JP3529162B2 - Infrared visible wavelength up-conversion material - 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 wavelength up-conversion material which emits re-radiated light containing a spectral component in the visible region when irradiated with infrared light.

[0002]

2. Description of the Related Art In recent years, the demand for an element for detecting infrared light has been increasing. Applications include lasers, LDs,
For example, the beam position of a light emitting element such as an LED is detected, patterns such as mode shapes are identified, and further, the breakage point of an optical fiber cable is searched. As a system applicable to such an application, a pure electric system such as an optical power meter using a semiconductor photo diode and a visual system using a vidicon, an image intensifier, an infrared excitation phosphor, etc. It can be roughly divided into a detectable system. However, the pure electric system has a high sensitivity, but it has a problem that it cannot be detected visually, and the vidicon and the image intensifier by this system are insufficient in sensitivity, and they are expensive. There is. Therefore, it can be detected visually and has relatively high conversion efficiency and sensitivity,
In addition, a system using an infrared-visible wavelength up-conversion material such as an inexpensive infrared-excited phosphor is promising.

The phosphor is excited by a suitable excitation source.
The light re-emitted from the excited phosphor can have various spectral distributions depending on the type of the phosphor. Therefore, the phosphor can be applied to various fields of application by combining with a suitable excitation source. Among such phosphors, the material called infrared excitation phosphor is
It is known as a phosphor that up-converts the wavelength of infrared light into visible light. As described above, in order to perform anti-Stokes wavelength conversion of infrared light into visible light having a significantly large photon energy, it is necessary to skillfully select the relationship between the material characteristics and the excitation wavelength. As an infrared light detecting element using a conventional infrared visible wavelength up-conversion material, an IR sensor card manufactured by QUANTEX is well known. When this IR sensor card is irradiated with infrared light, the IR sensor card emits light, for example, red or blue-green, depending on the material of the phosphor. These sensors need to be pre-excited (though it can be indoor light) before irradiation with infrared light, and infrared light excitation can be performed only after this pre-excitation process. However, when the infrared light detection element is continuously irradiated with infrared light, there is a problem that the conversion efficiency changes reversibly with time, and the visible light emission intensity gradually decreases.

On the other hand, some infrared-visible wavelength up-conversion materials which do not require pre-excitation have been reported. As a typical example, YF ₃ : Er, Yb, Y ₃ OCl ₇ : Er,
Yb (H. Kuroda et al., Journal of the Physical Society of Japan (J.Phys.Soc.Jpn.)
Vol. 33 No. 1 _{(1972) pp.125-141), NaLnF 4} : Er,
Yb (Ln: Y, Gd, La) (T. Kano et al., Journal of the Electrochemical Society (JE
lectrochem.Soc.) Volume 119 Issue 11 (1972) pp.1561-1564
), BaY ₂ F ₈ : Er, Yb (Y. Mita et al. Applied Physics Letters (Appl. Phys. Lett.) 23
Winding No. 4 (1973) pp.173-175), (PbF 2 -Ge
O ₂ ): Er, Yb (PbF ₂ —GeO ₂ ): Tm,
Yb (F. Auzel et al., Journal of the Electrochemical Society, Vol. 122, Vol. 1)
(1975) pp.101-107). These materials have a quantum counting function, that is, rare earth ions (mainly Er ³⁺ ions)
It utilizes the multiphoton excitation of.

The emission characteristics of rare earth ions in a solid strongly depend on the concentration of the rare earth ions themselves and the host material surrounding the rare earth ions. Fluoride, a mixture of a fluoride and an oxide, a mixture of a chloride and an oxide, etc. have been conventionally used as a base material utilizing multiphoton excitation of rare earth ions. However, the conversion efficiency of these materials for infrared light,
The sensitivity was low. As a result of a search for an infrared visible wavelength up-conversion material, the present inventors have found a new host material that does not contain oxygen and fluorine and that accommodates rare earth active ions (Er ³⁺ ions) in a large amount and uniformly. It was possible to obtain an infrared-visible wavelength up-conversion material having a higher conversion efficiency than the above material (Japanese Patent Application No. 4-115638). However, the irradiation infrared light wavelengths capable of wavelength conversion by these materials have been limited to 0.8 μm band, 0.98 μm band, and 1.5 μm band .

