CA1296879C - Method of preparing fluorescent material of small particle size - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A fluorescent material of small size is prepared by synthesizing a fluorescent material of predetermined molecular structure in a single phase, pulverizing the fluorescent material thus produced and then heat treating the pulverized material under conditions sufficient to recover the luminance characteristics which were lost as a result of pulverizing.

Description

f 1 ~ 4 4 S O N ~ T O K ~ ~ # 0 1 ~ P
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S P E C I F I C A T } O ~ j7 T I T L ~

"MET~3[0D OF PRE;PARIN~ FLUOR~3SOENT ~IATERI~i OF SMALL PP~ TIC~E S I æE n ~9~
: ~ield o~ the Invention ; Th~ present ~nvention is ln ~he ~ield o~ pr~par~ng ~luore~cent ~aterial o ~mall partic~e 6ize suitable for use on fluorescent ~urfaces of high luminanc~ and high fineness cathode ray t~bes ~uch as ~ho~e u~ed, ~or exa~ple, in airplane cockpits or in televlsion ~ro~ector60 Descr~e_lon o~ the P.r~iox Art Color cathode ray tubes used, or example, in cockpits o~ airplanes or ~or aolor talev~sion projectors must have a high re~olution ~ower, a hiyh deg~e o finene~s, and high luminance. Generally, ~he ~luorescent surface of a color cathode ray tube i~ Goated in a predeterm~n-d pattern such as a ~tr~pe or dot pattern wlth ~l~orescent materials correspondin~ to the prlmary colors, in a narrow wldth~ As the re301u~ion power and the~f ineDes~ h~ve been ~nar~a~ed, a hi~her density is required ~or ~he patternO A particle ~i~e o~ abou~ lO m~ons (um) which typlc-l ~or t~ usual flu~rescent ~at-ri:al particle~ 1s too rge to obt~in an opt~um coa~ing thickne~s ~or the ~}uorescent . ~
~ ~t~rial nece~sary or a~ta1ning high lumin~nce. In view of the :l ~o~e~olng, it i~ ne~essary :~o prepare ~luores~en~ material o~
. 8~all ~artiale ~ize ~n order to ~b~aln a color cathod~ ray tube of hl~h luminance and ~ high:degree of fin~ness.

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f l~f~ 17~ 44 SONY TOKYO #~1~ P07~
7J9 7~ 1 Fl~orescent materials o~ small particle size have been made by ~everal proce~ses in the prior art. A irst method lnvolve~ reducing the amount o~ ~lux added to the fluorescen~
m~terial ox avolding the u~e of the flux altogether upon foeming the fluorescent material, thereby suppre~sing crystal ~rowth.
A ~econd method involves filtering or ~ieving ~luoreæcent material o~ small par~icle size ~eparated from ~luore~cent material produced by the usual method.
A ~hird method con~i~ts o~ pulveri~ing fluorescent material produced in the u~ual manner into a smaller particle ~ize.
The irst metho~ involve~ the disadvantage that the particle ~rowth remains in an intermediate and thus un~table stage. A desired fluore~cent product cannot be ob~ained as a ~lngle pha~e which r~duces the luminance~
The second method Ls dlfficult to carry out and,p~ovides an extremely low yield.
The ~hird method involving pulverizing is not very acceptable becau~e pulverizing injures ~he pa~ticle surface ~o as to reduce ~he luminance as much as from 30 to 40~ o the inherent lumina~ce.
When the Fluore~aent pattern for each o~ the colors is made iner, the luminance ~ends to be lowered in the forma~ion of the fluorescen~ surface due to the pack~ng densi~y o~ ~he ~luor~6cen~ partlcles in each o~ the portlons and acco~dingly, a hlgher luminance is required o~ th~ fluoree~e~t particle~.

