Note: Descriptions are shown in the official language in which they were submitted.
3~
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However, these known fluorescent materials have dis-
advantages to be unsatisfactory from the practical viewpoints.
When the fluorescent material of a phosphate activated by
copper is used for a low pressure or high pressure mercury discharge
lamp, it is difficult to avoid a trouble of a serious decrease of lumi-
nous output because the activator of copper is oxidized by heating (such
as 600C) in a baking step (lehring) for the fluorescent material in the
preparation of a fluorescent lamp.
The fluorescent material of a halophosphate activated by
antimony has wide luminous region so as to emit an emission energy
even in near-ultraviolet wavelength region as invisible region.
Accordingly, it is difficult to obtain satisfactory luminous efficiency by
using it in a discharge lamp for lightening.
SUMMARY OF THE INVENTION:
It is an object of the present invention to overcome the above-
mentioned disadvantages and to provide novel bluish green emitting
fluorescent materials which are not inactivated in a baking step for a
preparation of a fluorescent lamp and whose luminous efficiency is
high.
The foregoing and other objects of the present invention have
been attained by providing a novel fluorescent material of an alkaline
earth metal boron phosphate activated by a divalen-t europium com-
pound having the formula m(Sr1 x y pBaxCayEupO)-(l-n)P205~nB203
wherein parameters x,y,p,m and n are respectively in the ranges:
O _ x ~ 0.5
O ~ y < 0.2
`'
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~8,570
0.001 _ p < 0.15
^ 1.75 _ m < 2.30
~; 0.05 _ n < 0.23
,:,
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
The fluorescent material of the present invention can be
obtained by blending raw materials having suitable element for the for-
mula such as CaC03, SrC03, BaC03, CaHPO4, SrHPO4, BaHPO4,
H3BO3, Eu2O3 etc, at ratios for forming the formula.
~;~ The mixture is charged in a heat resistant vessel such as a
silica crucible, and it is calcined at about 1,000 to 1,200C for suitable
time in a reducing atmosphere such as a mixed gas of nitrogen and
` hydrogen.
The raw materials can be compounds of each element which
can be converted to the corresponding oxide by a thermal decomposi-
tion. That is, hydroxides, nitrates, oxalates of each element can be
used as raw materials.
; The phosphate source and the boron oxide source should be
used.
As described below, the fluorescent materials of the present
invention emits bluish green light under exciting it by ultraviolet rays
having short or long wavelength, blue visible radiation or cathode radiation.
The fluorescent material having the formula wherein x = O
and y = O, is strontium boron phosphate having the formula
m(Srl_pEupO~ ~l-n)P203. nB203.
This flourescent material emits bluish green light under the emission
peak at 480 nm.
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When barium component is added to the strontium component
to be parameter x = about 0.5 as maximum content, the wavelength for
the emission peak is shifted to longer wavelength side to be about
490 nm.
When calcium component is added to the strontium component,
in said range of y, the emission spectrum is not substantially changed.
The maximum parameters x and y are defined to be 0.5 and
0.2, because the luminous ou-tpu-t is remarkably decreased and blue
light having the emission peak at about 410 to 430 nm is emitted if
these values are higher.
The blue light has low luminous OlltpUt to be low practical
value.
The parameters of m and n in the formula can be selected
as desired in said ranges. It is most preferably to be in the ranges of
1.9 _ m _ 2.1 and 0.14 _ n _ 0.18~ since the maximum luminous out-
put can be obtained by selecting the parameters of m and n in said ranges.
The europium content as the parameter p is defined in said
range, because an absorption of excited radiation is not enough and effec-
tive luminous output cannot be obtained when the parameter p is
smaller whereas a quantum efficiency is too low to use in a practical
purpose when the parameter p is higher.
It is most preferable to be in the range of 0.005 _ p < 0.05
because the fluorescent material having remarkably high luminous
output can be obtained.
As described above, the fluorescent material of the present
invention can be used for a fluorescent layer in a low pressure or
high pressure mercury discharge lamp or a cathode-ray tube.
