JP2633749B2 - Infrared-visible conversion phosphor and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared-visible conversion phosphor and a method of manufacturing the same, and more particularly to a wide operating wavelength selection range, high memory characteristics, high infrared-visible conversion efficiency, and high-speed writing of optical information. The present invention relates to a readable infrared-visible conversion phosphor and a method for producing the same.

[0002]

2. Description of the Related Art There are many known infrared-visible conversion phosphors for converting infrared light into visible light.
Infrared stimulable phosphors that can store writing light energy and can be read out by irradiating infrared light have recently attracted attention as optical rewritable memory materials and optical information processing materials. Infrared stimulable phosphor is a phosphor that emits light in the visible region when stimulated with infrared light after being excited by short-wavelength light or X-rays or radiation. Widely used for detecting external light. Europium (E) is added to calcium sulfide (CaS) and strontium sulfide (SrS).
Phosphors to which u) and samarium (Sm) or cerium (Ce) and Sm are added are known as phosphors having high infrared-visible conversion efficiency.

[0003] Prior to describing the technical background of the present infrared-visible stimulable phosphor and its manufacturing method, the operating principle of the infrared stimulable phosphor will be described first.

FIG. 2 shows one of the infrared stimulable phosphors, CaS:
This figure shows the band model of Eu and Sm.
(SPKeller and GDPettit “Quenching, stimulatio
n, andexhaustion studies on some infrared stimulabl
e phosphors ": Phys. Rev., 111 (1958) p. 1533), and the phosphor operates by the following two processes, an excitation process and a light emission process.

[0005] Eu upon irradiation with excitation process (1) excitation light ² +
Is ionized and emits electrons onto the conduction band to become Eu ³ +.

(2) The electrons excited on the conduction band are captured by Sm ³ + to become Sm ² +.

Light emission process (3) Electrons trapped by Sm ³ + are excited on the conduction band by stimulation of external light, and Sm ² + is converted to Sm ³ +
Becomes

[0008] (4) excited electrons on the conduction band are captured in Eu ³ +, Eu ³ + is the Eu ² +. At this time, Eu ² + transitions to the ground state by light emission transition and emits light. The emission at this time is infrared stimulated emission.

As can be seen from the above operating principle, the Eu element determines the wavelength characteristics related to the excitation light and the infrared stimulated emission,
The elements determine the wavelength characteristics for infrared stimulation. As described above, the element that controls the wavelength characteristics of the excitation light and the infrared stimulable emission is called the main activator, and the element that controls the wavelength characteristics of the infrared stimulus is called the sub-activator.

Since the wavelength characteristics are shared by the main activator and the sub-activator as described above, the infrared stimulating emission wavelength and the infrared wavelength sensitivity characteristics can be changed by changing the combination of the main activator and the sub-activator. It can be changed independently. That is, when only the sub-activator is changed without changing the main activator, it is possible to change the infrared wavelength sensitivity characteristics without changing the infrared stimulating emission wavelength. When only the main activator is changed without changing, only the infrared stimulating emission wavelength can be changed without changing the infrared wavelength sensitivity characteristics.

Table 1 shows the emission wavelengths of various infrared stimulable phosphors. For example, when the phosphor matrix is CaS, the primary activator is Eu and the secondary activators are Sm and Bi. sometimes,
The peak wavelength of the infrared wavelength sensitivity characteristic can be changed to 1.15 μm and 0.95 μm while keeping the peak wavelength of the infrared stimulating emission wavelength at 640 nm, and the secondary activator is Sm, the primary activator is Eu, When it is changed to Ce, the peak wavelength of the infrared photostimulated emission wavelength can be changed to 640 nm and 520 nm while the peak wavelength of the infrared wavelength sensitivity characteristic is 1.15 μm.

[0012]

[Table 1]

[0013]

However, there is a limit to the above-mentioned wavelength selectivity. For example, as is apparent from Table 1, the infrared stimulating emission wavelength is blue at 470 nm and the infrared wavelength sensitivity is high. An infrared stimulable phosphor having a characteristic peak wavelength of 1.15 μm cannot be obtained. This is a problem that cannot be essentially solved by the conventional method of simultaneously adding the main activator and the subactivator to the phosphor matrix.