17: 44 ~0~IY TOKYO #01~ P~g~
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~MMARY OF THE INVENTION
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The present invention s~eks to provide a method for prep~ring 1u~reacent mate~ial o~ small partic~ e size 1 n which a m~terial o~ ~igh lumina~ce can be obtained a~ a good yield.
In keeping with ~he pre~ent invention, a fluorescent material of small siz~ is achieved by ~ir~t ~ynthesizing a ~.
fluorescent material o~ predeterm~ned molecular structure in a Yin~le phase, pulverizing the thus prepared fluore~cent material whereby it~ lumine~cence i~ decreased and ~hen heat ~reating ~he pul~eri2ed m~teri31 under aondition6 ~uch that it recovers substantially all the luminescence lo~t as a result of pulverizing.
In the ~resent invention, a singl~ phase or mono-phase of the de~ired fluore~cellt compo~ition i8 ir9t prepared and then pulv~rized into ~ine particles. The ~ine particles are in the mono-pha6e but ~he luminance thereof is lowered as a result of the pulverizing. Then, th~ ~in~ particles are ~ubjected to heat treatmen~ by means ~ which the pulverized fine par~icles a~e ~intered and the luminance lost by pulverizing i~ rec~vered.
; In the pr~sent invention, a ~luorescent material which i5 ~table and possesses high luminance in the mono-phase is pr~pared through comp~ete arys~al growing and ~ubsequent pulv~rlzation. By applying the succeeding heat treatment, the luminanae low~r~d by the injury a~ th@ ~ur~ace of the particles 1~ recovered, ~hereby produci~g a fluorescent m~terial o~ high luminance and ~mall ~ar~icl~ size at a good yie~d.

~ ' ~ -3-fl~ 17:44 ~OI~Y TOKYO #~13 P0 3L~3~i~37~
~2,7 BRIEF DESCRIPTION OF T~E DRAWINGS

Ths ~eatures of the invention and the advantages ther20 ~11 b~come appa~ent rom ~he following descrip~ion o~ the pre~erred embodiment~ with reference to the accompanying drawings in whichs FI~S. 1~ 2 and 3 are enlarged views obtained f~om mloro~oopic photography after each of the steps for one ~mbodiment o~ the p~esent invention;
FIG. 4 i~ a di~gram illustra~ln0 particle size distribution after each of the steps;
FIG. 5 is a particle size dlstribution diagram for the invention and a comparative example;
~ IG~ 6 ~s an enl~rged view illuskrating the ~luore~ent par~icle~ obtained fr~m microscopic photography ~or comparative example~; ~
. FIG, 7 i~ a diag~am ~howing the ~elatlonship between the pulverization time and the paxticle ~ize and luminance; and FIG. 8 is a diagram lllustrating the particle size ~ist~ibution showlng the ~tep~ o the proce~s.

DESCRIPTION OF ~HE PREFERRED_EMBODIMEN~S

The ~ol}owing ~peci~ic ~xample~ illustrate the method o~
~he pr~ent invention as it i~ applied to various ~luorP~cent ~aterial~.

; A green pho~phores~ent m~terial of mono ~ha~e Y3A15012 s Tb was ~ynthe~ized ln the ~Eoll9wing manne~. F2r the 5ynthe~is, 321.78 g of Y~03, 254 . 9 9 ~f A1203 and 28.04 g of 3~ 17: ~4 ~ON~ TOKYO #~13 Pl0 ~L~9~i~37~

Tb4O7 wa~ used as the Rtarting material for forming one mol of Y3Al5O12 : Tb~ Tb~mol) t (Y + ~b~(mol) ~ j. The powders were mlxe~ and ~intered using 20 mol % BaF2 as a flu~. The sintering ocGurred at 1350 ~o 1600C ~or to hours, preferably, at 1500C
~or two hours, to obtain Y3A15O12: ~b. ~ methoa a6 disclosed in ~apanese Laid-Open Application No. Sho 58~57491 can be applied to the ~ynthe~is of Y3A15O12 : ~b, in which case the acid or alkali washing procedure after the ~ynthesis can be dispensed with.
The thus obtained Y3AlsO12 : Tb in the mono-phase was pulveri~ed as the ~econd ~tep. In the pulverization stage, the following mixture was charged into a 101iter ~olume polyethylene bottl~:
Y3A15O~ b ~ 2200 9 ~lumina ~all ~5 mm ~iameter~ 9600 g H2O -~ --- 3600 9 The mixture was subjected to ball mill pulverizatlon with a rotation o~ 6Q rpm for lS hours.
Then, 110 9 o~ BaF2 a~ the 1ux were added ~o the pulverization product and ~ubjected to ball mill pulverization fo~ an additional hour. Then, the balls we~e removed, and ~he products were filtered and dried.
A3 the ~hird ~ep, the products of pu~verization were charged in ~n alumi~a crucible, heated to 1500C a~ a ~emperature incre~e o~ ~00C per bour in a heatin~ urnace. ~r th~s ~rtlcular phosphor, the heat tre~ting t~mperature oan be carried~
out a~ emp~ature~ from a~out 1400 to 1700C. A~er malntaining the mixture at 10Q0 to 1500G for 1 to 6 hour~, preferably, at 1500C or two hours, the ~oduct~ were cooled in the furnace.
Then, ~n acld ox ~lkali wa~hing treatment was applied to remove the residu~l ~lux.