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- 48,570
It is most preferable to use in a low pressure mercury discharge lamp
from the viewpoints of degree of luminous output and position of emission
spectrum.
In the preparation of the fluorescent layer for the mercury
discharge lamp, the fluorescent material is dispersed in an organic
solvent (such as butyl acetate) or water containing a binder for prelimi-
nary forming a coated film such as nitrocellulose.
The fluorescent material of the present invention is chemical-
ly stable in these solvents without deterioration for a long time.
In the baking process for removing the binder by heating (about 600C),
the fluorescent material is highly stable and the luminous efficiency is
not substantially decreased.
The luminous efficiency of the strontium-magnesium phos-
phate activated by copper as the known fluorescen-t material is usually
decreased to about 50 to 80% by the baking process at about 600C where-
as that of the fluorescent material of the present invention is only about
2 to 5%.
That is, the fluorescent material of the present invention has
substantially no trouble in comparison with those of the known fluores-
cent materials.
The most important advantages of the fluorescent ma-terial
of the present invention is to be excited by visible blue radiation as well
as ultraviolet radiation.
The blue color mercury line spectrum at 405 nm and 436 nm
emitted from a mercury discharge lamp does not substantially contri-
bute for luminous efficiency because such blue light is quite less
sensitive as visible light.
The fluorescent material of the present invention absorbs
such blue light to convert it to bluish green light which is highly sen-
sitive as visible light.
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When the fluorescent material of the present invention is
used for the low pressure mercury discharge lamp (fluorescent lamp),
the luminous efficiency (lm/W) is at least the same or about 50% higher
than that of the calcium halophoshate activated by antimony, because
the fluorescent material oE the present invention gives high quantum
efEiciency and it is excited even by the blue mercury line spectrum
to concentra-te luminous energy in the range of wavelength of about 440 to
570 nm and to emit substantially no energy in short wavelength region
shorter than 440 nm.
The fluorescent material of the present invention has said
excellent luminous characteristics and various advantageous character-
istics and the industrial advantages are significant.
The present invention will be further illustrated by certain
examples.
EXAMPLES 1 to 7 and REFEREN~E:
The raw materials were blended at ratios shown in Table 1 to
obtain mixtures.
Each mixture was charged in a silica crucible and was fired
at the temperature shown in Table 1 in an atmosphere of a mixed gas
of nitrogen and hydrogen, for 3 hours.
The volumetric ratio of nitrogen to hydrogen was about 20 : 1
though it can be varied to a desired ratio. The trivalent europium
was reduced to the divalent europium.
Each fired product obtained by the firing was quenched
and pulverized as sieved to obtain each fluorescent material having the
formula shown in Table 1.
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In the emission spectrum of each fluorescent material, the
wavelength for the emission peak is shown in unit of nanometer (nm).
The fluorescent materials emi-t bluish green light having the emission
peak at wavelength of about 480 to 490 nm.
A luminous output of each fluorescent material under exciting
by ultraviolet radiation having wavelength of 254 nm was measured and
compared with a luminous output of the known calcium halophosphate
activated by antimony. A luminous output ratio (energy ratio) of
each fluorescent material to the known calcium halophosphate activated
by antimony as 100 is shown in Table 1.
The luminous output ra-tios of the fluorescent materials of
the present invention were higher than lO0.
