JP6939613B2 - Information recording method and information reading method - Google Patents

Description

The present invention relates to an information recording method using an alumina phosphor and a method of reading information from an alumina phosphor.

A method of recording information on a phosphor that emits fluorescence when irradiated with ultraviolet rays and irradiating the phosphor with ultraviolet rays to read out the information is widely known. For example, in Patent Document 1, information is printed on a work with fluorescent ink that emits light by irradiation with ultraviolet rays. When reading out the information, the work is irradiated with ultraviolet rays. As a result, the fluorescent ink emits visible light, so that the information printed by the fluorescent ink is visualized.

Japanese Unexamined Patent Publication No. 2004-314307

As described in Patent Document 1, if the information is recorded by using a phosphor that emits light by irradiating with ultraviolet rays, the information cannot usually be seen. Therefore, it is preferable from the viewpoint of information confidentiality. However, since the fluorescence is visible light, in a situation where the information reader is reading the information, the information is being read and the recorded information is easily known to a third party.

The confidentiality of the information is not sufficient in that the information recorded when the information reader is reading the information is easily known to a third party. In addition, just knowing that the information is being read is not sufficient in terms of the confidentiality of the information. More specifically, when a third party sees a situation in which the information reader is reading information, it can be seen that the information reader takes some action to emit visible light. A third party does not know until the treatment is ultraviolet irradiation, but the technique of irradiating ultraviolet light to emit visible light is widely known.

Therefore, if a third party sees the situation in which the information reader is reading the information, there is a risk that the third party will perform the following description. That is, it can be inferred that the third party is reading the information by irradiating the ultraviolet rays on the spot, and even if the contents of the recorded information cannot be known, the third party is subsequently irradiated with the ultraviolet rays. Then, there is a risk that the information recorded there will be read out. Therefore, it is not preferable from the viewpoint of confidentiality of information that a third party knows that the information is being read.

In addition, an information reader who may have seen the situation of reading information by irradiating ultraviolet rays to a third party should delete the information in order to prevent the information from being read by a third party. I sometimes think about it. However, if it is necessary to remove the fluorescent ink or the phosphor in order to erase the information, it is not easy to remove the information.

Fluorescent ink may be completely removed, but it is a laborious task. Further, in the case of a fluorescent substance, since it depends on the physical properties, it is required to change the physical properties. Therefore, it is practically impossible to erase the information. As described above, when the information is recorded with fluorescent ink or fluorescent material, it is not easy to erase the information. As a result, the information often remains in an easily readable state. The fact that the information remains in an easily readable state is not sufficient in terms of the confidentiality of the information.

The present disclosure has been made based on this circumstance, and an object of the present disclosure is to provide a highly confidential information recording method and information reading method.

The above object is achieved by a combination of the features described in the independent claims, and the sub-claims provide further advantageous specific examples. The reference numerals in parentheses described in the claims indicate, as one embodiment, the correspondence with the specific means described in the embodiments described later, and do not limit the disclosed technical scope.

The information recording method according to claim 1 for achieving the above object should record fluorescence on an alumina phosphor, which is an alumina capable of emitting fluorescence containing a wavelength of 330 nm by containing zinc as an impurity. By irradiating the irradiation range determined based on the information shape with fluorescence-reducing light having a wavelength longer than 230 nm, the alumina phosphor is irradiated with excitation light having a wavelength of 290 nm or shorter. It is provided with a recording step (S2) of setting the information recording state to emit the fluorescence in which the above is expressed.

The alumina phosphor in the information recording state by this information recording method emits fluorescence expressing the information shape when irradiated with excitation light having a wavelength of 290 nm or shorter. This fluorescence is light centered on a wavelength of 330 nm, that is, ultraviolet light. The excitation light is also ultraviolet light.

Therefore, even if a third party sees a situation in which the information reader irradiates the alumina phosphor in the information recording state with excitation light to read the information by this information recording method, the information is read out. I don't even know if I'm doing the work I'm doing. Therefore, the confidentiality of information is improved.

In addition, as will be described in the information retrieval method described later, the alumina phosphor in the information recording state is irradiated with excited fluorescence reduced light or non-excited fluorescence reduced light to reduce the emission intensity of fluorescence. It can be made unreadable. In this state, the information has been erased.

Therefore, when the information reader wants to erase the information, such as when the information has already been read, the information can be erased by irradiating the excitation fluorescence reduction light or the non-excitation fluorescence reduction light. The excited fluorescence reduced light means light in which fluorescence is emitted but the emission intensity of fluorescence is gradually reduced, and the non-excited fluorescence reduced light does not emit fluorescence, and then the alumina phosphor is excited. It is light that reduces the emission intensity of fluorescence when irradiated with the generated light (that is, excitation light).

Further, when the non-excited fluorescence reducing light is irradiated, the emission intensity of the fluorescence when the alumina phosphor is subsequently irradiated with the excitation light without emitting the fluorescence is reduced. When a third party who does not know the wavelength range of the excitation light irradiates various lights to read information from the alumina phosphor and makes trial and error, if the non-excitation fluorescence reduction light is irradiated too much, then , Information can no longer be read from the alumina phosphor even when irradiated with excitation light. For this reason, it is difficult for a third party who does not know the wavelength range of the excitation light to read the information from the alumina phosphor. For this reason as well, it can be said that the confidentiality of information is improved.

In the information recording method according to claim 2, one or a plurality of zinc, magnesium, and boron are ion-implanted into at least a part of the range in which the fluorescence expressing the information shape is emitted before the recording step. The implantation step (S0) is executed.

It was found that when one or more of zinc, magnesium, and boron were ion-implanted, the emission intensity of fluorescence was increased in the ion-implanted portion even when the same excitation light was irradiated. The data will be described later. Therefore, if this injection step is executed before the recording step, the light emission when the excitation light is irradiated can be combined with the decrease in the emission intensity when the excitation light is irradiated by irradiating the fluorescence reduction light. The intensity can be set to 3 or more gradations. Therefore, the information can be recorded in a more complicated state.