--$--l~f~ 17:44 ~ON~ TOKYO #~13 Pll~
~ 6~379 The fluorescen~ material thu~ obtained showed no ~ubstan~ial reduction ln the luminance a~ compared to the luminance o the originally synthe~ized mono-phase fluorescent ma~eriaL despite the treatment in the pulverization step. Taking an ~mission luminance o the fluorescent materi~l after the first step in the example a~ 100~, it was determined that the luminAnce was lowered to 70~ after ~he ~econd ~tep, but recovered ~o about g9.5~ a~ter the third ~tep.
FI~S. 1, 2 and 3 are en7arged views illus~ra~ing, re~pectively, the sta~e of particle~ after the ~irs~ synthesis ~tep, the ~ec~nd ~tep-o~ pulverizing, and the third, heat treat~n~ step obtained from a ~cannlng type electron micro~copic photograph. A~ can be seen from these Figures, ~ fluore~cent mater$al of large particle ~ize after the first 8tep shown in FI~. 1 15 irre~ularly c~aaked by the pulveriz~ng treatment in the ~econd step ~FIG. 2) but iluore6cen~ materlal of a ~ine particle size havin~ an excellent uniformity and improved ~haping p~opertie8 can be obtained through ~i~tering ~ith ~he heat treatment at the third ~tep (FIG. 3).
FIG, 4 ~hows the re~ult of measurem~nts of par~icle size dist~ibution o~ 1uorescent partieles in each of the step~, curve 1 showinq the particle size di~tribu~ion after ~he fir~t ~tep, curve 2 showing the particle size distrl bution after the ~econd step, that i#~ a~ter the ~ulveri~ing treatment, and curve 3 showing th~ particle ~ize distribution a~ter the ~interlng h~a'c ~reatment. ~t can be ~een that ~l~h~u~h the p~rticle~ are ~iner a~ter the third step a~ compared with the first step, the 1uoreQcent ma~e~ia~ which ha~ been pulverlzed in the eecond step was sintered.

~6--17: 44 SON~ TOKYO ~13 Pl~J~i~
61~3~9 It can be ~een that although the particle ~ize of the fluore~cent material can be reduced to less than one-half ~hat which exists in ~he mono-phase synthesis, there is no ~ubstantial r~duc~lQn in the lumi~ance due to pulverization under the ~ondition~ of Example 1.
~ n the method ~ preparing the ~luorescent material of small particle ~ize according to th~ presen~ i~vention, it ha~
been observed that if the pulveri~i~g ~tep in, for example, a ball mill i~ ca~ried out or to~ long, abno~m~lly grown large particle6 are genera~ed as a result of the hea~ treatment. For ~xample, in E~ample 1 where the ball mill treatment was applied fo~ 16 hour~ be~ore the heat t~eating step, ~he aQe~ag~ particle.
~læe in the particles be~ore heat trea~ent waB 3.3 um and the volum~ o~ particlea of les~ than um ~ize was about 5~ of the volume o~ particles o~ average particle ~ize as shown by curve (2~ in ~IG. 5 (corre3pondlng to cuve (~) in FIG~ 41.. The average particle size after heat treatment wa~ 5.9 um and the distribu~ion ~hown by curve (3) in FIG. 5 wa~ obtained. In the ca~e where the~b~ll mlll pulverization wa~ applied for 4B hours, the particle ~ize was a~ shown by curve ~4) in FIG. ~ in which the average particle slze wa~ 2.8 um and the volume o partlcles havlng a si~e of les~ than 1 um ~as about 30~ of the volume of partiale~ of average ~ze~ Then, a~ter hea~ ~reatment, the particl~ ~howed a~bnorm~l growth as large a~ 2~7 um in the av~ra~ pa~ticle ~ize as ~hown by the di~tribution ~urve ~5) in FI~i;. 5 and the luminance was about 85~ o~ the initial luminance.
In v~ew oi the abovg, it i~ de~irable to remove par~icles of le88 than 1 l~m particle ~i~e as by ~i~ving b~fore .

flelf~ 17:44 ~OMY TOKYO #013 Pl~
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~he heat treatm~n~ in the third ~tep to the extent that ~uch ~ub~lcron partlcles occupy leq~ than 5~ of the volume of the pa~ticle of average 6i ze.

