- Email: [email protected]
Photoluminescence and photoconductivity of undoped and doped zinc silicate
Journal of Luminescence 24/25 (1981) 321 Nortis-! loflasd Publishing Compassy
324
32!
PHOTOLOMINESCENCE AND PHOTOCONDUCTIVITY OF UNDOPED AND DOPED ZINC SILICATE H.Hess and E.Krautz Institut fUr Festkbrperphysik Tachniacha Universitht Craz A—8010 Craz, Petersgasae 16 Austria
pheteluminesccnce and phetecenductivity measurements nf densely sintarad zinc silicates undapad and daped with Mn,As,Ai and Ti have baen extended te the uv regien at temperatures between 20 K and 300 K where twa emissien bands exist fec undeped zinc silicate with peaks at 285 nm and 382 nm with ceetcacy temperature dependence. The phetecenductivity ef endeped zinc silicate can be enhanced by deping with Al end dimineshed by deping with Mn,As and Ti. The luminescence stimulatien ef Zn 2SiO4:Nn,As after exitatien can be achieved net enly by infraced but else by suitable ultravielet irradiatien. INTRODUCTION Nest previeus investigatiens en zinc silicate phesphers have been perfermed especially en zinc silicate activated with manganese te use the well knewn green emissien ef the phespher pewder fee luminescent screens and fluerescent lamps. Far a better understanding ef the mechanism ef the electrenic precesses invelved, hewever, it is useful te study else the eleetrenic trenspert phenemene during phes— pher excitatien end stimuletien wherefere ene needs, hewever, single crystals cc densely sineered plates. SAMPLC
PREPARATION
Zn2SiO4 has been prepared by saud bedy reactien ef carefully mixed pewders ef ultrapure ZnO, Si02 and pure ZnF9 in guartz tubes at 1200eC using the fellewing reactiens 1) 2Znb + 5i02—.- Zn25i04 and 2) 2ZnR2 + 25i0, Zn2SiO4 + SiF4. A surplus ef 0,1 mel 5102 has been mestly applied te eveid an excessive ZnO phase. After pewder milling plates were pressed end densely sintered at higher temperatures several heurs ep te l4GOeC. EXPERIMENTAL SET—Up The arrangement used te measure the excitetien end emissien spectra and the phetecenductivity in the range frem 20 K te 300 K has already been described in previeus publicetiens ( ,3) in detail wherefere here enly the results ebtained will be given. RESULTS Fee undeped Zn2SiD4 twe pheteluminescence bends in the uv have been ebserved with intensity peaks et 285 nm and 382 the cerrespending peaks ef the excitetien spectrum at 217 225 nm respectively. Fig.le shews fer the temperatures 20
0 D22—23!3/81/D000—0000/$0275 © North-Hulland
regien nm with nm and K, 200 K
II. I/coo, L As-ass N / P/sete/sssss/ssooccs1cc (550(1 /sIssstncnstJSSeDntt’ ef :jssc SI//sale’
32
15~
//1,~~~~m4__I 200
aaa
act
300
Wavslesgth
sin
ceo
oso
600
Fig.1 : Excitatiee spectrum fer 290 nm emissien)e) ,emissien spec— teem fee 217 em excitatien)b) ,fec undeped Zn 2SiO4 at different temperatures
~ ~ 0
200
400 0 200 density st Eueitation
400
Fig.2: Intensity ef uv bend emissien (peek 382 cm) depen— dance en excitatien intensity fer undeped Zn2SiO4 at tampers— teres 180 K — 610 K
and 290 K the excitetien spectra fee the emissien wavelength 290 em and Fig.lb the emissien spectra fee the excitatien wavelength 217 em fee Zn25i04 with a surplus ef 0,1 mel 3102. Nhereas the first uv emissien band with peak at 285 em shews a very sheet decay time c 1 o—~ nec) in the whele tempereture regien 20 K — 300 K the secend uv emissien bend with the peak at 382 em decays very slewly especially at lew temperaturOs te ecly 10% ef the initial value within 4 minutes. Thermeluminescence is feund enly fer the secend uv emis— sien bend in the temperature range ef 20 K te 250 K. This peeves a centinueus disteibutien ef shallew traps. The relatien between luminescence intensity and excitetien intensity changes in e different
1
0
300
400 500 Weue!ength!nm!—
600
Fig.3: Emissien spectra ef the twe uv bands ef undeped Zn25i04 at 250 K at different excitatien intensities (1:17) fee 218 em cxci— tatien wavelength. Intensity ef the first uv bands nermalizad te 1
200
020
240
260
Wove/ength/nm)—
.