In the information recording method according to claim 3, prior to the recording step, a preparatory step (S1) of irradiating light containing a wavelength of 230 nm or shorter is executed in a range in which fluorescence expressing an information shape is emitted. ..

The alumina phosphor can reduce the emission intensity of fluorescence to an unreadable intensity by being irradiated with fluorescence-reducing light. Even if the alumina phosphor has a reduced fluorescence intensity, by executing this preparatory step, the portion where the fluorescence emission intensity has decreased is emitted again with a high emission intensity fluorescence when the excitation light is irradiated again. It can be in a possible state. Therefore, by performing this preparatory step, the alumina phosphor can be repeatedly used as an information recording medium.

In addition, this preparatory step may be performed before the emission intensity of fluorescence decreases to an unreadable intensity. If this preparatory step is performed before the emission intensity of fluorescence decreases to an unreadable intensity, the emission intensity of fluorescence from the information shape can be made equal to the emission intensity of fluorescence from the periphery thereof. As a result, the information can be erased.

In the information recording method according to claim 4, one or a plurality of zinc, magnesium, and boron are ion-implanted into at least a part of the range in which the fluorescence expressing the information shape is emitted before the preparation step. The implantation step (S0) is executed.

Even when the preparation step is provided, the implantation step is performed before the preparation step, and one or more of zinc, magnesium, and boron are ion-implanted to increase the emission intensity of the ion-implanted portion. Can be done.

In the information recording method according to claim 5, the preparatory step irradiates a range in which the fluorescence in which the information shape is expressed is emitted with light having a wavelength of 215 nm or shorter.

Irradiation with light having a wavelength of 215 nm or shorter can quickly bring the alumina phosphor into a state capable of emitting high emission intensity fluorescence.

The information recording method according to claim 6 includes a storage step (S3) of storing the alumina phosphor in the information recording state in a dark place where ultraviolet light does not enter after the recording step. As a result, when it becomes necessary to read the information, it is possible to prevent the information from being in a state where it cannot be read.

In the information recording method according to claim 7, the recording step is executed in a dark place where ultraviolet light does not enter. As a result, it is possible to prevent insufficient recording of information on the alumina phosphor.

The information recording method according to claim 8 for achieving the above object should record fluorescence in an alumina phosphor which is an alumina capable of emitting fluorescence containing a wavelength of 330 nm by containing zinc as an impurity. By injecting one or more of zinc, magnesium, and boron into the ion injection region (30, 40) determined based on the information shape, the alumina phosphor has a wavelength of 290 nm or a shorter wavelength. This is an information recording method including an injection step (S0) in which an information recording state is set to emit fluorescence in which the information shape is expressed when the excitation light of the above is irradiated.

As described above, by ion-implanting one or more of zinc, magnesium, and boron, the emission intensity of fluorescence when irradiated with the same excitation light is increased. This means that information can be recorded if the shape of the ion implantation region is made into a shape determined based on the information shape. Therefore, the information can be recorded only by performing this injection step without performing the recording step of irradiating the fluorescence-reducing light.

In addition, the ion-implanted region is the same as the region without ion implantation in that the emission intensity of fluorescence is reduced by irradiating the fluorescence-reduced light. The fluorescence-reduced light is a general term for excited fluorescence-reduced light and non-excited fluorescence-reduced light.

In the ion injection region as well, the emission intensity of fluorescence is reduced by irradiating the fluorescence-reduced light. Therefore, if the fluorescence-reduced light is sufficiently irradiated, the emission intensity and non-ion injection of the ion-injected region when the excitation light is irradiated. The emission intensity of the region can be reduced to a emission intensity that is difficult to distinguish. If it becomes difficult to distinguish between the emission intensity in the ion-implanted region and the emission intensity in the non-ion implantation region, information cannot be read out. Therefore, it can be said that the confidentiality of information is high.

In the information recording method according to claim 9, light containing a wavelength of 230 nm or shorter is emitted in a range in which the alumina phosphor in the information recording state in the injection step emits fluorescence in which the information shape is expressed. The preparation step (S1) for irradiation is executed.

By executing the preparation step even for the alumina phosphor whose information is recorded in the injection step, the emission intensity at the time of reading the information can be increased.

The information recording method according to claim 10 includes a storage step (S3) of storing the alumina phosphor that has undergone the preparation step in a dark place where ultraviolet light does not enter. As a result, when it becomes necessary to read the information, it is possible to prevent the information from being in a state where it cannot be read.

The information reading method according to claim 11 for achieving the above object is an alumina phosphor, which is an alumina that emits fluorescence containing a wavelength of 330 nm by containing zinc as an impurity, and has a wavelength of 290 nm or When an excitation light containing a shorter wavelength is irradiated, the alumina phosphor in the information recording state that emits fluorescence expressing the information shape is irradiated with the excitation light, and the alumina phosphor emits light. It is provided with a readout step (S11) for observing ultraviolet light including a wavelength of 330 nm.

When the alumina phosphor in the information recording state is irradiated with excitation light, the fluorescence expressing the information shape is emitted. This fluorescence is ultraviolet light containing a wavelength of 330 nm. Therefore, ultraviolet light including a wavelength of 330 nm emitted from the alumina phosphor is observed. As a result, information can be read from the alumina phosphor in the information recording state.

When reading information in this way, the information reader irradiates ultraviolet light and observes the ultraviolet light, so even if a third party sees the situation of reading the information, the work of reading the information. I don't even know if I'm doing it. Therefore, a highly confidential information reading method is realized.

In the information readout method according to claim 12, in the readout step, the alumina phosphor is irradiated with excitation fluorescence reduction light which is light of 230 nm to 290 nm as excitation light, so that fluorescence expressing the information shape is emitted. , Reduces the emission intensity of fluorescence in which the information shape is expressed.

