KR100725036B1 - Activated caso4 phosphor - Google Patents

Abstract

Provided is a calcium sulfonate-based phosphor, which allows emission of two photons upon incidence of one photon through second order down conversion (SODC) energy transfer, and thus realizes a green, white or red phosphor having excellent light (quantum) efficiency. The vacuum ultraviolet ray-excited CaSO4-based phophor is activated with rare earth metal elements and is represented by the formula of Ca1-a-bXaREbSO4, wherein a is greater than 0.0001 and equal to or less than 0.15, b is greater than 0.0001 and equal to or less than 0.15, X is Li, Na, K or P, and Re is Tb, Dy, Sm or Eu. A green phosphor is realized when Re is Tb. A white phosphor is realized when Re is Dy. A red phosphor is realized when Re is Sm or Eu.

Description

Calcium Sulfate Phosphor

FIG. 1 shows the vacuum ultraviolet rays of pure CaSO ₄ (A), CaSO ₄ : Tb ³ + (B), CaSO ₄ : Dy ³ + (C) and CaSO ₄ : Sm ³ + (D) 1000 by excitation of 147 nm It is a magnified matrix emission spectrum

2 is a diagram illustrating energy levels of Sm, Eu, Tb, and Dy.

3 is YBO _3: Tb (A) and 147 nm where the emission spectrum of the _{Ca 0 .92 Na 0 .04 Tb 0} .04 SO 4 (B) of the present invention.

4 is an energy level diagram illustrating the energy transfer process by SODC when CaSO ₄ : Tb is excited with an energy of 147 nm.

Figure 5 is a vacuum ultraviolet ray for both the phosphor of _{Ca 0 .96 Na 0 .02 Tb 0} .02 SO 4 (A) of the present invention and the _{Ca 0 .96 Na 0 .02 Dy 0} .02 SO 4 (B) 147 nm Here is the comparative emission spectrum.

The present invention relates to a CaSO ₄ series phosphor, and more particularly to a CaSO ₄ series phosphor having high efficiency by vacuum ultraviolet excitation due to a second-order down conversion (SODC) effect.

Conventional CaSO ₄ has been used as a phosphor for thermoluminescence. CaSO ₄ phosphor prepared for thermal luminescence was prepared through a cumbersome process using sulfuric acid and a large amount of sulfuric acid vapor, the CaSO ₄ phosphor thus prepared did not have good photoluminescence properties.

Currently used vacuum ultraviolet ray and PDP phosphors use some of the ultraviolet ray phosphors generated by mercury discharge in order to have good light efficiency in vacuum ultraviolet ray. As described, there are various problems. Currently three primary colors of red, green, and blue phosphor for a PDP, respectively (Y, Gd) BO _3: mainly used to ^{Eu 2+: Eu 3 + (BAM} ), Zn 2 SiO 4: Mn 2 +, BaMgAl 10 O 17 and, but that is used in red _{(Y, Gd) BO 3:} . Eu 3 + is due to ultraviolet radiation at a photon emission in the 593 nm wavelength that was not emitted when used as an excitation source are a color coordinate is less than the that purpose (JP Boeuf J .. Phys D:... Appl Phys Vol 36, R53, (2003)), YBO 3: Tb 3 + and used as a green phosphor Zn ₂ SiO in with _4: Mn ²⁺ is the green using the ff transition of Mn If you need to change to another color quickly, such as sports events that require too fast transition speed due to the nature, the afterimage remains and deteriorates in a vacuum-ultraviolet environment (RP Rao, J. Elecrochem. Soc. Vol. 150 , No. 8, H165-H171, (2003)), on the other hand, in the case of BAM used in blue, A showed a deterioration characteristic in the vacuum ultraviolet environment, the efficiency of light emission in one of the baking process, in the PDP manufacturing process decreases because of Eu ^{2 +} having the characteristics that are three horizontal oxidation in an oxidizing atmosphere (B. Dawson, M. Ferguson, G. Marking and AL Diaz. Chem. Mater. Vol. 16, p. 5311, (2004).

On the other hand, SODC can not cause Stokes shift because the energy band gap of the mother is wide, and there is little or no overlap of the emission spectrum of the parent and the excitation spectrum of the activator so that energy transfer from the mother to the activator occurs in the same way as the BAM described above. Occurs when it is difficult. The fundamental reason for using the SODC phenomenon in phosphors is to enable two-photon emission for one photon incident, thereby increasing the luminous efficiency over conventional phosphors and, consequently, inert gas discharge or overall energy efficiency which is disadvantageous than mercury discharge in terms of efficiency. This is to compensate for the shortcomings of this low PDP TV. Since the energy of vacuum ultraviolet rays is more than twice the energy of the visible region, SODC (two-photon emission) is theoretically possible. Therefore, phosphors having quantum efficiency of 100% or more based on the fluoride matrix have been developed so far. (WW Piper, JA DeLuca, FS Ham, J. Lumin. Vol. 8, p. 344 (1974)). However, the fluoride matrix was difficult to be used practically because of its low luminous efficiency for 147 nm xenon discharge and its contamination by oxygen in the air, thereby reducing its properties.

