JP2013170205A - Phosphor for methane gas sensor, light source for methane gas sensor and methane gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that since in conventional methane gas sensors, the light-emitting peak of light emission spectrum in a 1.6 to 1.7 μm band of YAG: Ce, Er phosphor does not coincide with the absorption wavelength of the methane gas, which is 1,654 nm, the light emission intensity of absorption wavelength of the methane gas is small.SOLUTION: By changing YAG: Ce, Er phosphor to Y(Al, Ga)O: Ce, Erphosphor (YAGaG: Ce, Er phosphor) obtained by substituting the part of the Al in its parent material with Ga, the light emission peak of its light emission spectrum is shifted to the side of 1,654 nm which is the absorption wavelength of the methane gas.

Description

  The present invention relates to a phosphor for methane gas sensor, a light source for methane gas sensor, and a methane gas sensor.

  The first conventional methane gas sensor for measuring the methane gas concentration comprises a light source comprising a metal wire, a filament using ceramic resistance heating, or a heater. Since this light source has a broadband emission spectrum according to black body radiation including the absorption wavelength of 1654 nm of methane gas, the methane gas concentration can be measured by combining this light source with a predetermined light transmission filter. That is, infrared light including an absorption wavelength of 1654 nm absorbed by methane gas is irradiated to the methane gas to be measured, and the methane gas concentration is calculated from the amount of light absorbed by the methane gas at an absorption wavelength of 1654 nm using the Lambert-Beer law.

  However, in the first conventional methane gas sensor, most of the light is thrown away as heat, so the energy utilization efficiency is low, and thus the power consumption is high. Also, disconnection is likely to occur, and therefore the reliability is low. Thus, since the power consumption is high and the reliability is low, a real-time, maintenance-free sensor system could not be constructed.

  The second conventional methane gas sensor for measuring the methane gas concentration uses an InGaAsP semiconductor laser having an absorption wavelength of 1654 nm absorbed by methane gas as a light source (see Patent Document 1). In this case, since the absorption wavelength 1654 nm of methane gas is the emission wavelength, a wide range of methane gas concentrations can be measured with high accuracy.

  However, since the above-described second conventional methane gas sensor changes the emission wavelength and emission intensity of the semiconductor laser under the influence of the ambient temperature, it is necessary to control the semiconductor laser constantly with a Peltier element. The manufacturing cost was high and the power consumption was large. Therefore, it was impossible to construct a sensor system that is real-time and maintenance-free.

A third conventional methane gas sensor for measuring the methane gas concentration has a light emitting diode (LED) having an emission wavelength in the 1.4 to 1.7 μm band, for example, a light source composed of a GaN compound semiconductor blue LED, and an absorption wavelength of methane gas of 1654 nm. Ce ^3+, Er ³⁺ phosphor: Y ₃ Al ₅ O ₁₂ showing the infrared emission comprising (YAG: Ce, Er phosphor) was composed by combining a (see Patent Document 2). Therefore, the temperature characteristics are relatively good together with the LED phosphor, and it is not necessary to control the temperature constant.

JP 2008-2111245 A JP 2011-233586 A

  However, in the third conventional methane gas sensor described above, the emission peak of the emission spectrum of the YAG: Ce, Er phosphor in the 1.6 to 1.7 μm band coincides with the absorption wavelength of 1654 nm of methane gas as shown in FIG. Therefore, the emission intensity at the absorption wavelength of methane gas is still small. Therefore, low power consumption is insufficient and the accuracy of methane gas concentration measurement is insufficient, and as a result, there is a problem that the construction of a real-time, maintenance-free sensor system is insufficient.

  Accordingly, an object of the present invention is to provide a phosphor in which the emission peak of the emission spectrum of the phosphor is shifted to the absorption wavelength 1654 nm side of methane gas. Another object of the present invention is to provide a methane gas sensor light source and a methane gas sensor provided with the phosphor.

