Effects of radiationless processes on radiating states of excited crystals containing rare earth ion

Carlson, E. H.

English

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Final Repart 
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by 
Edward H. Carlson 
Contract NAS8~1I.200 
OPTICAL RiOPERTIES CF "SITION IONS IN CRYSTIIIS 
UNDER BOMBARDMENT EX ENERGETIC PARTTCIES, 
X AM> GAMMA RAYS AND LIGHT 
GPO PRICE $ 
CFSTI PRICE(S) $ 
Preparded for 
Microfiche (MF) 
ff 653 July65 
The George C. Marshall Space Flight Center 
Natianal Aeranautics and Space Administration 
Huntsville, Alabama 358l2 
Department af Physics 
University of Alabama 
University, Alabama 
15 September 1965; 
https://ntrs.nasa.gov/search.jsp?R=19650025347 2020-03-17T01:11:41+00:00Z
* I. Scope of Work 
The phenmena under study is the ernissicxi of l igh t  by crystals 
containing rare e a r t h  ims follawing excitation by various methods, 
including bcxnbardment by energetic electrons, potons, etc., x and 
gamma rays and W and visible light. 
by some process i n  the crystal, energy transfer processes carry  a 
portion of the energy t o  low lying levels i n  the rare earth ions 
Follawing absarption of energy 
whereupan a portion is radiated as W, visible and infrared light. 
The first (absorption) process, and the second (transfer) process 
W i l l  depend on the method of excitatim. faab proeess (emission 
and competing radiatiarless processes) will genera- be independent 
of the  mode af axcitation. 
We have cancantrated on elucidating the role of the radiatianless 
processes and their effect  cm the lifetimes af the radiating s ta tes  
because this is probably the simplest part of the whole chain t o  
understand . * 
11. Time Resolved Spectranetry 
Because the method of excitation is  of l i t t l e  importance t o  the 
study of the terminal processes, we used the most convenient source, a 
f lash  lamp. We wished t o  measure fluorescence intensity versus time 
a f t e r  excitation i n  order both t o  observe the build up of populatim i n  
the l a w  levels by process two (transfer) and the decay of population by 
process three (radiation and radiatianless processes). Figure 1 is  a 
-2- 
block diagram af the equipment used. 
Tektraslix 181 Time Mark Generator, which c m s i s t s  of a crystal c a t r o l l e d  
The tinu'ng is  controlled by a 
osc i l la tm at  10 Mc/sec, and decade scalars, 
10 m see triggers the f lash  lamp and sbwts a timing c i rcu i t  consisting 
of Tektronix 162 and 161 pulsera. The former generates a ramp which 
i s  fed t o  the 161 pulser. A t  a selected point on the ramp, the 161 is 
triggered and drives a keyer for the photmultiplier tube. 
The output pulse every 
The delay 
between the flash and the photanultiplier %n't pulse can be varied from 
1 sec t o  10 m sec. The photomultiplier lton't pulse was adjusted in 
the range 10 1 sec t o  5 m sec. 
1 t o  10 sec. and displayed on a chart recorder. 
The photo current w a s  averaged for  
III. Materials Studied 
A wide variety of crystals containing rare earths as doping were 
studied in order t o  find the optimum sy.stem f o r  study of the radiationless 
decay processes. These included 
sm2+   KC^ 
sm2+ :L& 
Pr3+ tLaCI.3 
Nd3+ :LaC13 
sm3+ : L ~ C  5
~ r ~ +  $caw04 
W+ :Caw% 
N@+ :CaWQ, 
s+-+ :Lac 
w+ :caF2'+ 
Nd3+ tCaF, 
snF+ + smZ+:caF; 
En2+ :c&F2 
Tb3+ :caF, 
Dy3+ tCaF, 
ce3+ :LG, 
w+ .:LaF, 
Eu3' :LS, 
Dy3+ tLaF3 
w+ :LaF3 
w+ tIaF3 
Nd3+ , I d 3  
Hd+ t W 3  
w+ :caF, 
-3- 
I n  addition, &IC& crystals with - two rare earth dopings (one always 
Sm2') were studied far possible energy transfer between the Sn?+ and 
the other rare earth i m .  Each of the 13 rare earths was t r ied as a 
second dopant. 
Iv. Results 
Results obtained that have 1; on published s f a r  are: (1) A 
paper containing preliminary results on Pr3' :Lac&,, Nd3+ :Lac& and 
Sm'':LaC&. These include r i s e  lifetimes fo r  and f a l l  lifetimes 
for all,  a t  77°K and 4.2"K. Also, the e x i t a t i o n  spectrum of SI$+ was 
determined. Reprints of tHs paper are appended. Further work an 
SI$+ :Lac& was reparted (2) at the Southeastern Section Meeting of the 
American Physical Society. 
and lifetimes of the two SmZ+ si tes  exls-bjng lin the h C 1 3  crystal. 
A n  abstract of this paper is appended. 
This included a discussion of the spectra 
I n  his Dissertation (3), Dr. Par t law gave resul ts  of a careful 
temperature dependence measurement on the Sn?+ r L a C b  lifetimes. 
found a striking dependence which indicates a multiphonan process; on 
He 
the order of 20 phmons, with energy 50 cm-l each, being generated Qy 
stimulated emission t o  act  as the radiatianless process which depopulates 
the excited level  of S2+. 
region 50 - 70°K. A paper sett ing for th  these resul ts  is being prepared 
This assumes importance i n  the temperature 
and reprints w i l l  be sent when they are ready. 
V. Publications by this Report 
(1) W. D. Partlow and E. H. Carlson, IIFluarescence Decay of lk3+, Nd3+, 
and Sm2+ in LaC&,ll J. Chem. phys. - 41, 3645 (1964). 