When irradiated with excitation fluorescence reduction light, the emission intensity is reduced while emitting fluorescence. Therefore, the number of times the information can be read can be limited. This improves the confidentiality of the information.

In the information readout method according to claim 13, after executing the readout step, the alumina phosphor is irradiated with non-excited fluorescence-reducing light having a wavelength longer than 290 nm and a wavelength shorter than 630 nm. The erasing step (S12) of reducing the emission intensity of the fluorescence expressing the information shape when the excitation light is irradiated is executed without emitting the fluorescence expressing the information shape.

When the information reader wants to erase the information, such as when the information has already been read, the information can be erased by irradiating the non-excited fluorescence reducing light. This further improves the confidentiality of the information. Further, when the information is erased in this way, the information can be easily erased because the alumina phosphor may be irradiated with the non-excited fluorescence reducing light.

It is a relational diagram of the energy level of a sapphire phosphor. It is a figure which shows the relationship between the irradiation wavelength and the emission wavelength. It is a figure which shows the relationship between the wavelength of the irradiating light and the emission intensity. It is a figure which shows the relationship between the concentration of Zn and the light emission intensity. It is a figure which shows the procedure of the information recording method. It is a figure which shows the procedure of the information reading method. It is a figure which shows the expression example of the information shape. It is a figure which shows the 2nd expression example of an information shape. It is a figure which shows the 3rd expression example of an information shape. It is a figure which shows the procedure of the information recording method which records information in the gradation of 3 or more gradations. It is a figure which shows the state which formed the ion implantation region 30 in an annular shape. It is a figure which irradiated the fluorescence reduction light to the sapphire phosphor of FIG. 11 to form the fluorescence reduction part 10. It is a figure which shows the ion implantation region 40 and the fluorescence reduction part 11, 12 having a shape different from FIG. It is a figure which shows the information recording method which does not use fluorescence reduction light.

[1. Characteristics of alumina phosphor]

[1.1 Fluorescence characteristics]
The present inventor has found that when zinc (hereinafter, Zn) is added as an impurity to alumina, it has an absorption spectrum at 215 nm, 230 nm and 260 nm, and emits fluorescence at wavelengths of 330 nm and 420 nm. In the experiment to confirm the fluorescence, Zn was added to the alumina crystal. Alumina crystals are often called sapphire. Therefore, in the following, an alumina crystal that emits fluorescence containing a wavelength of 330 nm by containing Zn as an impurity is referred to as a sapphire phosphor.

表１から推定できるエネルギー準位の関係図を図１に示している。図１に示すように、準位Ａと準位Ｂは相関があるが、準位Ｄと準位Ｂは相関が低くなっている。 Of the two emission wavelengths, the emission at 330 nm could be observed with excitation light at 215 nm, 230 nm and 260 nm. On the other hand, the light emission at 420 nm was very weak or did not emit light with the excitation light at 260 nm. Table 1 shows the light absorption wavelength of the sapphire phosphor and the energy ratio for each emission wavelength.

The relationship diagram of the energy levels that can be estimated from Table 1 is shown in FIG. As shown in FIG. 1, the level A and the level B have a correlation, but the level D and the level B have a low correlation.

FIG. 2 shows the relationship between the irradiation wavelength and the emission wavelength. FIG. 2 shows the results obtained by fluorescence spectrum measurement. As shown in FIG. 2, the peak of the emission wavelength is 330 nm, and the end of the irradiation wavelength on the long wavelength side is about 290 nm. From this, it is estimated that the boundary on the long wavelength side of the irradiation wavelength for emitting fluorescence including the wavelength of 330 nm is 290 nm.

On the other hand, the end of the mountain where the peak of the emission wavelength is 330 nm on the short wavelength side of the irradiation wavelength continues to the lower side where it is cut off in FIG. From this, it is presumed that there is no particular boundary on the short wavelength side of the irradiation wavelength for emitting fluorescence including a wavelength of 330 nm.

However, in consideration of the emission intensity, the irradiation wavelength for emitting fluorescence including the wavelength of 330 nm is preferably in the range of 200 nm to 290 nm, and more preferably in the range of 220 nm to 290 nm. The most preferable wavelength for emitting fluorescence including a wavelength of 330 nm is 260 nm.

[1.2 Reduction and recovery of emission intensity]
It was found that the light emission at 330 nm decreases the emission intensity when irradiated with excitation light when irradiated with light such as sunlight, a fluorescent lamp, or an incandescent lamp. However, it was also found that the emission intensity at 330 nm was restored by irradiating with light having wavelengths of 215 nm and 230 nm. On the other hand, it was also found that at the remaining excitation wavelength of 260 nm, the emission intensity at 330 nm hardly recovered.

Table 2 shows the relationship between the excitation wavelength and the signal recovery rate. The data shown in Table 2 examined the emission intensity at 330 nm when exposed to outdoor exposure for 2 hours in fine weather, irradiated with the irradiation wavelength and irradiation time shown in Table 2, and then irradiated with excitation light of 230 nm. It is a table. Since the wavelength of 215 nm recovers quickly, the irradiation time is set to 5 minutes.