Thi~ example lllu~tra~es a manner of obtaining red ~luorescent Materlal Y2O ~ : ~u fo~ u6e in color television receivers. ' As a fir~t step, there was a ~ixture made up containing:

2 3 25Q g 2 3 ~~~~~~~~~~~~~-~~~~~~~~ ~-~~- ~6.23 9 8 - 278,0 g ~C03 ~ 408.4 9 ~PO~ _ 39.6 9 ~ his mixture was charged in a 2 liter voLume alumina crucible equipped with a cap, heated to 800 to 1200C, ..
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prefer~bly, 1150~C at a temperature increase of 200C per hour And maintalned~at that temperature for to 10 hours, preferably, for two hours and then coole~ in the furna~e. The product was wa~hed with cold or warm water to a pH of 7 in order to remove re~idual polyeulfides and the like. The product was then filtered and dxied~
~ mixture co~pri~ing 1~ g o~ t~e ~hosphor obtained by the ~ir~ step, was c~m~ined with ~n slwmina ball havin~ ~
d~ame~er o~ ~ mm and weighing 480 ~, togethe~ wlth 180 ~c of wat2~ and charged in ~ 0.~ liter pol~ethylene ~ott~e where ~ wa5 sub~¢tea to ball milling under ~station a~ 100 rpm.

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~'~JI~ 17:44 ~ K`fO ~13 P14~

In th~ h~at treatment step, the ollowing mixture:

Y~O~S : ~u (obtaine~ by the 5e~0nd ~tep)- 110 9 S 32 g 2C3 ~ _____ 53 g (N~4~2~PO~ 39.6 g was charged in a 1 l iter volume alu~ina crucib~e, heated ~o 800 to 1100C, preferably, to 900 to lOOO~C at a temperature rise of 200~C per ho~r. It was maintained at that temperature for 1 ~o 10 houx~, pre~erably, ~vx 1 to 3 hours a~d cooled in the-furnace.
The product was then wa~hed wlth cold or warm water ~o obtain - -a fluorescent material o Y2O3S : Eu o~ mall particle size, FIG~ 7 ~how5 the r~5ult~ o me~ure~en~s o~ the re~pectlve averag~ particle siz~ o th~ fl~ore3cen~ ma~erial obtalnea by varying ~he pulverlzation tlme in the ball mill o~
~xamp~e 2, and the re~ec~Lve relative luminances th~reof.
~ he,pa~ticle 3ize requir~d ~or the fluosescent material ~ d~terminod w$th relation to th~ wldth o~ the fluor~sc~nt pattern ~ormed by the coatins o~ fluorescent m~erial, ~or ex~mple, tbe width o~ the 1uo~escent ~tripeO In the usua~
14-inch ~ype color televisf on rec~iv~r, the stripe width ~s ~bout 250 um and the ~verag~ pa~.cle ~i~o o~ She 1uore~cent par~cles ~y b~ on the o~er of 1~ um. On th~ ~her band, wher~ the st~i~e w~d h o~ the ~luroe~cent mate~ial ~s abGut 40 um ~ ~n the ~a~ of a cathode r~y tube o~ high ~lnenes~ about 2 wm o~
~a~tlclo 8~Z0 ~5 re~u~red ~or th~ ~luorescent materi~7~. A8 ~an b~ ~en ~o~ ~ 7, the rela~lY~ ~umina~ca of ~he Xluorescent ~eri~l ~eco~e~ lo~er ~ the averaqe partlcle ~ze o~ the ~luors Sent ma~eri~l b~come; 3~a~ b~ lumin~nc~ o~ the powd~r i~ abou~ 92~ i~ tho oa~e o~ a~ ~ve~age particl~ ~$~¢ o _g_ '' '' ' '"!~ f; f ~ 7 ~ ~ N Y T ~ I~ Y ~ # ~1 ~ P ~
~LZ~6~ ,Y7 2 um and, when the flu~e~cent ~urace of the high ~inene~3 cathode ray tube with 40 um ~tripe width wa~ manufactured using ~h~s ~luor~scent mat~rial, a avorable fluore~cent surface could be ob~ained, If a fluore~cent mat~rial of 10 um average particle Bi~e is u~ed in the ~ual process where the fluorescent stripe width i~ 40 um, the ~ilm thickness relative to the luminance i~
not at an optimum value.
Al~o ln ~xample 2, if the ball mill pulverization is carried out for too long a time, very 12rge particles are formed in the fluorescent ma~erial ~inally ob~ained a~ter the ~hird ~age ~n the ~ame manner ~6 explain~d in Example 1.
Exampl~ 3 Thi~ example deals with ob~ainin~ a red fluorescent material Y~03 s Eu ~or a cathode ray tube used in a p~ojec~ion television recei~er.
AB a fir~t qtep, ~he following mixture was made up:

~O3 ~ ~ 2175.6 9 2 3 -~ 8.4 g Ba~2 ~~~~~~~~~~~~~ ~-~~~~ ~~~~~~~~ 350.6 g EthanO~ 2650 CC