Next, problems in the memory characteristics of the infrared stimulable phosphor will be described.

[0015] Theoretically, the infrared stimulable phosphor should have an extremely stable ability to retain recorded information. In other words, in the Keller model described above, S
The level of m is about 1 eV from the conduction band of the phosphor matrix, which is extremely deep compared to the thermal energy of tens of meV. Therefore, re-emission of electrons occurs due to thermal disturbance. Because it is difficult.

However, the present inventors have conducted measurements on actual phosphors and found that the memory characteristics were not stable, and that the recorded information attenuated over time. FIG. 3 is an example of measuring the temporal change in the amount of retained initial recording information for an infrared stimulable phosphor obtained by adding Eu and Sm to CaS. As is clear from the figure,
It is not as stable as predicted by theory, and in just a few days the amount of recorded information is halved. As described above, the conventional infrared-visible conversion phosphor and the manufacturing method thereof have a drawback that the memory time is short.

The present inventors have repeated more experiments on the above memory characteristics and found that the deterioration of the memory characteristics is largely affected mainly by the amount of the main activator added. FIG. 4 is a graph showing the relationship between the concentration of the main activator and the half-life of the memory. As is apparent from the figure, the memory characteristics are significantly reduced by increasing the concentration of the main activator. This phenomenon cannot be explained by the conventional operating mechanism, and there is an interaction between the sub-activator and the main activator, and the electrons accumulated in Sm move to Eu to lose the recorded information due to the interaction. This indicates that a mechanism exists. It is known that the interaction between such ions depends on the distance between adjacent ions, and the interaction increases as the distance between ions becomes shorter. That is, the decrease in the memory characteristics due to the increase in the main activator is due to the fact that the distance between the main activator and the sub-activator is reduced due to the increase in the main activator.

Therefore, in order to improve the memory characteristics, the concentration of the main activator may be decreased and the distance between activators may be increased. However, the conventional method of mixing and adding the main activator and the sub-activator together. In, the light energy that can be stored with the decrease of the main activator concentration, that is, the infrared-visible conversion efficiency decreases, so that the main activator concentration cannot be reduced indefinitely, without sacrificing the infrared-visible conversion efficiency. It was essentially impossible to improve the memory characteristics.

Even when the memory characteristics are particularly improved by focusing only on the memory characteristics, the amount of the stored information is rapidly increased in an early stage after the information is recorded until the amount of the stored information reaches a constant value. There was a problem that reduction occurred. This situation is as shown in FIG. 5, in which the amount of accumulated information shows a characteristic that it suddenly attenuates in a few hours in the initial stage and then reaches a constant value. This is because the activators are statistically distributed in the phosphor matrix from extremely short to long distances between adjacent activators, and even if the concentration of the main activator is reduced, the distance between adjacent activators is short. The number of activator-subactivator pairs cannot be reduced to zero, and the recorded information will be lost due to the interaction between neighboring activators, resulting in a sharp decrease in the recorded information in the early stage after recording. It is due to. For this reason, in the conventional method in which the main activator and the sub-activator are uniformly added to the phosphor matrix,
It was essentially impossible to avoid a reduction in the initial recorded information.

Furthermore, when the conventional infrared-visible conversion phosphor and its manufacturing method are applied to an optical recording medium, if reading is performed immediately after information recording, the noise level due to afterglow generated after information recording is high, and reading is performed. The S / N ratio of the signal generated by this was extremely low, so that high-speed reading was not possible. This phenomenon is particularly remarkable when the conversion efficiency is increased by increasing the amount of the activator added, and as shown in FIG. 6, even when the signal level and the noise level due to afterglow are almost equal even after a lapse of more than ten seconds after information recording. is there. This phenomenon is related to the attenuation of the amount of stored information in the early stage after information recording described in the above description of the memory characteristics, and light is emitted when recombination occurs due to interaction between adjacent activators, and this is an afterglow. It is because it is observed as. For this reason, it is essentially impossible to avoid the occurrence of afterglow in the conventional method for the same reason as in the case of the above memory characteristics.