表２から分かるように、２１５ｎｍあるいは２３０ｎｍの光照射で、２３０ｎｍの光照射による３３０ｎｍの発光強度が回復する。回復比は、２３０ｎｍよりも２１５ｎｍの照射のほうが著しく大きい。表２の最右欄に示す回復比率を２３０ｎｍと２１５ｎｍで比較すると、２１５ｎｍの回復比率は２３０ｎｍの回復比率のおよそ９倍である。よって、２１５ｎｍの波長の光を照射すると、サファイア蛍光体は、迅速に強い発光強度の蛍光を発光可能な状態に回復すると言える。また、２１５ｎｍよりも短い波長の光でも２１５ｎｍの準位に励起させることができる。よって、２１５ｎｍまたは２１５ｎｍよりも短い波長の光を照射すると、サファイア蛍光体を、迅速に強い発光強度の蛍光を発光可能な状態に回復させることができると言える。 The recovery ratio of the raw data is the wavelength of 230 nm after irradiating the light of each irradiation wavelength shown in Table 2 for the irradiation time shown in Table 2 with respect to the emission intensity measured by irradiating the wavelength of 230 nm before outdoor exposure. It is the ratio of the emission intensity measured by irradiating with. On the other hand, each numerical value after the irradiation time correction is a value obtained by multiplying the raw data of the wavelength of 215 nm by 4. This is because when the irradiation time of the wavelength of 215 nm is the same as that of other wavelengths, the irradiation time is quadrupled.

As can be seen from Table 2, light irradiation at 215 nm or 230 nm restores the emission intensity at 330 nm due to light irradiation at 230 nm. The recovery ratio is significantly higher at 215 nm than at 230 nm. Comparing the recovery ratios shown in the rightmost column of Table 2 at 230 nm and 215 nm, the recovery ratio at 215 nm is about 9 times the recovery ratio at 230 nm. Therefore, when irradiated with light having a wavelength of 215 nm, it can be said that the sapphire phosphor quickly recovers fluorescence having a strong emission intensity to a state in which it can emit light. Further, even light having a wavelength shorter than 215 nm can be excited to a level of 215 nm. Therefore, it can be said that when the sapphire phosphor is irradiated with light having a wavelength shorter than 215 nm or 215 nm, the fluorescence having a strong emission intensity can be quickly restored to a state in which it can emit light.

The recovery ratio when irradiated with a wavelength of 260 nm is 1.2 as shown in the second column from the left in Table 2. That is, even if the wavelength of 260 nm is irradiated, the emission intensity of 330 nm is hardly recovered.

[1.3 Wavelength that reduces emission intensity]
It was stated that sunlight irradiation reduces the emission intensity at 330 nm. Next, the experimental results for investigating which wavelength has an influence on the decrease in emission intensity are shown. Table 3 shows the results of observing the fluorescence at 330 nm by irradiating with light of 215 nm for 2 minutes, irradiating with light of 200 nm to 700 nm for 10 minutes, and then irradiating with excitation light of 260 nm. Further, FIG. 3 is a graph of Table 3.

これら表３、図３から分かるように、発光強度の減少は、波長が２３０ｎｍより長くなるあたりから急激に生じていることが分かる。そして、発光強度の減少は、波長が４２０ｎｍよりも長くても生じていることが分かる。

As can be seen from Table 3 and FIG. 3, it can be seen that the decrease in emission intensity suddenly occurs when the wavelength becomes longer than 230 nm. Then, it can be seen that the decrease in emission intensity occurs even if the wavelength is longer than 420 nm.

Assuming that the emission intensity at the left end in the graph of FIG. 3 is the emission intensity before the emission intensity is reduced, it can be said that the wavelength range from at least 230 nm to 630 nm is the wavelength range for reducing the emission intensity. The light that reduces the emission intensity of fluorescence is hereinafter referred to as fluorescence-reduced light. Light in the wavelength range of 230 nm to 630 nm is fluorescence-reduced light.

On the other hand, as described above, if the wavelength is shorter than 290 nm, the sapphire phosphor can be excited to emit fluorescence having a wavelength of 330 nm. Therefore, in the wavelength range of 230 nm to 630 nm, the wavelength range of 230 nm to 290 nm can excite the sapphire phosphor. Light from 230 nm to 290 nm is referred to as excitation fluorescence reduction light among the fluorescence reduction light.

On the other hand, light having a wavelength longer than 290 nm and a wavelength shorter than 630 nm does not excite the sapphire phosphor. Light in this wavelength range is referred to as non-excited fluorescence-reduced light among fluorescence-reduced lights.

[1.4 Duration of light emission state]
As shown in Table 2, the emission intensity is restored by irradiating with light of 215 nm or 230 nm. When irradiated with excitation light, the state in which fluorescence of observable emission intensity of 330 nm can be emitted is hereinafter referred to as a state in which light can be emitted. It was found that the duration of the luminescent state was 55 days or more when stored in a dark place.

[1.5 Impurities that contribute to fluorescence]
Next, the results of examining impurities added to the sapphire crystal will be described. The sapphire crystal without impurities has no absorption spectrum at 260 nm and does not emit fluorescence at 330 nm. By adding impurities, it will emit fluorescence at 330 nm.

Table 4 shows the relationship between the sample to which a plurality of impurities are added and the emission intensity. Further, FIG. 4 shows the concentration of Zn and the emission intensity shown in Table 4.

これら図４、表４に示す不純物の数値は、ＴＯＦ−ＳＩＭＳによる定性分析値である。また、発光強度は、屋外暴露を５分間行った後、２１５ｎｍの光を５分間照射した後で測定した。測定では、２６０ｎｍの波長で励起させ、３３０ｎｍの蛍光の発光強度を測定している。

The numerical values of the impurities shown in FIGS. 4 and 4 are qualitative analysis values by TOF-SIMS. The emission intensity was measured after outdoor exposure for 5 minutes and then irradiation with 215 nm light for 5 minutes. In the measurement, it is excited at a wavelength of 260 nm, and the emission intensity of fluorescence at 330 nm is measured.

As shown in FIG. 4, the sample 4 has a high concentration of Zn, and the sample 3 has a low concentration of Zn. Then, the sample 4 has the strongest emission intensity, and the sample 3 has almost no emission intensity. Further, in Samples 1 and 2, the Zn concentration is between Sample 3 and Sample 4, and the emission intensity is also between Sample 3 and Sample 4. From this, it can be estimated that Zn contributes to the emission of a wavelength of 330 nm.