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above technical problems. The object of the present invention is that pre-excitation is not required and that the visible light emission intensity is high even when infrared light is continuously irradiated. An object of the present invention is to provide an infrared-visible wavelength up-conversion material applicable to an infrared light detection element having practical conversion efficiency and sensitivity for infrared light having a wavelength of 1.3 μm that does not change.

[0007]

The present invention provides the following (1) or
It is an infrared-visible wavelength up-conversion material made of an inorganic material having the configuration shown in (2) . (1) An infrared-visible wavelength up-conversion material containing one or more of each of the following elements or compounds of group A, group B and group C (however, not containing Er) . (2) Contains one or more each of the following elements or compounds of group A, B and D, or one or more of each element or compound of group A, B, C and D (however,
Infrared visible wavelength up-conversion material characterized by containing no Er) . Group A: dysprosium (Dy) and its chlorides Group B: neodymium (Nd), praseodymium (Pr),
Holmium (Ho) and chlorides thereof Group C: Gadolinium (Gd) Chloride or Gadolinium compound containing no oxygen or fluorine D Group: Ca, Sr, Y, La, Ba, Lu, Pb, T
l, Bi, K, Na chloride or compounds of these elements that do not contain oxygen or fluorine

In the present invention, an element having an absorption level in the 1.3 μm band is co-added with an element having an emission level in the visible region, so that the higher level in the 1.3 μm band, which has never been reported before. An infrared visible wavelength up-conversion material with sensitivity was obtained. That is, the infrared visible wavelength up-conversion material of the present invention is Dy as an additive substance that plays a role of absorption center, and at least one element of Nd, Pr and Ho as an additive substance that plays a role of emission center. , In the form of element or chloride,
At least G
d and Cl, or its oxygen, characterized in that it comprises a compound containing no oxygen Tsu Fu. Here, instead of Gd, Ca, S
r, Y, La, Ba, Lu, Pb, Tl, Bi, K, N
It is also possible to use a or the like.

The chloride-based material constituting the host material in the material of the present invention has a lower phonon energy of the host material than the conventionally used oxide or fluoride-based materials.
Therefore, it is considered that non-radiative transition from the excited level to the level immediately below is less likely to occur and the lifetime at the excited level is lengthened, which enables efficient luminescent transition.

The infrared / visible wavelength up-conversion material of the present invention can be produced, for example, by the following method. That is, Dy, Nd, gadolinium (Gd), chlorine (C
l), or a material composed of a compound containing neither oxygen nor fluorine is mixed in a predetermined mixing ratio and heated and baked in an appropriate container. The raw materials used are DyCl ₃ , Nd
Chlorides such as Cl ₃ and GdCl ₃ are preferred, but Dy ₂
Using oxide raw materials such as O ₃ , Nd ₂ O ₃ and Gd ₂ O _{3 and} other raw materials, while heating in an atmosphere furnace, HCl and C
It is also possible to flow a highly reactive gas such as l ₂ and to carry out the calcination while causing the chlorination reaction. The firing conditions are the type of raw material used,
An appropriate range may be determined depending on the mixing ratio, the properties of the intended product, etc., for example, in a heating furnace, 650 to 1200
It can be performed by heating at a temperature of 10 ° C. for 10 minutes to several tens of hours.

During this time, a mixed gas of Ar, Cl ₂ and H ₂ or a mixed gas of CCl ₄ and N ₂ is flowed to prevent mixing of oxygen and water, and as an atmosphere for chlorinating oxides and the like contained in the raw material. It is preferable to set. It is preferable that the material after firing is gradually cooled down to a temperature of about 600 to 650 ° C. at a relatively moderate temperature lowering rate, for example, about 5 ° C./minute. Further, in order to prevent oxidation of the raw material due to contact with oxygen or moisture, it is preferable to perform all operations from weighing the raw material to blending, melting and firing under N ₂ or Ar gas atmosphere.

As a raw material container used at the time of firing, a material that does not react with the raw material at the firing temperature and is not corroded by chlorine-based gas is used. For the purposes of the present invention, crucibles such as glassy carbon, quartz, platinum and gold are suitable.

In addition to the solid phase or liquid phase reaction, the material may be produced by a vapor phase reaction such as a vacuum vapor deposition method, a sputter vapor deposition method, and a chemical vapor deposition (CVD) method. In addition, the infrared-visible wavelength up-conversion material of the present invention may be added with a third component having a specific function such as Yb as a sensitizer in addition to the above-mentioned raw materials, within a range not departing from the spirit of the present invention. It goes without saying that it includes those that have been changed or improved.

