1 white LED the principle of operation process of the current structure of the white LED light-emitting process is divided into two steps, first first electricity carrier composite luminescence of the LED chip, chip emit blue light photons through the output window of phosphor coating, some of these blue photon transmission through directly, the rest of the blue light photon is the quantum into yellow light, so the white LED light source output blue and yellow light mix of white light.
2 LED chip carrier of composite luminescence of luminous
the LED chip is the process of the chip carrier composite process.
After power on the chip of free electrons within the n-type semiconductor layer in the barrier layer under the electric field to accelerate into the p-type semiconductor layer, and holes in the compound (
See figure 1)
, at the same time, in the form of photons released from all the energy barrier layer electric field and the kinetic energy of the original free electron itself.
If the barrier potential difference V, the electronic charge for e, electronic original mv2/2, the motion of the composite when the photon energy emitted by the carrier for the sum of the two, namely the eV + mv2/2, because the free electrons are not consistent with the kinetic energy of the original, it accord with Fermi distribution rule.
So the LED the blue light spectrum of radiation for a certain bandwidth, the center wavelength and barrier potential difference, while the bandwidth is determined by the free electron kinetic energy.
Figure 1
carrier recombination luminescence
the current material is generally used to launch blue LED chip is GaN, the LED chip barrier layer of electric potential V material 2.
62 -
2.
74 ev, and the material, structure, extension process, processing temperature and the working environment and working temperature and so on.
Figure 2 shows the GaN was favorable for the formation of the materials of the principle of the LED chip.
the principle of figure 2 LED structure due to the barrier potential of the LED to 2.
62-2.
74 ev, so launch center wavelength of 450 nm -
470 nm blue spectral band, the emission spectrum is shown in figure 3.
Figure 3 shows that the blue spectral band is very narrow, and the whole band in visibility function is lower than 0.
The area of 1, light efficiency is very low.
This kind of low light efficiency, low color blue spectral band is can't be directly used for general illumination.
the launch of the blue spectrum figure 3 the LED phosphors in
3 white LED light quantum transformation under the
white LED is actually a part with the LED emission blu-ray inspire yellow phosphor, produce a certain share of yellow, blue and yellow light is obtained mixture of white light.
This kind of white LED emission spectra showed in figure 4.
By the visible spectrum of the lack of green and red light, especially red share is too little, so the white LED color rendering index is low, color temperature is higher.
4 blue
leds inspire yellow phosphor mixed spectrum
adjusting phosphor coating thickness can regulate the percentage of blue and yellow light, which regulates the radiation of the luminous efficiency and color temperature of white light.
The experimental results show that in figure 5 and table 1.
Test in the four samples of phosphor coating thickness, in turn, increases by about 15%, the results show that experiment III phosphor coating thickness is moderate, the luminous efficacy and color rendering index and color temperature is better than other thickness (
Stable work, about 40 lm/w)
And close to the actual product parameters.
When the phosphor coating slants thin,
我,(二)
Yellow light component is too little, color temperature is very high, photosynthetic efficiency and luminous flux are very low.
And when the phosphor coating too thick (
IV)
, though low luminous efficacy of blue light into full visibility function high yellow light, blue light disappear completely from the spectrum, high luminous flux is supposed to, but the actual flux instead dropped sharply.
This suggests that the phosphor coating under the light quantum transformation also absorb a larger share of blue and yellow light.
Coating thickness, light quantum transformation under the more thoroughly, but also absorbed photons.
When coating over time output naturally lowers the best thickness, so the phosphor coating thickness must be strictly controlled, otherwise the lamp parameters especially photosynthetic efficiency will be affected by the larger.
figure 5 phosphors on the optical parameters of
table 1 phosphors on the optical parameters of
editor: gather
