Infrared-visible converting stimulable phosphor

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to an infrared-visible conversion phosphor, and particularly to an infrared-visible conversion element having high infrared-visible conversion efficiency.

【0002】

[Conventional technology]

With the progress of optical communication, optical components and devices using 1.3 μm and 1.55 μm infrared light have been used in various places in recent years, and the demand for detectors for detecting these infrared lights is rapidly increasing.

【0003】

Detectors that detect infrared light include light detectors that use semiconductor elements and infrared detectors that use infrared visible conversion phosphors. Of these, the infrared visible conversion phosphors are red to the naked eye. Since it is possible to check the presence or absence of external light and it is inexpensive, it is in high demand as a simple light detector. Among the infrared visible conversion phosphors, the infrared bright phosphor to which samarium (Sm) is added has sensitivity to 1.3 μm and 1.55 μm infrared light used in optical communication, and is particularly sensitive to light. Widely used for inspection of communication equipment.

【0004】

The infrared luminescent phosphor is a phosphor that emits light in the visible region when it is irradiated with infrared rays to a phosphor that has been excited by irradiating it with light of a short wavelength in advance, and is mainly composed of alkali earth metal chalcogens. Europium (Eu) or cerium (Ce) is widely used as an activator, and Sm is widely used as a by-activator. In this case, infrared irradiation causes the electrons captured in Sm to move to the main activator and recombine with the main activator to cause infrared visible conversion.

【0005】

Since the Sm concentration at which the infrared visible conversion efficiency is maximized is about several hundred ppm, Sm is conventionally added so that the Sm concentration in the phosphor is about several hundred ppm. In addition to this, as described in the Fluorescent Handbook (published by Ohmsha, 1987.12: 141), a few to 10% of a flux is often added to the fluorescent material. Flux is alkaline carbonate, sulfate, NH₄There are Cl and the like. In particular, since Li compounds significantly promote particle growth and diffusion of activators, phosphors to which Li compounds are added in a weight ratio of several% to several tens of percent are also widely used. In addition, US Pat. No. 4,812,660 states that lithium fluoride contributes to the development of meltability. As a specific example, lithium fluoride is 10% by weight and calcium sulfide is by weight. Infrared fluorescee with 90%, 150 ppm Sm and 550 ppm cerium sulfide is described.

【0006】

[Problems to be Solved by the Invention]

As described above, in the infrared luminescent phosphor of the present invention, infrared visible conversion is performed by moving the electrons captured by Sm to the main activator. Therefore, the Sm concentration and the infrared visible conversion efficiency should be proportional, but in the conventional composition, the concentration of Sm that actually contributes to the infrared visible conversion is 1% or less of the added concentration, and the added Sm is effective. Has the drawback of not contributing to infrared visible conversion.

【0007】

On the other hand, even if an attempt is made to increase the concentration of the effective activator by increasing the concentration of Sm, the infrared visible conversion efficiency is saturated when the Sm concentration is only about several 100 ppm, and the addition of more Sm causes a decrease in efficiency. There is a drawback that the infrared visible conversion efficiency does not improve even if the Sm addition concentration is increased.

【0008】

In addition, a phosphor to which a melting agent of several% to several tens of percent is added for the purpose of particle growth of phosphor particles and diffusion of an activator has a drawback that the luminous efficiency is lowered, although the particle growth and diffusion effects are exhibited. It was. Therefore, the conventional infrared luminescent phosphor cannot further improve the efficiency, and has a drawback that the infrared visible conversion efficiency is low.

【0009】

The present invention has been proposed to improve the above-mentioned drawbacks, and an object of the present invention is to provide an infrared-visible conversion phosphor having high infrared-visible conversion efficiency.

【0010】

[Means for solving problems]

In order to achieve the above object, the gist of the present invention is to add at least Sm to chalcogenides of alkaline earth metals and at least one of the elements (Li, Na, K, Rb, Cs) belonging to Group Ia of the Periodic Table. In the infrared brilliant phosphor to which the above is added, the total atomic number concentration of the elements belonging to the group Ia is 10 times or less the atomic number concentration of Sm, which is present in the infrared visible conversion phosphor. To do.

