Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.chem.msu.ru/rus/cryst/srschool/pdf/mikhailin.pdf Äàòà èçìåíåíèÿ: Wed Dec 7 15:27:12 2005 Äàòà èíäåêñèðîâàíèÿ: Sat Dec 22 14:46:54 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: tail

Synch rotron radiation in sol id state spectroscopy
V.V. Mi khai li n
Optics and S pectr osc op y Dep ar t me nt, Ph ysics F acult y, M .V.Lo m on oso v M osco w Stat e Uni ver sit y, V or ob' e vy G or y, 119 99 2, M o sco w, R ussia

Uni que s pec tral features and ti me s truc ture of s ync hrotron radi ati on al l ows one to us e thi s ki nd of exc i tati on i n i nves ti gati on of el ec troni c rel axati on proc es s es i n i ns ul ators wi th wi de band gap. T he knowl edge of thes e proc es s es is i mportant for unders tandi ng of s c i ntillati on effi ci enc y in c rys tal s . Lumi nes c enc e exc i tati on tec hni que i s c onveni ent for s tudy of energy t rans fer i n thes e s ys tems and for i nves ti gati on of c rys tal energy structure. In general , l umi nes c enc e exci tati on s pec tra c an be s ubdi vi ded i nto s everal s pec tral regi ons :

Direct ex citatio n of low est d e fect ex cited state Ioniz ation of d ef ects b y ph otons w ith e nergy b elow th e matrix forb idden ga p Ex citation of matrix Urbach tail Ex citation of ex citons Prod uction o f se parated l ow - energy electro n- h ole pa irs Prod uction o f h igh - energ y e lectron- h ole pairs foll ow ed b y im pact ex citation/i oniz ation of d ef ects
E ac h of thes e regi ons is c harac teri zed by di fferent rol e of rel a xati on c hannel s . P oss i bl e c hannels of energy trans fer and rel axati on are di s c uss ed i n the pres entati on.

Ab sorption co effic ient in w id e ph oton en ergy ra nge and d iff erent processes stud ied usi ng sy nch rotron rad iati on ex citation of lumin escenc e
Ex citon

Dyn amics of electron ic relax ation in wid e b an d gap solids 100 as 1 fs
Multi-ion sati on i e e e h 2Eg e­e sc atte ri ng threshold

1 ps
Atomi c di splace me nt M odi fi c ati on of sol i d: e de sorpti on locali sati on , , de fe ct creation e ph

1 ns
El ec tr on en y erg
C OND UC TION BA ND

Urb ach ab s o rp tio n

Co re ex cito n Electro n -co re hole pair

Energy tr ansfer P hoton e mi ssi on

Ex cited d efect

h

Eg ex 0

h

lum

VALENCE BAND

Ev Auge r th hold res e h h 10
­14

Hole ener gy

ph h h

h Vk + ph

h

CORE BA ND

Lattice vibrations

Io n ized d efect + electro n

Electron-hole pair

10

­16

s

s

10

­12

s

10

­10

s

10

­8

s

time

1


Ioni zati on of de fects by pho tons wi th energy below the matri x forbi dden gap Exci tati on of matri x Urbach tai l
Urb ach ab s o rp tio n

Yb3+ c ha rg e tra n sf er lu min esc en c e ( CT L) exc ita tio n ( G u era ssi mo va e t a l)
Urbach t ail region Excit on Separat ed e-h pairs CT L s pe ct ra a n d exc it at spect ra of ses quioxides wit h diffe re nt tim e wi t emp er at ur e 1 0 i o n of CT L me asured n do ws, K.

slow

Ex citon

fast

fast slow

Slo w/ f ast emi ssi on r at i o in cre as es wit h en er gy i n Ur ba ch t a il r eg io n, i. e. slow co mponent in creas es wit h de local izat io n.

fast slow

Io n ized d efect + electro n

Q u ant um Yie ld, a. u.