[0014]

The function of the infrared / visible wavelength up-conversion material of the present invention is 1.
FIG. 1 shows an example of the emission spectrum when excited with a semiconductor laser (LD) light in the 3 μm band. The emission peak wavelengths by Nd ³⁺ ions are 520 to 540 nm and 580 to 60
0 nm, 660 to 670 nm, and 800 to 830 nm. The emission intensity of 580 to 600 nm is the strongest in the visible region and is recognized as yellow by the naked eye. This 1.3μ
No pre-excitation is required for wavelength conversion from m band to visible light. Further, the visible light emission intensity does not change even when the infrared light in the 1.3 μm band is continuously irradiated. From this result, this infrared visible wavelength up-conversion material does not require pre-excitation, does not change the visible emission intensity even during continuous irradiation of infrared light, and has sensitivity to infrared light in the wavelength range of 1.3 μm. You know that you have. In addition, this infrared visible wavelength up-conversion material is 1.3
It has high sensitivity to infrared light in the 0.8 μm band as well as in the μm band.

In FIG. 2, 530 nm, 590 nm and 670 n
The dependency of the emission peak intensity of each of m and 810 nm on the excitation light intensity of 1.3 μm is shown. The gradient of each emission peak intensity with respect to the excitation light intensity [Sx, X: emission wavelength (nm)] is
2 <S ₅₃₀ <3, 2S ₅₉₀ <3, 2 <S ₆₇₀ <3, 1S
₈₁₀ <2. This result is 1.3 μm to 530
It is shown that the wavelength conversion to nm, 590 nm and 670 nm requires a three-step excitation process, and the wavelength conversion from 1.3 μm to 810 nm requires a two-step excitation process.

FIG. 3 shows 4f of Dy ³⁺ and Nd ³⁺ ions.
The energy level diagram of an electron is shown. In the emission spectrum of FIG. 1, 530 nm, 590 nm, 670 nm, and the peak of 810nm are respectively Nd ³⁺ ions 4
Radiative transition of f-electron from excited level to ground level, ⁴ G _7/2
→ ⁴ I _9/2 , ⁴ G _5/2 (or ² G _7/2 ) →
_{^{4 I 9/2, 4 F}} 9/2 → 4 I 9/2, and ² H _9/2 → ⁴ I
_Probably emitted by _9/2 .

530n by irradiation with infrared light in the 1.3 μm band
An example of a possible mechanism of the m, 590 nm emission process will be described below. 3, by infrared light irradiation of 1.3 .mu.m, Dy ³⁺ ions 4f electrons of the ground level ⁽⁶ H
_15/2 ) to the excitation level ( ⁶ H _9/2 ) and the transition from the excitation level to the ground level ( ⁶ H _9/2 → ⁶ H _15/2 ). The transition energy at this time is non-radiative and adjacent to Nd ³⁺
It is transmitted to the ions and excited from the ground level ( ⁴ I _9/2 ) of the Nd ³⁺ ion to the excitation level ( ⁴ I _15/2 ).
By repeating the same energy transfer twice, two-stage excitation is performed from the excitation level ( ⁴ I _15/2 ) of the Nd ³⁺ ion to the _higher excitation level ( ² H _9/2 ). Three-stage excitation is performed from the excitation level ( ² H _9/2 ) to the _higher excitation level ( ⁴ G _7/2 ). The transition of a part of Nd ³⁺ ions from the excited state ⁽⁴ G _7/2) to ground level ⁽⁴ G _7/2 → ⁴
I _9/2 ) resulting in emission of 530 nm, and another part is relaxed from the excitation level ( ⁴ G _7/2 ) to the level directly below ( ⁴ G _5/2 or ² G _7/2 ) without radiation. Then, the transition from that level to the ground level ( ⁴ G _5/2 or ² G _7/2 → ⁴ I _9/2 ) is performed and 59
The light emission is 0 nm.

