Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
PHN. 8241.
~{3g6~ :
The invention relates to a luminescent screen
provided with a luminescent alkaline earth borate acti-
vated by bivalent europium. Furthermore, the invention
relates to a low-pressure mercury vapour discharge lamp
provided with such a luminescent screen and to the
luminescent borate itseIf.
Activating alkaline earth borates by bivalent
europium is known. Materials are obtained which, when
excited by ultraviolet radiation show the relatively
narrow band emission of bivalent europium. Depending
on the host lattice used this emission band is located
in the deep blue or the near ultraviolet part of the
spectrum. The barium octaborate (BaB8013) activated ;
by bivalent europium, which has an emission band having
its maximum value at approximately 400 nm is known.
United States Patent Specification 3,657,141 discloses ~ -
strontium fluoroborate (SrB406 5F) which is activated
by bivalent europium and the emission band of which has
its maximum value at approximately 370 nm. A disadvan-
2Q tage of the known fluoroborate is that it is difficult
to produce and may give rise to an undesired release o~
fluorine into the atmosphere. Japanese Patent Applica-
tion 74/67,892 which has ~een ~aid open to public inspec~
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1089641 1 1. 11 . 7G
ti.on, disclose.s a calc:ium conta:in:in~ strontiul1l tetra-
bo:rate wh:ich i s ae-tivated by blvalent europiulll, for
examp]e SrO 9CaO 1BI~07. 1~hen exci-ted by shortwave
ultl~a-vio].e-t radiation this n1ate:rial has an er~:ieieIlt
emission w]lose maxilnum vcLlue is at approxinlately 370
nm and a hal~-wicl-th value o~ approxima-tely 20 ntn.
Sueh a narrow-halld emission in the l~ave].en6th
ran.ge between 350 and 390 mn may be used to grea-t
advantage for inf`lueneing photoehemieal proeesses
sueh as lacquer ha:rden:ing, hardening of gypsurn,
photo-po]ymerisation, xerograpby and SUC]1 like. It
is an object of $he invention to provide new l~lmi-
~nescent materials which may be used fcr such purpo
ses.
A luminescent screen according to the inven-
tion. i.s provided wi-th a lutninescen-t alkcnline earth
bora$e, aetivated by bi.valent europiu:n ancl is eharae-
~ terized in that the borate sat:isfies the for~lula
: Sr1 MexEu Bll07, in. whicll Me sta.nds ~or a-t least
: ` 20 one o:E -the ele~ne:nts barium and magnesi.~-lln and in
whic:h 0 ~ x ~ 0.25 and 0.003 ~ p ~ 0.20.
The lun-l:inescent allcal:ine ear-th. borate in a ~ :
luminescen-t screen accorcling to t;he in~en-tioIl can be
excited ver-y well by shortwave u:Ltravlol.et radi.at:ion
~or ex~ pl.e the racliatlon o:~ a low-prcssu.re mercu:ry
VaPOIIr diSC1la.rge .1 anlP (nla:;.n]Y 25/~nm) . T~:Le ernlssion
the-rJ. ohtainc~d :i.s a :na:l:row-~ban~l emiss:io:lL~i.tll.cL maxim~
. ~
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1l.ll.76
969~
. al; appro~imately 368 nm and a hal~-wi{l-th value o~ ap-
proxi.lllate].y 18 nm.
'l`he host lat-tice of -the lunlineseent nlater:Lals
according to the inven-tion consists o:t` s-tront:i.ul11
tetraborate in which part of the s-trontium is re- ..
placed by ba*ium and/or lllagnesiun1. 'Nle crystal. s-truc-
ture of stron-tium tetraborate (orthorllon1b:ic syl11n1etry)
is maintained. It was surprisingly f`ourld that SUCIl a
replaceme:nt resul-ts in an increase in the quantun1 e:~
ficiency and in the radiation output compa.red with
the pure s-tron-tium tetraborate. A still lar~er gain
in radlation output is obtained with respect to the
known, ca:Leium-eontainirlg st:ron-tium tet~abora-teO It
was ~ound that alreacly sma.1:L quan-ti.ties of bar:iu.m
and/or magnesi.um gi-ve ri.se to an increase in the : .