Fig.4: Excitatien ainteraci Zn2SiO4 A12O3 deping fee sien at 290 K,1) 2) 0,03, 3) 0,3, A1203
spectra ci with different 400 nm emia0,0004 4) 1 mel S
H. Hess, A. Krautz
/ Photoluminescence assdp/totoconductivity
of zinc silicate
323
manner between 180 K and 610 K as te be seen in Fiq.2. The relation is nearly linear between 290 K and 370 K whereas sublinear at lower and superlinear at higher temperatures. The spectral distribution of luminescence does not only depend en temperature but also on the excitation intensity as shown in Fig.3. For constant temperature the longer uv emission band is favoured for low exciting intensity whereas the shorter uv emission band for higher exciting intensity (17:1). Similar behaviour is known for several sulfide phosphors with two emission centers. Tile excitation spectrum for 382 nm emission intensity is remarkable changed at 290 K when the Zn 2SiO4 is doped with different concentrations of AI2O3 from 0,0004 to 10 mol% A1203 as to be seen in Fig.4. Highest luminescence efficiency is obtained for 1 mol% A1203 in Zn2SiO4 at 290 K for the 400 em emission at 240 em excitation wavelength. The luminescence intensity at 400 nm remarkable increases at 290 K and the excitation is extended to longer wavelengths. tOy doping Zn2SiO4 with A12O3 the decay time and the thermal stimulation of the stored light sum increases. The photoconductivity of Zn2S1O4 is increased by doping with 0,1 mol% 2. If A1203 distinctly for longer wavelengths with a peak at the 245 exciting nm as irradiation is increased to 150 energy ~aw/cm2 was the 5/uK/cm photoconductivity could shown in Fig.5. The excitation be proved up to 520 em at the A1 203 doped samples. The rise and decay times for the pheteconductivity of undeped and A12O3 doped Zn2SiO4 is quite different as to be seen in Fig.6. In this case the If Zn2S1O4 Zn2SiO undoped Zn2SiO4 was excited by 224 em and the A12O3 2. doped by 250 em wavelength. The excitation energy was 5 1uW/cm 4 is doped with MnO, As2O5, Ti02 or V205 the phetoconductivity is diminirUed for irradiation in the short uv region. 10
I
/
A
‘\
1 Zn
/ \
/‘\
/
~ f
.
2SiO4 2. Zn2S~0~ A ~0~(0,1%)
Kig.5: Photoconductivity cxci— tation spectra corrected for equal excitation intensity for uncioped and Al203 doped sintered samples.
\
~
~200
250
300
350
Wavelersgth (cml—
1
1. Zrs2SiO4
~3~’
—1
20.5 Z
/
2.Zn2Si0~Al203(0j%) Fig.6:Rise
/
50 Time 100 cU ____________________________
and decay
curves
of
photoconductivity for undoped (1) and Al203 doped zinc silica— te (2) . Excitation wavelength 224 em (1) 250 nm 2. (2) . Excita— tion energy 5 ~sW/cm
134
Ii fAts. L AvIary
f’/seu)rI/aarr( f/ri mc! phetec u/rib/do 0 of zoo it/i a/i
dnrk~JgQ 0m dark
thernOluranesience
3
293K
ii
I
120
/~\T-2OK
/
~?J~_~/\ ~
I~ 4
/
8
12
16
21
a
—
rtj.7 :Photoatisloiarion cC zn2Sih4 riSe (0,066) ,As (0,015) to 360 na irrad.t— ation followed t-r ti~orsial at.tmoiatod lom.ineaconre. Liijht SUn) 2t-0:thorinot 2r rr~idoal 0)1:pliotostisroiatod, tbermal atiisotatod atimolat~on, otter p1iotostimolat~on. i2~2~~ ~
200
3~
0i~
600
800
Wavelength nm)-—
H ;:3.dHirrtral ii.LorilOiiL.iei/ .zt rho hotoatilation ot Zn2Sit4~.i1n,Ac at constant ~rraoiaH.onw3rI1 160 ~K/r:ni at 20 1~ and 293 i~.