The preferred embodiments of the present invention will be summarized below. (1 ) One or more each of an element or compound of group A , B and C, or one or more each of an element or compound of group A, B and D, or group A, group B, group C and Materials composed of one or more of each of the elements or compounds of group D are mixed in a predetermined mixing ratio, and N ₂ is used in an appropriate container.
Alternatively, it is heated and baked at a temperature of about 650 to 1200 ° C. for 10 minutes to several tens of hours in an Ar atmosphere, and then about 600 to 65.
A method for producing an infrared-visible wavelength up-conversion material, which comprises gradually cooling to a temperature of 0 ° C.

(2 ) Infrared visible wavelength up-conversion material in which the materials of Group A, Group B and Group C are in the following composition ranges: Group A: 0.1 to 5 mol% (preferably 0.1 to 5 mol%) 2 mol%) Group B: 0.1 to 30 mol% (preferably 0.5 to 15 mol%) Group C: 65 to 99.8 mol% (preferably 83 to 99.4 mol%) ( 3 ) Infrared visible wavelength up-conversion material in which the materials of Group A, Group B and Group D are in the following composition ranges: Group A: 0.1 to 5 mol% (preferably 0.1 to 2 mol% ) Group B: 0.1 to 30 mol% (preferably 0.5 to 15 mol%) D group: 65 to 99.8 mol% (preferably 83 to 99.4 mol%) ( 4 ) Infrared / visible wavelength up-conversion material in which the materials of Group A, Group B, Group C and Group D are in the following composition ranges: Group A: 0.1 to 5 mol% (preferably 0.1 to 2 mol% ) Group B: 0. -30 mol% (preferably 0.5-15 mol%) C group: 0.1-99.7 mol% (preferably 53-98.4 mol%) D group: 0.1-99 0.7 mol% (preferably 1 to 30 mol%)

[0020]

EXAMPLES Next, the present invention and its effects will be specifically described by way of examples. The present invention and its effects are not limited to the materials, compositions, and manufacturing methods described in the examples below. For example, when Dy or Nd is added to the material used in the present invention as another compound or as a single element, the addition concentration is changed, or in addition to these, another impurity element is added at the same time. When, for example, Yb or the like is added as a sensitizer, or when the material matrix composition is changed, for example, Gd is Y,
Other rare earth elements such as La and Lu, alkaline earth elements such as Ca and Sr, heavy metal elements such as Pb, Tl and Bi,
When changing to an alkaline element such as K or Na, or
Similar effects can be expected even when the base material contains other compounds. Needless to say, the same effect can be obtained by using another light emitting element having a similar emission spectrum component instead of the LD light source.

Example 1 The emission spectrum shown in FIG.
The infrared visible wavelength up-conversion material that re-emits
Create. First, DyCl, a commercially available powder reagent₃, Nd
Cl₃, GdCl ₃(All are 99.9% or more pure)
To a predetermined composition (for example, DyCl₃: NdCl₃: Gd
Cl₃= 0.5: 0.5: 99 mol%)
After that, the mixture was ground in a mortar and stirred and mixed at the same time. Then this
The mixed raw material powder was put into a glassy carbon crucible. That
Then, the crucible was placed in an electric furnace maintained at 650 ° C.
After that, the temperature of the electric furnace was raised. Firing temperature is 750-8
Hold at 50 ° C for about 1 hour to fully dissolve and react the raw materials
After that, the temperature was gradually lowered at a rate of about 5 ° C./minute. Furnace
After the temperature reaches 650 ℃, take out the sample and make
Completed. Note that Ar + Cl is always present in the furnace during firing.₂
+ H₂Gas (or CCl_Four+ N₂Gas etc.)
Oxidation contained in the raw material while preventing the mixture of oxygen and water
The atmosphere was such that things were salified. Also, with oxygen and moisture
To prevent the oxidation of the raw materials due to contact, weigh the reagents.
, All the operations from blending, melting, and sintering are N₂There
Was performed in an Ar gas atmosphere. Made in this way
Infrared visible wavelength up-conversion material, 1.3μm LD light (1
Fig. 1 shows the emission spectrum when excited with a power of 4 mW).
Shown in. The luminescence at this time is recognized as yellow by the naked eye.
It