Exci tati on of matri x Urbach tai l Exci tati on of exci tons Producti on of separate d low -energy electron-hole pairs

Urbach tail effec t in PbW O4 exci tati on spectra
1.0 0.8 0.6 0.4 0.2 0.0 3 .5 2.0 4.0

lg ( )

T emp er at ur e d ep e nd en ce of PW O exc it at i on s p ect ra shows t w o phenom ena: (1) dependence of exc it at i on spect rum in Ur bac h abs or pt io n r eg io n d ue t o cha n ge of t h e f ra ct io n of abs or be d ra di at i on in t h e 200K 30 K sam pl e a nd
150K

Urb ach ab s o rp tio n

Ex citon

em . 40 0nm 30 K 150 K 20 0 K
4.5 5 .0 5 .5 6.0 6. 5

d

-1

Q uant um Yield, a.u.

1.5 1.0

em . 520 3 1 2

nm 0K 50 K 00 K

(2) i ncr eas in g of t h qu ant um y ie ld region of s epar pa irs (s ee be lo

e sl o pe of wit h T i n t h e at e d e- h w)

0.5 3 .5 4.0 4.5 5 .0 h , e V 5 .5 6.0 6. 5

Electron-hole pair

PW O exc it at i on s p ect ra f or blue (t o p) a nd green (b ot t om) em iss ion bands

2


Producti on of separate d low -energy electron-hole pairs

Prob ab ility of bind in g or separati on of th e co mpon ents of an el ectron- h ole pair vs th eir energy

Ex citon

C pled ele ctro ou n a nd hol e S o t-d ay h r ec 1.0 iss io em n

S p at ed elec tro an h le e ar n do Lo g-d cay emiss io ne n

The nature of this curve is the increas of e elec tron-hole se pa ration w pair energy ith and the decreas of di rect recombination e with this se pa ra tion:

0.8

Probab lit y i

0.6

t Lowe s en erg y o f th e bo un de d sta te

0.4

Lowest energy of th e i onized stat e

0.0

Electron-hole pair

Energ o an electron hole pair yf -

l(E)=R

0.2

R0 increases wit h decrease of t emperat ure, t heref ore t his probabilit y is t emperat ure dependent :

0

T

T he ef f ec t o f elec tro n k in etic en erg y o n the ef f ic ien c y of en erg y tra n sf er to the lu min esc en c e c en ter a s a f u n c tio n o f temp era tu re ( Sp a ssk y e t a l)
1
Quantum yield, a.u.

Producti on of hi gh-energy elec tron-hole pai rs followed by impact exci tati on/i onization of de fects

ZnW O4 , a //E LHe T RT

R e fle c tiv ity , a.u .

a
0

Zn W O4 : (a) ­quantum yield sp ectra at R T and LHeT an d refl ectiv ity (th in cu rv e); (b ) ­ the ratio of th e above qu an tu m yield s p ectra.
LHeT

Electron-hole pairs

1,0
RT /LH e T r a ti o

0,8 0,6 0,4 5 10 15 Phot o n e n e r gy , e V 20

Excit at ion spect rum t emperat ure dependence is described in previous slide

RT

b

3


MgO:Al ­ threshold o f multi pli cati on of electroni c exci tati ons (C h. Lus hc hi k, Mi k hai l i n et al )
30 2 20 1 10 a, 101 , 0 6
6

T w o ty p es of rec o mbin a tio n c ha nne excito n ic o n e (u p p er p a rt) an d reco mbin atio n (lo w er p a rt). Fig u res o n t he rig h t di sp la y ty p ic a l en erg y de the q u a n tu m y ield o f the se c ha n n e

ls: o n a cen tre p en den c e o f ls

-1

cm-1


R,%


2

R
0 0

1

E xac t pos i l oc ated i n of R and meas urem photoemi s

ti on of e-e s c atteri ng thres hol d the regi on of abrupt dec reas e c an be es ti mated usi ng ent of l umi nes c enc e and total s i on exc i tati on s pec tra

h, a.un. , rb. .

