Light-emitting diode LED torch (Light Emitting Diode) is a kind of electrical energy can be converted to light energy conversion devices with low voltage, low power consumption, stable performance, long life, impact resistance, vibration resistance, light weight, small size, low cost, fast response, etc. light. Therefore, the display device and short-range, low-speed fiber-optic communication light source has a wide range of applications, especially in recent years, blue, violet and ultraviolet LED flashlight rapid development of the field of LED lighting to replace incandescent and fluorescent possible.
White LED flashlight's produce in two ways: The first method is the red, green and blue LED torch combined to produce white light; The second method is to use LED flashlight to excite other luminescent materials mixed to form white light, which uses blue LED with yellow fluorescent light, or a blue LED emitting green light with the red phosphor light distribution in two, or by violet or ultraviolet LED flashlight to excite the red, green, and blue phosphors so.
From the current development trend, in terms of feasibility, practicality and commercialization aspects, the second method is far superior to the first method, therefore synthesized with good special phosphor luminescence characteristics are critical. Currently, the use of blue, violet or ultraviolet LED torch with phosphor to produce white light technology has been relatively mature, but can be applied to LED red phosphor, is not a valid conversion efficiency is low, that is unstable nature large lumen. Therefore, high efficiency and low light decay LED flashlight with red phosphor development is becoming a major domestic and foreign companies and research institutions research hotspot.
A sulfide series red phosphor
The series of phosphors divalent europium as an activation agent in the ultraviolet, violet and blue light excitation emission peak wavelength of the broadband emission is greater than 600nm. Figure 1 shows the contents of the various europium sulfide emission spectrum of the red phosphor. However, the emission intensity with increasing content of europium, first increased and then decreased, the strongest launch europium content of 0.1% or so. Figure 2 shows the excitation spectra of these phosphors. The figure shows that under these phosphors at 350nm and 400nm above can be effectively excited, and with europium content is different, the shape of the excitation spectrum is not significantly different, but the excitation intensity significantly different. It can be seen, the divalent europium activator content of the phosphor luminescence efficiency have a significant impact, but the content of the number of excitation and emission spectra of the position and the shape is not significantly affected.
The series of alkaline earth metal sulfide phosphor as a substrate, various elements and alkaline earth metal content on the excitation and emission spectra of phosphors have different effects. Figure 3 is Ca, Sr different than the case of 460nm when excited with blue light emission spectrum of the phosphor. As the calcium content increases, the emission peak moves toward longer wavelength, and the emission was significantly enhanced. Figure 4 is Ca, Sr ratio different from the case of the excitation spectrum of the phosphor. Excitation and emission spectra are similar trends: With the calcium content increases, the excitation peak shifted towards longer wavelength, and the peak was significantly enhanced. These changes expand the scope of application of the phosphor. Depending on the chip and application needs, you can choose different excitation and emission peaks of the series phosphors.
Sulfide phosphors biggest drawback series: nature is not stable enough, large lumen. The main reason is: the use of the process, the sulfur is likely to precipitate, a divalent europium to oxidation. For this reason, in the preparation process, we conducted a test of adding auxiliary agents, and in the latter powder preparation, surface treatment test. By adding auxiliary agents and surface treatment, effectively slowing the deliquescent powder, sulfur oxidation and precipitation of phosphor stability has been greatly improved.
Second, the rare earth aluminum (gallium) deep red phosphor salts
Trivalent rare earth cerium activated aluminum (gallium) salt phosphor absorbs blue light and emits yellow light as phosphor, has been widely used in the manufacture of blue excitation phosphor white LED torch. Trivalent cerium activated rare-earth aluminum (gallium) salt phosphor developed, based on the year we further developed the rare earths and other transition metal elements of rare earth activated aluminum (gallium) salts deep red phosphor, the low color moderately higher CRI white LED preparation, as well as the preparation of colorful color LED foundation. Figure 5 is different from the active agent content of the rare earth aluminates phosphor emission spectra. Aluminates phosphor emission peak at 680nm or more, and gallants emission peak wavelength longer than the 700nm. However, the emission intensity with different content of active agent, changed regularly. Figure 5 Figure 6 is a corresponding excitation spectra of rare earth aluminates phosphor. Active agent content in different, the shape of the excitation spectrum and the excitation peak position is almost no change. The figure shows that the series of phosphors can be the range of 400-470nm blue-violet light and 560-630nm range of orange light effectively excited. Thus, the fluorescent light can be used effectively excited by two, one is issued blue blue LED flashlight chip, the other one is issued by the red LED chip red, in both the excitation light, fluorescence emit light crimson pink. Since LED torch chips of different emission colors, and matched with other luminescent color phosphors, can be prepared with different luminescent colors, different uses of LED flashlight, as with the blue LED chip matched to the deep red phosphor and the green phosphor can be prepared a very good color rendering white LED torch. Using the orange LED flashlight light can be used to excite the phosphors create some special monitoring equipment.
Third, the alkaline earth and transition metal composite oxide red phosphor
Sulfide red phosphor stability needs to be improved, while the rare earth aluminum (gallium) salt red violet and ultraviolet phosphor can be effectively excited. To this end, we have developed a new type of alkaline earth and transition metal composite oxide red phosphor. The series can be UV phosphor, violet and blue light effectively excited. The series of phosphors trivalent europium activator, under the action of the excitation source is trivalent europium emits red emission characteristics. Figure 7 is a type of the contents of europium metal composite oxide of alkaline earth and transition of the excitation spectrum of the red phosphor. These phosphors at 362nm, 382nm, 394nm, 416nm and 464nm appeared around both strong excitation peak. And these just cover the ultraviolet wavelengths, violet and blue LED emitter region, so the series of phosphors can be used for ultraviolet, violet and blue LED excitation of semiconductor lighting device. Eu content in different, the shape of the excitation spectrum of the phosphor and the excitation peak position is almost no change. However, the intensity of the peak excitation europium content with different changed regularly. Figure 8-10 for these phosphors of different excitation wavelengths in the emission spectrum of the excitation. The figure shows that these phosphors at different excitation wavelengths are 612nm and 616nm emit other trivalent europium characteristic lines, is a good red emission phosphor. With the europium content is different, the shape of the emission spectrum is not significantly different, but the emission intensity is different. It can be seen, trivalent europium activated alkaline earth and transition metal composite oxide suitable for ultraviolet, violet and blue light excitation, is a good red phosphor. As is stable trivalent europium-activated, and the matrix is a stable oxide system, so the series of phosphors good stability, light is small.
With the preparation of GaN technology breakthroughs, blue, violet and ultraviolet LED flashlight emergence and found that increasing attention of Governments, research institutions and multinational attention. Red LED torch with a phosphor is the bottleneck. Paper developed three phosphors will greatly promote the development of the red phosphor, for lower color temperature, higher color rendering, higher luminous efficiency development and lay a foundation. Welcomed the device development and production units with us unite together to push forward.