In order to solve the above-described problems, the phosphor for a methane gas sensor according to the present invention is made of Y ₃ (Al, Ga) ₅ O ₁₂ : Ce ³⁺ , Er ³⁺ . The emission peak of the emission spectrum of this phosphor shifts to the absorption wavelength 1654 nm side of methane gas. Preferably, the substitution ratio of Ga to Al is 20 mol% or more and 60 mol% or less, the Ce ion concentration for Y and Er is 0.1 mol% or more and 5 mol% or less, and the Er ion concentration for Y and Ce is 2 mol% or more. 4 mol% or less.

A light source for a methane gas sensor according to the present invention is provided on a light emitting element that emits ultraviolet light and / or visible light, and Y ₃ (Al, Ga) ₅ O ₁₂ : Ce ³⁺ , Er ³⁺ And a phosphor layer containing the phosphor.

  Furthermore, a methane gas sensor according to the present invention includes the above-described light source for methane gas sensor, a cell for introducing and discharging methane gas having a light source for methane gas sensor provided at one end, and a light receiving element provided at the other end of the cell. To do.

  According to the present invention, the emission peak of the phosphor shifts to the absorption wavelength side of methane gas, so that it is possible to reduce power consumption and improve the accuracy of methane gas concentration measurement. As a result, it is real-time and maintenance-free. It is possible to construct a sensor system.

It is a table | surface for demonstrating the optimal composition ratio Al and Ga of the YAGaG: Ce, Er fluorescent substance which concerns on this invention. It is a figure which shows the emission spectrum of the conventional sample of FIG. 1, Sample 1, Sample 2, Sample 3, and Sample 4. It is a table | surface for demonstrating the optimal composition Ce with respect to Y and Er of the YAGaG: Ce, Er fluorescent substance which concerns on this invention. It is a table | surface for demonstrating the optimal composition Er with respect to Y and Ce of the YAGaG: Ce, Er fluorescent substance which concerns on this invention. 5 is a flowchart for explaining a method of manufacturing the YAGaG: Ce, Er phosphor shown in FIGS. 1, 3, and 4. It is a figure which shows the light source for methane gas sensors using the YAGaG: Ce, Er fluorescent substance which concerns on this invention. It is a figure which shows the methane gas sensor using the light source of FIG. It is a figure which shows the emission spectrum of the YAG: Ce, Er fluorescent substance of the 3rd conventional methane gas sensor.

The inventor of the present application uses a Y ₃ (Al, Ga) ₅ O ₁₂ : Ce ³⁺ , Er ³⁺ phosphor (YAGaG: Ce,) in which YAG: Ce, Er phosphor is partially replaced with Ga. By using an Er phosphor, the emission peak of the emission spectrum was successfully shifted to the absorption wavelength 1654 nm side of methane gas.

  That is, in the YAG: Ce, Er phosphor, the energy obtained by the Ce ions absorbing blue light from the light source among the emission center ions moves to the Er ions to excite the Er ions. As a result, when the Er ions relax their energy from the excited state to the ground state, they emit light of the emission spectrum in the infrared region.

  In order to shift the emission spectrum described above, it is necessary to change the excitation energy level of the Er ion. When this Er ion is excited, electrons in the energy level of the 4f orbit are in the same 4f orbit. After being excited to a high energy level, infrared light is emitted, and a process called a 4f-4f transition is obtained in which the transition to the low energy level of the 4f orbit is made again. In lanthanoid ions, the 4f orbit is not the outermost shell, so it is not affected by adjacent atoms or ions in the crystal, and therefore the energy level is constant, and as a result, its emission spectrum does not change. It was thought. Also, if the energy level changes, the probability of energy transfer from Ce ions to Er ions may also change, and it has been impossible to predict the emission intensity of the emission spectrum.

Next, the optimum mol% of the Al, Ga composition ratio of the Y ₃ (Al, Ga) ₅ O ₁₂ : Ce ³⁺ , Er ³⁺ phosphor will be described.