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.1
~0 ~ O
p; ~ o
_ _
J~ o
a~ O O O O O
a ~,
0 04
4~ ~ O O O O O
. '~ '~' ~ ~ U~ ~ ~O
~ ~ ~ ~ ~ ~,
E~
00 0~ 0~ 0~ ~ ~ C~ ~ C~
~1 ~ ~ ~ O ~ C~l ~ O ~ ~ ~ O ~ ~ ~ ~ O O~ 1- C`l ~ O
'~ ~ ~ O O O ~ O O O ~ O O O ~, O O O O O O O O O
J~ `-
E3 O o ~ ~ ~ o ~ ~ ~ o ~ ~ ~ o o ~ ~ ~ o o ~ ~ ~
3 `~ ~ ~ ~ O ~ O~ ~ P l C~ ~ g P~ C~ P~ g lq ~l
S l 5~ ~ ~ ) h n~
~i P:; ~ V~ Cq ~ L~ u7 p:~ ~ ~ C~ ~ ~ C~ l u~
~ _
0~ 0~ 0~ 0
p: ~ P~
C~I O O O oo
~C~ p~c~l U~ ou~
0,~
C~ . . O O
O ~ O C~I CO~i o~
4~ O O O O O
a~ 0~ ~ ~1 ~1
.~ O ~1 ~ ~
~ ~ ~ ~ ~0
~ ~ ~ C~ Fq p:
o~ ~ ~ ~
O O O O O
~ ~J ~1 ~ ~-i
C~J C`l ~ ~`3 ,
a ~ c~ ~ ~ ~
~ _
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~rl O ~ 00 ~ O
C`J ~ O
:q~ _
C) ~ O O O
P ~ ~ ~
o ~ _
~o o o
., . .,, C_~ ~ ~ l
a~ ,, _
~ ~ oo o ~ c~ ~o o ~
~ ~ U~ ~ o C~ ~ o ,~ ~ o
,_ 's~ ~ ~ o o o o o ~ o o o o o _
a~ ~ ~ O o ~ Cf) ~7 ~ O O O
o ~ ~ o o o o ~ P~ ~ o o o
~-1
~, ~
.. ~ '~
o ~o
~ o C`l rd
C~ P: ~CO
r- S~ ;U
. ~ _ a~
_ W
,, , ~ ~ . ~ '' .
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48,570
Figure 1 shows emission spectra of -the fluorescent mate-
rials of Examples 1,3,5 and 7 under exciting by ultraviolet radiation
254 nm.
As it is clear from Figure 1, the Eluorescent materials of
the present invention emit most of the luminous energy in relatively
narrow bluish green wavelength region and do not substantially emit the
luminous energy in wavelength region shorter than about 440 nm.
In Figure 1, the broken line shows the emission spectrum
of calcium halophosphate activa-ted by antimony, and the peaks height
of the spectrum is given as 100.
The emission spectra of Examples 2,4 and 6 are not shown in
Figure 1 and they are respectively similar to those of Examples 1, 5
and 1.
Figure 2 shows an exci-tation spectrum of the fluorescent
material of Example 1. In Figure 2, the relative luminous output ratio
is shown as function of wavelength of excited radiation under the consider-
a-tion of the maximum luminous output as 100.
As it is clear from Figure 2, the fluorescent material of the
invention is satisfactorily excited even by ultraviolet radiation having
short wavelength or long wavelength and also by visible blue radiation.
The excitation spectra of the fluorescent materials of Exam-
ples 2 to 7 are substantially the same with that of Example 1.
Each straight tube type fluorescent lamp (40W) was prepared
by using the fluorescent material of Example 1 and 3 and the known
calcium halophosphate activated by antimony and the characteristics of
each lamp were tested. The results are shown in Table 2.
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; TABLE 2
Luminous effi- Luminous effi-
ciency at zero ciency at 500 Maintenance factor
Fluorescent material hour of lighten- hours of light- (%)
ing (lm/W) ening (lm/W)
A B 100 x (B/A)
Example 1 68.2 66.9 98.1
: Example 3 47.0 46.2 98.3
Calcium halo-
phosphate activated 45.0 42.4 94.2
with antimony
It is clear from Table 2 that the fluorescent lamps using
the fluorescent materials of the present invention have excellent superior
characteristics on the luminous efficiency and the maintenance factor
to those of the reference.
Various fluorescent materials were prepared by varying
parameters m,n and p in the formula of Example 1 and the luminous
outputs of the fluorescent materials were measured. ~he results are
shown in Figures 3,4 and S.
Figure 3 shows a relation of the relative luminous outputs
; to the value m of the fluorescent materials having the formula
m(SrO 89Euo 02) o.84P205 0.16B203 (egcited by ultraviolet radiation
having wavelength of 254 nm).
It is clear from Figure 3, that effective luminous output
is obtained in the range of m = 1.75 to 2.30 especially m = 1.90 to 2.10.