2

2

To ta l photoems s on ii (e lec tro ns w ith e ne r gy a b ov e w or k fu nc tio n)

1 1 0 10 20


30

L u min es ce nc e Ex c ita tio n

h , eV

hn,

60

CaWO 4
40 2E g 20 Eg 3Eg 0 0 5 10 15 20 25

Ex perime ntally ob served tw o types of reco mb inatio n ch annels
Luminescence excitation spectra of intrinsi c luminescence of

Mani festati on of core exci tons i n opti cal functi ons i n VUV regui on

CaWO4

(uppe r pa ne l ) [S. I. Gol ovkova , A. M. Gurvi c h, A. I. Kra vc he nko, V. V. Mi kha ilin, A. N. Va si l 'e v, Phy s. St a t . Sol . (a ), 77 (1983) 375] a nd activator luminescence of

Co re ex cito n Electro n -co re hole pair

CaSO4 :Sm
60 40 20 0 0 5 10 15 20 25 30 35 40 Eg 2E g

[I. A. Ka menski k h, V. V. Mi kha ilin, I. N. Shpi nko v a nd A. N. Va si l 'e v, Nuc l . Inst r. a nd Me t h. , A282 (1 989) 599 ] (m i ddl e pa ne l )

3E g

C aSO4 :Sm

4


5d Pb

2+

Refl ec tiv it y, L He T CaM oO4 Sr MoO 4 BaM oO4 PbM oO4

Mani festati on of core exci tons i n in opti cal func ti ons i n VUV regui on
I nt ensit y o core excit on peaks correlat es wit h f t he nat ure of t he bot t om of t he conduct ion band (Kolobanov, Spassky et al). Cat ion core excit ons a e visible only if t he r lowest st at es of conduct ion band are f ormed f rom ca ion st a es (Pb and Ba molibdat es). t t

The rea sons of li gh t yi eld ins ta bility i nduc ed by ra di a ti on ·Cr eat ion of t h e r ever sible dam age: a) tr an sient def ect s - clo se F- H pair s b) Ch an ge o f elect ro n ic st at e o f deep def ect lev els in th e f or bidden en er gy gap ·Cr eat ion of t h e ir r ever sible dam a ge: a) st able F- H pair s b) def ect co n glo m er at es

5p Ba
0( 4)

2+

4

R e fl ec ti vit y, a .u .

4p Sr
0( 3) 0( 2)

2+

3

Ref lect ivit y shows no struct ure in core excit on region if t he lowest st a es are f ormed f rom t complex anion st at es (Sr and Ca molibdat es).
CondB ( MoO4 2- antibonds tates)

2
2+

3p Ca

1
0( 1)

VB ( MoO4 2- bonds tates)

15

20

25

30

35

P ho t on en erg y, eV

Pb

2+

Ba

2+

Sr2+ Ca2+

Benef i ts of VU V a nd X- ra y S R i n ra di a ti on da ma ge s tu dy
W 10 1

How to s tudy radiation eff ects using l uminescence spectroscopy
· Changes of lum inescen ce em ission sp ect r a ( addit ional em ission bands) · Ch an ges o f decay k in et ics ( r adiat ion def ect s can r esult in sh ar p en in g o f in it ial st ages o f decay an d in cr easin g of slow co m ponent ) · Ch an ges o f en er gy t r an sf er ( r adiat ion def ect s can ch an ge r at io of sever al r elaxat ion ch annels)

·

·

·

VUV ( e spec ia lly XUV) a nd X-r ay photons pr oduce the sa me spectr um of elem entary elec tr onic e xc ita tions ( e lec tr on- hole pa ir s, e xc itons, c ore le ve l e xc ita tions, initia l de f e c t f orma tion sta ge s) a s highe ne r gy ionizing pa r tic le Absor ption c oe f f ic ie nt in XUV a nd X-r ay r e gion is e xtr em e ly high ( 104 to 106 cm-1 ) , ther ef or e accum ula te d dose in the thin absor ption la ye r becom e s SR spect ral dist ribut ion f or huge various elect ron energy Unique spe c tra l f e a tur e s a nd tim e str uc ture , a nd high (R= 32 m) inte nsity of sy nc hr otr on r a dia tion a llow one to use this kind of e xc ita tion in inve stiga tion of de f e c ts a nd the ir c r ea tion in insula tor s with wide ba nd ga p.
6 Ge V 10
-1

5

-2 10

4

10

-3

3

-4 10

2

-5 10

1

10

-6

1 0

3 -

1 0

-2

-1 10

1

10

1 0 , nm

2

5


Usa ge of S R i n X -ra y regi on i n the s tudy of PW O ra di a ti on ha r dnes s

Radi ati on damage i n PWO
· Dose r at e is ab out 1 kG y/sec ( in thin a bsor pti on layer , d~ 10-5 cm) Deg r adatio n / e nha ncing o f emissio n und er ir r adiati on dep en ds on the e missio n spectr al r eg ion Fast and slow r ec o ver ing of r adiatio n def ects ( u pp er pan el)

