CN113551797A - Method for testing two-dimensional temperature distribution of LED fluorescent powder surface - Google Patents
Method for testing two-dimensional temperature distribution of LED fluorescent powder surface Download PDFInfo
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Abstract
A method for testing two-dimensional temperature distribution of the surface of LED fluorescent powder comprises the following steps: 1) placing the fluorescent powder coating type LED on a temperature control table, controlling the temperature of the temperature control table to take at least 3 temperature points, and simultaneously electrifying a sample to light the sample; 2) the test sample is focused by a high-power microscope, the spectrum of each pixel point is collected by combining an optical fiber spectrometer and the high-power microscope, and the visible light wavelength [ lambda ] of each pixel point is calculated1,λ2]Obtaining the normalized light power of each pixel point by the normalized fluorescent powder spectrum in the range; 3) respectively performing least square linear processing on each pixel point position on a plurality of spectral images under a plurality of groups of temperatures to obtain a calibration coefficient and an intercept; 4) lighting the sample at a rated current, and repeating the step 2), and obtaining a surface temperature matrix of the fluorescent powder according to the normalized optical power and the slope; and finally, carrying out noise reduction treatment and abnormal point repairing to finally obtain accurate two-dimensional temperature distribution on the surface of the fluorescent powder.
Description
Technical Field
The invention relates to the field of photoelectric illumination and display, in particular to a method for testing two-dimensional temperature distribution of the surface of LED fluorescent powder.
Background
Fluorescent materials are widely used in the field of semiconductor illumination and display. At present, fluorescent materials mainly comprise rare earth fluorescent powder, quantum dot fluorescent powder and the like. The performance of the phosphor is related to the stability and reliability of the Light Emitting Device (LED). Among the properties of phosphors, thermal performance is a very critical property, and temperature is an important index for reflecting the thermal performance. The increase in temperature not only causes a decrease in the luminescent efficiency (i.e., thermal quenching) of the phosphor, but also decreases the lifetime and reliability of the light-emitting LED. Therefore, accurately characterizing the temperature of the phosphor and the two-dimensional or even multidimensional spatial distribution thereof is the key to reflect the performance of the device and guide the improvement of the device performance.
The methods currently available for characterizing the surface temperature of phosphors are mainly micro thermocouple methods and infrared thermography. The micro thermocouple obtains temperature by surface contact with fluorescent powder or a semiconductor chip, which is a contact method, but is easy to damage the device. The infrared thermal imaging method obtains the thermal field distribution of the surface of the fluorescent powder by calibrating the emissivity of the material. However, the resolution of the infrared thermography method is not high enough, and only the two-dimensional temperature distribution of the surface of a sample with a relatively flat surface can be tested. For the LED coated by fluorescent powder, the shape is irregular, the surface is covered by a curved lens, and the accuracy of a test result is influenced by adopting an infrared thermal imaging method. In addition, infrared thermography also relies on the determination of the emissivity of the material. Except for an infrared thermal imaging method, at present, no reliable method is available for easily and accurately acquiring the two-dimensional temperature distribution of the surface of the fluorescent powder, namely, a non-contact test method with high resolution for the two-dimensional temperature distribution of the surface of the fluorescent powder is absent at present.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a method for testing two-dimensional temperature distribution of the surface of LED fluorescent powder, which has the characteristics of high resolution and non-contact.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for testing two-dimensional temperature distribution of the surface of LED fluorescent powder comprises the following steps:
1) placing a fluorescent powder coating type LED on a temperature control table, controlling the temperature of the temperature control table to at least take 3 temperature points (enough fitting data is fully ensured), and simultaneously, energizing a sample with a small current to light, wherein the small current is 1% -3% of the rated current of the LED, so that the self-heating effect is avoided;
2) focusing a test sample by a high-power microscope, collecting the spectrum of each pixel point on the surface of the fluorescent powder or the fluorescent powder silica gel mixture by combining a fiber spectrometer and the high-power microscope, and calculating the visible light wavelength [ lambda ] of each pixel point1,λ2]Normalizing the fluorescent powder spectrum in the range, and acquiring the area S (m, n) of the fluorescent powder spectrum of each pixel point in the range, namely the normalized light power of each pixel point;
3) the method comprises the steps of respectively carrying out least square linear processing on a plurality of spectral images at a plurality of groups of temperatures at each pixel point position to obtain calibration coefficients, namely slope K (m, n) and intercept b (m, n);