No correlation with the emission intensity of Zn was found in other impurities, that is, Mg, Cr, Cu, and Ni. From this, it can be estimated that the impurity that contributes most to the emission of fluorescence at 330 nm is Zn.

It is unclear whether the function of recovering the emission intensity at 330 nm by irradiating with a wavelength shorter than 230 nm is achieved only by Zn doping, or whether other impurities also contribute.

However, it is considered that Mg may be involved as another impurity. The reason for this consideration is as follows. Most of the samples with a large amount of Mg added have a high emission intensity (Samples 1, 2, and 4). Also, Mg is known to be associated with fluorescence at 420 nm, and fluorescence at 420 nm is associated with an absorption spectrum at 215 nm, as shown in FIG. Therefore, when Mg is added, light having a wavelength of 215 nm is easily excited. This is because, as described with reference to Table 2, 215 nm is a wavelength that greatly restores the emission intensity of 330 nm due to excitation light irradiation.

[Summary of characteristics of 1.6 sapphire phosphor]
Summarizing the characteristics of the sapphire phosphor, it can be said that it has the following characteristics.
-When irradiated with excitation light having a wavelength shorter than 290 nm, the electrons of the sapphire phosphor transition to the excited state.
-The wavelengths of fluorescence when the transitioned electron transitions to the ground state are 330 nm and 420 nm.
-For fluorescence at 330 nm, the emission intensity is reduced by irradiation with fluorescence-reduced light, which is light having a wavelength of 230 nm or more.
-On the other hand, for fluorescence at 330 nm, the emission intensity at the time of subsequent irradiation with excitation light is restored by irradiating light shorter than 230 nm.
-Once the emission intensity is restored, if it is stored in an environment where a wavelength of 230 nm or more is not irradiated, the emission intensity at the time of irradiation with excitation light is maintained for a long period of time.

[2. Information recording method and information reading method]
Next, an information recording method and an information reading method using a sapphire crystal having the above-mentioned characteristics will be described. FIG. 5 shows the procedure of the information recording method, and FIG. 6 shows the procedure of the information reading method.

[2.1 Information recording method]
First, the information recording method shown in FIG. 5 will be described. Step (hereinafter, the step is omitted) S1 is a preparation step, and prepares for writing information. In the information writing preparation, the entire information recording area of the sapphire phosphor is made capable of emitting light as described above. The shape of the sapphire phosphor is not particularly limited. Various shapes can be selected according to the size of the information to be recorded. In order to enable light emission, for example, the information recording region of the sapphire phosphor is irradiated with light containing a wavelength of 215 nm for 10 seconds.

The light emitted here may include a wavelength shorter than 230 nm, as described with reference to Table 2. The irradiation time is appropriately set according to the wavelength to be irradiated.

Subsequent S2 is a recording step, and information is written to the sapphire phosphor after executing S1. In writing information, the sapphire phosphor whose entire information recording area is made capable of emitting light in S1 is irradiated with fluorescence-reduced light. For example, as fluorescence reducing light, light of 260 nm is irradiated for 1 second. When light of 290 nm to 380 nm is used instead of the light of 260 nm, as described with reference to FIG. 3, the emission intensity when irradiated with the excitation light is higher than that of the case of irradiating the light of 260 nm for the same time. It can be lowered quickly.

The reduced fluorescence light irradiates the sapphire phosphor in a state where the portion other than the information shape is masked. The irradiation range is a range including the masked portion and its surroundings. Irradiation with reduced fluorescence light reduces the emission intensity of the information-shaped portion when irradiated with excitation light. That is, when the excitation light is irradiated, the emission intensity of the information-shaped portion is relatively lower than the emission intensity of the surrounding portion. Therefore, the information shape part looks black.

Instead of masking a portion other than the information shape and irradiating the region including the masked region with the reduced fluorescence light, the region of the information shape may be irradiated with the reduced fluorescence light with a light beam. The irradiation range of the fluorescence-reducing light at this time is the region of the information shape.

The information writing preparation (S1) and the information writing process (S2) are preferably performed in a dark place where ultraviolet light does not enter. A dark place where ultraviolet light does not enter is, for example, a box or room where light does not enter, which houses a sapphire phosphor, an ultraviolet light source, and a UV camera. Since ultraviolet light is irradiated at the time of preparing for information writing and at the time of information writing processing, it is possible to work even in a dark place if these ultraviolet lights are detected by a UV camera. Further, in the information writing process, when irradiating the excitation fluorescence reducing light such as ultraviolet light having a wavelength near 260 nm, the work may be performed by detecting the fluorescence with a UV camera. A bandpass filter may be provided inside the UV camera or on the sapphire phosphor side of the lens of the UV camera in order to attenuate wavelengths other than the wavelength to be detected.

S3 is a storage step, in which the sapphire phosphor subjected to the information writing process is stored in a dark place at room temperature. This dark place is a place where ultraviolet rays do not enter. Store the sapphire fluorophore in the dark until the information needs to be retrieved. This is to prevent the information from being unreadable when the information needs to be read. The dark place is preferably a portable place such as a box.

[2.2 Information reading method]
Next, the information reading method shown in FIG. 6 will be described. The person who executes the information reading method is usually different from the person who executed the information recording method, but the person who executes the information recording method may execute the information reading method.

S11 is a read step. In the readout step, the sapphire phosphor is irradiated with excitation light and emission at 330 nm is observed. Light at 330 nm can be observed with a CCD camera.

FIG. 7 shows a state in which the letter “D” can be observed on the sapphire phosphor. This "D" is the fluorescence reduction portion 10, and the fluorescence reduction portion 10 has an information shape. The surrounding area is the fluorescent portion 20. The fluorescence emission intensity of the fluorescence portion 20 when irradiated with the excitation light is relatively stronger than that of the fluorescence reduction portion 10. The information shape can be observed by this relative difference in emission intensity. That is, the information shape is expressed by the relative difference in emission intensity.