When the present inventors doped CaSO ₄ as a parent and doped Tb, Sm, Eu, and Dy together with the charge compensator as the activator, the present inventors had excellent sensitivity, thermal stability, radiation stability, and the like. Unlike energy transfer mechanisms in vacuum ultraviolet phosphors, quantum efficiencies of over 100% can be realized by an energy transfer mechanism called second-order down conversion (SODC), which allows two photons to be emitted for one photon incident. With this in mind, the present invention has been completed.

The present invention is to provide a vacuum ultraviolet-excited CaSO ₄ series phosphor having a simple manufacturing method and high quantum efficiency.

In addition, the present invention is to provide a practical vacuum ultraviolet-excited CaSO ₄ series phosphor using a new energy transfer mechanism, Second-order down-conversion (SODC).

According to the present invention, there is provided a CaSO ₄ series phosphor activated by a rare earth represented by the following formula.

Ca _{1 -a- b} X _a RE _b SO ₄

Wherein 0.0001 <a ≦ 0.15, 0.0001 <b ≦ 0.15, X is Li, Na, K or P and Re is Tb, Dy, Sm or Eu

The reason for the range of b is 0.0001 <b≤0.15 is because rare earth doping of 15% or more cannot be expected to improve the characteristics, and the characteristic improvement of 0.01% or less is insignificant. In the above formula, preferably 0.001 <a ≦ 0.10, 0.001 <b ≦ 0.10, Re is preferably Tb or Dy and X is preferably Na. The charge compensator X is intended to compensate for the charge imbalance that occurs when Do is doped with Re having a different valence of Ca having a valence of 2 (for example, Tb has a valence of 3).

The CaSO4-based phosphors have Tb-green, Dy-white, Sm-red, and Eu-red depending on the type of rare earth element to be doped. As a preferred embodiment of the present invention, CaSO ₄ activated by Tb represented by the following formula A series green phosphor is provided.

Ca _{1 -a- b} X _a Tb _b SO ₄

Wherein 0.0001 <a ≦ 0.15, preferably 0.01 <a ≦ 0.10, 0.0001 <b ≦ 0.15, preferably 0.001 <b ≦ 0.10, and X is Li, Na, K or P and preferably X is Na.

The CaSO 4 series phosphor activated by the rare earth of the present invention can also be represented by the following formula.

CaSO ₄ : Re, X

Wherein X is Li, Na, K or P and 0.15 mol or less of Ca and Re is Tb, Dy, Sm or Eu

The CaSO ₄ series phosphor activated by the rare earth of the present invention is preferably a CaSO ₄ series green phosphor wherein Re is Tb. X is preferably Na.

In general, the energy transfer mechanism in the vacuum ultraviolet phosphor is described using the emission spectrum of the mother and the emission spectrum of the active agent doped in the mother. For example, injecting excitation energy into a matrix of BAM that is doped with nothing results in the emission spectrum of the matrix. However, when doped with Eu ^{2 +} of the parent active agent to get up the energy transferred to the activator ion in the matrix reduces the emission spectrum of the matrix and thus when the emission spectrum of Eu ^{2 +} of active agent.

However, the CaSO ₄ : RE (where RE represents a rare earth element and contains Tb, Sm, Eu, Dy, etc.) phosphor prepared in the present invention can be described as a new energy transfer mechanism, SODC (Second-order down-conversion). have. The present invention is not described by conventional energy transfer mechanisms such as superposition of the emission spectrum of the parent and the excitation spectrum of the active agent or Stokes shift by doping CaSO ₄ with rare earths such as Tb, Sm, Eu and Dy. It provides the first practical phosphor described by Second-order Down Conversion.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Figure 1 is a 1000-fold magnification of the maternal emission spectrum by vacuum ultraviolet 147 nm excitation of nothing doped CaSO ₄ prepared in the present invention (A) and CaSO ₄ : Tb ^{3 +} (B) in the maternal emission spectrum region, CaSO _4: illustrates the overlap the excitation spectrum of the 545 nm emission of ^{Sm 3 + (D): Dy} 3 + (C), CaSO 4.