radiation output. ~t a value of lhe bari.um- and./or
magnesium contents x equal to 0.05, ~or example, a ::
. considerab:Le gain'lmay already be obtainecl. I~len Large
. quantiti.es of the stron-tiuni are replacecl by ba:riu
ancd/or magMesill~n tlle radiat:ioIl o-u-tput decreases again. :
: Thererore not mo:re than 25 rnol.% of the s-tront:i.wl1
(x ~ O. 25) is repl.aced. The eu:ropium content p may
be chosen be-tween the above-menti.oned w:i.de li.mils. -' '
For va:lues o~ p ~rll:;.cl~ a:re smaller -than 0.003, ra--
diation outputs are obtai.ned w}l:icJl are too sma:l.:l. ' '
I'or p:ract;i.cal purposes and :~or values oI' p wh:ic}l ex-
eeed 0,20 the :radi.lLt;.i.on OUtpllt beeolrles -too sma:l.l ow- ::
PI~N 82 ~T 1
11.11.76
~85~64~
. img to concelltra-t:ioll querlclling~
part:icu:l.ar advanl,age o~ the luminescent
~orates accorcling to the invention i5 that -they can
he obtained as a compa:rative:Ly coarse-grained powder.
Tllis applies especially to -the magnesium-subs-tituted
borates according to the inventlon wh,ose average gra;.n
size (determined by means Or -the ~isher Su'b Sieve 5izer)
is approximately 5.0/u. It is much easier to apply such
a powder in a luminescent screen than the known calciwn
containing strontium tetraborate (approximately 1.5/u)
and the known pure strontium -tetraborate (approximately
303/u) obtained in a similar manner, l~ur-thermore, the
lurninescent properties O:r such a co,arse-grained powcler
are preserved nluch better when apply~ing it in screens.
.
15~ The 'highest radiant e:~f,iciencies are o'btain-
ed with bora-tes which satisfy the above-men-tioned for~
.- .
' mula, where 0.05 ~ x ~ 0.20 ancl 0.01~ p ~ 0.05. There- ',
fore these values o~ x and p are p:referrecl.
A luminescent screen according -to -the i.nven-
ti.on LS pre:~erably u.setl in a low-pressll:re morcury
vapour d:ischarge :Lamp as the luminescellt borates
are opl;imal:ly exci-ted by -the 25LI nm rad.iation o:~
s-uch a lamp.
'I'h,e inven-tion wil:l now be fur-tller exp:Lain-
. . .
e-l with rererence to a num1~er of examp:Les antl measure~ '
ments and a drawingr.
lrL the draw~.ng D'iB. 1 S]l.OWS C~ agrall:llllal;iCa lly
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. PllN 82ll1
964~ 1.7G
a low-p:ressllre me.rcury vapo1l:r discharge :Lamp acco:rdin~
l;o -l;l~.e :inventi.on. ancl Fig. 2 shows -the spec-tral el1er~y
dist:r:i.b-ut:;on o:[` the emitte(l rac1.iation o~ two boral.es
accord:ill~ to the inven.tio~
~igr. 1 shows a low pressure mercury vapour
discharge lamp wlt]l an enve:10pe 1. l~lectrodes 2 and
3 are disposed at -the ends o:~ the lamp be-t~een ~.~hich
the dlsch.arge is~maintained. The ins;de of the en-
velope 1 is coated ~ith a luminesce.ll-t la5rer 4 ~hich
contains a luminescent borate according to the in-
vention. This luminescen-t :Layer may be app].ied to the
envelope 1 in a prior ar-t me-t:ilod. ~.
~ .
o.88 mo]e SrC03
0.10 mole BaC03 -~
: 0,01 mole ~u203 and
1~ 00 mole I-I B0 ..
are suspendecd in one litrc of water o~ 70C. I-JN03 :is
aclded to this suspension so tha-t a so:Lution is ob- .:
tained. ~pproxima-tely 2 l o~ a mixt~ire (1 : 1 volume .
parts) oI` NlII~O~I and a po].ar orgall.ic solven~, for
exan1ple acetone, are carefùlly ad.cled to thi.s so:l.u-
-t:ion so that a mi.xed hyclrox:i.de preci.pita-tes. T:he:re-
a~`ter -the precip:i.-tate :is :~iltered o:~f and dri.ed. :~
Therea:rter it :is hea-ted ~o:r 2 hours at c~00C in ai.l~.
The product then obtained :Ls cooled a:ncl pulver:i.~.e(l
whereafter lt is heatecl once mo:re~ now ~or 3,5 h.ol1.:rs
.
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-- - lQ~964~ PH~J 82~1
at 920C in a nitrogen current which contains 0.75 vol.
of hydrogen. After cooling and pulverizing the lumines-
cent material which satisfies the formula SrO 88BaO loEuo O
B407 is ready for use. The spectral energy distribution
of this material at excitation by short-wave ultraviolet
radiation (mainly 254 nm) is shown in Fig. 2 (curve 1).