In order to make it possible to observe the character "D" as the information shape, in S2, the portion other than the character "D" may be masked and irradiated with the fluorescence-reducing light. If the range including the letter "D" is irradiated with the fluorescence-reducing light, the irradiation range is not particularly limited.

S12 is an erasing step. The erasing step is performed when it is desired to erase the information recorded on the sapphire phosphor. For convenience of explanation, the procedure following S11 is described, but only S11 may be executed, or only S12 may be executed.

In the erasing step, the sapphire phosphor is irradiated with unexcited fluorescence-reducing light. In particular, light having a wavelength of 280 nm to 410 nm is preferable. This is because, as shown in FIG. 3, the emission intensity is most reduced in this wavelength range. The irradiation time is a time when the emission intensity is almost eliminated, and this time is determined in advance based on an experiment.

[Summary of information recording method and information reading method]
When information is recorded in the sapphire phosphor by the information recording method shown in FIG. 5 and the information is read out by the information reading method shown in FIG. 6, the information reader is in the information recording state of the alumina phosphor. Is irradiated with excitation light. As a result, the sapphire phosphor emits fluorescence in which the information shape is expressed. The information reader observes the fluorescence and reads out the information.

This fluorescence is ultraviolet light containing a wavelength of 330 nm. The excitation light is also ultraviolet light. Therefore, even if a third party sees the situation of reading the information, it is not even known whether or not the work of reading the information is being performed. Therefore, a highly confidential information reading method is realized.

Further, when the fluorescence is emitted from this sapphire phosphor, it is irradiated with light having a wavelength of 290 nm or shorter. Of the wavelengths shorter than 290 nm, 230 nm to 290 nm are excitation fluorescence reduction light, that is, light that reduces fluorescence. Therefore, the number of readouts can be limited by using excitation fluorescence reduction light. Confidentiality is improved in this respect as well. When the excitation fluorescence reduced light is irradiated more than the number of times of reading, the emission intensity of fluorescence is reduced to an unreadable level. Therefore, the information has been deleted.

The information recorded on the sapphire phosphor can also be erased by irradiating light having a wavelength longer than 290 nm and a wavelength shorter than 630 nm, which is non-excited fluorescence-reducing light. By using light in this wavelength range, information can be erased without emitting fluorescence.

Further, when the sapphire phosphor, which is in a state of not emitting observable fluorescence with the excitation light of 230 nm to 290 nm, is irradiated with a wavelength shorter than 230 nm in the preparation step (S1), it is again 330 nm with the excitation light of 230 nm to 290 nm. It recovers to the state of emitting the fluorescence of. Therefore, the sapphire phosphor can be repeatedly used as an information recording medium. In particular, by irradiating light having a wavelength of 215 nm or shorter, the fluorescence can be quickly restored to a state in which it can emit light.

In addition, when the fluorescence is restored to a state in which it can emit light, the information can be erased at the same time. This is because the entire irradiation range emits fluorescence of the same intensity, and there is no difference in the emission intensity between the information shape portion and its surroundings. Since the information that does not need to be read can be erased, the confidentiality of the information is improved. Further, since the information can be erased by irradiating with light, the information can be easily erased. Since the information can be easily erased, it is possible to prevent the information from remaining without being erased even though the information should be erased. In this respect as well, the confidentiality of information is improved.

[3. Information recording method with 3 or more gradations]
In the information recording method of 2.1, as shown in FIGS. 7, 8 and 9, when the information reading method is carried out, a portion having a relatively strong emission intensity and a portion having a relatively weak emission intensity This is an information recording method that enables information to be read by the occurrence of. That is, the information recording method of 2.1 was a method of recording information in two gradations.

On the other hand, here, a method of recording information with three or more gradations will be described. Ion implantation is partially performed on the sapphire phosphor in order to record information in gradations of 3 or more gradations.

The element to be ion-implanted is any one of Zn, Mg, and B, or a plurality of them. The effect of ion-implanting these Zn, Mg, and B will be described. Table 5 shows the emission intensities of the ion-implanted sample and the non-ion-implanted sample. The depth at which the ions are injected can be calculated to be 80 nm or less from the experimental conditions. The concentration of the injected ions is 0.3% as shown in Table 5. This concentration is the concentration in the sample up to the deepest ion implantation depth of 80 nm. The total thickness of the sample was 1.6 mm.

発光強度は、２６０ｎｍの波長の光を含む励起光を照射して、３３０ｎｍの発光を観測したものである。励起光の照射強度および照射時間は、すべての試料において同一である。ここでは発光強度はカウント数で示しており、相対的な値であることを意味する。

The emission intensity is obtained by irradiating excitation light including light having a wavelength of 260 nm and observing emission at 330 nm. The irradiation intensity and irradiation time of the excitation light are the same for all the samples. Here, the emission intensity is indicated by a count number, which means that it is a relative value.

As can be seen from Table 5, when Zn, Mg, and B are injected, the emission intensity increases as compared with the case where ions are not injected. Further, it can be estimated that the emission intensity increases even if a plurality of types of ions among these Zn, Mg, and B are injected.

Further, it can be seen that the emission intensity of B is stronger than that of Zn and Mg even at the same concentration. Therefore, the emission intensity can be changed by making the element to be injected different in one injection region and another injection region. In addition, it can be estimated that the emission intensity changes if the ion implantation concentration is different. There is no particular upper limit to the concentration to be injected into the sapphire phosphor, but if the injection amount is too large, it will no longer be sapphire, so the injection amount must be within the range in which the physical characteristics of sapphire can be maintained.

Using the characteristics shown in Table 5, ion implantation is performed on the sapphire phosphor in order to record information in gradations of 3 or more gradations. As the sapphire phosphor for ion implantation, various sapphire phosphors described above can be used.