Optical
stimulation .ta ohs 000cc) ter hot:i zi..nr si itr~ote piaoaplorc tO lie acie ii 05 4i~t]i Monad Ac otter chart cv radiation (Ac 280 nm) )2,~ ) To deride ohothor short at radiation r.ftorta stis:oiation or (joonchiar aftr.c ocr tttnq ••aith shorter or oarcionqtaa rho c;1e~a rurros have 00011 raoasorod oi tO i~rorr”tdi ~ irr~~~ iatien solid line) or w~thoot proreodiacj irradiation (dashed lint) . The rosolts arc shown in Ftc. 7zt , t . in case or Zn 5SiO4:lin tile onriral stimulated ltpht sort 2 Dh nrarlr rHoala J2 whoroas in rasoof dopino with tin and As a~wapa 2 ph i a lardr:r than dX . troop t t rai o tisorlat~en deeper traps ran ho emptied which ia riot pose thto in a thermal process. In the wicolrwareienqth ranqo inoasorra from 286) err t.n 1200 osi •ti:e oddi tionai iro adiatirci brinor-r airot only atiwciatioa for both Zn2SiO4 doped vi ti~ 31:1 arid a 1144) tsr deoirn~ wttal 71)) and 3 OUjiOOC~I
Stirr soectral distrlhotten of tiii..i oot~rat stimo tarod li!:jtit sea 2 p1: of ZIHSIO4 dopod with 5)0 and As at irradtctirnoaierov 110 82K/c r~ or 20 K r,nd 295 K is shown tn Pio.8. Thointonsitp ot atlmolated lowi— nosrenro at the boor oesu)eratore oxeorea mat nf hrqher tomperaturo in the~~~~)i3ele spectral ranqe meaar.rrod . f t the intoan~ to of •tiie attmo— latinp radiation is enoanrod very htdh then optIcal e tHiola H.oii r.an ho measured pot hopond 650 ow. i)IiFKFKKCKS 1) /2) /1) /4)
Lovorens ,ii. 0. , An tntrodoetiorl to LerLinosrenro ot Solids (Dover Pobliratinna, Now Perk 1968) ilosa,N.and Kraets,K.,Arra phra.Aostriara 46 (1977) 139—f52. Keas,K.and Kraots,K.,phpa.stat.sel.)a) 51 /1979) 391—396 Ctany,J.F.and Sai—Ualasz,G.A.,d.)hlortrerhecn.Kor. 127 (1980) 2458—2464.
324
32!
PHOTOLOMINESCENCE AND PHOTOCONDUCTIVITY OF UNDOPED AND DOPED ZINC SILICATE H.Hess and E.Krautz Institut fUr Festkbrperphysik Tachniacha Universitht Craz A—8010 Craz, Petersgasae 16 Austria
pheteluminesccnce and phetecenductivity measurements nf densely sintarad zinc silicates undapad and daped with Mn,As,Ai and Ti have baen extended te the uv regien at temperatures between 20 K and 300 K where twa emissien bands exist fec undeped zinc silicate with peaks at 285 nm and 382 nm with ceetcacy temperature dependence. The phetecenductivity ef endeped zinc silicate can be enhanced by deping with Al end dimineshed by deping with Mn,As and Ti. The luminescence stimulatien ef Zn 2SiO4:Nn,As after exitatien can be achieved net enly by infraced but else by suitable ultravielet irradiatien. INTRODUCTION Nest previeus investigatiens en zinc silicate phesphers have been perfermed especially en zinc silicate activated with manganese te use the well knewn green emissien ef the phespher pewder fee luminescent screens and fluerescent lamps. Far a better understanding ef the mechanism ef the electrenic precesses invelved, hewever, it is useful te study else the eleetrenic trenspert phenemene during phes— pher excitatien end stimuletien wherefere ene needs, hewever, single crystals cc densely sineered plates. SAMPLC
PREPARATION
Zn2SiO4 has been prepared by saud bedy reactien ef carefully mixed pewders ef ultrapure ZnO, Si02 and pure ZnF9 in guartz tubes at 1200eC using the fellewing reactiens 1) 2Znb + 5i02—.- Zn25i04 and 2) 2ZnR2 + 25i0, Zn2SiO4 + SiF4. A surplus ef 0,1 mel 5102 has been mestly applied te eveid an excessive ZnO phase. After pewder milling plates were pressed end densely sintered at higher temperatures several heurs ep te l4GOeC. EXPERIMENTAL SET—Up The arrangement used te measure the excitetien end emissien spectra and the phetecenductivity in the range frem 20 K te 300 K has already been described in previeus publicetiens ( ,3) in detail wherefere here enly the results ebtained will be given. RESULTS Fee undeped Zn2SiD4 twe pheteluminescence bends in the uv have been ebserved with intensity peaks et 285 nm and 382 the cerrespending peaks ef the excitetien spectrum at 217 225 nm respectively. Fig.le shews fer the temperatures 20
