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Thin-film ZnS:MnF2 temperature sensor with visual indication
Sensors and Acruarors A, 30 ( 1992) 63 -65
63
Thin-film ZnS:MnF, temperature sensor with visual indication S Antonov,
I Ivanov,
V Mlronov
and Yu
Sukharev
Department qf Mumeiecrromcs, Odessa Polylechnrc Instrrule, Schevchenko Avenue, 1, Odessa (Ukrame)
Abstract Tbm-film electrohnnmescent (TF EL) altematmg current structures are now well known, and are used m flat-panel displays, mdlcator devxes and other devices for vlsuahnng mformatlon In this work the temperature dependence. of electrolummescent spectra of a TF EL structure based on ZnS MnF, phosphor IS described Thus structure IS a possible temperature sensor for optron and other devices
1. Introduction Magnanese (Mn), which is introduced mto a ZnS thm film, 1s wdely known as an activator of electrolummescence in &m-film electrolummescent (TF EL) alternating current structures The double msulatmg thm-film phosphor ZnS Mn has a great bnghtness of emlsslon (1000-3000 cd m-*), an efficiency from 1 to 2 lm W-’ and sticlently hgh rehablhty to be used as the flat screen of personal computers and word processors It IS known that the lummescence of the TF phosphor ZnS Mn arises from the 4T,(4G) + 6A, (%) optical transition m Mn” ions The arrangement of the energy levels m the Mn2+ ions depends on the crystallmlty fields m their vlamty The changes of symmetry of the crystallmlty fields lead to either merging or splitting of the energy levels The electrolummescent spectrum 1s a good indicator of structural transformation m the ZnS Mn thm films Normally one enusslon band m the EL spectrum with a maximum at 858 nm (yellow-orange colour) 1s found for the TF EL structure based on ZnS Mn The analysis of papers which have been pubhshed up to now has been based on this fact At the same time Sukharev et al [l] observed three emlsslon bands with maxnna at 605, 710 and 805 nm m the EL spectrum of ZnS Mn The presence of enusslon bands m the red (R) and infrared (IR) regions of the spectrum IS connected with the interaction between Mn2+ ions at high manganese concentrations m ZnS films There 1s no mformatlon about
the dependence of EL spectra of TF EL structures on temperature
2. Preparation aud characteristics of TF EL structures In this work TF EL structures based on ZnS MnF2 phosphor are mvestlgated The technology and condltlons of obtaining the TF EL structures have been described m earlier papers [2,3] Figure 1 shows normalized EL spectra for different MnF, concentrations m the phosphor at 300 K The EL spectra were investigated by a KSVU-23 type spectral-calculatmg complex The mam emlsslon band with a maxlmum at 585 nm IS displaced to the long-wave regon of the spectrum and there 1s an increase of mtenslty of the ri and 1R emlsslon bands, as shown m Fig 1 The temperature dependence of the EL spectrum m the 300-450 K regon has been measured for the TF EL structure based on ZnS MnF, phosphor The intensity of the mam orange emlsslon band has little dependence on temperature, but the R and IR emlsslon bands increase m intensity with temperature as shown m Fig 2 The dependence of the mtensltles of the R and IR enusslon bands on temperature 1s most important m the mltlal part of the bnghtness-voltage charactenstlc (mterval from point A to pomt D m Fig 3) So, m the case when the alternatmg dnvmg voltage between the two electrodes of the TF EL structure 1s fixed, for example 140 V (5 kHz), we can see the Elsevler Sequoia
;p; I 300
600
500
700
A ,nm
350
1
I
400
I
450 T, K
Fig 4 Dependence of brightness from temperature the dnvmg voltage I, 130 V, 2. 14OV, 3, ISOV
at fixed levels of
Fig 1 Electrolummescence spectra of TF EL structures based on ZnS MnF, at different concentrations of the activator 1, 0 1 mol “XI, 2, 0 3 mol %, 3, 0 5 mol “AI,4 1 0 mol u/u, 5, 2 0 mol ‘I/u,6, 3 0 mol %
I
10’
used to carry out visual control of temperature changes This effect may be used m engmeermg, for example, m optron devtces
‘n
I
5 P
ti
3. Emission mechanism of TF EL structure with increasing temperature
H
0 5-
100
600
500
800 e
Apm
Fig 2 EL spectra of TF EL structure based on ZnS MnF, phosphor at different temperatures I. 350 K, 2, 400 K, 3, 450 K
cd
B*_2
E
In
F
103 60 10
