I. Introduction
In recent years, the development of GaN-based white light-emitting diodes (LEDs) has received great attention [1]. Because of its high efficiency, energy saving, environmental protection, small size and long life, it is known as the fourth generation of illumination light after incandescent lamps, fluorescent lamps and gas discharge lamps [2]. In particular, white LEDs have made great progress in terms of luminous efficiency, service life, and brightness.
The preparation method of white LED is mainly realized by combining blue LED chip with YAG phosphor (ie, light conversion method) [3]. Therefore, it is of great significance to develop YAG phosphors that can be excited under blue light (440-470 nm) and have high conversion efficiency, low attenuation, and optimized LED white package concentration. It has also become the focus of current solid-state lighting research.
At present, SMD-type package products use medium or coarser-sized phosphor products for the production of white LEDs in order to achieve the highest brightness in the packaging process, but this will cause the color concentration of white light package to decrease and target. Several low-rate problems have led to a large inventory of foreign goods in packaging manufacturers, which has increased production costs.
In response to this problem, Bo Rui Optoelectronics has recently developed a new YH series product, which has a finer particle size and a narrower particle size distribution coefficient while maintaining high light efficiency, which is suitable for the application manufacturers. The dual requirements of light efficiency and concentration are of great importance.
Based on the comparison of the basic performance of YH series phosphors and similar products on the market, this paper comprehensively compares the initial light efficiency, heat quenching performance and light decay performance of YH series phosphors with similar products on the market. On this basis, through the mass production packaging test, the light color concentration of the phosphor is further studied, which provides a useful support for optimizing the mass production technology of white LED.
Two test materials and methods
2.1 Basic performance comparison test of phosphor
In this paper, three kinds of phosphors were selected for comparative analysis and application performance test. The principle of sample selection includes two aspects: the emission wavelength is consistent and the relative brightness is equivalent. According to this principle, a certain type of imported products and a domestic manufacturer's phosphor powder products with the band and brightness of Bo Rui's homemade YH302 products are selected, which are numbered sample-1, sample-2 and sample-3 respectively.
2.1.1 Comparison of light efficiency indicators
Table 1 lists the basic optical performance indicators of the three types of phosphors. From the data in the table, it can be seen that the main wavelength, half-width and relative brightness of the three phosphor samples are basically equal.
Table 1 Basic performance indicators of phosphors
2.1.2 Microtopography
Figure 1 is a scanning electron micrograph of the three phosphors, which can reflect that the three phosphor particles are spherical and have a good dispersion state. In contrast, the sample-1 phosphor sample corresponding to YH302 has a smaller particle size. .
Figure 1 Phosphor microscopic morphology
2.1.3 Particle size and distribution
Figure 2 shows the particle size distribution curves of the three phosphors. Comparing the center particle size and distribution width of the three phosphors, YH302 has the smallest particle size and a center particle size of 10.47 μm. The central particle size of the phosphors is about 13~14μm. At the same time, the particle size distribution coefficient of sample-1 is 0,688, which is significantly smaller than the data of the other two phosphors. Table 2 lists the particle size data for the three phosphors.
Table 2 Particle size and particle size distribution of phosphor
Figure 2 Particle size distribution of three phosphors
2.2 Initial light effect comparison test
The blue LED chip used in the packaging experiment is a product of Taiwan Jingyuan Optoelectronics Co., Ltd. The chip size is 10*23mil, the main wave is 455~457.5 nm, and the brightness is 26-28mw. It is packaged with a bracket of SMD type 3528. The light source illuminates the test current of 20 mA, and the number of test beads of each phosphor is 20, and the light conversion efficiency of the phosphor is evaluated by comparing the initial luminous flux and the light effect of the three phosphors. The test instrument adopts Hangzhou Zhongwei Optoelectronic LED manual light separation and color separation system (model is ZWL-3901).
2.3 Light decay performance comparison test
The prepared lamp beads were aged at a current of 30 mA, and 10 beads were randomly taken, and the data was tested every 500 hours, and the total aging time was 3000 hours. The aging instrument adopts Hangzhou Zhongwei Optoelectronic LED low power aging instrument (model ZWL-150).
2.4 Light color concentration measurement comparison test
Firstly, the powder-to-gel ratio of the three phosphors is basically determined through a small test to ensure that the three phosphors achieve the same color coordinate range. Then import the automatic packaging production line for mass production packaging. The chip still uses Taiwan's wafer photoelectric products, the size is 10 * 23mil, the main wave is 455 ~ 457.5 nm, the brightness is 26-28mw. The bracket is SMD3528. The dispenser uses Musashi MPP-1, the solid crystal machine adopts AMS manufacturer automatic crystallizer (model AD820), and the wire bonding machine adopts AMS manufacturer's automatic wire bonding machine (model IHAWK) to illuminate the test current 20mA, each Phosphors were used to make 50,000 lamp beads respectively. Finally, the fully automated SMD high-speed spectroscopic system (model ZWL-X7ZH) of Hangzhou Zhongwei Optoelectronics was used for spectroscopic testing, and the drop rate was compared.