An object of the present invention is to solve the above-mentioned problems of the prior art, to provide a wide operating wavelength selection range, high memory characteristics, high infrared-visible conversion efficiency, and high-speed writing and reading of optical information. An object of the present invention is to provide an infrared-visible conversion phosphor that can be used and a method for producing the same.

[0022]

SUMMARY OF THE INVENTION The object of the present invention is to provide a powdery phosphor prepared by using an alkaline earth metal chalcogenide as a phosphor base material and adding at least one element A selected from europium, cerium, manganese and copper. And a powdered phosphor to which at least one element B selected from samarium, bismuth, and lead is added, and then mixed and sintered to fuse both phosphor particles, thereby obtaining an element in the phosphor. This can be achieved by using an infrared-visible conversion phosphor in which the concentration distribution of A and the concentration distribution of element B are differently added.

[0023]

As described in the section of the prior art, the phosphor of the prior art has a constitution in which both the main activator and the subactivator are homogeneously distributed in the phosphor. The distance between activators (hereinafter, referred to as ion-pair distance) could not be controlled independently of the added concentration, and the ion-pairs with a short distance between ion pairs increased with the increase in concentration, resulting in a decrease in characteristics. Since the phosphor of the present invention is added so that the concentration distribution of the main activator and the concentration distribution of the subactivator are different from each other, the number of ion pairs with a short distance between ion pairs can be suppressed, As a result, the effective activator concentration can be increased, the infrared-visible conversion efficiency can be improved, and the memory characteristics can be improved.

First, with regard to the wavelength characteristics, by applying the method for producing an infrared-visible conversion phosphor of the present invention, a phosphor to which a main activator is added and a phosphor to which a sub-activator is added are independently selected. Therefore, the infrared stimulable emission wavelength and the infrared wavelength sensitivity characteristic can be set independently, and the wavelength selection range can be wider than that of the conventional phosphor. For example, by using SrS to which the main activator Ce is added and CaS to which the subactivator Sm is added, 1.1 is obtained.
An infrared-visible conversion phosphor that has a maximum value of infrared wavelength sensitivity characteristics at 5 μm and emits blue light can be obtained.

With respect to the memory characteristics, the addition of the main activator concentration distribution and the sub-activator concentration distribution in a different manner greatly reduces the number of main activator-subactivator pairs present in close proximity. This is equivalent to a reduction, whereby the memory damping effect due to the interaction between activators can be suppressed, and the memory characteristics can be greatly improved. For this reason, even if the addition concentration is increased, the memory characteristics are not reduced, and a phosphor having both good memory characteristics and good infrared-visible conversion efficiency can be obtained.

Furthermore, since the occurrence of afterglow due to the memory attenuation is suppressed, the S / N ratio of the read light is high, and high-speed writing and reading of optical information can be performed.

[0027]

EXAMPLES Hereinafter, the infrared-visible conversion phosphor of the present invention and the method for producing the same will be specifically described with reference to examples.

[0028]

[Example 1] CaS was used as a phosphor base material, Eu was selected as a main activator element, and Sm was selected as a subactivator element.
An example in which the concentration is different from the concentration will be described.

