Brief introduction to the luminescence mechanism of LED light source

Now, as the supply chain of the LED industry matures, the entry threshold is low, and a large number of small enterprises have poured in, resulting in an oversupply of the LED industry. In addition, due to the low capacity utilization rate of enterprises, they are definitely not able to compete with the big brands in the market. Philips , Osram and GE, these big companies have actively occupied the main LED lighting market through vertical integration or strategic alliance layout. Whether it is the gross profit margin that has been exploited layer by layer or the strong enemies around, small factories cannot escape the huge market pressure.

China has rich non-ferrous metal resources, and gallium and indium reserves are rich, accounting for 70%-80% of the world's reserves, which gives China a resource advantage in developing the semiconductor lighting industry. By 2010, the output value of the entire Chinese LED industry will exceed 150 billion yuan. As early as 2002, Japan spent 5 billion yen to promote white light lighting, and the fiscal budget for the entire plan was 6 billion yen.

With the rapid growth of LED penetration, a price war will come in 2010. Because LED is different from the traditional sales model of separate lamps and light sources, under this pressure, some companies cannot balance product quality and price competitiveness and may fall into the fate of mergers and acquisitions or being eliminated.

2010年5月7日-12日，河南省照明学会组织照明专家及企业家一行赴日考察了日本照明现状，发现日本的 LED照明 现状并不尽如人意。

近年来，在照明领域最引人关注的事 件是半导体照明的兴起。20世纪90年代中期，日本 日亚 化学公司的Nakamura等人经过不懈努力，突破了制造 蓝光 发光二极管（LED）的关键技术，并由此开发出以荧光材料覆盖 蓝光LED 产生白光光源的技术。

led是Light Emi ttingDiode(发光二极管)的缩写。发光二极管是一种新型固态 冷光源 ，LED的最显著特点是使用寿命长， 光电 转换效能高、抗震性能好、使用方便等优点，在照明系统中的应用越来越广泛。在同样 照度 下， LED灯 的 电能 消耗和寿命比白炽灯和日光灯都有明显的优势。

The development of various white light emitting methods and the development of a new generation of phosphors have greatly improved the luminous efficiency of LEDs . Currently, the industrialized products have increased from 45lm/w to 100lm/w (by 2009, Cree 's cold white light efficiency at 350mA has exceeded 100lm/W, and warm white light has exceeded 75lm/W). The research level is 160lm/w, and the target highest level is expected to reach more than 200lm/w. The life span is 40,000 hours to 80,000 hours.

1. The luminous mechanism of LED light source

The principle of light emission is quite different from that of incandescent lamps or gas discharge lamps. The spontaneous light emission of LEDs is caused by the recombination of electrons and holes.

LED is composed of a P layer formed by a P-type semiconductor , an N layer formed by an N-type semiconductor, and an active layer in the middle composed of a double heterojunction. The active layer is the light-emitting area. Electrons are injected into the PN junction using an external power source . Under the action of forward bias, the electrons in the N region will diffuse in the positive direction and enter the active layer, and the holes in the P region will also diffuse in the negative direction and enter the active layer. When the electrons and holes recombine, spontaneous radiation light will be generated, as shown in Figure 1. Due to the different materials used in LED, the energy levels occupied by electrons and holes in its diode are also different. The difference in energy levels affects the energy of the photons after combination and produces different wavelengths of light, that is, different colors of light, such as red, orange, yellow, green, blue or invisible light.

2. White LED

The emergence of white light LEDs has provided white light LED semiconductor lighting for more and more indoor and outdoor lighting projects. The luminous efficiency of white light LEDs has made great progress, and white light LEDs have even begun to challenge the status of traditional light sources.

There are two main ways to obtain white light LEDs: the first is to obtain white light through phosphor conversion; the second is to package LED chips of different colors together and mix multiple chips to emit white light. For the above two methods, according to the number of primary color light sources involved in the mixed white light, they can be divided into a two-primary color system and a multi-primary color system.

Phosphor-converted white LED

(1) Two-color phosphor conversion white light LED

The two-color white LED is made of blue LED chips and YAG phosphors. The blue chip generally used is InGaN chip, and AlInGaN chip can also be used. The advantages of the blue chip LED with YAG phosphor method are: simple structure, low cost, and relatively simple manufacturing process. However, this method also has several disadvantages, such as the blue LED efficiency is not high enough, resulting in low efficiency of white LED; the phosphor itself has energy loss; the phosphor and packaging materials age over time, resulting in color temperature drift and shortened life, etc.

(2) Three-color phosphor conversion LED

Tri-color phosphor LEDs can effectively improve the color rendering of LEDs while maintaining high luminous efficiency. The most common method to obtain tri-color white light LEDs is to use ultraviolet LEDs to excite a group of tri-color phosphors that can be effectively excited by ultraviolet radiation .

Compared with the method of obtaining white light by using blue LED + YAG phosphor, the method of using ultraviolet LED + three-primary color phosphor is easier to obtain white light with consistent color, because the light color of LED is only determined by the ratio of phosphor. In addition, this type of white light LED has high color rendering, adjustable light color and color temperature, and the use of high conversion efficiency phosphor can improve the light efficiency of LED.

However, the method of UV LED + three-primary color phosphor still has certain defects, such as low efficiency of phosphor in converting UV radiation; difficulty in mixing powders; easy aging of packaging materials under UV light and short life span, etc. Moreover, the red and green phosphors with high conversion efficiency are mostly sulfide systems, which have poor luminous stability and large light decay.