JP2007115467A - Discharge lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp having a phosphor layer, with high brightness and high light transmittance. <P>SOLUTION: The discharge lamp is composed of a discharge tube, an ultraviolet-ray source arranged inside the discharge tube, and a phosphor layer applied on an inner wall of the discharge tube. The phosphor layer contains BaMgAl<SB>10</SB>O<SB>17</SB>:Eu<SP>+2</SP>as blue-color phosphor, of which, a ratio of the size of secondary particles as an aggregation of primary particles to that of the primary particles ranges between 1.7 and 2.0. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a discharge lamp, and more particularly to a discharge lamp that excites and emits light by irradiating a phosphor layer with ultraviolet rays.

  For example, a cold cathode discharge lamp is used for a backlight of a liquid crystal display device, a small illumination device, and the like. A phosphor layer is formed on the inner wall of the glass tube, and the phosphor is excited and emitted by ultraviolet light derived from a discharge such as a rare gas or mercury. It is desirable that the phosphor layer has a high luminance and a high light transmittance when used in a discharge lamp.

For the color display device, for example, phosphors emitting three colors of red, green, and blue are used. Not only the brightness but also the appearance of the color under the illumination, that is, both efficiency and high color rendering properties are required. In order to satisfy both, a three-wavelength fluorescent lamp is widely used. As a phosphor of the three-wavelength fluorescent lamp, for example, a divalent europium-activated barium magnesium aluminate (BAM) phosphor BaMgAl ₁₀ O ₁₇ : Eu ^{+2 having} an emission wavelength peak near 450 nm and emitting blue light, emission wavelength A cerium / terbium-activated lanthanum phosphate phosphor LaPO ₄ : Ce, Tb, which emits green light, has a peak in the vicinity of 545 nm, a europium-activated yttrium oxide phosphor Y ₂ having an emission wavelength peak in the vicinity of 611 nm and emitting red light. O ₃ : Eu is used.

In Patent Document 1, the average particle size is 0.5 to 15 μm and the ratio of the major axis to the minor axis is 1 in order to make a phosphor having a small particle size, a near-spherical phosphor, and a dense and homogeneous phosphor screen. Transparent spherical particles represented by a composition formula of Ln ₂ O ₃ : R (Ln is at least one of La, Gd, Lu, Y, and R is at least one of the lanthanide group) that is 0.0 to 1.5; A phosphor containing ultrafine particles with a particle size of 0.2 μm or less containing the same constituent elements and adhering to the surface of transparent spherical particles in a proportion of 0.001 to 0.5% by weight is proposed. In order to produce this phosphor by supplying the raw material phosphor together with the carrier gas into the thermal plasma, and after the treatment for a short period of time, the concentration of the activator is different from that of the obtained phosphor. It teaches that it is desirable to use a non-granulated raw phosphor having a primary particle size of 2-20 μm.

  It also teaches that even when the secondary particle size of the raw material phosphor is too large, the particle size of the obtained phosphor becomes large and is not suitable for practical use. Here, the secondary particles refer to particles in which primary particles that are single particles are aggregated.

Japanese Patent No. 3329598 (Japanese Patent Laid-Open No. 8-134443) JP 2004-206929 A JP 2003-197147 A

  An object of the present invention is to provide a discharge lamp having a phosphor layer, high brightness, and high light transmittance.

According to one aspect of the present invention,
A discharge tube;
An ultraviolet light source provided in the discharge tube;
The phosphor layer applied to the inner wall of the discharge tube, and as a blue phosphor, the ratio of the diameter of secondary particles, which are a collection of primary particles, to the primary particle diameter is in the range of 1.7 to 2.0. A phosphor layer containing BaMgAl ₁₀ O ₁₇ : Eu ⁺² ;
A discharge lamp is provided.

  By selecting the ratio of the secondary particle diameter to the primary particle diameter within the range of 1.7 to 2.0, high luminance and high transmittance can be obtained.

  FIG. 1A is a cross-sectional view schematically showing a configuration example of a cold cathode discharge lamp. A phosphor coating 12 is formed on the inner surface of the glass tube 11, and cylindrical and bottomed metal electrodes 13 are disposed on both ends of the glass tube 11. The ends of the lead-in wire 14 hermetically sealed at both ends of the glass tube 11 are connected to the metal electrode 13. A metal 16 that adsorbs the impurity gas is provided inside the metal electrode 13 as necessary. Inside the glass tube 11, a discharge medium such as mercury and Ne—Ar mixed gas is sealed.