This mixture was charged in a Z0 l~ter volume ps~lye~hylene bo~tle and mixed with r~tataor~ a~ 30 ~p~n ~or 20 hour~. The mixtur~ wa~ the~ placed in a 2 }i~er volume alumina crucible with a cap and h~ted to a ~emp~rature of 140~ to 1600C, preferably, a~ 1500C, with a temperature increase Q~ ~
20~C p~r hour. It was maint~lned at that tempera~ure ~or 1 to 6 hours, preferably, for 1 ko 3 hours and the~ cooled in the furnace. ~h~ powder w~ pa~sed through a 100 me~h ~i~ve and disintegraked.
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I Y T ~ K Y O # ~1 ~ p 1~687~
A~ a ~econd etep~ the foll~wlng materia1s were char~d '~

in a 1~ 1iSer volume polyethylene bot~e:
i Y2O3:Eu (obtain~d in the f ir~t step)-- 2Z00 9 BaCl ~2H O ~ 100 y Al~mina ball, 5 ~m diameter -~ - 9600 9 Ethanol ~ 3600 cc The mixture wa~ ~ubjec~ed to ball milling under rotation at 65 rpm for 15 hours. The pulverize~ mate~ial wa~ fi1~erea, dri~d and then disintegrated through ~ 100 mesh sieve. . - '.
In ~he thlrd ~tep, the mixture obtained wa~ charged in a ~ liter ~olume alumlna cru4ible With cap, heated to a temperature o 1000 to 1500C, preferably, o 1400C u~ing a tempexature riqe 200C per hour. I~ was maintained ~r 1 t~ 6 hours, pre~erably, for 1 to 3 hours and then coole~ in the fuxnaae. Thereaf~er, 1000 g o the f1uorescent materia1 was subjecte~ ~a acid wa~hing by ~tirring ~or 60 minutes with 1500 cc o~ 33 HNO3 to remove the re6idual ~lux, washed with water to a neutral p~, ~iltered ~nd dried. The thu6 obtained fluorescent material was Y2O3;
Eu 1uorescent material with a 2.4 um average particle size and exhibi~ing the particle ~ize di~tribution ehown by curve 10 in FIG. 8. Curves 11 and 12 in that F$0ure show the particle size of thi~ e~ample aft2r the fir~t and seGond ~tep, respectively.
It wlll be unde~tood ~h~t Utillzing the process o~ the present invention produc~ ~ine partLcle ~ze material which can .
b~ manu~a~tu~d with litt1~ or ~o reduction ~n lum~nanc~.
Ac~o~dingly, ~ color cathode ~ay tube of hi~h lu~inanc~ and high finen~s~ ~or u8e 1Q airplane cockpit~ O~ televi~ion prvjertors ~an be ben~lted by using th~ ~luorescent ~a.~rial ~aco~ding to the pre~en~ lnvent1On.

, 1~f~ 07 SON~ TOK~O #1~1~ p0~fi5 :3LZ~61~

It ~q111 be understood that various modi~icatior~s can be ~ade to ~he de~arlbed embodirn~nts without departing from the scope o~ the prescnt inventlon. I

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Claims (4)

1. A method of preparing a fluorescent material of small particle size which comprises:
synthesizing a fluorescent material consisting of Y3A15O12:Tb, Y2O2S:Eu or Y2O3:Eu in a single phase;
pulverizing the thus prepared fluorescent material whereby its luminescence is decreased.
sieving the pulverized material so that particles of less than one micron particle size constitute less than 5% by volume of the sieved material, forming a mixture of the sieved fluorescent material and a flux, the mixture consisting of Y3Al5O12:Tb and BaF2 flux, Y2O2S:Eu and Na2CO3-(NH4)2HPO4-S flux or Y2O3:Eu and BaCl2. 2H2O
flux and heat treating said mixture at a temperature according to the following schedule:
Y3A15O12:Tb and BaF2 flux at 1400° to 1700° C.
Y2O2S:Eu and Na2CO3-(NH4)2HPO4-S flux at 900°
to 1000° C., and Y2O3:Eu and BaC12,2H2O flux at 1400° C.
the heat treatment in each instance being sufficient so that the fluorescent material recovers substantially all the luminescence lost as a result of pulverizing.

2. A method according to claim 1 wherein said fluorescent material is Y3A15O12:Tb.

3. A method according to claim 1 wherein said fluorescent materials is Y2O2S:Eu.

4. A method according to claim 1 wherein said fluorescent material is Y2O3:Eu.