(2) E. H. Carlson and W. D. Partlow, "Fluorescence Rise and Decay 
Lifetimes of sm2+ in LaC5,II Bull. Am. Phys. Soc., Ser. 11, -' 10 262 (1965). 
( 3 )  W. D. Partlow, ttFluorescence Decay nf the SI@+ Ion i n  Lanthanum 
Chloride, 'I F'h.D. Dissertation, University of Alabama (1965) . 
(11) A paper on t h e  temperature dependence of S$+:LaC&, i s  being 
prepared, and reprints w i l l  be sent when available. 
Time 
Mark 1- 
Gener- 
.j -atar_I 
Gener- 
Photo- 
Keyer 
1 t 
De laye d 
Pulse 
Gen . 
TIME RESOLVED SPECTROIETER 
u Phot cniiultipler 
. 
Reprinted from THE JOURNAL OF CHEMICAL PHYSICS, Vol. 41, No. 11. 3645-3646, 1 December lW, 
Printed in U. S. A. 
, 
Fluorescence Decay of Pr+, NdS+, and Sm*+ 
in LaC1,t 
W. D. P u n o w  AND E. H. CARISON 
U n k M  of A l a b m ~ ,  University, Akbama 
( R d v e d  1 1  September 1964) 
ECAY curves for various levels of P r ,  NdH, and D Sm*+ in LaCl, single crystals were obtained by 
measuring' the intensity of fluorescence lines as a func- 
tion of the time after illuminating the crystal with a 
repetitively flashed EG&G FX-6A flash lamp. The 
intensity was measured by applying a pulse' to an EM1 
9558B photomultiplier tube. Measurements were made 
both a t  77" and 4.2"K. Selective excitation wavelengths 
were obtained both by using filters and monochroma- 
tors. The results are displayed in Table I. 
The findings for SmX are of special interest. Fluores- 
cence is observed within the 4y configuration from two 
levels ( A  and B )  about 1300 cm-1 apart to the 'P 
ground multiplet. The excitation of A and B is prob- 
ably due to nonradiative transitions from levels of the 
4f65d configuration, which may be populated by al- 
lowed transitions from the ground state.' 
When observed with steady-state apparatus, the 
fluorescence from A is more intense than that from B at 
77°K. The opposite is true at 4.2"K. We note also that 
the lifetime of the B level is the same a t  77" and 4.2OK. 
The relative intensity increase from A a t  77°K indi- 
cates a temperature-dependent excitation process and 
the intensity-versus-time curve for A a t  77°K shows an 
initial rise followed by decay. The rise time of A at 
77°K is 5!?%&5% ~ S P C  while the decay time of B is 
2000 psec. Thus the B-+A nonradiative process found 
in isoelectronic Eu* chelate' does not obtain here. 
The excitation spectrum (fluorescence intensity 
versus exciting 'wavelength) was obtained for the 
fluorescing levels of Sm*+ and is shown in Fig. 1. NO 
difference could be detected between the excitation 
spectra for A and B nor between 77" and 4.2"K. We 
4Ooo 4000 0000 1500 
WAVELENGTH.ANGSTROMS 
FIG. 1. Excitation spectrum for the B-+W transition of Sm*+ 
at 4.2"K. Excitation is by a tungsten lamp through a monochrom- 
ator with a band pass of 60 A. 
conclude either that the A level is populated at  77°K 
from a higher level (not B )  of the 4f" configuration, or 
that some Sm*+ ions in special lattice sites have a rapid 
conversion B+A at 77°K (giving a rise time of 50 
psec to the A fluorescence and quenching the B fluores- 
cence) while others do not (giving rise to a weaker B 
fluorescence with a "normal" lifetime of 2000 psec) . 
No structure was found in the p$aks of the excitation 
spectrum using a resolution of 1.6 A, and it is concluded 
that the broad peaks represent absorption bands in the 
4fW configuration. 
i This work w a b  supported by :hc Xa:icx! !-erc~antics and 
Space Administration under contracts NAS8-5029 and NASS- 
11200. 
G.  E. Peterson and P. hf. Bridenbaugh, J. Opt. Soc. Am. 52, 
1079 (1962). 
* We wish to thank D. E. Kerr for several hehful discussions on 
instrumentation and for the loan of equipment 'in the early stages 
of this work. 
'G. H. Dieke and R. S a ~ p ,  J. Chem. Phys. 36, 371 (1962). 
'M. L. Bhaumik, J. Chem. Phys. 41, 574 (1964). 
TAB- I. Fluoraance dcay lifetimes of W, NdW, and Sm* in Lac&. 
Dary time (micnweconds) 
L 
Southeastern Section of the American PhCysical Society, Chattanooga, 
a November 5-7, 196k 
I 
Fluorescence Rise and Decay Ufetimes of SI?+ i n  I a C b ,  W. D. PARTW 
(Introduced by W, G. Moulton) AND E, H. CARISON, University of Alabama 
Time resolved spectroscopy by means of sample illumination by 
repetitive flash and time-delayed pulsing of a photomultiplier detectm 
was utilized. Various wavelength regims i n  the excitation were obtained 
by f i l t e r s  and a monochromator. 
intensity as a functiun of time af ter  the f lash  could be seen. 
lifetimes were 10 msec and 2 msec for the A and B levels' respectively. 
A t  77%, the fluorescence from A showed an i n i t i a l  rise with a lifetime 
A t  b.Z''K, no i n i t i a l  r i s e  i n  fluorescence 
Decay 
of 56 ysec and a decay of 3.5 msec. rm, E ahm~c? mly a decay time of 
2.1 msec. Possible explanations for this behavior w i l l  be discussed. 


Optical properties of transition ions in crystals under bombardment by energetic particles, x and gamma rays and light final report

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