We have cart-red out an mvesttgatron of the EL kmetrcs to explam the nature of the opttcal transrtlon m a TF EL structure based on ZnS MnF, phosphor Electrolummescence bnghtness waves were recorded by a KSVU-23 devtce for the pulse exetanon (z, = 100 ms) shown m Fig 5(a) Two emssron waves, 515 and 710 nm wavelength, were picked out of the spectrum The EL bnghtness waves are shown m Fig 5(b) and (c), respectrvely In both cases the bngbtness waves are m phase with the excrtatlon pulse (without any dtsplacement m time) Consequently, only a mechamsm of emrsslon-inter-central optical transttron m the
D
10'
U exe
6 A
_i:; 100 130
t
B 150
170
-t
U,V Fig 3 Bnghtness-voltage characterlstlc smusoldal excltatlon (5 kHz)
i-l
of TF EL structure
under
mcrease of bnghtness of the EL emlsston wtth temperature Figure 4 shows the dependence of EL brightness on temperature for a TF EL structure based on ZnS MnF2 at mdrcated fixed excltatlon voltages It is evident that TF EL structures can be
615 ‘B 1
1710Lt “ht
Rg 5 TIlne dependence of (a) dnvmg pulse, (b) brightness 615 nm wavelength, (c) brightness at 710 nm wavelength
at
65
Mn*+ Ions took place At the same time, the decay time of the EL emlsslon m the orange region of the vlslble spectrum IS 350 ms (see Fig 5(b)), while the EL enusslon decay time m the red region IS 800 ms (see Fig 5(c)) Consequently, Mn’+ ions m the excited state m thm-film ZnS MnF, phosphor have two hfetnnes Obviously, mdlvldual Mn2+ centres and complex Mn *+-F- centres m the ZnS thm film took part m the emlsslon of light quanta Shallow donor centres of the incoherent F- ions m the ZnS film may supply the charge carriers for the excltatlon of Mn2+ -F- complex centres and Mn*+ mdlvldual centres The excitation of the complex Mn 2+-F- centres takes place at a lower
driving voltage than excltatlon of mdlvldual Mn*+ centres, smce the section of impact excitation of the complex optical centres IS larger than the mdlvldual one
References 1 Yu G Sukharev, S Yu Antonov and V S Mlronov, Thm-film phosphors for displays of personal computers -M Zname, (1987) 30-35 2 J Benolt et al, Study of highly concentrated ZnS Mn a c EL dcvaxs, Phys Status Soladt (a), 83 (1984) 709-717 3 T Suyama, N Sawara, K Okamoto and Y Hamakawa Multlcolonng of thm-film electrolummescent devxe, Jpn J Appl Phys, 21(1981) 383-387
63
Thin-film ZnS:MnF, temperature sensor with visual indication S Antonov,
I Ivanov,
V Mlronov
and Yu
Sukharev
Department qf Mumeiecrromcs, Odessa Polylechnrc Instrrule, Schevchenko Avenue, 1, Odessa (Ukrame)
Abstract Tbm-film electrohnnmescent (TF EL) altematmg current structures are now well known, and are used m flat-panel displays, mdlcator devxes and other devices for vlsuahnng mformatlon In this work the temperature dependence. of electrolummescent spectra of a TF EL structure based on ZnS MnF, phosphor IS described Thus structure IS a possible temperature sensor for optron and other devices
1. Introduction Magnanese (Mn), which is introduced mto a ZnS thm film, 1s wdely known as an activator of electrolummescence in &m-film electrolummescent (TF EL) alternating current structures The double msulatmg thm-film phosphor ZnS Mn has a great bnghtness of emlsslon (1000-3000 cd m-*), an efficiency from 1 to 2 lm W-’ and sticlently hgh rehablhty to be used as the flat screen of personal computers and word processors It IS known that the lummescence of the TF phosphor ZnS Mn arises from the 4T,(4G) + 6A, (%) optical transition m Mn” ions The arrangement of the energy levels m the Mn2+ ions depends on the crystallmlty fields m their vlamty The changes of symmetry of the crystallmlty fields lead to either merging or splitting of the energy levels The electrolummescent spectrum 1s a good indicator of structural transformation m the ZnS Mn thm films Normally one enusslon band m the EL spectrum with a maximum at 858 nm (yellow-orange colour) 1s found for the TF EL structure based on ZnS Mn The analysis of papers which have been pubhshed up to now has been based on this fact At the same time Sukharev et al [l] observed three emlsslon bands with maxnna at 605, 710 and 805 nm m the EL spectrum of ZnS Mn The presence of enusslon bands m the red (R) and infrared (IR) regions of the spectrum IS connected with the interaction between Mn2+ ions at high manganese concentrations m ZnS films There 1s no mformatlon about
the dependence of EL spectra of TF EL structures on temperature
