Fluorescent material and fluorescent lamp using same

A red light fluorescent material is disclosed which contains simultaneously phosphorus and at least one alkaline earth metal selected from among magnesium, calcium, strontium, and barium, each in an amount in the range of from 10.sup.-6 to 10.sup.-3 mol per mol of a europium-activated rare earth oxide fluorescent material substantially represented by the general formula, (L.sub.1-x Eu.sub.x).sub.2 O.sub.3, (wherein L stands for at least one element selected from among rare earth elements and x for a numerical value in the range of 0.01.ltoreq.x.ltoreq.0.20). This red light fluorescent material possesses the nature of manifesting high initial luminescent brightness (efficiency) and entailing only slight decline of efficiency during the lighting of lamp. A fluorescent lamp has a fluorescent material layer formed as deposited on the inner wall surface of a glass tube and containing as at least a red luminescent component the fluorescent material mentioned above. This fluorescent lamp is capable of repressing the degradation of luminescent efficiency and luminescent chromaticity by aging.

TECHNICAL FIELD 
This invention relates to a europium-activated rare earth oxide fluorescent 
material and fluorescent lamps using the fluorescent material, and more 
particularly to a red light emitting fluorescent material manifesting a 
high color-rendering property at high efficiency and proving to be 
advantageously usable as in three band type fluorescent lamps, for 
example, and fluorescent lamps using the fluorescent material. 
BACKGROUND ART 
It is universally known that a europium-activated yttrium oxide fluorescent 
material (Y.sub.2 O.sub.3 :Eu) excels in such fluorescent properties as 
brightness and color of the luminescence excited by an electron beam and 
an ultraviolet ray and, owing to this feature, finds utility as a red 
light component fluorescent material for color cathode ray tubes and as a 
red light component fluorescent material for three band type fluorescent 
lamps. 
Various fluxes have been heretofore studied with a view to enabling such 
europium-activated rare earth oxide fluorescent material as mentioned 
above to acquire an exalted luminescent efficiency. For example, such 
compounds as lithium phosphate (refer to JP-A-56-99,276), borates of 
alkaline earth metals (refer to JP-A-55-161,883), aluminum phosphate 
(refer to JP-A-58-52,382), barium borate (refer to JP-A-59-45,384), oxides 
of alkaline earth metals (refer to JP-A-58-127,777), and barium 
fluoride.magnesium fluoride (refer to JP-A-61-266,488) have been proposed 
as fluxes for the europium-activated yttrium oxide fluorescent material. 
The fluorescent material using such a flux as mentioned above acquires a 
conspicuous increase in crystal size and the fluorescent lamp using this 
fluorescent material enjoys an exalted initial luminescent efficiency. For 
the reason shown hereinbelow, however, the fluorescent lamp entails the 
problem that the luminescent efficiency thereof gradually dwindles with 
the elapse of the lighting time thereof. 
The process for the manufacture (synthesis) of an ordinary fluorescent 
material includes a step of washing. The conventional flux is normally 
removed at this step of washing. In the case of the fluorescent material 
which is produced with such a flux as mentioned above, the decline of the 
luminescent efficiency with the elapse of the lighting time of the lamp 
may be logically explained by a postulate that a minute amount of this 
flux will remain therein after the washing step and the residual flux will 
gradually react with such component substances of the fluorescent lamp as 
glass and mercury. 
When the red light fluorescent material has the luminescent efficiency 
thereof degraded by aging as described above, this degradation results in 
a decline of the luminescent brightness for the fluorescent lamp. In the 
three band type fluorescent lamp, the degradation entails an alteration of 
the luminescent chromaticity and inevitably impairs the quality of the 
fluorescent lamp seriously. 
An object of this invention is to provide a red light fluorescent material 
which possesses high initial luminescent brightness (efficiency) and 
causes only a small degradation in the efficiency of the fluorescent lamp 
while in use. Another object of this invention is to provide a fluorescent 
lamp which uses this fluorescent material and consequently manifests high 
color-rendering property and high luminescent brightness while repressing 
the alteration of luminescent brightness and luminescent chromaticity by 
aging. 
