Stable red ceramic phosphors and technologies including the same
Wavelength converters including coarse particles/grains of a red nitride phosphor are disclosed. In some embodiments the red nitride phosphor is a (Ca,Sr,Ba) 2 Si 5 N 8 :Eu phosphor with a D50 grain size or a D50 particle size that is ≥5 microns. The red nitride phosphor may be encapsulated within an organic matrix or present in an inorganic matrix. In the latter case, the inorganic matrix may include fine grains with a D50 grain size <5 microns. Methods of making such wavelength converters and devices including such wavelength converters are also described.
1. A wavelength converter, comprising:
a matrix; and
a wavelength conversion material within the matrix;
wherein:
the wavelength conversion material comprises a (Ca x Sr y Ba z ) 2 Si 5 N 8 :d % Eu phosphor, wherein d is the amount of Eu in atomic percent, and the following relationships are met:
0.03< x≤ 0.07;
0.4< y≤ 0.5;
0< z< 1;
x+y+z= 1; and
1.5≤ d≤ 5; and
said (Ca x Sr y Ba z ) 2 Si 5 N 8 :d % Eu phosphor has a D50 grain size greater than or equal to 5 microns; and wherein said matrix is an inorganic matrix selected from the group consisting of optically transparent metal nitrides, metal oxynitrides, metal activated silicon nitride phosphors where a concentration of metal activator is greater than 0 but less than 2 atomic %, and silicon nitrides having the formula (Ca x Sr y Ba z ) 2 Si 5 N 8 where x, y, and z have the same relationship as mentioned with respect to the phosphor; wherein said inorganic matrix has a D50 grain size <5 μm.
2. The wavelength converter of claim 1 , wherein said (Ca x Sr y Ba z ) 2 Si 5 N 8 :d % Eu phosphor has a D50 grain size greater than or equal to 10 microns.
3. The wavelength converter of claim 1 , wherein said (Ca x Sr y Ba z ) 2 Si 5 N 8 :d % Eu phosphor has a D50 grain size ≥15 microns.
4. The wavelength converter of claim 1 , wherein said inorganic matrix has a D50 grain size <1 μm.
5. The wavelength converter of claim 1 , wherein said inorganic matrix is selected from the group consisting of aluminum nitride, Ca—SiAlON, an (Sr, Ba) 2 Si 5 N 8 :Eu phosphor where the concentration of Eu is greater than 0 but less than 2 atomic %, and (Ca x Sr y Ba z ) 2 Si 5 N 8 .
6. The wavelength converter of claim 5 , wherein said inorganic matrix is an (Ca x Sr y Ba z ) 2 Si 5 N 8 , and a ratio of Ca, Sr, and Ba in (Ca x Sr y Ba z ) 2 Si 5 N 8 is the same or substantially the same as a ratio of Ca, Sr, and Ba in said (Ca x Sr y Ba z ) 2 Si 5 N 8 :d % Eu phosphor.
7. The wavelength converter of claim 1 , wherein said phosphor has a D50 grain size ≥15 μm.
8. A lighting device comprising the wavelength converter of claim 1 .