  FIG. 1B schematically shows the configuration of the phosphor coating 12. Red (R), green (G), and blue (B) phosphor particles 21 are distributed. Each phosphor is subjected to pulverization (dispersion) processing by a pulverizer, a homogenizer, a ball mixer, or the like in order to turn a sintered body, which is a glass-like lump, into a powdery phosphor during manufacture at the phosphor manufacturer. By this dispersion treatment, phosphor particles in a moderately dispersed state are obtained. At this time, the surface structure of the BAM particles is easily broken, and the luminous efficiency is lowered due to physical damage. For this reason, phosphor manufacturers deliver BAM in a state of strong aggregation to some extent without being completely dispersed. A user mixes each phosphor with a binder to form a slurry, which is applied to a glass tube. The inventor performed the mixing process by rotating the container on a turntable without using a ball in the mixing process. In this mixing process, it is considered that the phosphor particles are not physically damaged. After applying the slurry, a treatment such as baking is performed as necessary to form a phosphor film in which phosphor particles are distributed. The binder disappears and there is no binder in the finished lamp.

  During operation, ultraviolet (UV) light 23 generated by discharge is incident on the phosphor particles 21. The phosphor 21 excited by the incident UV light 23 emits fluorescence 24. The fluorescence 24 passes through the glass tube 11 and is led out. The phosphor particles 21 have a property of being easily aggregated. Aggregation makes it difficult to transmit excitation light and light emission, and thus it is considered preferable that they are dispersedly arranged in the transparent binder material 22. It is considered that the particle size distribution of the phosphor particles 21 affects the dispersed arrangement of the phosphor particles 21. The inventor considered that the secondary particle size relative to the primary particle size of the phosphor particles affects the external efficiency.

  The primary particle diameter D1, which is the diameter of a single particle, can be measured by an air permeation method (for example, the Fischer diameter determined by the Brane method in which the pressure is also changed, in particular, the Fischer method using a measuring instrument manufactured by Fischer). The secondary particle diameter D2, which is the diameter of the aggregate obtained by aggregating the primary particles, can be measured as a D50 value by a laser method. The smaller the ratio R = D2 / D1 of the secondary particle diameter D2 to the primary particle diameter D1, the higher the dispersion state. The larger the ratio R, the stronger the aggregation. In general, it is known that the phosphor is physically damaged by the dispersion treatment, the fluorescence intensity decreases, and the fluorescence intensity increases as the primary particle diameter increases.

The standard product r of the blue phosphor BAM has a primary particle diameter of 2.8 μm and a secondary particle diameter of 6.0 μm, and the ratio of the secondary particle diameter to the primary particle diameter is R = 6.0 / 2.8 = 2. 1 (2.14). The primary particle size is a value measured by an air permeation method at the manufacturer, and the secondary particle size is a value measured by the applicant's laser method. From the measurement accuracy, the effective number is 2 digits. Samples different from the standard product in secondary particle size / primary particle size (= R) were prepared. A BAM sample s1 having a primary particle diameter D1 of 2.8 μm, the same as the standard product, a secondary particle diameter D2 of 5.7 μm, and a ratio R = D2 / D1 = 2.0 (2.03) was prepared. The secondary particle size is a value measured by the applicant's laser method. The green phosphor LaPO ₄ : Ce, Tb, the red phosphor Y ₂ O ₃ : Eu were the same, and a lamp using the standard product BAMr as the blue phosphor and a lamp using the sample s1 as the blue phosphor were prepared. .

  FIG. 2A shows the output luminance when the phosphor film thickness is changed for the lamp using the sample s1 and the lamp using the standard product r. The lamp using the sample s1 showed higher luminance than the lamp using the standard product r in the film thickness range of about 20 μm to about 37 μm, and showed a maximum luminance improvement of about 4.5%. When the primary particle size is the same, the luminance can be improved by about 4.5% by reducing the secondary particle size from 2.1 to 2.0.

  Furthermore, a BAM sample s2 having a primary particle diameter D1 of 3.7 μm, a secondary particle diameter D2 of 7.0 μm, and a ratio R = D2 / D1 = 1.9 (1.89) was prepared. The primary particle size is a value measured by the air permeation method at the manufacturer, and the secondary particle size is a value measured by the applicant's laser method. Although the primary particle diameter was different, a lamp using the sample s2 was also prepared and the luminance was measured.

  FIG. 2B is a graph showing the luminance of the lamp using the sample s2 compared with the luminance of the lamp using the standard product r. The lamp using the sample s2 showed higher brightness than the lamp using the standard product r in the region having a film thickness of about 19 μm to about 36 μm or more. The improvement in brightness is obvious, but the primary particle size is different and cannot simply be compared.

Various BAM samples were prepared by different manufacturers.

The primary particle size is a value measured by an air permeation method at the manufacturer, and the secondary particle size is a value measured by the applicant's laser method.