A method of recording information with three or more gradations will be described with reference to FIG. In FIG. 10, impurities are ion-implanted in S0. The impurities here are any one of Zn, Mg, and B, or a plurality of them. The concentration to be injected can be set as appropriate.

The shape of the ion-implanted region is arbitrary. FIG. 11 is a diagram illustrating a state in which the ion implantation region 30 is formed in an annular shape. Since the emission intensity of fluorescence is increased by implanting ions, the ion implantation region 30 can be said to be a portion where fluorescence is increased. Using the sample prepared in S0, the information is recorded by performing S1 and below as described above. The information reading method may be [2.2 Information reading method].

FIG. 12 shows a state in which the character “D” shown in FIG. 7 is written as information in S2 using the sapphire phosphor shown in FIG. 11, and the information “D” is read out in S11. Since the ion implantation region 30 is formed in an annular shape in S0, when the excitation light is irradiated, the emission intensity of the three portions of the fluorescence reduction portion 10, the fluorescence portion 20, and the ion implantation region 30 is increased as shown in FIG. Different from each other. That is, the information is expressed in three gradations.

FIG. 13 shows the ion implantation region 40 and the fluorescence reduction portions 11 and 12 having different shapes from the conventional ones. The ion implantation region 40 shown in FIG. 13 is a quadrangle. The fluorescence-reducing portions 11 and 12 form one arrow as a whole.

First, impurities are implanted into the ion implantation region 40 in the implantation step (S0). In S2, in order to form these fluorescence-reducing portions 11 and 12, as shown in FIG. 13B, these fluorescence-reducing portions 11 and 12 are exposed and the other portions are masked. In the state shown in FIG. 13B, a part of the surface portion of the sample exposed in the shape of an arrow is an ion-implanted region 40, and the rest is an ion-implanted region.

In the example shown in FIG. 12, the ion implantation region 30 was a portion different from the portion irradiated with the fluorescence reduction light, but as shown in FIG. 13, the ion implantation region 40 and the fluorescence reduction light were irradiated. There may be overlap in the parts. The position, shape and size of the ion-implanted regions 30 and 40, the portion irradiated with the fluorescence-reduced light, and their positional relationship indicate the fluorescence expressing the information shape. Various changes are possible depending on the range.

The entire sample is irradiated with fluorescence-reducing light in the state shown in FIG. 13 (b). Irradiation with reduced fluorescence light reduces the emission intensity of the unmasked arrow-shaped portion when irradiated with excitation light. However, the ion-implanted region 40 has a relatively high initial emission intensity as compared with the region where the ions are not implanted. Further, by adjusting the irradiation time of the excitation light, the degree of decrease in the emission intensity can be adjusted.

Therefore, when the irradiation time of the excitation light is adjusted, as shown in FIG. 13C, when the information is read out in S3, two fluorescence reduction portions 11 and 12 having different emission intensities can be observed. As a result, FIG. 13C shows a four-step scale in which the emission intensity decreases in the order of the portion of the ion implantation region 40 other than the fluorescence reduction portion 12, the fluorescence portion 20, the fluorescence reduction portion 12, and the fluorescence reduction portion 11. The tone has been obtained. In the example of FIG. 13, four levels of gradation can be obtained without changing the concentration of the injected ions depending on the location.

In this way, if the injection step (S0) is executed before the recording step (S1), it is excited by irradiating the fluorescence-reducing light in combination with the reduction in the emission intensity when the excitation light is irradiated. The emission intensity when irradiated with light can be set to 3 gradations or more. Therefore, the information can be recorded in a more complicated state.

[4. Information recording method that does not use fluorescence reduction light]
As described with reference to FIGS. 11 and 5, by ion implantation, the emission intensity when the excitation light is irradiated can be made different between the ion implantation regions 30 and 40 and the non-ion implantation region. This means that information can be recorded if the shapes of the ion implantation regions 30 and 40 are made into a shape determined based on the information shape. Therefore, even if the information writing step (S2) is not executed and the fluorescence reducing light is not irradiated, the sapphire phosphor can be put into the information recording state by executing the injection step (S0).

FIG. 14 shows an information recording method for putting a sapphire phosphor into an information recording state without using fluorescence-reducing light. In the method shown in FIG. 14, S2 is removed from FIG. Others are the same as in FIG. When each step shown in FIG. 14 is executed, for example, the annulus shape shown in FIG. 11 can be recorded on the sapphire phosphor as information.

The information reading method may be [2.2 Information reading method]. Further, when erasing the information, it is sufficient to irradiate the fluorescence-reducing light. The fluorescence-reduced light may be excited fluorescence-reduced light or non-excited fluorescence-reduced light.

If the ion-implanted region is also sufficiently irradiated with the fluorescence-reducing light, the emission intensity of fluorescence when irradiated with excitation light can be reduced to an emission intensity that is difficult to distinguish from the emission intensity of the non-ion-implanted region. The irradiation time of the fluorescence-reduced light is a time during which the emission intensity decreases until the emission intensity from the ion implantation region is almost eliminated even if the excitation light is irradiated, and this time can be determined in advance. Further, the irradiation of the fluorescence-reducing light may be terminated after actually irradiating the excitation light and confirming that the emission intensity is sufficiently low.

If it becomes difficult to distinguish between the emission intensity in the ion-implanted region and the emission intensity in the non-ion implantation region, information cannot be read out. Therefore, it can be said that the confidentiality of information is high.

The information recording method that does not use the fluorescence reduction light recovers to a state in which information can be read again by irradiating the light irradiated in the preparation step (S1), that is, the light containing a wavelength of 230 nm or shorter. .. In this sense, light containing a wavelength of 230 nm or shorter can be called recovery light.

Information cannot be read from the sapphire phosphor having reduced emission intensity in the ion-implanted region without irradiating with recovery light. Even if a third party who does not know this obtains a sapphire phosphor having a reduced emission intensity in the ion implantation region, it is difficult to read information from the sapphire phosphor.