First, 500 ppm of europium oxide (Eu ₂ O ₃ ) was added.
150 ppm of added CaS phosphor and samarium oxide (Sm ₂ O ₃ )
The added CaS phosphor was manufactured. After each of these phosphors is sufficiently pulverized by a ball mill until the average particle size becomes 1 μm or less, the mixed powder is placed in an alumina furnace tube, and a mixed gas of Ar ₂ gas and H ₂ S gas is placed in the tube. While flowing, it was heated at a temperature of 1200 ° C. for 2 hours and sintered. Since the phosphor after sintering becomes a fused mass,
This was further pulverized to obtain a powder having an average particle size of about 50 μm.
The phosphor thus obtained was placed in a scanning electron microscope, and the fluorescence emitted from the phosphor by electron beam irradiation was inspected while scanning the electron beam. As a result, the Eu concentration distribution and Sm
Was added so as to be different from the concentration distribution of The infrared-visible conversion phosphor had an infrared-visible conversion efficiency of 6%, and the accumulated amount of recorded information after lapse of 5,000 hours was 80% or more of the initial writing amount. On the other hand, the infrared-visible conversion efficiency of the conventional phosphor obtained by adding the same amount of activator to CaS at the same time and then sintering is 1% or less, and the recorded information can be accumulated in only several tens of hours. The amount was reduced to less than 50% of the initial writing amount. From the above results, it can be seen that the infrared-visible conversion phosphor of the present invention is extremely superior in both the infrared-visible conversion efficiency and the memory characteristics as compared with the conventional phosphor.

[0030]

Example 2 Strontium selenide (Sr) doped with Ce
Se) and CaS with Sm added.
An example of a phosphor added so that the Ce concentration distribution and the Sm concentration distribution are different will be described.

First, a SrSe phosphor containing 1500 ppm of cerium oxide (CeO ₂ ) and a CaS phosphor containing 150 ppm of samarium oxide (SmO ₂ ) were manufactured. And then mixed. The mixed powder was placed in an alumina furnace tube, and Ar gas was flowed into the furnace tube at a temperature of 1200 ° C. for 2 hours.
Sintered for hours. Since the phosphor after sintering was in the form of a fused mass as a whole, it was further pulverized into a powder having an average particle size of about 50 μm.

The phosphor thus obtained was placed in a scanning electron microscope, and the fluorescence emitted from the phosphor by electron beam irradiation was inspected while scanning the electron beam. As a result, the Ce concentration distribution and the Sm concentration distribution were determined. Was confirmed to have been added so as to be different. In addition, the infrared wavelength sensitivity characteristics of this phosphor exhibited a wide wavelength sensitivity characteristic having a center wavelength of 1.15 μm. The peak wavelength of the infrared stimulating emission wavelength is 470 nm.
Therefore, an infrared-visible conversion phosphor which has sufficient sensitivity to 1.3 μm and 1.55 μm semiconductor lasers and emits blue light was obtained. 1.3 μm, 1.
Nothing emits blue light with sensitivity at 55 μm, and according to the present invention, the selectivity of the wavelength characteristics of the infrared-visible conversion phosphor is expanded, and it becomes possible to design a phosphor suitable for various applications such as a display element. .

[0033]

Example 3 CaS phosphor fine powder to which Eu was added and Sm
An example of a phosphor added so that the concentration distribution of Eu and the concentration distribution of Sm in the phosphor are different from each other by mixing and heating and sintering the CaS phosphor fine powder to which phosphor is added is added.

First, calcium carbonate, europium oxide, sodium carbonate and sulfur were mixed so that the Eu concentration in CaS after firing the phosphor was 500 ppm, and the mixture was filled in an alumina crucible, covered with an electric furnace. Placed inside, heated at 1000 ° C. for 1 hour, the obtained sintered body was crushed and washed with water to remove unreacted raw materials, and further washed with ethanol.
By drying, CaS with an average particle size of 100 nm or less
: Eu phosphor fine particles were obtained. In addition, CaS
Mix calcium carbonate, samarium oxide, sodium carbonate, and sulfur so that the Sm concentration in the mixture becomes 100 ppm, fill in an alumina crucible, cover and install in an electric furnace, and heat at 1000 ° C for 1 hour. And pulverize the obtained sintered body,
After removing unreacted raw materials by washing with water, washing with ethanol and drying, the average particle size is 100 nm.
The following CaS: Sm phosphor fine particles were obtained. CaS obtained by the above: Eu phosphor particles and CaS: after mixing the Sm particles, was placed in an alumina core tube, 1200 ° C. while flowing a mixed gas of Ar gas and H ₂ S in the reactor core tube
For 4 hours and sintered. Since the phosphor after sintering became a lump as a whole, this was further pulverized to obtain a powder having an average particle diameter of about 50 μm.

