Phosphors are the basic materials used in LED packaging, and their characteristics determine the color characteristics of LEDs. Phosphors with similar specifications from different manufacturers may differ in the following aspects due to their different manufacturing methods and additives:
1, phosphor morphology
The best phosphor morphology is the perfect crystal form of this material. Taking YAG powder as an example, the most efficient phosphor is a spherical phosphor particle with an unbroken surface.
OK sample topography
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2, the particle size distribution of the phosphor
The particle size distribution of the phosphor is usually expressed by the width factor S, S = (D90 - D10) / D50. In the case where the center particle diameter D50 is close, the smaller the S value, the more uniform the phosphor distribution. When the reaction is on the package, the BIN rate is higher.
3. Aging of phosphors
The aging properties of phosphors are mainly determined by factors such as crystallinity, surface morphology and particle size distribution. A phosphor having a good crystal surface morphology is particularly excellent in aging properties. Since the smaller particle phosphor has a larger specific surface area, its aging performance is worse than that of a larger particle. Therefore, the phosphors with a concentrated particle size distribution are more consistent because each of the phosphor particles tends to be uniform.
In summary, the same color zone and the same color temperature are obtained, and the same chip and the same manufacturer phosphor are used to package the light source with the same chip and different manufacturers of phosphor powder. The light source obtained by the former package is more concentrated in the color region and color temperature of the light. The consistency is better. Although color LEDs of different colors such as red, yellow, green, blue, and purple can be prepared without using phosphors, since the luminous efficiencies of these different color LEDs are very different, after using phosphors, certain bands of LEDs can be utilized. The advantage of high luminous efficiency is to prepare light sources of other wavelength bands, and different color temperature coordinate points can also be controlled to form characteristic light color points.
Common red phosphors include sulfide series, silicate series, and nitride series. Since the sulfide series phosphors are unstable and cause vulcanization of the silver-plated layer of the LED holder, they have been used less frequently. Therefore, the stability of the silicate and nitride series red phosphors is mainly analyzed below.
Red phosphor corrosion resistance test
Sample: silicate red phosphor packaged in warm white 3528 lamp beads, color temperature 2700K;
A number of warm white 5730 lamp beads are packaged in a nitride red phosphor, with a color temperature of 3000K.Test 1: silicate series inorganic acid resistance test
The results showed that when the complete lamp bead was immersed, the color of the lamp bead did not change with the naked eye, but the fluorescent adhesive peeled off and the fluorescent gel changed color.
Test 2: Silicate series inorganic acid resistance test
Both the complete lamp bead and the stripped lamp are discolored, in order to verify whether the degree of discoloration will occur in the acetic acid environment, the soaking time of the device will be intact.
The above experiments show that the acidic environment of hydrochloric acid and acetic acid will cause the decomposition of the silicate red phosphor of the 3528 device, but the complete device will only react in the environment of acetic acid.
Test 3: Comparative experiment of different phosphors resistant to organic acids
The silicate series warm white 3528 lamp beads and the nitride series warm white 5730 lamp beads were simultaneously placed in a vinegar Solution and immersed for 24 hours at room temperature to compare the photoelectric parameters and appearance of the two devices. The results are as follows:
The results of the photoelectric measurement parameters are as follows:
Analyze the spectral changes as follows:
The test results show that the lamp beads of 3528 silicate type red phosphors decompose the phosphor in the environment of acetic acid, the color temperature of the lamp beads increases, and the main wavelength of the spectrum shifts blue. The lamp of the 5730 nitride-type red phosphor did not change significantly in the acetic acid environment.
Analysis conclusion: The red phosphor of the silicate series can be decomposed in an acidic environment such as acetic acid, resulting in an increase in the color temperature of the lamp bead. Therefore, when selecting packaging materials, it is necessary to select suitable raw materials in combination with the application of the product and the environmental conditions that may be encountered.
With the price war competition incentives in the general lighting market, the production of special light color points will become a new selling point of the product. This requires close cooperation between the packaging company and the phosphor manufacturer. It poses new challenges to the technology and R&D capabilities of phosphor companies. Domestic phosphor companies will also form a reshuffle, and companies with no technical know-how and determination to sustain development will be eliminated.
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