On the other hand, a legitimate user who knows that the information is read out again by irradiating the recovery light can easily read the information from the sapphire phosphor again by irradiating the recovery light.

Although the embodiments have been described above, the disclosed techniques are not limited to the above-described embodiments, the following modifications are also included in the disclosed scope, and other than the following, within a range that does not deviate from the gist. It can be implemented with various changes.

<Modification example 1>
In the above-described embodiment, a sapphire phosphor is shown as an example of the alumina phosphor. That is, alumina was a crystal. However, an amorphous alumina phosphor may be used.

<Modification 2>
The mode of expressing the information shape is not limited to the mode in which the entire information shape is the fluorescence-reduced portion 10. In FIG. 8, the outline portion of the information shape is the fluorescence reduction portion 10. Further, in FIG. 9, the fluorescence reduction portion 10 is set around the information shape.

<Modification example 3>
The preparation step (S1) is a step for increasing the emission intensity when the excitation light is irradiated, and when the emission intensity when the excitation light is irradiated is high or when the excitation light is irradiated, the emission intensity is increased. If it is not necessary to do so, the preparation step can be omitted. For example, if the time of exposure to sunlight, which is light containing reduced fluorescence, is not so long, it is possible to obtain a level of emission intensity at which information can be detected even if the preparation step is omitted. Be done.

<Modification example 4>
The preparation step (S1) in FIG. 10 is preparation for writing information, whereas the preparation step (S1) in FIG. 14 is the same as S1 in FIG. 10, but is preparation for reading information. It can be said that. Therefore, when S0 of FIG. 14 is executed, S1 may be executed before reading the information, that is, before executing S11 of FIG. In this case, it is not necessary to execute the storage step (S3) and store the sapphire phosphor in the information recording state in a dark place where ultraviolet light does not enter. Therefore, it is easy to store the sapphire phosphor in the information recording state.

10, 11, 12: Fluorescence reduction part, 20: Fluorescence part, 30, 40: Ion implantation region, S0: Ion implantation step, S1: Preparation step, S2: Recording step, S3: Storage step, S11: Reading step, S12 : Erase step

Claims (13)

Alumina phosphor, which is an alumina capable of emitting fluorescence containing a wavelength of 330 nm by containing zinc as an impurity, reduces fluorescence at a wavelength longer than 230 nm in an irradiation range determined based on the information shape to be recorded. By irradiating with light, the alumina phosphor is put into an information recording state that emits fluorescence expressing the information shape when irradiated with excitation light having a wavelength of 290 nm or shorter. An information recording method including (S2). Prior to the recording step, an injection step (S0) is performed in which one or more of zinc, magnesium, and boron are ion-implanted into at least a part of the range in which the fluorescence expressing the information shape is emitted. The information recording method according to claim 1. The information recording according to claim 1, wherein a preparatory step (S1) of irradiating light containing a wavelength of 230 nm or shorter in a range for emitting fluorescence in which the information shape is expressed is executed before the recording step. Method. Prior to the preparatory step, an injection step (S0) is performed in which one or more of zinc, magnesium, and boron are ion-implanted into at least a part of the range in which the fluorescence expressing the information shape is to be emitted. The information recording method according to claim 3. The information recording method according to claim 3 or 4, wherein the preparatory step irradiates light containing a wavelength of 215 nm or a wavelength shorter than the wavelength of 215 nm in a range in which fluorescence expressing the information shape is emitted. The invention according to any one of claims 1 to 5, further comprising a storage step (S3) of storing the alumina phosphor in the information recording state after the recording step in a dark place where ultraviolet light does not enter. Information recording method. The information recording method according to any one of claims 1 to 6, wherein the recording step is performed in a dark place where ultraviolet light does not enter. For an alumina phosphor, which is an alumina capable of emitting fluorescence containing a wavelength of 330 nm by containing zinc as an impurity, zinc is formed in the ion injection region (30, 40) determined based on the information shape to be recorded. By ion-injecting one or more of magnesium and boron, the information shape is expressed when the alumina phosphor is irradiated with excitation light having a wavelength of 290 nm or shorter. An information recording method including an injection step (S0) for setting an information recording state in which fluorescent light is emitted. The preparatory step (S1) of irradiating the alumina phosphor in the information recording state in the injection step with light containing a wavelength of 230 nm or shorter in the range in which the fluorescence expressing the information shape is emitted. ) Is executed. The information recording method according to claim 8. The information recording method according to claim 8 or 9, further comprising a storage step (S3) of storing the alumina phosphor in the information recording state in a dark place where ultraviolet light does not enter. Information when an alumina phosphor, which is an alumina that emits fluorescence containing a wavelength of 330 nm due to the inclusion of zinc as an impurity, is irradiated with excitation light containing a wavelength of 290 nm or shorter. A readout step in which the alumina phosphor in an information recording state that emits fluorescence whose shape is expressed is irradiated with the excitation light, and ultraviolet light including a wavelength of 330 nm emitted from the alumina phosphor is observed. An information reading method comprising (S11). In the readout step, by irradiating the alumina phosphor with excitation fluorescence reduction light which is light of 230 nm to 290 nm as the excitation light, the information shape is expressed while emitting fluorescence in which the information shape is expressed. The information reading method according to claim 11, wherein the emission intensity of the fluorescent light is reduced. After performing the readout step, the alumina phosphor is irradiated with non-excited fluorescence-reducing light having a wavelength longer than 290 nm and a wavelength shorter than 630 nm, whereby the fluorescence in which the information shape is expressed is expressed. The information reading method according to claim 11 or 12, wherein the erasing step (S12) for reducing the emission intensity of the fluorescence expressing the information shape when the excitation light is irradiated is executed without causing the light to be emitted.

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