FIG. 3 shows the results of measuring the luminance of the monochromatic phosphor coating film after forming a monochromatic phosphor coating layer with these BAM samples. The luminance of the standard product r11 was 16.8 μm and the maximum value was 137 cd / m ² . When the samples s11, s12, and s13 having a primary particle diameter of about 3 μm equivalent to the standard product r11 are seen, the maximum luminance is 134 cd / m ^{2 with} a film thickness of 10.7 μm and the sample s12 (R = 1) in the sample s11 (R = 1.4) .5) was 136 cd / m ² at a film thickness of 14.1 μm, and Sample s13 (R = 3.3) was 132 cd / m ² at a film thickness of 24.9 μm. From the viewpoint of luminance, the ratios R of 1.4, 1.5 and 3.3 are considered not so good.

  Samples s21, s22, and s23 having a primary particle size of about 4 μm seem to exhibit a maximum brightness higher than samples s11, s12, and s13 having a primary particle size of about 3 μm as a whole. This is consistent with the general knowledge that the larger the primary particle size, the higher the luminance.

More specifically, sample s21 (ratio R = 1.3) has a film thickness of 10.8 μm and a luminance of 141 cd / m ² , and sample s22 (ratio R = 1.7) has a film thickness of 15.8 μm and a luminance of 144 cd / m 2. ² and a brightness exceeding the standard product r11. In sample s23 (R = 3.8), the film thickness was 36.8 μm and the luminance was 136 cd / m ² . From the brightness point of view, the ratio R = 1.3, 1.7 is considered to give good results. The ratio R = 3.8 is considered not very good.

  FIG. 4 shows the results of measuring the transmittance of these phosphor coating films. If the transmittance is low, the light emitted from the phosphor cannot be sufficiently extracted outside. The horizontal axis indicates the film thickness in units of μm, and the vertical axis indicates the light transmittance at a wavelength of 550 nm almost in the center of the visible region in unit%. The code | symbol attached | subjected to each curve is the code | symbol of the same sample as FIG. It is a general characteristic of the transmittance of an absorbing film that the transmittance decreases exponentially as the film thickness increases. The transmittance higher than the characteristic of the standard product r11 is shown by s23 (ratio R = 3.8), s13 (ratio R = 3.3), and s22 (ratio R = 1.7) in order from the high transmittance. is there. The transmittance is lower than the standard product in s12 (ratio R = 1.5), s21 (ratio R = 1.3), and s11 (ratio R = 1.4). Regarding the samples s11 to s23, although there is some disturbance, the ratio R = D2 / D1 of the secondary particle diameter to the primary particle diameter decreases as a whole and the transmittance decreases. The transmittance of the standard product r11 (ratio R = 2.1) is comparable to that of the sample s12 (ratio R = 1.5). From the viewpoint of transmittance, it is desirable that the ratio R = D2 / D1 of the secondary particle diameter to the primary particle diameter is 1.7 or more.

  Summing up these results, the ratio R = D2 / D1 of the secondary particle diameter of the BAM phosphor to the primary particle diameter is 1.7 to 2.0 from the viewpoint of the luminance obtained from the light emission of the phosphor and the external extraction efficiency. It is preferable to set in the range.

  As mentioned above, although this invention was demonstrated along the Example, this invention is not limited to these. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

1A and 1B are a cross-sectional view schematically showing a configuration of a cold cathode discharge lamp, and a partially enlarged view thereof. In FIGS. 2A and 2B, only the blue phosphor BAM, the ratio R of the secondary particle diameter to the primary particle diameter is made smaller than that of the standard product r, and the samples s1, s2 using the same phosphor for the green phosphor and the red phosphor It is a graph which shows the brightness | luminance with respect to the film thickness of contrast with the brightness | luminance of the standard goods r. FIG. 3 is a graph showing the change in luminance with respect to the film thickness of the standard product r11, samples s11 to s13, and s21 to s23 only for the blue phosphor. FIG. 4 is a graph showing a change in transmittance with respect to the film thickness of the standard product r11, samples s11 to s13, and s21 to s23 only for the blue phosphor.

Explanation of symbols

11 Glass tube 12 Phosphor coating 13 Metal electrode 14 Lead wire 16 Metal material r Standard product s Sample

Claims (2)

A discharge tube;
An ultraviolet light source provided in the discharge tube;
The phosphor layer applied to the inner wall of the discharge tube, and as a blue phosphor, the ratio of the diameter of secondary particles, which are a collection of primary particles, to the primary particle diameter is in the range of 1.7 to 2.0. A phosphor layer containing divalent europium activated barium aluminate / magnesium BaMgAl ₁₀ O ₁₇ : Eu ⁺² ;
Having a discharge lamp. The phosphor layer further contains, as a green phosphor, a cerium / terbium-activated lanthanum phosphate phosphor LaPO ₄ : Ce, Tb, and a red phosphor as a europium-activated yttrium oxide phosphor Y ₂ O ₃ : Eu. The discharge lamp according to claim 1.

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