Example 2 DyCl ₃ , PrCl ₃ and G
dCl ₃ (both having a purity of 99.9% or more) is formed into a predetermined composition (for example, DyCl ₃ : PrCl ₃ : GdCl ₃ =
1: 0.5: 98.5 mol%), and an infrared-visible wavelength up-conversion material was produced in the same manner as in Example 1. The infrared visible wavelength up-conversion material produced in this way was
FIG. 4 shows the emission spectrum when excited with LD light of μm (power of 14 mW). The luminescence at this time is recognized as orange by the naked eye. 6 in the emission spectrum of FIG.
The peaks at 00 nm and 810 nm are P
Radiant transition of 4f electron of r ³⁺ ion from excited level to ground level, etc., ¹ D ₂ → ³ H ₄ , and ¹ D ₂ → ³ H ₆ (or ⁶ F _5/2 → of Dy ³⁺ ion) ^It is considered that the emission is due to ⁶ H _15/2 ). In FIG. 5, 1.
The dependence of 3 μm excitation light intensity is shown. The gradient of the emission peak intensity with respect to the excitation light intensity was 2 <S ₆₀₀ <3. This result indicates that the wavelength conversion from 1.3 μm to 600 nm requires three-step excitation process.
As in the case of, energy transfer occurs from the Dy ³⁺ ion to the Pr ³⁺ ion, and the Pr ³⁺ ion ^undergoes multi-step excitation ( ³ H ₄
→ ³ by ^{_{F 4 → 1 G 4 → 1}} D 2) is the fact, Pr ³⁺
It is considered that luminescence of ions can be obtained.

Example 3 DyCl ₃ , HoCl ₃ , G
dCl ₃ (each having a purity of 99.9% or more) is formed into a predetermined composition (for example, DyCl ₃ : HoCl ₃ : GdCl ₃ =
0.5: 10: 89.5 mol%), and an infrared-visible wavelength up-conversion material was produced in the same manner as in Example 1. The infrared / visible wavelength up-conversion material thus produced was
FIG. 6 shows an emission spectrum when excited with LD light of 3 μm (power of 14 mW). The luminescence at this time is recognized as orange by the naked eye. In the emission spectrum of FIG.
The peaks at 650 nm and 540 nm in the visible region are radiative transitions from the excitation level of the 4f electron of the Ho ³⁺ ion to the ground level, ⁵ F ₅ → ⁵ I ₈ , and ⁵ S ₂ → ⁵ I _{8 respectively.}
It is considered that the light is emitted by. In FIG. 7, 650 nm and 540
nm emission peak intensity dependency of 1.3 μm excitation light intensity is shown. The slope of each emission peak intensity with respect to the excitation light intensity is
Were respectively _{2 <S 65 0 <3,2 <} S 540 <3. This result shows that wavelength conversion from 1.3 μm to 650 nm and 540 nm requires three stages of excitation processes, respectively. As in the case of Example 1, Dy ³⁺ ions are converted to Ho ³⁺ ions. It is considered that the energy transfer occurs and the Ho ³⁺ ions are excited in multiple stages ( ⁵ I ₈ → ⁵ I ₇ → ⁵ I ₄ → ⁵ F ₃ ), whereby the emission of the Ho ³⁺ ions can be obtained.

Example 4 DyCl ₃ , NdCl ₃ , B
aCl ₂ (each having a purity of 99.9% or more) with a predetermined composition (for example, DyCl ₃ : NdCl ₃ : BaCl ₂ =
0.5: 0.5: 99 mol%), and an infrared-visible wavelength up-conversion material was produced in the same manner as in Example 1. The infrared visible wavelength up-conversion material produced in this way was
When excited with LD light of μm, an emission spectrum similar to that in FIG. 1 was obtained, and the emission at this time was visually recognized as yellow.

Example 5 DyCl ₃ , PrCl ₃ , B
aCl ₂ (each having a purity of 99.9% or more) has a predetermined composition (for example, DyCl ₃ : PrCl ₃ : BaCl ₂ =
1: 0.5: 98.5 mol%), and an infrared-visible wavelength up-conversion material was produced in the same manner as in Example 1. The infrared visible wavelength up-conversion material produced in this way was
When excited with LD light of μm, an emission spectrum similar to that in FIG. 4 was obtained, and the emission at this time was visually recognized as orange.

(Example 6) DyCl ₃ , HoCl ₃ , B
aCl ₂ (each having a purity of 99.9% or more) with a predetermined composition (for example, DyCl ₃ : HoCl ₃ : BaCl ₂ =
0.5: 10: 89.5 mol%), and an infrared-visible wavelength up-conversion material was produced in the same manner as in Example 1. The infrared / visible wavelength up-conversion material thus produced was
When excited with LD light of 3 μm, an emission spectrum similar to that of FIG. 6 was obtained, and the emission at this time was visually recognized as orange.