DISCLOSURE OF THE INVENTION 
The present inventors performed various studies on this problem of the 
residual flux for the purpose of improving the luminescent efficiency of 
the europium-activated rare earth oxide fluorescent material and further 
preventing the luminescent efficiency from being degraded by aging. As a 
result, it has been ascertained that when phosphorus and an alkaline earth 
metal are simultaneously contained at fixed rates, they prevent the 
residual flux from reacting with the component substances of the 
fluorescent lamp and greatly diminish or eliminate the degradation of the 
luminescent efficiency of the europium-activated rare earth oxide 
fluorescent material due to the elapse of the lighting time. 
This invention has been perfected based on the knowledge mentioned above. 
The fluorescent material of this invention is a europium-activated rare 
earth oxide fluorescent material substantially represented by the general 
formula: 
EQU (L.sub.1-x Eu.sub.x).sub.2 O.sub.3 ( 1) 
(wherein L stands for at least one element selected from among the rare 
earth elements and x for a numerical value falling in the range of 
0.01.ltoreq.x.ltoreq.0.20) and characterized by containing phosphorus and 
at least one alkaline earth metal selected from among magnesium, calcium, 
strontium, and barium, each at a ratio in the range of from 10.sup.-6 to 
10.sup.-3 mol, per mol of the europium-activated rare earth oxide 
fluorescent material mentioned above. 
The fluorescent lamp of this invention is a fluorescent lamp which is 
provided with a fluorescent material layer formed as deposited on the 
inner wall surface of a glass tube and is characterized in that the 
fluorescent material layer contains at least as a red light component 
thereof a fluorescent material containing phosphorus and at least one 
alkaline earth metal selected from among magnesium, calcium, strontium, 
and barium, each at a ratio in the range of from 10.sup.-6 to 10.sup.-3 
mol, per mol of the europium-activated rare earth oxide substantially 
represented by the formula (1) mentioned above. 
The fluorescent material of this invention is basically formed of a rare 
earth oxide fluorescent material activated with trivalent europium. The 
reference symbol L used in the formula (1) mentioned above represents rare 
earth elements including yttrium. Specifically, it stands for at least one 
rare earth element selected from among yttrium (Y), gadolinium (Gd), 
lanthanum (La), and lutecium (Lu). The content of europium in the 
europium-activated rare earth oxide fluorescent material, as the value of 
x in the formula (1) mentioned above, is in the range of from 0.01 to 
0.20. If the europium content is less than 0.01 as the value of x, the 
concentration of the activating agent is unduly low and the luminescent 
intensity is insufficient. If this content exceeds 0.20, the luminescent 
brightness is degraded by concentration quenching. 
For the fluorescent material of this invention, the ratios of the contents 
of phosphorus and the alkaline earth metal to the amount of the rare earth 
oxide fluorescent material activated with trivalent europium as 
represented by the formula (1) mentioned above constitute one important 
factor. It is important that phosphorus and the alkaline earth metal 
should be simultaneously contained each at a proportion in the range of 
from 10.sup.-6 to 10.sup.-3 mol per mol of the fluorescent material 
mentioned above. 
If the content of either phosphorus or the rare earth metal is smaller than 
10.sup.-6 mol per mol of the europium-activated rare earth oxide 
fluorescent material, the initial luminescent brightness will be unduly 
low. If the content of either of the two elements under consideration 
exceeds 10.sup.-3 mol, the decline of the luminescent efficient will 
exacerbate. By causing the contents of phosphorus and the alkaline earth 
metal each to fall in the range of from 10.sup.-6 to 10.sup.-3 mol per mol 
of the fluorescent material, a stable compound is produced between the 
phosphorus and the alkaline earth metal to permit satisfaction of high 
luminescent brightness and repression of the degradation of luminescent 
efficiency by aging as well. More desirably, the contents of phosphorus 
and the alkaline earth metal each fall in the range of from 10.sup.-6 to 
10.sup.-4 mol per mol of the europium-activated rare earth oxide 
fluorescent material mentioned above. 
The effect of the simultaneous addition of phosphorus and the alkaline 
earth metal mentioned above can be attained so long as this alkaline earth 
metal is at least one member selected from among magnesium, calcium, 
strontium, and barium. In these alkaline earth metals, barium and calcium 
prove particularly desirable from the viewpoint of initial luminescent 
brightness and alteration of luminescent brightness by aging. 
The red light fluorescent material of this invention can be produced as 
follows, for example. 