  As initial conditions, Y, Ce, Er are set to 94 mol%, 3 mol%, and 3 mol%, and the Ga substitution range for Al is adjusted in the range of 0 mol% to 100 mol% as shown in Fig. 1 (A). The conventional sample, sample 1, sample 2, sample 3, sample 4, and sample 5 were prepared. FIG. 1B shows the actual amounts of oxide and flux charged in the conventional sample, sample 1, sample 2, sample 3, sample 4, and sample 5.

  When the conventional sample, sample 1, sample 2, sample 3, and sample 4 are used as the phosphor layer in the methane gas sensor of FIG. 7, assuming that the emission intensity at the methane gas absorption wavelength of 1654 nm of the conventional sample is 100, sample 1 and sample The emission intensities of Sample 2, Sample 3 and Sample 4 at the methane gas absorption wavelength of 1654 nm were 137, 145, 128 and 87, respectively. Note that the emission intensity of sample 5 could not be detected. The emission spectra of the conventional sample, Sample 1, Sample 2, Sample 3, and Sample 4 measured using a spectroradiometer are shown in FIG. Thus, the substitution range of Ga for Al is preferably 20 mol% or more and 60 mol% or less, and the optimum value is 40 mol%. In other words, if the Ga substitution is less than 20 mol%, the emission peak does not shift sufficiently, whereas if the Ga substitution exceeds 80 mol%, the crystal structure changes and the Ce ions cannot absorb blue light. This is because the emission intensity at a methane gas absorption wavelength of 1654 nm cannot be increased.

Next, the optimum mol% of the composition Ce with respect to Y and Er of Y ₃ (Al, Ga) ₅ O ₁₂ : Ce ³⁺ , Er ³⁺ phosphor will be described.

  As the initial condition, Er is set to 3 mol%, and the optimum mol% of Al and Ga already determined are set to 60 mol% and 40 mol%, and the concentration of Ce with respect to Y is 0.1 mol% to as shown in FIG. Sample 6, Sample 7, Sample 8, Sample 9, Sample 10, Sample 11, and Sample 12 were prepared by adjusting within the range of 5 mol%. FIG. 3B shows the actual amounts of oxide and flux charged in Sample 6, Sample 7, Sample 8, Sample 9, Sample 10, Sample 11, and Sample 12.

  When Sample 6, Sample 7, Sample 8, Sample 9, Sample 10, Sample 11, and Sample 12 are used as the phosphor layers in the methane gas sensor of FIG. 7, the emission intensity at the methane gas absorption wavelength of 1654 nm of the conventional sample is 100. For example, the emission intensity of Sample 6, Sample 7, Sample 8, Sample 9, Sample 10, Sample 11, and Sample 12 at a methane gas absorption wavelength of 1654 nm was 104, 129, 137, 146, 145, 137, and 126. Thus, the concentration of Ce with respect to Y is preferably 0.1 mol% or more and 5 mol% or less, and the optimum value is 2 mol%. That is, when the concentration of Ce is less than 0.1 mol%, the number of Ce ions is small, and Ce ions cannot absorb blue light, and therefore, the emission intensity at a methane gas absorption wavelength of 1654 nm cannot be increased. This is because if the concentration exceeds 5 mol%, the light emission efficiency decreases due to concentration quenching, so that the emission intensity at the methane gas absorption wavelength of 1654 nm cannot be increased.

Next, the optimum mol% of the composition Er with respect to Y and Ce of the Y ₃ (Al, Ga) ₅ O ₁₂ : Ce ³⁺ , Er ³⁺ phosphor will be described.

  As shown in FIG. 4 (A), the optimum mol% of Al, Ga, and Ce already determined is 60 mol%, 40 mol%, and 2 mol%, and the Er concentration relative to Y is 0.1 mol% to 5 mol%. The sample 13, the sample 14, the sample 15, the sample 16, and the sample 17 were prepared by adjusting the range. FIG. 4B shows the actual amounts of oxide and flux charged in Sample 13, Sample 14, Sample 15, Sample 16, and Sample 17.