Figure 4 shows a relation of the relative luminous outputs
to the value n of the fluorescent materials having the formula
(SrO 98Euo 02o) (l-n)p2os nB25
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It is clear from Figure 4, the specific lumination according
to the present invention can be given in a range of n = 0.05 to 0.23,
and high luminous outpu-t can be given in a range of n=0.14 to 0.18.
; Figure 5 shows a relation of the relative luminous outputs to
the value p of the fluorescent materials having the formula
(Srl pEupO) 0.84P205-0.16B203.
It is clear from Figure 5, effective luminous output is obtained
in a range of p = 0.001 to 0.15 and especially in a range of p = 0.005 to
0.05.
; In these figures, strontiwn was used as the alkaline earth
metal. Thus, it was confirmed that the substantially same tendency is
given in the case of barium or calcium when the content is in said range.
As it is clear from these examples and description, the fluore-
scent materials of the present invention are alkaline earth boron phos-
phates activated by divalent europium compound.
According to various analyses such as X-ray diffraction
analysis, chemical elementary analysis and luminous characteristic
analysis, it was found that these fluorescent materials are in a form of
single compound though a crystalline structure is not clearly found.
In the X ray diffraction analysis, -the fluorescent materials
of the present invention impart the specific X-ray diffraction data.
When the parameter m or n of the fluorescent material is out
of said range, a different compound is partially formed together with the
fluorescent material of the present invention.
That is, in the latter case, the different diffraction fringe
which is different from the specific diffraction fringe of the fluorescent
material of the present invention is found and the luminous output is
lowered, as practical disadvantageous problems.
Figure 6 shows X-ray diffraction spectrum of the fluorescent
material of Example 1. - 12 -
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EXAMPLE 8 (Preparation)
The fluorescent material of Example 1 was prepared as
follows.
SrHP04308.4g (1.68 mole)
SrC0341.33g (0.28 mole)
H3B0319.74g (0.32 mole)
Eu2037.04g (0.02 mole)
The raw materials were charged in a ball mill made of alumina, and
mixed and pulverized to prepare a mixture. The mixture was charged
in a silica crucible and fired at 1140C for 3 hours in an electric
furnace in an atmosphere of a mixed gas of nitrogen and hydrogen
(volumetric ratio of N:H = 20:1). The fired product was quenched
and pulverized and sieved. The resulting fluorescent material emitted bluish
green light under exciting it by ultraviolet radiation or cathode radia-tion.
According to a chemical analysis, the result was substantially
confirmed with that of the compound 2SrO 98Euo 020Ø84P205 0.16B203.
According to X ray diffraction analysis of the flourescent
material, the X ray diffraction spectrum being substantially the same with
Figure 6 was ob~ained.
EXAMPLE 9 (Preparation)
SrHP04308.4g (1.68 mole)
Sr(N03)259.26g (0.28 mole)
H3B0319.79g (0.32 mole)
Eu2037.04g (0.02 mole)
,
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The raw materials were mixed with 500 cc of water and they
were thoroughly stirred and dried on an evaporating dish in a drier
heated at 150C. The dried mixture was charged in a silica crucible
and fired at 1130C for 2 hours in a mixed gas of nitrogen and hydro-
gen (volumetric ratio of N:~l = 20:1) containing 1.5 vol % of steam.
The product was quenched and pulverized and sieved to obtain the fluore-
scent material having the same formula with -that of Example 1. The
fluorescent material can be used without any treatment.
EXAMPLE 10 (Preparation)
The raw materials of Example 8 were charged and mixed in
a ball mill. The mixture was charged in a silica crucible and fired
at 1000C for 1 hour in air. The product was quenched and pulverized
and sieved and then, the product was further fired at 1150C for 1.5 hours
in a mixed gas of Example 9 containing 1.5 vol % of steam.
The product was ~uenched and pulverized and sieved to obtain the fluore-
scent material of the present invention.
The fluorescent material emitted bright bluish green light
under exciting it by ultraviolet radiation or cathode radiation.
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