First, the starting materials such as a rare earth element oxide like 
yttrium oxide and various additive components are prepared. The europium 
sources usable herein include europium oxide and europium carbonate and 
the phosphorus sources include phosphates and hydrogen phosphates of such 
alkaline earth metals as Mg, Ca, Sr, and Ba. The alkaline earth metal 
sources usable herein include oxides, hydroxides, and carbonates of 
alkaline earth metals which are easily converted at elevated temperatures 
into oxides of alkaline earth metals. 
Then these starting materials are weighed out so as to satisfy 
stoichiometrically the formula (1) mentioned above and, at the same time, 
satisfy the condition that 10.sup.-6 to 10.sup.-3 mol of phosphorus and 
10.sup.-6 to 10.sup.-3 mol of the alkaline earth metal should be 
simultaneously contained per mol of a europium-activated rare earth oxide 
fluorescent material represented by the formula (1) mentioned above and 
are then thoroughly mixed to obtain a mixture as a raw material for the 
fluorescent material. This mixing may be carried out in a wet state by the 
use of a ball mill, a mixer mill, or a mortar or in a dry state by the use 
of water or alcohol. 
The fluorescent material of this invention may be enabled to contain 
therein phosphorus and an alkaline earth metal by positively adding a 
phosphorus source and an alkaline earth metal source as starting materials 
in the process for manufacture of a europium-activated rare earth oxide 
fluorescent material. Alternatively, phosphorus and an alkaline earth 
metal may be added to form a flux in the europium-activated rare earth 
oxide fluorescent material and their residual amounts after the washing 
step may be adjusted. To be specific, a phosphorus-containing flux 
selected from among phosphorus oxide (P.sub.2 O.sub.3), lithium phosphate, 
and aluminum phosphate and an alkaline earth metal-containing flux 
selected from among borates, fluorides, and oxides of alkaline earth 
metals are added to the mixture as the raw material for the fluorescent 
material and adjusting the amounts of these fluxes to be added and the 
process of manufacture so that phosphorus and an alkaline earth metal may 
be contained in the ranges mentioned above in the finally produced 
fluorescent material. Otherwise, the manufacture of the fluorescent 
material of this invention may be implemented by using either of the 
fluxes mentioned above per se and, at the same time, adding the remainder 
reflux to the starting materials. Then, the mixture as the raw material 
for the fluorescent material mentioned above is packed in a refractory 
vessel such as an alumina crucible or a quartz crucible and subjected to 
firing therein. This firing is carried out once or twice or more times in 
air (oxidative atmosphere), a neutral atmosphere such as an atmosphere of 
nitrogen gas or an atmosphere of argon gas, or a reducing atmosphere such 
as an atmosphere of nitrogen gas containing a small amount of hydrogen gas 
at a temperature in the range of from 1000.degree. C. to 1350.degree. C., 
preferably from 1200.degree. C. to 1300.degree. C. The firing time is 
variable with such factors as the amount of the mixture as the raw 
material for the fluorescent material to be packed in the refractory 
vessel and the firing temperature. Generally, when the firing temperature 
is in the range mentioned above, the firing time which proves proper is in 
the range of from 0.5 to 6 hours, preferably from 1 to 4 hours. After the 
firing, the fired process is pulverized, washed (as with water, a weak 
mineral acid, a weak alkali, or a weak organic acid), dried, and 
classified by the use of a sieve as generally practiced in the process for 
manufacture of a fluorescent material. Thus, the fluorescent material of 
this invention is obtained. 
The fluorescent lamp of this invention is possessed of a fluorescent 
material layer containing at least as a red luminescent component the 
fluorescent material of this invention described above. This fluorescent 
material layer may be formed solely of the fluorescent material of this 
invention. It may be otherwise formed of a mixed fluorescent material 
consisting of a red light fluorescent material of this invention with a 
red light fluorescent material and a green light fluorescent material or a 
mixed fluorescent material optionally further incorporating therein a deep 
red light fluorescent material and a bluish green light fluorescent 
material. The fluorescent material layer may be used in various forms. 
The fluorescent lamp of this invention is particularly suitable for the 
so-called three band type fluorescent lamp which uses such a mixed 
fluorescent material as mentioned above. When it is utilized for the three 
band type fluorescent lamp of the kind mentioned above, various blue light 
fluorescent materials and green light fluorescent materials heretofore 
known to the art may be used besides the red light fluorescent material of 
this invention.

