Patent Application
20070272899
The present invention is to disclose a fluorescent powder for blue-light emitting diodes, which is, for example but not limited to, an inorganic fluorescent powder based on garnet-structure yttrium gadolinium with a chemical formula of (Y,Gd)3Al5-x(Mg,Si)xO12 (x=0˜3), wherein the ratio of yttrium to gadolinium varies to ensure the shifting peak values of the excited Ce+3 and Cr+3 radiations.
The said fluorescent powder is based on, for example but not limited to, a garnet-structure yttrium gallium with a chemical formula as (Y,Gd)3Al5-x(Mg,Si)xO12 (x=0˜3). Ce+3 used as an exciter to be excited by blue and blue-green visible lights of wavelength 400-500 nm to re-radiate a wideband radiation of half-width Δλ0,5>110 nm and/or narrowband radiation of half-width Δλ=20˜40 nm with the radiation peak shifting to 535˜550 nm.
The ratio of Y and Gd ions of the said fluorescent powder ranges from 2.8:0.2 to 1:2, increasing as the peak value of the excited Ce+3 radiation. The optimum concentration of Yttrium and Gallium is 0.005-0.05%, wherein the mole ratio of magnesium oxide and silica oxide in Yttrium Gallium garnet is MgO:SiO2=1±0.02 to ensure the peak radiation value shifting 20-40 nm toward longer wavelength.
First, the reason of choosing the fluorescent powder with garnet cubic structure is that the structure has a good compatibility with the d-d electron active centers such as Ce+3. In the experiment for the present invention, the best light intensity can be emitted when the garnet-structured fluorescent powder was excited by Ce+3. Second, the said chemical compositions of the compound allow two methods to shift the peak value of emitted lights toward longer wavelength. The first method is to partially replace Y ion with Gd ion, shifting the Ce+3 radiation toward higher wavelength by 535-590 nm. The second method is to partially replace the Al+3 ions with a pair of ions, Mg+2 and Si+4 for example, in the anion lattice.
In the first said method, the excited radiation spectrum is gradually and slowly shifting toward longer wavelength by 1 nm per 1% Gd ion replaced by 1% Y ion.
In the second said method, two Al+3 are replaced by a pair of Mg+2 and Si+4, yielding a sudden change in the excited Ce+3 radiation wavelength by 35 nm. The difference between the two methods of shifting lower toward higher wavelength is resulted from the difference in the coordination numbers of replaced ions. The coordination number of Gd ion is 8-12, while that of Al ion is 4-6. An ion with larger coordination number will experience slower change in its surrounding ions. When Al ion having smaller coordination number in the garnet-structured fluorescent powder is replaced with doped Mg+2 and Si+4, a sudden change in the force field of the lattice will be resulted.
The fluorescent powder for blue-light emitted diode according to the present invention is characterized in using the garnet-structure yttrium gadolinium as its base with the ratio of Y and Gd ions ranging from 2.8:0.2 to 1:2, which in changed with the shifting peak value of excited Ce+3 and/or Cr+3, wherein the optimum concentration of Yttrium and Gallium is 0.005˜0.05%.
Also, the concentrations of Mg+2 and Si+4 in the present fluorescent powder can be adjusted by changing the chemical compositions as below:
Compared with the same valence replacement between Y and GD, the replacement of Al+3 with Mg+2 and Si+4 is different in valence, wherein Mg+2 replacing Al+3 will form a (MgAl)′ center with a negative charge equivalent to the positive charge of the (SiAl)• center formed by the replacement of Al+3 with Si+4, i.e. (MgAl)′=(SiAl)• This condition demands the equality between Mg and Si atoms in the garnet crystal.
Furthermore, it was discovered experimentally that when the difference between Mg or Si atoms and the other element, Si or Mg, respectively, doesn't excess ±0.02, the peak in the radiation spectrum will shift 20-40 nm toward longer wavelength. The fluorescent powder designed according to the experimental findings is characterized in that the molar mass between the magnesium oxide and silica oxide is MgO:SiO2=1±0.02, and thus the peak in the radiation spectrum will shift 20-40 nm toward longer wavelength.
The fluorescent powder of garnet-structure yttrium gadolinium doped with Al and Si-doped according to the present invention can be produced in industrial class solid-state synthesizing method under high temperature, weak reduction environment with yttrium oxide (purity=99.99%), gadolinium oxide, magnesium oxide, silica, aluminum oxide (99.95%), cerium oxide, and chromium oxide (99.9%).
For two methods of replacing ions described above, YGd and Al
Mg+Si, in the garnet structure, there is no loss of photon radiated by the fluorescent powder. From the absorbent spectrum, it is clear that all the said materials can well absorb the radiation of the visible light spectrum since the mixed powder shows yellow and orange colors.
The fluorescent powder for blue-light emitted diode according to the present invention is based on a garnet-structure Yttrium Gadolinium with the ratio of yttrium to gadolinium being Y:Gd=2.8:0.2˜1:2, which is changed with the shifting peak value of emitted Ce+3 and/or Cr+3 radiation. Thus, it can overcome the shortcomings of the prior art of fluorescent powder for blue-light emitted diodes.
While the invention has been described by way of example and in term of a preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 095118800 | May 2006 | TW | national |