【0011】

[Action]

The present inventors have investigated in detail the cause of the low effective Sm concentration that contributes to the infrared visible conversion with respect to the Sm addition concentration, and the cause of the decrease in the infrared visible conversion efficiency due to the increase in the Sm addition concentration.

【0012】

As a result, in the infrared fluorescee phosphor, the alkaline earth metal, which is a divalent cation, is replaced with Sm, which is a trivalent cation in the phosphor. It was clarified that the effective Sm concentration, which contributes to infrared visible conversion, decreases due to the collapse and defects.

【0013】

Regarding the cause of the decrease in infrared visible conversion efficiency due to the addition of the melt, the charge is neutral because monovalent ions with a concentration two orders of magnitude higher than the Sm concentration to be added in the conventional manufacturing method are added. It was found that the efficiency was reduced because the conditions were broken and the effective Sm concentration that contributed to the infrared visible conversion was reduced.

【0014】

Therefore, in order to improve the infrared visible conversion efficiency, the effective Sm concentration that contributes to the infrared visible conversion efficiency may be increased by satisfying the charge neutrality condition.

【0015】

A case where Li, which is a group Ia element, is added to calcium sulfide to which Sm is added will be specifically described as an example. 2 Ca²⁺Ions, each Sm³⁺And Li⁺When replaced with, the total valence of positive ions is 4+ before and after the replacement, and there is no excess or deficiency of charge. Therefore, the charge neutral condition is maintained, the effective Sm concentration is increased, and the infrared visible conversion efficiency is improved. Group Ia element is Sm³⁺Since it is added to compensate for the charge of Sm, it is most effective if the amount of Group Ia element added is the same as the amount of Sm added, but even if it is lower than the Sm addition concentration, the charge is applied to a part of the added Sm. The effect appears because compensation is performed. Further, when the group Ia element is excessively added, the divalent maternal cation is replaced by the ion of the monovalent group Ia element, so that the number of electrons becomes excessive, the charge neutral condition is disrupted, and the efficiency is lowered again.

【0016】

Figure 1 shows the relationship between the ratio of the amount of Group Ia elements added to the amount of Sm added and the relative infrared visible conversion efficiency. The relative infrared visible conversion efficiency is an infrared visible conversion efficiency expressed based on the infrared visible conversion efficiency of a conventional phosphor to which a Group Ia element is not added. As shown in Fig. 1, when the amount of Group Ia element added is up to 10 times the amount of Sm added, higher efficiency can be obtained than when no element is added, but when it is added more than that, the efficiency is lower than when no element is added. .. Therefore, the amount of Group Ia added must be determined in correlation with the Sm concentration added to the infrared fluorescee phosphor, and the amount must be within 10 times the Sm concentration. Therefore, for example, as described in Examples of US Pat. No. 4,812,660, when lithium fluoride is added by weight ratio of 10%, calcium sulfide is added by weight ratio of 90%, Sm is added at 150 ppm, and cerium sulfide is added at 550 ppm. As described above, there is no correlation between the amount of Sm added and the amount of Group Ia added, and when the amount of Group Ia element added is nearly 1000 times the amount of Sm added, the efficiency is rather reduced.

【0017】

[Example]

Hereinafter, the present invention will be described in more detail with reference to examples.

【0018】

(Example 1) In this example, an infrared visible conversion phosphor in which Li, Na, K, Rb or Cs is added to an infrared fluorescee phosphor in which Eu and Sm are added to calcium sulfide will be described.

【0019】

Europium oxide and samarium oxide were added to calcium sulfide, and lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, and cesium carbonate, which are carbon oxides of Group Ia elements, were added to prepare five types of phosphors. The amount of europium oxide and samarium oxide added was determined so that the atomic number concentrations of Eu and Sm in the phosphor were 500 ppm and 150 ppm, respectively. Each phosphor was produced by varying the addition concentration of the carbon oxide of the Group Ia element, and the atomic number concentration of each element was adjusted by the inductively coupled luminescence analysis method. As a result, the concentration was 15 ppm to 15000 ppm.