[0027]

As described above, since the infrared / visible wavelength up-conversion material of the present invention has high sensitivity to infrared light in the wavelength band of 1.3 μm, pre-excitation is not required and the infrared light There is an advantage that it can be applied to an element capable of visually detecting infrared light, in which the visible light emission intensity does not change even during continuous irradiation.

[Brief description of drawings]

FIG. 1 shows an infrared / visible wavelength up-conversion material of the present invention having a wavelength of 1.
It is a graph which shows an example of an emission spectrum obtained when excited by infrared light of 3 μm.

FIG. 2 shows the infrared-visible wavelength up-conversion material of the present invention having a wavelength of 1.
It is a graph which shows an example of the excitation light intensity dependence of each emission peak intensity in the emission spectrum obtained when excited by 3 μm infrared light.

FIG. 3 shows Dy ³⁺ showing a 530 nm and 590 nm emission process when the infrared visible wavelength up-conversion material exhibiting the emission spectrum shown in FIG. 1 as re-emitted light is excited by infrared light in the wavelength band of 1.3 μm. 2 is an energy level diagram of 4f electrons of Nd ³⁺ ions.

FIG. 4 shows an infrared / visible wavelength up-conversion material of the present invention having a wavelength of 1.
It is a graph which shows an example of an emission spectrum obtained when excited by infrared light of 3 μm.

FIG. 5 shows the infrared visible wavelength up-conversion material of the present invention having a wavelength of 1.
It is a graph which shows an example of the excitation light intensity dependence of the emission peak intensity in the emission spectrum obtained when excited by 3 μm infrared light.

FIG. 6 shows the infrared visible wavelength up-conversion material of the present invention having a wavelength of 1.
It is a graph which shows an example of an emission spectrum obtained when excited by infrared light of 3 μm.

FIG. 7 shows the infrared visible wavelength up-conversion material of the present invention having a wavelength of 1.
It is each emission peak intensity in an emission spectrum obtained when excited by infrared light of 3 μm.

Continued Front Page (72) Inventor Wu Uhu 4-7-25 Harigaya, Urawa-shi, Saitama, Ltd. Sumita Optical Glass Co., Ltd. (56) Reference JP-A-2-168688 (JP, A) Journal of the Ph Physical Society of Japan, 1972, Vol. 33, No. 1,125-141 (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 2/02 C09K 11/08 JISST file (JOIS) CA (STN)

Claims (3)

(57) [Claims] 1. A infrared visible wavelength up-conversion material composed of an inorganic material, said material at least the following group A, B group 及
And at least one element or compound of group C
(However, Er is not included) Infrared visible wavelength up-conversion material characterized by the above-mentioned. Group A: dysprosium (Dy) and its chlorides Group B: neodymium (Nd), praseodymium (Pr),
Holmium (Ho) and their chloride group C: gadolinium (Gd) chloride or oxygen, fluorine
Gadolinium compound not containing 2. An infrared-visible wavelength up-conversion material made of an inorganic material, wherein the material contains at least one of each of the following elements A, B and D elements or compounds.
(However, Er is not included) Infrared visible wavelength up-conversion material characterized by the above-mentioned. Group A: dysprosium (Dy) and its chlorides Group B: neodymium (Nd), praseodymium (Pr),
Holmium (Ho) and their chlorides Group D: Ca, Sr, Y, La, Ba, Lu, Pb, T
l, Bi, K, Na chloride or oxygen, fluorine is not included
Compounds of these elements 3. An infrared-visible wavelength up-conversion material comprising an inorganic material, wherein the material is at least the following Group A, Group B ,
An infrared-visible wavelength up-conversion material containing at least one element (not including Er) of each of the elements or compounds of group C and group D. Group A: dysprosium (Dy) and its chlorides Group B: neodymium (Nd), praseodymium (Pr),
Holmium (Ho) and their chloride group C: gadolinium (Gd) chloride or oxygen, fluorine
Gadolinium compound D group not containing : Ca, Sr, Y, La, Ba, Lu, Pb, T
l, Bi, K, Na chloride or compounds of these elements that do not contain oxygen or fluorine