2. Preparation aud characteristics of TF EL structures In this work TF EL structures based on ZnS MnF2 phosphor are mvestlgated The technology and condltlons of obtaining the TF EL structures have been described m earlier papers [2,3] Figure 1 shows normalized EL spectra for different MnF, concentrations m the phosphor at 300 K The EL spectra were investigated by a KSVU-23 type spectral-calculatmg complex The mam emlsslon band with a maxlmum at 585 nm IS displaced to the long-wave regon of the spectrum and there 1s an increase of mtenslty of the ri and 1R emlsslon bands, as shown m Fig 1 The temperature dependence of the EL spectrum m the 300-450 K regon has been measured for the TF EL structure based on ZnS MnF, phosphor The intensity of the mam orange emlsslon band has little dependence on temperature, but the R and IR emlsslon bands increase m intensity with temperature as shown m Fig 2 The dependence of the mtensltles of the R and IR enusslon bands on temperature 1s most important m the mltlal part of the bnghtness-voltage charactenstlc (mterval from point A to pomt D m Fig 3) So, m the case when the alternatmg dnvmg voltage between the two electrodes of the TF EL structure 1s fixed, for example 140 V (5 kHz), we can see the Elsevler Sequoia
;p; I 300
600
500
700
A ,nm
350
1
I
400
I
450 T, K
Fig 4 Dependence of brightness from temperature the dnvmg voltage I, 130 V, 2. 14OV, 3, ISOV
at fixed levels of
Fig 1 Electrolummescence spectra of TF EL structures based on ZnS MnF, at different concentrations of the activator 1, 0 1 mol “XI, 2, 0 3 mol %, 3, 0 5 mol “AI,4 1 0 mol u/u, 5, 2 0 mol ‘I/u,6, 3 0 mol %
I
10’
used to carry out visual control of temperature changes This effect may be used m engmeermg, for example, m optron devtces
‘n
I
5 P
ti
3. Emission mechanism of TF EL structure with increasing temperature
H
0 5-
100
600
500
800 e
Apm
Fig 2 EL spectra of TF EL structure based on ZnS MnF, phosphor at different temperatures I. 350 K, 2, 400 K, 3, 450 K
cd
B*_2
E
In
F
103 60 10
We have cart-red out an mvesttgatron of the EL kmetrcs to explam the nature of the opttcal transrtlon m a TF EL structure based on ZnS MnF, phosphor Electrolummescence bnghtness waves were recorded by a KSVU-23 devtce for the pulse exetanon (z, = 100 ms) shown m Fig 5(a) Two emssron waves, 515 and 710 nm wavelength, were picked out of the spectrum The EL bnghtness waves are shown m Fig 5(b) and (c), respectrvely In both cases the bngbtness waves are m phase with the excrtatlon pulse (without any dtsplacement m time) Consequently, only a mechamsm of emrsslon-inter-central optical transttron m the
D
10'
U exe
6 A
_i:; 100 130
t
B 150
170
-t
U,V Fig 3 Bnghtness-voltage characterlstlc smusoldal excltatlon (5 kHz)
i-l
of TF EL structure
under
mcrease of bnghtness of the EL emlsston wtth temperature Figure 4 shows the dependence of EL brightness on temperature for a TF EL structure based on ZnS MnF2 at mdrcated fixed excltatlon voltages It is evident that TF EL structures can be
615 ‘B 1
1710Lt “ht
Rg 5 TIlne dependence of (a) dnvmg pulse, (b) brightness 615 nm wavelength, (c) brightness at 710 nm wavelength
at
65
Mn*+ Ions took place At the same time, the decay time of the EL emlsslon m the orange region of the vlslble spectrum IS 350 ms (see Fig 5(b)), while the EL enusslon decay time m the red region IS 800 ms (see Fig 5(c)) Consequently, Mn’+ ions m the excited state m thm-film ZnS MnF, phosphor have two hfetnnes Obviously, mdlvldual Mn2+ centres and complex Mn *+-F- centres m the ZnS thm film took part m the emlsslon of light quanta Shallow donor centres of the incoherent F- ions m the ZnS film may supply the charge carriers for the excltatlon of Mn2+ -F- complex centres and Mn*+ mdlvldual centres The excitation of the complex Mn 2+-F- centres takes place at a lower
driving voltage than excltatlon of mdlvldual Mn*+ centres, smce the section of impact excitation of the complex optical centres IS larger than the mdlvldual one
References 1 Yu G Sukharev, S Yu Antonov and V S Mlronov, Thm-film phosphors for displays of personal computers -M Zname, (1987) 30-35 2 J Benolt et al, Study of highly concentrated ZnS Mn a c EL dcvaxs, Phys Status Soladt (a), 83 (1984) 709-717 3 T Suyama, N Sawara, K Okamoto and Y Hamakawa Multlcolonng of thm-film electrolummescent devxe, Jpn J Appl Phys, 21(1981) 383-387