2 is a diagram showing energy levels of Sm, Eu, Tb, and Dy (WT Carnall, GL Goodman, K. Rajnak, and RS Rana, J. Chem. Phys., Vol. 90, p. 3443 (1989)) . The energy level in the LaF ₃ matrix, but due to the shielding effect of the 5S ² 5P ⁶ electron shell, does not change in the other matrix. 34.01 x 10 ³ cm ^{- 1} of the line represents the energy that corresponds to the half of the vacuum UV ^{147 nm (68.02 x 10 3 cm} -1) is used to excite the sample.

3 is YBO _3: shows a comparison of the emission spectrum by 147 nm excitation of the Tb (A) of carrying out prepared in Example 1 and _{Ca 0 .92 Na 0 .04 Tb 0} .04 SO 4 (B). YBO _3: Tb emission spectrum area ratio of the _{Ca 0 .92 Na 0 .04 Tb 0} .04 SO 4 is 1: 1.35.

Figure 4 shows the energy transfer process by SODC when CaSO ₄ : Tb is excited with an energy of 147nm. When 147 nm vacuum ultraviolet rays generated by Xenon discharge enter the mother CaSO ₄ , the SO ₄ ^{2 -} anion is excited to form a charge transfer (CT) state, and this energy is a single non-radiative transition. Since there is no place to transfer energy, the energy is split into two photon energies between the ⁵ H ₅ and ⁵ D ₃ levels, which simultaneously emit two photons.

5 is the second embodiment and the embodiments prepared in Ca _{0 .96 3 Na 0 .02 Dy 0 .02 SO} 4 CaSO 4 , and Ca _0.96 Na _0.02 Dy _0.02 SO ₄ vacuum ultraviolet rays of the two phosphors of CaSO ₄ 147 nm here The emission spectra are compared with each other.

According to the present invention, CaSO ₄ undoped with nothing is very weak in intensity of emission spectrum when excited with vacuum ultraviolet rays of 147 nm, as shown in FIG. 1, and has very little overlap with the excitation spectrum of the rare earth as an active agent. Since the excited spectra are ff transitions that are prohibited by the selection rule, the efficiency of energy transfer through the superposition of the spectra is very poor. SO ₄ ² In addition to the CaSO ₄ generated by accepting a vacuum ultraviolet ^ray-exciton (exciton) are very efficiently transfer energy to the active agent. Unlike high-mobility free excitons generated in the conduction band, SO ₄ ^{2 -} excitons in CaSO ₄ due to the incidence of energy that does not reach the conduction band have a form of self-trapped excitons (STE). Greatly limited (E. Nakazawa, Chem. Phys. Lett., Vol. 56, p. 161 (1978)). Since CaSO ₄ has a very large band gap of about 10 ev, it causes Stokes shift and cannot transfer energy from the mother to the activator. With such a mechanism, if there is little or no probability of energy transfer from the mother to the activator and an energy level equal to half of the incident energy is at the energy level of the activator, the SODC mechanism can transfer energy to the activator [DL Dexter, Phys. Rev. Vol. 108, p. 630 (1957) and IL Sommerdijk et al., J. of Lumin. Vol. 8, p. 341 (1974)]. However, CaSO4: RE (RE = Tb, Sm, Eu, Dy) satisfies this condition well. Here, the energy level corresponding to half of the incident energy (147 nm) is Tb.

In particular, SOb occurs because Tb satisfies the condition of SODC well, and as shown in Example 1, the quantum efficiency is 100% or more. On the other hand, for other active agents such as Sm, Eu, and Dy, there is no energy level corresponding to half of the incident energy. In this case, the energy injected into the CaSO ₄ matrix undergoes a mitigation process quickly because there is no energy level of an appropriate activator that can transfer energy, and the SODC can be generated by satisfying the SODC during the relaxation. However, since all energy is relaxed and does not transfer energy to the activator, there is also the possibility of transferring energy to the defect of the mother during the relaxation process. Therefore, when doping an activator other than Tb, (i) the energy level corresponding to half of the incident energy Absence and (ii) cross relaxation will result in quantum efficiency of less than 100% when excited with 147 nm of energy from xenon discharges.

Hereinafter, the present invention will be described in detail by way of examples. These examples are intended to illustrate the invention and should not be construed as limiting the protection scope of the invention. (NH ₄ ) ₂ SO ₄ used for the atmosphere is decomposed into SO ₂ and NH _{3 in} the supply and heat treatment of SO ₄ required when the activator is doped into the mother, and thus Tb ₄ O _{7, in} which trivalent and _tetravalent coexists, 3 To reduce the horizontal.