0 D22—23!3/81/D000—0000/$0275 © North-Hulland
regien nm with nm and K, 200 K
II. I/coo, L As-ass N / P/sete/sssss/ssooccs1cc (550(1 /sIssstncnstJSSeDntt’ ef :jssc SI//sale’
32
15~
//1,~~~~m4__I 200
aaa
act
300
Wavslesgth
sin
ceo
oso
600
Fig.1 : Excitatiee spectrum fer 290 nm emissien)e) ,emissien spec— teem fee 217 em excitatien)b) ,fec undeped Zn 2SiO4 at different temperatures
~ ~ 0
200
400 0 200 density st Eueitation
400
Fig.2: Intensity ef uv bend emissien (peek 382 cm) depen— dance en excitatien intensity fer undeped Zn2SiO4 at tampers— teres 180 K — 610 K
and 290 K the excitetien spectra fee the emissien wavelength 290 em and Fig.lb the emissien spectra fee the excitatien wavelength 217 em fee Zn25i04 with a surplus ef 0,1 mel 3102. Nhereas the first uv emissien band with peak at 285 em shews a very sheet decay time c 1 o—~ nec) in the whele tempereture regien 20 K — 300 K the secend uv emissien bend with the peak at 382 em decays very slewly especially at lew temperaturOs te ecly 10% ef the initial value within 4 minutes. Thermeluminescence is feund enly fer the secend uv emis— sien bend in the temperature range ef 20 K te 250 K. This peeves a centinueus disteibutien ef shallew traps. The relatien between luminescence intensity and excitetien intensity changes in e different
1
0
300
400 500 Weue!ength!nm!—
600
Fig.3: Emissien spectra ef the twe uv bands ef undeped Zn25i04 at 250 K at different excitatien intensities (1:17) fee 218 em cxci— tatien wavelength. Intensity ef the first uv bands nermalizad te 1
200
020
240
260
Wove/ength/nm)—
.
Fig.4: Excitatien ainteraci Zn2SiO4 A12O3 deping fee sien at 290 K,1) 2) 0,03, 3) 0,3, A1203
spectra ci with different 400 nm emia0,0004 4) 1 mel S
H. Hess, A. Krautz
/ Photoluminescence assdp/totoconductivity
of zinc silicate
323
manner between 180 K and 610 K as te be seen in Fiq.2. The relation is nearly linear between 290 K and 370 K whereas sublinear at lower and superlinear at higher temperatures. The spectral distribution of luminescence does not only depend en temperature but also on the excitation intensity as shown in Fig.3. For constant temperature the longer uv emission band is favoured for low exciting intensity whereas the shorter uv emission band for higher exciting intensity (17:1). Similar behaviour is known for several sulfide phosphors with two emission centers. Tile excitation spectrum for 382 nm emission intensity is remarkable changed at 290 K when the Zn 2SiO4 is doped with different concentrations of AI2O3 from 0,0004 to 10 mol% A1203 as to be seen in Fig.4. Highest luminescence efficiency is obtained for 1 mol% A1203 in Zn2SiO4 at 290 K for the 400 em emission at 240 em excitation wavelength. The luminescence intensity at 400 nm remarkable increases at 290 K and the excitation is extended to longer wavelengths. tOy doping Zn2SiO4 with A12O3 the decay time and the thermal stimulation of the stored light sum increases. The photoconductivity of Zn2S1O4 is increased by doping with 0,1 mol% 2. If A1203 distinctly for longer wavelengths with a peak at the 245 exciting nm as irradiation is increased to 150 energy ~aw/cm2 was the 5/uK/cm photoconductivity could shown in Fig.5. The excitation be proved up to 520 em at the A1 203 doped samples. The rise and decay times for the pheteconductivity of undeped and A12O3 doped Zn2SiO4 is quite different as to be seen in Fig.6. In this case the If Zn2S1O4 Zn2SiO undoped Zn2SiO4 was excited by 224 em and the A12O3 2. doped by 250 em wavelength. The excitation energy was 5 1uW/cm 4 is doped with MnO, As2O5, Ti02 or V205 the phetoconductivity is diminirUed for irradiation in the short uv region. 10
I
/
A
‘\
1 Zn
/ \
/‘\
/
~ f
.