MODE FOR EMBODYING THE INVENTION 
Now, the present invention will be described below with reference to 
working examples. 
EXAMPLES 1 TO 4 
For the manufacture of europium-activated yttrium oxide fluorescent 
materials represented by the composition formula, (Y.sub.0.95 
Eu.sub.0.05).sub.2 O.sub.3, phosphorus sources and strontium sources were 
mixed at suitable ratios with starting materials to obtain a plurality of 
fluorescent materials having a fixed phosphorus concentration and a 
varying strontium concentration. 
Specifically, 214.7 g of yttrium oxide [Y.sub.2 O.sub.3 ] and 17.6 g of 
europium oxide [Eu.sub.2 O.sub.3 ] were weighed out and combined with 
0.015 g of ammonium phosphate [(NH.sub.4).sub.3 HPO.sub.4 ] and further 
with a varying amount of strontium oxide [SrO] and they were thoroughly 
mixed. Then, the resultant mixture was packed in an alumina crucible and 
fired therein in an oxidizing atmosphere at 1350.degree. C. The fired 
process consequently obtained was subjected to such ordinary treatments as 
pulverization, dispersion, washing, drying, and classification with a 
sieve to obtain a fluorescent material. Thus, phosphorus was contained in 
a fixed proportion of 10.sup.-5 mol and strontium was contained in varying 
proportions of 10.sup.-7 mol (Comparative Example 1), 10.sup.-6 mol. 
(Example 1), 10.sup.-5 mol (Example 2), 10.sup.-4 mol (Example 3), 
10.sup.-3 mol (Example 4), and 2.times.10.sup.-3 mol (Comparative Example 
2), respectively per mol of the europium-activated yttrium oxide 
fluorescent material represented by the composition formula mentioned 
above. 
Then, fluorescent lamps (FL20SS/18) of a construction shown in FIG. 1 were 
produced by an ordinary method using the various fluorescent materials 
which were obtained in Examples 1 to 4 and Comparative Examples 1 and 2. 
In a fluorescent lamp 1 shown in FIG. 1, a fluorescent material layer 3 
was formed as deposited on an inner wall surface 2a of a glass bulb 2. A 
discharge gas of a prescribed pressure, namely a mixed gas of mercury with 
such a rare gas as argon, was sealed in the glass bulb 2. Electrodes 4 
were attached one each to opposite end parts of the glass bulb 2. By the 
application of a prescribed voltage between these electrodes 4, the 
fluorescent material layer 3 was caused by an excitation source to emit 
light. 
The various fluorescent lamps obtained as described above were tested for 
initial luminescent brightness and for luminescent brightness after 1000 
hours' lighting of the lamps. The results of the test are shown in FIGS. 
2a and 2b. The magnitudes of luminescent brightness indicated in these 
graphs represent relative values (%) determined based on the luminescent 
brightness of the europium-activated yttrium oxide fluorescent material 
including neither phosphorus nor strontium [(Y.sub.0.95 Eu.sub.0.05).sub.2 
O.sub.3 ] taken as 100. 
It is clearly noted from the graphs of FIGS. 2a and 2b that the strontium 
concentration is desired to be not more than 10.sup.-3 mol from the 
viewpoint of the initial luminescent brightness and to be not less than 
10.sup.-6 mol from the viewpoint of the luminescent brightness 
respectively, per mol of the europium-activated yttrium oxide fluorescent 
material. It is also confirmed that fluorescent lamps excelling in both 
initial luminescent brightness and luminescent brightness after 1000 
hours' lighting of lamp are obtained by using fluorescent materials of the 
working examples simultaneously containing 10.sup.-5 mol of phosphorus and 
10.sup.-6 to 10.sup.-3 mol of strontium. 
EXAMPLES 5 TO 8 
Fluorescent materials containing barium at a fixed proportion of 10.sup.-5 
mol and phosphorus at varying proportions of 10.sup.-7 mol (Comparative 
Example 3) 10.sup.-6 mol (Example 5), 10.sup.-5 (Example 6), 10.sup.-4 mol 
(Example 7), 10.sup.-3 mol (Example 8), and 2.times.10.sup.-3 mol 
(Comparative Example 4), respectively per mol of a europium-activated 
yttrium oxide fluorescent material of the composition formula, (Y.sub.0.94 
Eu.sub.0.06).sub.2 O.sub.3, were prepared by suitably adjusting the mixing 
rations of various starting materials and following the procedure of 
Example 1. 