4) illuminating a sample by using LED rated current, repeating the step 2), calculating the surface temperature of the fluorescent powder of each pixel point to be T (m, n), and obtaining a normalized light power matrix and a slope matrix according to the step 3) according to the formula (1), wherein the corresponding data of the pixel points in the two-dimensional space are combined together to form a fluorescent powder surface two-dimensional temperature distribution matrix;
T(m,n)＝[S(m,n)-b(m,n)]/K(m,n) (1)
5) in the testing process, due to the reasons of uneven distribution of fluorescent powder particles, light scattering and absorption and the like, the linearity R of not all pixel points is caused2Are phenomena above 0.9 and are commonly referred to as outliers. In order to avoid temperature errors caused by abnormal points, obvious abnormal points are found in the data processing process, and then the algorithm is used for noise reduction processing to reduce errors caused by the abnormal points. The invention adopts a convolution filtering algorithm to carry out noise reduction processing and abnormal point restoration, and finallyAnd obtaining accurate two-dimensional temperature distribution of the surface of the fluorescent powder.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the method mainly obtains a spectral image with high resolution through a high-power microscope and an optical spectrometer, respectively calibrates each pixel point on the spectral two-dimensional image point by utilizing the linear correlation characteristic of the normalized spectral power and the temperature of the fluorescent powder in a certain visible wavelength range of each pixel point on the spectral two-dimensional image to obtain a correlation linear coefficient matrix, further calculates to obtain a fluorescent powder surface two-dimensional temperature matrix under the normal working state of the LED, and adopts a proper algorithm such as convolution filtering to perform noise reduction treatment and abnormal point restoration to finally obtain accurate fluorescent powder surface two-dimensional temperature distribution.
The invention realizes the high-resolution and high-precision test of the two-dimensional temperature distribution of the surface of the LED fluorescent powder, and makes up the defects of the traditional thermal imaging method for testing the two-dimensional temperature distribution of the surface of the fluorescent powder coated LED, such as low resolution and the like.
The method can be suitable for two-dimensional temperature measurement with high resolution of white light LEDs of any fluorescent powder type, such as LED devices prepared by quantum dots such as borate, silicate, nitride, fluoride, CdSe and the like, and is also partially suitable for light emitting devices such as LED chips and the like.
Drawings
FIG. 1 is a linear relationship between a single-point pixel temperature T and an area S;
FIG. 2 shows the two-dimensional temperature distribution of the surface of the phosphor of the LED sample at 300 mA;
FIG. 3 is a surface temperature distribution diagram of the phosphor under hyperspectral conditions;
FIG. 4 is a temperature comparison of L01 in FIG. 3 of the method of the present invention and infrared thermal imaging;
fig. 5 is a temperature comparison of L02 in fig. 3 of the inventive method and infrared thermal imaging.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects of the present invention clearer and clearer, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.
The device adopted by the method comprises a temperature control table, a power supply, a high power microscope, a high spectrum camera and high spectrum software.
The invention discloses a method for testing two-dimensional temperature distribution of the surface of LED fluorescent powder, which comprises the following steps:
(1) the method comprises the steps of adopting a fluorescent powder LED sample with an SMD structure, wherein the fluorescent powder LED sample comprises CaAlSiN3: Eu2+ with a certain concentration ratio, placing the fluorescent powder LED sample on a temperature control table, and setting the temperature of the temperature control table to be 30 ℃, 45 ℃ and 60 ℃. The power supply supplies a small current of 10mA to the sample to light (the sample is rated with a large current of 300 mA).
(2) The method comprises the steps of focusing a sample through a high-power microscope, collecting spectrum information of each pixel point on the surface of fluorescent powder through a hyperspectral camera, extracting fluorescent powder spectrum in a certain wavelength range through hyperspectral software, carrying out normalization processing, obtaining the area of the fluorescent powder spectrum of each pixel point in the range, and calculating normalized light power S (m, n).
(3) And respectively carrying out linear processing on each pixel point on the three spectral images of the three groups of temperatures by adopting a linear least square method to obtain a calibration coefficient, namely slope K (m, n) and intercept b (m, n), of each pixel point. The linearity of a certain pixel point is as shown in figure 1.
(4) And (5) energizing the power supply with a large current of 300mA to lighten the sample, and repeating the step (2). After the anomaly point processing, the two-dimensional temperature of the surface of the phosphor can be obtained by calculation, namely the two-dimensional temperature distribution of the surface of the phosphor, as shown in fig. 2.