2SiO4 2. Zn2S~0~ A ~0~(0,1%)
Kig.5: Photoconductivity cxci— tation spectra corrected for equal excitation intensity for uncioped and Al203 doped sintered samples.
\
~
~200
250
300
350
Wavelersgth (cml—
1
1. Zrs2SiO4
~3~’
—1
20.5 Z
/
2.Zn2Si0~Al203(0j%) Fig.6:Rise
/
50 Time 100 cU ____________________________
and decay
curves
of
photoconductivity for undoped (1) and Al203 doped zinc silica— te (2) . Excitation wavelength 224 em (1) 250 nm 2. (2) . Excita— tion energy 5 ~sW/cm
134
Ii fAts. L AvIary
f’/seu)rI/aarr( f/ri mc! phetec u/rib/do 0 of zoo it/i a/i
dnrk~JgQ 0m dark
thernOluranesience
3
293K
ii
I
120
/~\T-2OK
/
~?J~_~/\ ~
I~ 4
/
8
12
16
21
a
—
rtj.7 :Photoatisloiarion cC zn2Sih4 riSe (0,066) ,As (0,015) to 360 na irrad.t— ation followed t-r ti~orsial at.tmoiatod lom.ineaconre. Liijht SUn) 2t-0:thorinot 2r rr~idoal 0)1:pliotostisroiatod, tbermal atiisotatod atimolat~on, otter p1iotostimolat~on. i2~2~~ ~
200
3~
0i~
600
800
Wavelength nm)-—
H ;:3.dHirrtral ii.LorilOiiL.iei/ .zt rho hotoatilation ot Zn2Sit4~.i1n,Ac at constant ~rraoiaH.onw3rI1 160 ~K/r:ni at 20 1~ and 293 i~.
Optical
stimulation .ta ohs 000cc) ter hot:i zi..nr si itr~ote piaoaplorc tO lie acie ii 05 4i~t]i Monad Ac otter chart cv radiation (Ac 280 nm) )2,~ ) To deride ohothor short at radiation r.ftorta stis:oiation or (joonchiar aftr.c ocr tttnq ••aith shorter or oarcionqtaa rho c;1e~a rurros have 00011 raoasorod oi tO i~rorr”tdi ~ irr~~~ iatien solid line) or w~thoot proreodiacj irradiation (dashed lint) . The rosolts arc shown in Ftc. 7zt , t . in case or Zn 5SiO4:lin tile onriral stimulated ltpht sort 2 Dh nrarlr rHoala J2 whoroas in rasoof dopino with tin and As a~wapa 2 ph i a lardr:r than dX . troop t t rai o tisorlat~en deeper traps ran ho emptied which ia riot pose thto in a thermal process. In the wicolrwareienqth ranqo inoasorra from 286) err t.n 1200 osi •ti:e oddi tionai iro adiatirci brinor-r airot only atiwciatioa for both Zn2SiO4 doped vi ti~ 31:1 arid a 1144) tsr deoirn~ wttal 71)) and 3 OUjiOOC~I
Stirr soectral distrlhotten of tiii..i oot~rat stimo tarod li!:jtit sea 2 p1: of ZIHSIO4 dopod with 5)0 and As at irradtctirnoaierov 110 82K/c r~ or 20 K r,nd 295 K is shown tn Pio.8. Thointonsitp ot atlmolated lowi— nosrenro at the boor oesu)eratore oxeorea mat nf hrqher tomperaturo in the~~~~)i3ele spectral ranqe meaar.rrod . f t the intoan~ to of •tiie attmo— latinp radiation is enoanrod very htdh then optIcal e tHiola H.oii r.an ho measured pot hopond 650 ow. i)IiFKFKKCKS 1) /2) /1) /4)
Lovorens ,ii. 0. , An tntrodoetiorl to LerLinosrenro ot Solids (Dover Pobliratinna, Now Perk 1968) ilosa,N.and Kraets,K.,Arra phra.Aostriara 46 (1977) 139—f52. Keas,K.and Kraots,K.,phpa.stat.sel.)a) 51 /1979) 391—396 Ctany,J.F.and Sai—Ualasz,G.A.,d.)hlortrerhecn.Kor. 127 (1980) 2458—2464.