  When Sample 13, Sample 14, Sample 15, Sample 16, and Sample 17 are used as the phosphor layers in the methane gas sensor of FIG. 7, assuming that the emission intensity at the methane gas absorption wavelength of 1654 nm of the conventional sample is 100, Sample 13 and Sample 14, 15 and 16, the emission intensity at the methane gas absorption wavelength of 1654 nm was 95, 112, 140, 146, 128. Thus, the Er concentration relative to Y is preferably 2 mol% or more and 4 mol% or less, and the optimum value is 3 mol%. In other words, when the Er concentration is less than 0.1 mol%, the number of Er ions is small, and Ce ions cannot absorb blue light, and therefore, the emission intensity at the methane gas absorption wavelength of 1654 nm cannot be increased. This is because if the concentration exceeds 5 mol%, the light emission efficiency decreases due to concentration quenching, so that the emission intensity at the methane gas absorption wavelength of 1654 nm cannot be increased.

Thus, according to the Y ₃ (Al, Ga) ₅ O ₁₂ : Ce ³⁺ , Er ³⁺ phosphor in which YAG: Ce, Er phosphor is substituted with Ga for a part of its matrix Al, The emission intensity at an absorption wavelength of 1654 nm increases. In particular, the substitution range of Ga for Al is preferably 20 mol% or more and 60 mol% or less, and the optimum value is 40 mol%, and the concentration of Ce ion for Y is preferably 0.1 mol% or more and 5 mol% or less, and the optimum value is Further, the Er ion concentration with respect to Y is preferably 2 mol% or more and 4 mol% or less, and the optimum value is 3 mol%.

Next, a method for producing Y ₃ (Al, Ga) ₅ O ₁₂ : Ce ³⁺ , Er ³⁺ phosphor will be described with reference to FIG.

First, referring to the weighing step 501, oxides Y ₂ O ₃ , CeO ₂ , Er ₂ O ₃ , Al ₂ O ₃ , YAGaG: Ce, Er phosphor constituent elements Y, Ce, Er, Al, Ga Ga ₂ O ₃ and BaF ₂ as a flux are used and weighed, for example, so as to have a mol ratio of the sample 16 in FIG. For example, yttrium oxide Y ₂ O ₃ uses 99.99% pure Shin-Etsu Chemical, alumina oxide Al ₂ O ₃ uses 99.9% pure Kanto Chemical, and gallium oxide Ga ₂ O ₃ uses 99.99% pure Furuuchi Chemical. Cerium oxide CeO ₂ is manufactured by Shin-Etsu Chemical Co., Ltd. with a purity of 99.99%, erbium oxide Er ₂ O ₃ is manufactured by Shin-Etsu Chemical Co., Ltd. with a purity of 99.99%, and barium fluoride BaF ₂ is manufactured by Kanto Chemical Co., Ltd. with a purity of 99%. Use the product. Instead of oxides, carbonates, hydroxides, nitrates, chlorides, fluorides, etc. that become oxides upon heating may be used.

  Next, referring to the mixing step 502, the materials from the weighing step 501 are thoroughly mixed. The mixing method is not particularly limited, and may be dry mixing or wet mixing with an organic solvent such as alcohols typified by ethanol and acetone. At the time of mixing, manual operation using a mortar may be used, and a device such as a ball mill or a V-type blender may be used. For example, ball mill mixing is performed for 5 hours together with alumina balls. When the wet mixing is performed, the drying process is performed by suction filtration. Also, after drying, for example, a # 100 mesh sieve is used to transfer the powder whose particle size has been adjusted to a crucible. In this case, the crucible is generally made of an oxide, particularly alumina, but it is also possible to use a metal such as graphite, boron nitride, or molybdenum.

  Next, referring to the firing step 503, the firing is performed in a non-oxidizing atmosphere, for example, in a reducing atmosphere of 96% nitrogen and 4% hydrogen. Usually, such a mixed gas atmosphere of nitrogen and hydrogen is used, but a reducing atmosphere using nitrogen or activated carbon may be simply used. The firing temperature is 1400-1800 ° C., and the firing time is 2-6 hours.