The non-zero element (namely the correlation coefficient R) in the LED surface temperature distribution matrix at each current is obtained through calculation2>Pixel point of 0.9) average value (T)m) And the measured average temperature result (T) of the micro thermocouplet) For comparison, the results are shown in Table 1. Wherein D represents a temperature deviation value, i.e., D ═ Tm-TtL. The comparison result shows that the deviation value between the measured average temperature of the LED surface and the result measured by the thermocouple temperature measuring method is within 5 ℃, which shows that the result of the temperature measuring method is accurate and reliable.
TABLE 1 comparison of LED phosphor surface temperature test results
| Working current (mA) | Method Tm(℃) | Thermocouple Tt(℃) | D＝|Tm-Tt|(℃) |
| 100 | 36.8 | 35.9 | 0.9 |
| 200 | 47.5 | 48.1 | 0.6 |
| 300 | 56.4 | 57.2 | 0.8 |
| 400 | 70.5 | 66.7 | 3.8 |
| 500 | 74.5 | 75.5 | 1.0 |
Fig. 4 and 5 are comparisons of infrared thermal imaging results with the present invention. Two straight lines L01 (horizontal) and L02 (vertical) are respectively taken on FIG. 3 for one-dimensional temperature distribution comparison. The result of the invention is basically consistent with the result of the infrared thermal imaging, which shows that the result of the temperature measurement method of the invention is accurate and reliable, and the method can be popularized to the multi-dimensional fluorescent powder temperature distribution test.
The method can be suitable for two-dimensional temperature measurement with high resolution of white light LEDs of any fluorescent powder type, such as LED devices prepared by quantum dots such as borate, silicate, nitride, fluoride, CdSe and the like, and is also partially suitable for light emitting devices such as LED chips and the like.
Claims (2)
1. A method for testing two-dimensional temperature distribution of the surface of LED fluorescent powder is characterized by comprising the following steps:
1) placing the fluorescent powder coating type LED on a temperature control table, controlling the temperature of the temperature control table to take at least 3 temperature points, and simultaneously, energizing a sample with small current to light so as to avoid the self-heating effect;
2) focusing a test sample by a high-power microscope, collecting the spectrum of each pixel point on the surface of the fluorescent powder or the fluorescent powder silica gel mixture by combining a fiber spectrometer and the high-power microscope, and calculating the visible light wavelength [ lambda ] of each pixel point1,λ2]Obtaining the normalized light power of each pixel point by the normalized fluorescent powder spectrum in the range;
3) the method comprises the steps of respectively carrying out least square linear processing on a plurality of spectral images at a plurality of groups of temperatures at each pixel point position to obtain calibration coefficients, namely a slope and an intercept;
4) illuminating the sample by using the LED rated current, repeating the step 2), and obtaining a fluorescent powder surface temperature matrix by using a linear formula according to the normalized optical power matrix and the slope matrix obtained in the step 3); and finally, performing noise reduction treatment and abnormal point restoration by adopting a convolution filtering algorithm, and finally obtaining accurate two-dimensional temperature distribution of the surface of the fluorescent powder.
2. The method for testing the two-dimensional temperature distribution of the surface of the LED fluorescent powder according to claim 1, which is characterized by comprising the following steps: the small current is 1% -3% of the rated current of the LED.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114047224A (en) * | 2021-11-24 | 2022-02-15 | 江苏省特种设备安全监督检验研究院 | Method for testing junction temperature and temperature distribution of gallium nitride-based blue light LED |
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| CN110057466A (en) * | 2019-05-05 | 2019-07-26 | 厦门大学 | A kind of surface temperature measurement method based on LED fluorescence emission spectrum |
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| US4885633A (en) * | 1988-06-13 | 1989-12-05 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Quantitative surface temperature measurement using two-color thermographic phosphors and video equipment |
| US20120264236A1 (en) * | 2011-04-15 | 2012-10-18 | Chang Gung University | Fluorescent powder applying device and method capable of detecting instantly color temperature of white light in a manufacturing process |
| CN109060164A (en) * | 2018-09-25 | 2018-12-21 | 厦门大学 | Luminescent device temperature distribution measuring apparatus and measurement method based on micro- EO-1 hyperion |
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Application publication date: 20211026 |