Example 1

Preparation of _{Ca 0 .92 Na 0 .04 Tb 0} .04 SO 4

CaSO ₄ as parent _. 0.02 mol of 2H ₂ O, 0.0002 mol of Tb ₄ O ₇ as the activator, 0.0024 mol of NaCl 3 times as charge compensator, and 0.004 mol of (NH ₄ ) ₂ SO ₄ for the atmosphere. After uniformly mixing the material and heat-treated at 750 ℃ for 2 hours, the heat-treated powder in distilled water to decompose the aggregated particles during the heat treatment, ultrasonic vibration for 30 minutes, filtered on a filter paper to remove moisture and dried do

YBO the _{Ca 0 .92 Na 0 .04 Tb 0} .04 SO 4 and the phosphor quantum efficiency of 85% was prepared in a known _3: shows the emission spectra by the vacuum ultraviolet ray 147 nm here for Tb phosphor in FIG. Quantum efficiency is calculated as the probability of transition at each energy level, and the transition probability is represented by the area of the emission spectrum, and thus the quantum efficiency can be calculated only by comparing the area of the emission spectrum with the same Tb-doped material. The YBO3 calculated in this way: the emission spectra of Tb and _{Ca 0 .92 Na 0 .04 Tb 0} .04 SO 4 area ratio is 1: 1.35 because _{CaSO 4: Tb (4%)} , the quantum efficiency of Na (12%) Is 115%, and the SODC shows that the quantum efficiency is 100% or more.

Marking the energy transfer process in the _{Ca 0 .92 Na 0 .04 Tb 0} .04 SO 4 phosphor shown in FIG. A matrix of 147 nm energy generated in the xenon discharge CaSO ₄ is absorbed and SO ₄ ^{2 -} a charge transfer state of generation, and the energy is not a place to pass energy in a single non-radiative transition with energy of ⁵ H ₅ ^It splits into two photon energies between the ⁵ D ₃ levels and simultaneously excites two Tb ions, resulting in two photons being emitted for one photon incident.

 Example 2

Preparation of _{Ca 0 .96 Na 0 .02 Tb 0} .02 SO 4

It was prepared by the method of Example 1 except that 0.0001 mol of Tb ₄ O _{7 and} 0.0012 mol of NaCl were used as charge compensators. Quantum efficiency is calculated as the probability of transition at each energy level, and this transition probability is represented by the area of the emission spectrum, allowing quantum efficiency calculations only by comparing the area of the emission spectrum with the same Tb-doped material. Since the emission spectral area ratio of YBO ₃ : Tb and Tb-activated CaSO ₄ of the present invention calculated as described above is 1: 1.2, the quantum efficiency of the prepared Tb-activated CaSO ₄ is 108% and the quantum efficiency is 100. It is found to be above% and it is released through the SODC.

Example 3

Preparation of _{Ca 0 .96 Na 0 .02 Dy 0} .02 SO 4

It was prepared in the same manner as in Example 1 except for changing the active agent to Dy. FIG. 5 compares the emission spectra of the Tb activated CaSO ₄ phosphor of Example 2 with the 147 nm excitation of the Dy activated CaSO ₄ phosphor of Example 3. FIG. As shown in FIG. 2, Dy has more energy levels than Tb. However, Dy is ^{_{4 F 9/2 + 6 H 15/}} 2 → 6 F 3/2 + 6 due to the cross relaxation caused by H _5/2 ⁴ F _9/2 level, a quenched (quenching), so the emission efficiency is lowered It is estimated.

The rare earth-doped CaSO ₄ prepared by the present invention has high photoluminescence efficiency, thermal stability, and radiation stability, and thus may be usefully used as a phosphor in fields such as discharge lamps and PDP TVs using vacuum ultraviolet rays.

Claims (11)

A rare earth activated vacuum ultraviolet excitation type CaSO ₄ series phosphor represented by the following formula. Ca _1-ab X _a RE _b SO ₄ Wherein 0.0001 <a ≦ 0.15, 0.0001 <b ≦ 0.15, X is Li, Na, K or P and Re is Tb, Dy, Sm or Eu The CaSO ₄ series phosphor according to claim 1, wherein 0.001 <a ≦ 0.10 and 0.001 <b ≦ 0.10. The CaSO ₄ series green phosphor according to claim 2, wherein Re is Tb. The CaSO ₄ series green phosphor according to claim 3, wherein X is Na. The CaSO ₄ series white phosphor according to claim 2, wherein Re is Dy. 6. The CaSO ₄ series white phosphor according to claim 5, wherein X is Na. 3. The CaSO ₄ according to claim 2, wherein Re is Sm or Eu. Series red phosphor. 8. The CaSO ₄ series red phosphor according to claim 7, wherein X is Na. delete delete delete

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