【0020】

As a specific production method, a raw material in which calcium sulfide, europium oxide, samarium oxide, and carbon oxides of Group Ia elements are mixed is placed in a core tube, and fired at 1200 ° C. for 2 hours using an electric furnace. The diffusion of added elements into calcium sulfide and the growth of crystal grains were attempted. During firing of the raw material, a mixed gas of argon and hydrogen sulfide was flowed into the furnace core tube for the purpose of preventing oxidation of the raw material and preventing the occurrence of sulfur deficiency.

【0021】

Figure 2 shows the results of measuring the infrared visible conversion efficiency of the infrared luminescent phosphor produced in this way. The vertical axis in FIG. 2 shows the relative infrared visible conversion efficiency, and the infrared visible conversion efficiency of the infrared luminescent phosphor when the Group Ia element is not added is set to 1. The horizontal axis shows the atomic number concentration of each Group Ia element (Li, Na, K, Rb, Cs). In the figure, the curves (a) are the results when Li is added, (b) is Na, (c) is K, (d) is Rb, and (e) is Cs.

【0022】

As is clear from FIG. 2, in any case, when the Group Ia element is added to 10 times or less of the Sm concentration of 150 ppm, that is, to 1500 ppm or less, the infrared visible conversion efficiency is higher than when the Group Ia element is not added. It is clear that the infrared visible conversion efficiency is improved by adopting the infrared visible conversion phosphor according to the present invention.

【0023】

(Example 2) In this example, an infrared visible conversion phosphor in which Li, Na, K, Rb or Cs is added to an infrared fluorescee phosphor in which Eu and Sm are added to strontium sulfide will be described.

【0024】

In addition to europium oxide and samarium oxide, strontium sulfide was added with lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide, which are sulfides of Group Ia elements, to prepare five types of phosphors. The amount of europium oxide and samarium oxide added is 500ppm and 150ppm in terms of atomic number concentration, respectively, and the concentration of sulfide of Group Ia elements is 4 types of atomic number concentration of 15ppm, 150ppm, 1500ppm and 15000ppm for each group Ia element. , The infrared visible conversion efficiency was investigated.

【0025】

Similar to Example 1, a raw material in which strontium sulfide, europium oxide, samarium oxide, and sulfides of Group Ia elements are mixed is installed in a core tube, and is added by firing at 1200 ° C. for 2 hours using an electric furnace. Diffusion of the element into strontium sulfide and grain growth were attempted. During firing of the raw material, a mixed gas of argon and hydrogen sulfide was flowed and fired for the purpose of preventing oxidation of the raw material and preventing the occurrence of sulfur deficiency.

【0026】

When the infrared visible conversion efficiency of the infrared luminescent phosphor produced in this manner was measured, the results shown in FIG. 3 were obtained. The vertical axis of Fig. 3 shows the relative infrared visible conversion efficiency as in Fig. 2, and the horizontal axis shows the atomic number concentration of each Group Ia element (Li, Na, K, Rb, Cs). is there. In the figure, the curve (a) is the result when Li is added, (b) is Na, (c) is K, (d) is Rb, and (e) is the result when Cs is added.

【0027】

As is clear from FIG. 3, in any case, when the Group Ia element is added at l0 times or less of the Sm concentration of 150 ppm, that is, at 1500 ppm or less, the infrared visible conversion efficiency is higher than when the Group Ia element is not added. It is clear that the infrared visible conversion efficiency is improved by adopting the infrared visible conversion phosphor according to the present invention.

【0028】

[Effect of the invention]

If the infrared-visible conversion phosphor has the configuration of the present invention, the concentration of the effective activator that contributes to infrared-visible conversion can be increased, so that the infrared-visible conversion efficiency is improved and the infrared-visible conversion efficiency is high. It becomes possible to provide an infrared visible conversion phosphor.

[Simple explanation of drawings]

[Figure 1]

It is a graph which shows the relationship between the ratio of the addition amount of the group Ia element to the addition amount of Sm, and the relative infrared visible conversion efficiency.

[Figure 2]

It is a graph which shows the relationship between the group Ia element atomic number concentration and the infrared visible conversion efficiency of the infrared visible conversion phosphor of Example 1. FIG.

[Fig. 3]

It is a graph which shows the relationship between the group Ia element atomic number concentration of the infrared visible conversion firefly body of Example 2 and the infrared visible conversion efficiency.