectra of optical absorption lnα0(hν); lnα
PI(hν) (a) for BSO (a, 1, 1′), BSO:Ag (a, 2,
2′), BSO:Mo (a, 3, 3′) and BSO:Cu (a, 4, 4′) crystals and spectra of photoconductivity ln∆σ
P
0 ,
ln∆σ
∗PI(b) for BSO (b, 1, 1′),BSO:Ag (b, 2, 2′), BSO:Cu (b, 3, 3′) crystals after illumination
by dark blue light. T = 80 K. Curves lnα0(hν) and lnα
PI(hν) are displaced on a vertical line
on 3 (a, 1, 1′), 0.5 (a, 2, 2′), 2 (a, 3, 3′) and 6 (a, 4, 4′) units. Spectra of photoconductivity
BSO:Cu and BSO:Ag are displaced on a vertical in relation to spectra BSO on 14 and 9 units,
accordingly.
The spectra of photoexcited state ∆αPI(hν) and ∆σ∗PI(hν) are characterized by an increase
of absorption and photoconductivity with the change of the absorption band structure, while the
photoconductivity spectra become more diffusive (figure 1).
There is no correlation between the spectral distribution of absorption and photoconductivity.
There are no absorption peaks related to a doped photosensitivity threshold within the IR and
the absorption shoulder is considerably shifted with respect to the band of the increased photo-
sensitivity in a visible spectral range (figure 1a, b). It seems that intra-center absorption creates a
background that veils the absorption peaks of the “doping level – allowed band” types.
The impurity effect on PCE and IPC is as follows. Cu ions considerably increase PCE in a
visible range of spectra and decrease in IR. There are additional absorption bands in near IR due
to Ag-ions. Mo-ions provide the PCE in a visible range higher than in the undoped BSO crystals
(figure 2a).
The IPC is observed in the overall investigated spectral range. In the long-wave range the effect
is weak and is typical of semiconductors, i.e. it is conditioned by filling the impurity levels. In
a short-wave range (adjacent to absorption edge) IPC is too strong and ∆∗σPI(hν) spectra are
rather complicated. In BSO crystals the illumination causes a reduction of photosensitivity in a
band near 2.5 eV. Near the fundamental absorption edge, intensive bands of IPC with hνmax ≈
290
Photochromic effect and photoconductivity in Bi12SiO20 crystals
3 eV and 3.03 eV are observed and PCE decreases. In BSO:Cu crystals, IPC takes place only in
narrow boundary bands. (figure 2b). PCE and IPC spectra are essentially different. IPC spectra
distribution have a form of a band adjacent to the UV - edge of investigated range (figure 2a),
whereas PCE bands are shifted to its middle part (figure 2b).
Figure 2. Spectra of PCE ∆α
PI(hν) (a) and IPC ∆σ
∗PI(hν) (b) for BSO (a, 1, b, 1), BSO:Cu
(a, 2, b, 2), BSO:Mo (a,3), BSO:Ag (a, 4, b, 3) crystals. T = 80 K.
The ∆αPI(hν), α0(hν) and αPI(hν) spectra analysis within the framework of the ligand crys-
talline field theory shows that photochemical reactions are responsible for the following changes
of the doping ion charge: Cu3+
−→Cu2+; Ag+
−→Ag2+; Mo5+
−→Mo4+, during transition to
the metastable photoinduced state. Cu- and Ag-ions replace Bi3+-ions in octahedral and Mo-ions
replace Si4+-ions in tetrahedral positions of BSO lattice. Distinctions between the temperature
dependences of photoinduced absorption and induced photoconductivity turn out to be another
confirmation of distinctions of the PCE and IPC nature (figure 3). They contain the regions of in-
Figure 3. The temperature dependences of photoinduced optical absorption by light (a) and
photoinduced photoconductivity (b) with hν = 1.65 eV for BSO crystals (a, 1, b, 1), BSO:Cu
(a, 2, b, 2), BSO:Ag (a, 3, b, 3).
291
T.V.Panchenko, K.Yu.Strelets
creasing and decreasing of ∆αPI(hν) and ∆∗σPI(hν) dependences in different temperature intervals.
Moreover, the ∆σPI(T ) dependences show the effects of thermoactivation and thermal extinction
of photoconductivity which may be described using a model of the two-center recombination [8].
We assume that a distinction between PCE and IPC consists in the following. PCE is mainly
due to intra-central optical transitions in doping centers. The charge state of these centers changes
due to photochemical reactions. IPC is due to the photoinduced redistribution of the charge carries
between local levels in a forbidden gap which are responsible for photoconductivity in a spectral
range adjoining the absorption edge or due to the charge transitions from the valance band on
the shallow levels forming the tails of states near the valence and conductivity bands. The com-
monness of PCE and IPC excitement spectra can be explained by the fact that the transport of
photo-excited charge carries is a common link in the mechanisms of both effects. The drift and dif-
fusion components provide a photocurrent under IPC excitement and only the diffusion component
provides PCE. If the carrier transport takes place under recombination on slow-centers, then PCE
and IPC intensification is observed. If recombination is realized by means of fast centers, then IPC
and PCE decrease. High degree of the shallow level filling near the band conductivity bottom is a
necessary condition for PCE. Apparently it assists the electron localization and the charge state
change of deep centers responsible for PCE.
References
1. Egorysheva A.V., Burkov V.I., Kargin Yu.F., Vasilev A.Ya, Volkov V.V., Skorikov V.M., Inorganic
Materials, 2001, 37, No. 8, 812.
2. Nechitailov A.A., Krasinkova M.V., Mokrushina E.V., Petrov A.A., Kartenko N.F., Prokofev V.V.,
Inorganic Materials, 2000, 38, No. 8, 820.
3. Panchenko T.V., Kopylova S.Yu., Ferroelectrics, 2005, 322, 69.
4. Rjeily H.Bou., Ramaz F., Petrova D., Gospodinov M., Bruat B., SPIE Procceding, 1997, 3178, 169.
5. Borowiec M.T., Stasyuk I.V., SPIE Procceding, 1997, 3178, 173.
6. Panchenko T.V., Truseeva N.A., Strelets K.Yu., Functional Matterials, 2005, 12, No. 4, 707.
7. Panchenko T.V., Osetsky Yu.G., Truseeva N.A., Ferroelectrics, 1995, 174, 61.
8. Panchenko T.V., Fiz. Tverd. Tela, 2000, 42, 4, 641 (in Russian).
Фотохромiзм та iндукована фотопровiднiсть чистих
i легованих кристалiв силiкосиленiта
Т.В.Панченко, К.Ю.Стрiлець
Днiпропетровський нацiональний унiверситет,
49050, вул. Наукова 13, 49050 Днiпропетровськ, Україна
Отримано 13 квiтня 2007 р., в остаточному виглядi – 18 травня 2007 р.
У спектральному дiапазонi 0.5–3.5 eV дослiдженi стацiонарнi i фотоiндукованi спектри оптичного по-
глинання i фотопровiдностi, чистих i легованих iонами Cu, Ag i Mo кристалiв Bi12SiO20. Спостерiгали
вплив легування на фотохромний ефект i iндуковану фотопровiднiсть, отримали температурнi за-
лежностi фотоiндукованого оптичного поглинання i фотопровiдностi. Показана вiдсутнiсть кореляцiї
у спектральному розподiлi i у температурнiй залежностi обох ефектiв.
Ключовi слова: фотохромний ефект, оптична абсорбцiя, фотопровiднiсть, кристали силенiту
PACS: 78.20.-e, 78.40.-q
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