  Next, referring to the cleaning step 504, since the flux component remains after firing, cleaning is performed using nitric acid. Furthermore, it is dried after washing with ion exchange water.

  Finally, referring to the particle size homogenization step 505, the desired phosphor is obtained by sifting through a # 200 mesh screen.

The Y ₃ (Al, Ga) ₅ O ₁₂ : Ce ³⁺ , Er ³⁺ phosphor produced in this way was identified by observing the crystal phase with an X-ray diffractometer. I was able to confirm. Further, it was confirmed that there was no composition deviation from the above-mentioned charged amount.

  FIG. 6 is a view showing a light source 10 for a methane gas sensor using a YAGaG: Ce, Er phosphor according to the present invention.

  In FIG. 6, a light emitting diode (LED) element 4 is provided on the bottom surface of the recess 3 of the frame base 2 on the substrate 1. The electrodes of the LED element 4 are electrically connected to the wiring pattern (lead frame) 1 a of the substrate 1 by bonding wires 5. In addition, a phosphor layer 6 containing a YAGaG: Ce, Er phosphor according to the present invention is formed in the recess 3. Further, a filter 7 is formed in the opening of the recess 3 so as to cover the phosphor layer 6.

  For example, blue light from the LED element 4 excites the YAGaG: Ce, Er phosphor of the phosphor layer 6. As a result, the phosphor layer 6 emits infrared light including an emission peak with a methane gas absorption wavelength of 1654 nm, and this infrared light is emitted to the outside through the filter 9. On the other hand, the blue light transmitted from the LED element 4 without exciting the YAGaG: Ce, Er phosphor in the phosphor layer 6 and the fluorescence in the visible light region emitted by the phosphor layer 6 are absorbed by the filter 9. Alternatively, it is not reflected inside the recess 3 of the frame base 2 and released to the outside.

  Further, in the process of excitation-fluorescence emission in the YAGaG: Ce, Er phosphor of the phosphor layer 6, heat is generated by the phosphor itself due to Stokes shift. Such heat is released to the outside through the filter 9 in contact with the phosphor layer 6. The heat generated in the LED element 4 and the phosphor layer 6 is radiated through the heat radiating substrate 1 and the frame base 2 in addition to the filter 9 described above, and also by a heat radiating body such as a heat sink (not shown). Heat can be dissipated.

  The substrate 1 is made of resin, ceramic or metal as a package member. In particular, silicon or metal is preferable from the viewpoint of thermal conductivity and heat dissipation. In addition, you may comprise the board | substrate 1 and the frame base | substrate 2 integrally.

  Depending on the material of the frame base 2, ultraviolet rays and / or visible light from the LED element 4 and the phosphor layer 6 may be emitted as glare to the outside through the frame base 2. In order to prevent this glare light, a black coating layer, a metal layer, or the like for blocking ultraviolet rays and / or visible light may be formed on the inner surface or outer surface of the recess 3 of the frame base 2. In particular, when a metal layer is formed on the inner surface of the recess 3, infrared rays are efficiently reflected and guided in the direction of the filter 9, and leakage of visible light or the like to the outside is prevented, which is preferable in terms of high output.

  The LED element 4 includes, for example, a p-type layer, an n-type layer made of a direct transition type compound semiconductor, and a light emitting layer sandwiched between these layers, and two electrodes for supplying current to the p-type layer and the n-type layer. Have These electrodes are connected to the wiring pattern 1a on the substrate 1 by bonding wires 5, and emit light corresponding to the band gap of the light emitting layer by supplying a current. The direct transition type compound semiconductor described above is preferably a nitrogen gallium (GaN) compound semiconductor having an emission peak wavelength of 450 nm that emits light in the ultraviolet to green region. Fluctuation is relatively small and temperature characteristics are good.