Then, fluorescent lamps (FL20SS/18) similar to those of Example 1 were 
produced by an ordinary method using the fluorescent materials which were 
obtained in Examples 5 to 8 and Comparative Examples 3 and 4. These 
fluorescent lamps were tested for initial luminescent brightness and 
luminescent brightness after 1000 hours' lighting of lamp. The results of 
the test are shown in FIGS. 3a and 3b. The magnitudes of luminescent 
brightness indicated in these graphs represent the relative values (%) 
determined based on the luminescent brightness of a conventional 
europium-activated yttrium oxide fluorescent material including neither 
phosphorus nor strontium [(Y.sub.0.94 Eu.sub.0.06).sub.2 O.sub.3 ] taken 
as 100. 
It is clearly noted from the graphs of FIGS. 3a and 3b that fluorescent 
lamps excelling in both initial luminescent brightness and luminescent 
brightness after 1000 hours' lighting of lamp are obtained by using 
fluorescent materials of the working examples simultaneously containing 
10.sup.-5 mol of barium and 10.sup.-6 to 10.sup.-3 mol of phosphorus per 
mol of the europium-activated yttrium oxide fluorescent material. 
EXAMPLES 9 TO 12 
Fluorescent materials containing phosphorus at a fixed proportion of 
10.sup.-5 mol and magnesium at varying proportions of 10.sup.7 mol 
(Comparative Example 5), 10.sup.-6 mol (Example 9), 10.sup.-5 mol (Example 
10), 10.sup.-4 mol (Example 11), 10.sup.-3 mol (Example 12), and 
2.times.10.sup.-3 mol (Comparative Example 6), respectively per mol of a 
europium-activated yttrium oxide fluorescent material represented by the 
composition formula, (Y.sub.0.95 Eu.sub.0.05).sub.2 O.sub.3, by suitably 
adjusting the mixing ratios of the various starting materials and 
following the procedure of Example 1. 
Then, fluorescent lamps (FL20SS/18) similar to those of Example 1 were 
produced by an ordinary method using the various fluorescent materials 
which were obtained in Examples 9 to 12 and Comparative Examples 5 and 6. 
These fluorescent lamps were tested for initial luminescent brightness and 
luminescent brightness after 1000 hours' lighting of lamp. The results of 
the test are shown in FIGS. 4a and 4b. The magnitudes of luminescent 
brightness indicated in the graphs represent the relative values (%) 
determined based on the luminescent brightness of a conventional 
europium-activated yttrium oxide fluorescent material containing neither 
phosphorus nor magnesium [(Y.sub.0.95 Eu.sub.0.05).sub.2 O.sub.3 ] taken 
as 100. 
It is clearly noted from the graph of FIGS. 4a and 4b that fluorescent 
lamps excelling in both initial luminescent brightness and luminescent 
brightness after 1000 hours' lighting of lamp are obtained by using 
fluorescent materials of the working examples simultaneously containing 
10.sup.-5 mol of phosphorus and 10.sup.-6 to 10.sup.-3 mol of magnesium 
per mol of the europium-activated yttrium oxide fluorescent material. 
EXAMPLES 13 TO 16 
Fluorescent materials containing calcium at a fixed proportion of 10.sup.-5 
mol and phosphorus at varying proportions of 10.sup.-7 mol (Comparative 
Example 7), 10.sup.-6 mol (Example 13), 10.sup.-5 mol (Example 14), 
10.sup.-4 mol (Example 15), 10.sup.-3 mol (Example 16), and 
2.times.10.sup.-3 mol (Comparative Example 8), respectively per mol of a 
europium-activated yttrium oxide fluorescent material represented by the 
composition formula, (Y.sub.0.93 Eu.sub.0.07).sub.2 O.sub.3, by suitably 
adjusting the mixing ratios of the various starting materials and 
following the procedure of Example 1. 
Then, fluorescent lamps (FL20SS/18) similar to those of Example 1 were 
produced by an ordinary method using the various fluorescent materials 
which were obtained in Examples 13 to 16 and Comparative Examples 7 and 8. 
