Nakamura Nichia company for the first time, such as use blue LED with yellow phosphor powder into the synthesis of white LED. He the yellow phosphor powder for Y3Al5O12: Ce3 + (hereinafter referred to as YAG: Ce3 +), this kind of fluorescent powder in the 470 nm range near a strong broadband absorption, and then inspire 540 nm nearby yellow, LED itself emission blue light and fluorescent powder excitation of yellow white formed by the union. Later, YAG: Ce3 + because of its transformation efficiency, high thermal stability and stimulate band width and so on superiority, has become a mainstream technology of white light.
To one: the development of new fluorescent powder
YAG: Ce3 + is the earliest is widely used in the white led technology a phosphor powder, but due to its emission spectrum of less red component, it is difficult to obtain high color rendering index and low colour temperature white light led; On the other hand, the continuous development of the semiconductor lighting push people to develop higher conversion efficiency of the phosphor powder. At the early stage, through the YAG: Ce3 + to add (Ca, Sr) S: Eu2 +, Ca, Sr) Ga2S4: Eu2 + red green fluorescent powder to achieve high color rendering index, low colour temperature requirements, but because this kind of alkaline earth metal sulfide, the chemical and physical properties is not stable, easy deliquescence, volatile and corrosive and so on, and can not meet the demand of 200W led flood lighting industry. Recently, people have developed a good thermal stability and chemical stability of red phosphors, can completely replace alkaline earth metal sulfide achieve high color rendering index, low colour temperature white light LED, because it has the silicon nitrogen (oxygen) tetrahedral structure, known as nitrogen oxides, and has higher efficiency of excitation. At present, foreign companies with phosphors in LED technology mature, and hold most of the important patents. They through the phosphors patent holding and occupation LED the market, YAG: Ce3 + phosphor powder patent main Nichia possession by [U.S. 5998925], Osram is occupied Tb3Al5O12: Ce3 + phosphor patent [U.S. 6812500, 6060861652693,], TG, LWB and Tridonic hold blending Eu2 + (SrBaCa) 2 sio4si: Al, B, P, Ge patent [U.S. 6809347], Intematix hold blending Eu2 + (SrBaMg) 2 sio4o: F, Cl, N, S patent [U.S. 20060027781, 200627785200281 22]. In domestic, LED by fluorescent powder research mostly focused on the scientific research institutions, mainly to the existing fluorescent powder materials such as synthesis and luminous property research and technology development in industrialization doing enough. To 2: white light LED optical model and development
Fluorescent powder used in white light LED, still need according to the specific needs of LED and decide, such as fluorescent powder particle size and so on. To fluorescent powder research mainly focus on the optical properties of the phosphors for white LED packaging performance influence, such as take efficiency of light, color space distribution and light color quality above. In these studies, using monte carlo ray tracing method using optical software simulation LED packaging structure of the optical performance, will be treated to a phosphor layer Mie scattering material, so can through the optical simulation for white LED excitation and emission characteristics, but the simulation doesn't take into account the fluorescent powder concrete scattering characteristics, lack of experimental verification.
To three: new fluorescent powder coating way
The traditional fluorescent powder coating way as the point powder mode, namely the fluorescent powder and colloidal mixture filling to chip support cup bowl, then oven heating. This kind of coating way phosphor powder quantity is difficult to control, and because everywhere exciting light is different, make the white LED is easy to appear the macula lutea or blue spot of light color uneven phenomenon. PhilipsLumileds the company put forward conformal coating of the phosphor powder coating way, they flip chip LED chip surface covering a layer thickness consistent phosphor layer and improve the white 200W led Flood light color stability. The company also in the chip surface it deposits a layer of phosphor powder method to realize excitation. These coating way is will chip and phosphor powder contact. H.L uo researchers such as optical simulation results show that the fluorescent powder and chip contact near field excitation method, increased the excitation light back scattering loss and reduce the device take efficiency of light. Australia's Sommer the numerical simulation method to simulate the PhilipsLumileds phosphors conformal coating structure, the results showed that the coating methods do not provide better Angle uniformity. With the deepening of the white LED optical simulation, phosphor powder far field excitation scheme shows more superiority.
To 4: high current injection and heat dissipation structure
In order to meet the needs of the general lighting highlight throughput, and the people improve the single chip driving power, in the past 1 w high power chip is injected into the 3 w, 5 w, or even higher. This makes the ReWenTi white LED is more and more serious, people USES various cooling technologies, such as heat pipe, micro heat pipe, water, air and other methods to implement LED heat dissipation.