  The phosphor layer 6 is formed by mixing the YAGaG: Ce, Er phosphor manufactured by the manufacturing method of FIG. 5 with a silicone resin binder resin, filling the recess 6 and curing the resin. For example, the resin curing conditions are heating at 80 ° C. for 1 hour, and then heating at 150 ° C. for 4 hours. As a result, the phosphor layer 6 and the substrate 1 are in close contact with each other, and the substrate 1 and the frame base 2 are fixed. However, the phosphor layer 6 may be formed as a thin film on the inner surface of the filter 9 and may include a cavity in the recess 6.

  The filter 9 has an action of blocking ultraviolet rays and / or visible light from the LED element 4 and the fluorescent layer 6 that cause glare other than desired infrared rays including an absorption wavelength of 1654 nm of methane gas. In addition to this function, the filter 9 also has the function of releasing heat generated by the phosphor layer 6 itself due to the Stoke shift. Thereby, the output fall by the temperature quenching of the fluorescent substance layer 6 is suppressed. As a material for the filter 9, silicon that is transparent to infrared rays and has some thermal conductivity is used.

  FIG. 7 is a view showing a metal gas sensor using the light source of FIG.

In FIG. 7, the light source 10 and the light receiving element 22 such as a phototransistor of FIG. 6 are provided on the upstream side and the downstream side of a cell 21 having a gas inlet 21a and a gas outlet 21b for metal gas. Reference numeral 23 denotes a filter that allows only light in the vicinity of an absorption wavelength of 1654 nm of methane gas to pass, 24 denotes a chopper that turns on and off the light L from the light source 10 to the light receiving element 22, and 25 denotes the light source 10, the light receiving element 22, and the chopper 24. It is a microcomputer comprising a control circuit for controlling, for example, a CPU, ROM, RAM, I / O and the like.

  In FIG. 7, the control circuit 25 turns on and off the light source 10 and opens the chopper 24 to receive the output Io from the light receiving element 22. As a result, the control circuit 25 calculates the methane gas concentration in the cell 21 using the Lambert-Barre law. As necessary, the control circuit 25 transmits the measured methane gas concentration to the center in real time.

1: Substrate
1a: Wiring pattern (lead frame)
2: Frame base
3: Recess 4: LED element 5: Bonding wire 6: Phosphor layer 10: Light source 20: Methane gas sensor 21: Cell 21a: Gas inlet 21b: Gas outlet 22: Light changing element 23: Filter 24: Chopper 25: Control circuit

Claims (6)

A phosphor for methane gas sensor comprising Y ₃ (Al, Ga) ₅ O ₁₂ : Ce ³⁺ and Er ³⁺ . The substitution ratio of Ga to Al is 20 mol% or more and 60 mol% or less,
Ce ion concentration with respect to Y and Er is 0.1 mol% or more and 5 mol% or less,
The phosphor for a methane gas sensor according to claim 1, wherein the Er ion concentration with respect to Y and Ce is 2 mol% or more and 4 mol% or less. A light emitting element that emits ultraviolet light and / or visible light;
A light source for a methane gas sensor, comprising: a phosphor layer provided on the light-emitting element and including a phosphor composed of Y ₃ (Al, Ga) ₅ O ₁₂ : Ce ³⁺ , Er ³⁺ . The substitution ratio of Ga to Al is 20 mol% or more and 60 mol% or less,
Ce ion concentration with respect to Y and Er is 0.1 mol% or more and 5 mol% or less,
The light source for a methane gas sensor according to claim 3, wherein the Er ion concentration with respect to Y and Ce is 2 mol% or more and 4 mol% or less.   The filter further comprises a filter that is formed on the phosphor layer and does not transmit ultraviolet light and visible light from the light emitting element and the phosphor layer, but transmits only infrared light from the phosphor layer. 4. A light source for the methane gas sensor according to 3. A light source for a methane gas sensor according to any one of claims 3 to 5,
A cell for introducing and discharging methane gas, wherein the light source for the methane gas sensor is provided at one end;
A methane gas sensor comprising: a light receiving element provided at the other end of the cell.

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