These fluorescent lamps were tested for initial luminescent brightness and 
luminescent brightness after 1000 hours' lighting of lamp. The results of 
the test are shown in FIGS. 5a and 5b. The magnitudes of luminescent 
brightness indicated in the graphs represent the relative values (%) 
determined based on the luminescent brightness of a conventional 
europium-activated yttrium oxide fluorescent material containing neither 
phosphorus nor calcium [(Y.sub.0.93 Eu.sub.0.07).sub.2 O.sub.3 ] taken as 
100. 
It is clearly noted from the graph of FIGS. 5a and 5b that fluorescent 
lamps excelling in both initial luminescent brightness and luminescent 
brightness after 1000 hours' lighting of lamp are obtained by using 
fluorescent materials of the working examples simultaneously containing 
10.sup.-5 mol of calcium and 10.sup.-6 to 10.sup.-3 mol of phosphorus per 
mol of the europium-activated yttrium oxide fluorescent material. 
EXAMPLE 17 
A europium-activated gadolinium oxide fluorescent material represented by 
the composition formula, (Gd.sub.0.95 Eu.sub.0.05).sub.2 O.sub.3, was 
prepared by the same method as used in Example 2 so as to contain 
10.sup.-5 mol of phosphorus and 10.sup.-6 mol of strontium therein per mol 
of the europium-activated gadolinium oxide fluorescent material. 
A fluorescent lamp (FL20SS/18) similar to that of Example 1 was produced by 
an ordinary method using the fluorescent material consequently obtained 
and then tested for initial luminescent brightness and luminescent 
brightness after 1000 hours' lighting of lamp. The test yielded 
satisfactory results, 102 and 103, respectively based on the luminescent 
brightness of a conventional europium-activated yttrium oxide fluorescent 
material [(Gd.sub.0.95 Eu.sub.0.05).sub.2 O.sub.3 ] containing neither 
phosphorus nor strontium taken as 100. 
It is clearly noted from this working example that a fluorescent lamp 
excelling in both initial luminescent brightness and luminescent 
brightness after 1000 hours' lighting of lamp is obtained by causing an 
europium-activated gadolinium oxide fluorescent material to contain both 
phosphorus and strontium. 
EXAMPLE 18 
By the same method as used in Example 2, a europium-activated rare earth 
oxide fluorescent material represented by the composition formula, 
(Y.sub.0.8 Gd.sub.0.15 Eu.sub.0.05).sub.2 O.sub.3, was prepared so as to 
contain 10.sup.-5 mol of phosphorus and 10.sup.-6 mol of strontium per mol 
of the europium-activated rare earth oxide fluorescent material. 
A fluorescent lamp (FL20SS/18) similar to that of Example 1 was produced by 
using the fluorescent material consequently obtained and then tested for 
initial luminescent brightness and luminescent brightness after 1000 
hours' lighting of lamp. The test yielded satisfactory results, 101 and 
102, respectively based on the luminescent brightness of a conventional 
europium-activated yttrium oxide fluorescent material [(Y.sub.0.8 
Gd.sub.0.15 Eu.sub.0.05).sub.2 O.sub.3 ] containing neither phosphorus nor 
strontium taken as 100. 
It is clearly noted from this working example that a fluorescent lamp 
excelling in both initial luminescent brightness and luminescent 
brightness after 1000 hours' lighting of lamp is obtained by causing an 
europium-activated rare earth oxide fluorescent material to contain both 
phosphorus and strontium. 
The working examples cited above represent cases of applying this invention 
to rare earth oxide fluorescent materials using yttrium oxide and 
gadolinium oxide, for instance. The same effect of this invention as 
described above is attained in rare earth oxide fluorescent materials 
using lanthanum oxide (La.sub.2 O.sub.3), lutecium oxide (Lu.sub.2 
O.sub.3), and mixed crystals thereof [such as, for example, (Y.sub.0.9 
La.sub.0.1).sub.2 O.sub.3 ]. 
Industrial Applicability 
As described above, this invention allows provision of a red light 
fluorescent material which manifests high luminescent brightness and 
suffers from only slight decline of luminescent brightness of lighting 
lamp by aging. By using this fluorescent material as a red luminescent 
component in a three band type fluorescent lamp, a fluorescent lamp which 
not only manifests high luminescent brightness but also excels in 
stability of lighting lamp to resist the effect of aging can be realized.