Luminescence characteristics and optimization of (La,Gd)Sr2(Al,B)O5:Ce phosphor for white light emitting diodes

Luminescence properties of (La,Gd)Sr₂(Al,B)O₅:Ce phosphors were investigated by changing the content of Gd and B substituent. The Gd or B substitution was confirmed to improve the emission intensity. The emission peak of LaSr₂AlO₅:Ce was shifted to the longer wavelength due to the enlargement of crystal-field splitting for Ce³⁺ activators as the result of the unit-cell volume reduction when the Gd and B atoms are substituted. In the B-substituted samples, in addition to the cell volume reduction, the change in the lattice covalency due to the large electronegativity difference between B³⁺ and Al³⁺ has additionally contributed to shift the emission peak. The crystallite sizes of phosphors were enlarged using small amount of Gd and B atoms. Also, the absorption for the 4f→5d absorption of Ce³⁺ ions in UV/visible spectrum was greatly enhanced by the substitution of both Gd and B. Therefore, it was concluded that the enhancement of the emission intensity via the substitution is due to the increase in the crystallinity and the light-absorption ability. Finally, the optimized sample La_0.89Ce_0.01Gd_0.1Sr₂Al_0.9B_0.1O₅ had about 368% improved emission intensity compared with La_0.99Ce_0.01Sr₂AlO₅.