The phosphor obtained as described above was placed in a scanning electron microscope, and the fluorescence emitted from the phosphor by electron beam irradiation was inspected while scanning the electron beam. As a result, the concentration distribution of Eu and the concentration of Sm were determined. It was confirmed that they were added so as to have different distributions. Further, the infrared-visible conversion phosphor had an infrared-visible conversion efficiency of 8%, and the write amount of recorded information after lapse of 5000 hours was 80% or more of the initial write amount. On the other hand, the infrared-visible conversion efficiency of the conventional phosphor obtained by adding the same amount of activator to CaS and then sintering is 1% or less, and In several tens of hours, the write amount of recorded information decreased to 50% or less of the initial write amount. From the above results, it can be seen that both the infrared-visible conversion efficiency and the memory characteristics of the infrared-visible conversion phosphor of the present invention are extremely superior to those of the conventional configuration.

When the reading characteristics of the phosphor of the present invention obtained in each of the above embodiments were recorded after recording information, as shown in FIG. 1, there was no noise due to afterglow, and the S / N ratio was extremely low. A high signal was obtained. 1 is compared with FIG. 6, it is known that the phosphor of the present invention has an extremely high S / N ratio.

In the above embodiment, examples of CaS, SrS or SrSe phosphors in which Eu and Ce are added as main activators and Sm is added as a subactivator have been described. MgS, CaS, SrS, B
When using chalcogenides of alkaline earth metals such as aS, MgSe, CaSe, SrSe, and BaSe and mixtures thereof, and adding Mn and Cu as main activators and Bi and Pb as subactivators, the operating wavelength selection width It was possible to realize an infrared-visible conversion phosphor having a wide range and high memory characteristics and high infrared-visible conversion efficiency.

[0038]

As described above, the infrared-visible conversion phosphor and the method for producing the same are used as the phosphor and the production method according to the present invention, that is, the concentration distribution of the primary activator in the phosphor and the secondary distribution. By using a phosphor that is added so that the concentration distribution of the activator is different, the problems of the prior art can be solved, and the operating wavelength selection range is wide, and the memory characteristics and infrared-visible conversion efficiency are both high. An outside-visible conversion phosphor could be provided.

In addition, the present invention provides a method for producing the phosphor of the present invention having the above characteristics by mixing and sintering the phosphor containing the main activator and the phosphor containing the subactivator. We were able to.

[Brief description of the drawings]

FIG. 1 is a diagram showing a temporal change in a signal level when information is recorded on an infrared-visible conversion phosphor of the present invention and then read out.

FIG. 2 is a view showing the operation principle of an infrared stimulable phosphor.

FIG. 3 is a diagram showing recorded information retention characteristics of a conventional infrared stimulable phosphor.

FIG. 4 is a graph showing the dependency of the recording information retention characteristics of a conventional infrared stimulable phosphor on the concentration of a main activator.

FIG. 5 is a diagram showing recording information retention characteristics of a phosphor having excellent memory characteristics among conventional infrared stimulable phosphors.

FIG. 6 is a diagram showing a temporal change of a signal level when reading is performed after information is recorded on a conventional infrared stimulable phosphor.

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Claims (2)

(57) [Claims] An alkaline earth metal chalcogenide is used as a phosphor base material, and the phosphor base material contains at least one element A selected from europium, cerium, manganese, and copper, and samarium, bismuth, and lead. At least one element B selected from the group consisting of: and a concentration distribution of the element A and a concentration distribution of the element B in the phosphor are spatially different from each other. Infrared-visible conversion phosphor. 2. A powdered phosphor C containing an alkaline earth metal chalcogenide as a phosphor base material and added with at least one element selected from europium, cerium, manganese and copper, and samarium, bismuth and lead. A powdered phosphor D to which at least one element selected from the group is added is mixed and heated and sintered to fuse the phosphor C powder particles and the phosphor D powder particles. A method for producing an infrared-visible conversion phosphor, comprising producing the infrared-visible conversion phosphor described in the above.