·V EP P -3 (Bud ke r INP ): Fl ux of 10 16 ph /s with energy from 2 to 100 K eV ("white " X -ra ys) ·DCI (Lure, Orsa y): Flux of 10 12 ph/s of mo no ch roma ti zed 15 K eV X -ra y p ho ton s

·

·

Dose depen denc e for di fferen t regi ons of PW O emi ssi on spec trum ex c i te d by X -ra y S R
(a) Gr een emis sion (480 n m) ­ fast de gr ada tion a t fir s t 10 sec follo we d b y much slower de gr ada tion (b) Blue emissi on (380 n m) is mor e sta ble u nder irradiation (c) Few cases of i ncr ease of emission i n in ter me diate r ange (430 nm ) un der ir r adiation ­ the ev idence of ne w emis sion ce nter pr od uctio n

Lead Tungstate scintil l ators
·20 PbWO4 c r yst als of f ir st ge ne r at ion ·1 M G y dose acc umulat e d in t hi n sur f ac e laye r in 10 min, 15 Ke V e xc it at ion ( DCI, Or say) ·green emission is much more se nsit ive t o irradiat ion

R elative Lig ht Y ield, I1MGy/I0x1 00%

12 0

1. 1

LU MIN ESCENC E INTENSITY, a rb .u . n

430 nm
1. 0

c
b

nm380 nm470
10 0

0. 9

380 nm 480 nm a

80

0. 8 0 1 00

Ti me, sec

2 00 TI M E, se c

30 0

4 00

60

0

5

10

15

20

Number of the sample

6


Correlati on be tw een the radi ati on i nduced vari ati on of li ght yi eld and the pro fi le of emissi on spectrum, decay ki neti cs and the shap e of opti cal transmi ssi on ( I, II and III ­ di fferen t samples)

TIME , se c
0 1. 00 0. 95 0. 90 0. 85 0. 80 0. 75 0. 70 1. 00 0. 95 0. 90 0. 85 0. 80 0. 75 0. 70 0 200 400 600

WAVEL ENGT H, nm
350 400 450 500 550

Exci tati on by 90 eV photo ns ( SuperACO)
·Dose r at e is ab out 1 kG y/sec ( in thin abs or pti on l a yer , d~ 10-5 cm) ·Deg r adatio n / e nha ncing o f emissio n und er ir r adiati on dep en ds on the e missio n spectr al r eg ion ·Fast and slow r ec o ver ing of r adiatio n def ects ( u pp er p an el)

LU MINE SCE NCE INT E NCIT Y,a rb.un (for a l l Y)

III II I

I II

c

380 nm

a
II I

III

d
470 nm
II I II

10

5

10

4

b
200 400

10

3

I
600 2 00 250

III
300 350

TIME , se c

TIME , ns

PWO emis sion spectrum expl anation

How to mea sure nonli nea r ex c i ta ti on ef f i ci enc y?
Modul ati on of S R s pec trum by the grati ng s pec tral effi c i enc y wi th s harp pec ul i ari ti es al l ows one to es ti mate the order of the proc es s S harp s truc ture due to P t c overi ng of the grati ng di s s api ars i n 1st order fas t P W O emi s s i on and 2nd order s l ow P W O emi s s i on

PbW O4

·Fas t ( b lue) c o mpon ent ­ ex c iton ic ( Pb) e mis s io n, ( s hou ld b e l ine ar w ith ex c itatio n inte ns ity ) ·Slow ( gr een) c o mpon ent ­ def ec t r ec ombi nati on e mis s io n, ( s hou ld be n on- l ine ar ( quadr at ic ?) w ith ex c itation int ens ity )

7


Concl usions
Fundamental mechani sms of electroni c relaxati on i n large bandgap soli ds and energy transfer can be studi ed by analysi s of lumi nescence exci tati on spectra and ki neti cs exci ted by V UV -X synchrotron radi ati on photons, especi ally usi ng Ti me-Resolved L umi nescence V UV Spectroscopy. Hi gh flux of SR ena bles to simulate and i nvesti gate radi ati on damage effec ts.

8