In Fig. 2 the wavelength ~ (in nm) is plotted on the
horizontal axis and the radiant energy E (in arbitrary
units) on the vertical axis. The borate according to
the invention appears to have its maximum of emission
at 368.5 nm and to have a half-width value of 17.9 nm.
For comparison, Fig. 2 also shows the spectral energy
distribution of the known lead-activated barium disili- ~;
cate, a luminescent material which up to the present has - -
been frequently used in low-pressure mercury vapour
discharge lamp for generating radiation in the ultra- ~-
violet part of the spectrum (the dotted curve a).
Example II
The procedure as in Example I is repeated in which,
however, 0.93 mole SrC03 and 0.05 mole BaC03 are used
instead of the quantity specified in Example I. The
luminescent material obtained has the formula
SrO 93Bao.osEuo.o2 4 7
Example III
Example I is repeated but instead of the BaC03 0.05
mole MgC03.Mg(OH)2.3H20 is used. The material then
obtained satisfies the formula SrO 88MgO loEuo 02B407.
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~L089~i41 11.11.7G
Curve 2 in Fig. 2 shows l;:ll.e spectral energ~ ~istri.bu-t:ion
o:f` -thi.s mate:ri a] .
e :r ~
._ .
Examp:le I is repeated, w:ith t:he prov.is:ion that the :~irst
heating for 2 hours in a:ir is now perf'ormed at a tem-
perature oI` 850C. The product obtainecl has the same
~ormula as the material o~ examp:Le I. The average
graiIl diameter of the powder is 4.2/u.
E.xarllp.l e V . :
Exal11ple I is again repeated, howeve:r, the :~irst heat-
ing operation is er~ected at 900C.,The luminescent .
materi.al obtained which sa-tis:ries -the formula speci-
fied i.n Example ,1, has an average grain dian1eter o~ . .
6.7/~
Exam~le VI .' '
A materi.al with -tlhe for1nula as speci.:~ied in Example I -~
Y 0.88 ao.1oEuo.o2B4o~7 may also be obtained by
carefully Il1i.xing in a ball mlll~
o.88 mole SrC03
0.10 mole BaC03'
0.01 mole Eu203 ~ :
1~.oo mole 113B03 ..
~ : Theree.fter th.e mixture is heated in air in an open.
: crucih]e :~or 2 hours at 850C. A:~ter cooling the pro~
duct obtai.rled i.~s pulveri7,ed and t}len heatecl a~air1, .
now ~o:r 3.5 hours at 920C .i.n n.itro~roll atmospb.ere
whi.cl]. con-tai:ns 0.75 voL./~o o:l' h~d:rogerl. Af'ter cooli1~g
.
PllN ~2~
1 1 . 1 1 . 7 G
~(3896~
and pulveri~ g t:b.e lumi.n.escent borate is ready for
use.
The resu.lts o~ measurclllents on tlle materi.als
obta-i.ned w:ith the exal1l]?les menti.on.ed above are sum-
ma.rized i.n the table herebelow. Eor each example tlhe
table states, besi.des the ~ormula o~ the ]umilLescent
material, in the column LO th.e ultraviolet-radlation
ou-tput in ~ wi-th respect to the radi.ation output o:~
the known, lead-acti~ated bari.um disilicate, and in
tlle column dm the average grain diameter in /um. Eor
comparison the measurements on the known s-trontium
tetrabora-te and the kno~n calc:Lwn-contai.ning stron-
ti.um tetrabora-te and the known s~ron-tium :~luoroborate
respectively, are gi~ren as examples a, b and c. These
~ 15 ~ known materials are prepareci. i:rL the same manner as L
: ~ : speci:ried in Example I.
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~ Exalllplc ~ormllla LO ( ~) dnl(/ul f)
~ _____
a SrO 98EUo~ 02 /l 7 208 3~ 3
b SrO 88Cao .10 0 ~ o2B407 184 1.5
c SrO 9gEUo . o2Bl~o6. 5 168 2.2
I SrO 88BaO.10~U0.02 4 7 226 3.4
II SrO 93Bao. o5Euo~ 02 4 7 224 _
III SrO 88Mgo . 1 oEuo . 02 1~ 7 218 5.0
IV SrO ggBao.1oE~lo. o2 /~ 7229 4.2
V SrO ggBao.1oEllo.o2 /~ 7 22~ 6.7
VI SrO 88BaO.10EUO.OZ 4 7 224 /f .7
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