Luminescent properties of (Sr, Zn)Al2O4:Eu2+,B3+ particles as a potential green phosphor for UV LEDs

(Sr1-x, Zn-x)(1-y)(Al-1.98, B-0.02)O-4:Eu-y(2+) green phosphor particles for ultraviolet fight-emitting diodes (UV LEDs) were prepared by spray pyrolysis and their luminescent properties were investigated with changing the reducing temperature, the concentration of the activator, and the ratio of Sr to Zn. For the Sr(Al-1.98, B-0.02)O-4:Eu2+ phosphor, pure monoclinic SrAl2O4 phase was formed when the post-treatment temperature was 1100-1200 degrees C. Over 1300 degrees C, however, the Sr4Al14O25 phase appeared as a minor phase, which induced a blue shift in the emission peak. The highest intensity of Sr(Al-1.98, B-0.02)O-4:Eu2+ phosphor was achieved when the reducing temperature and the content of Eu2+ were 1200 degrees C and 10 mol % of the strontium, respectively. It was found that the substitution of 10-50% Zn atoms instead of the strontium greatly enhanced the 520 nm green emission, especially for the excitation wavelength range from 380 to 420 nm. At the high Zn concentration (x > 0.7), a new blue (460 nm) emission was observed and stable even at ambient temperature. This blue emission disappeared when the Zn content became lower than 0.7. The excitation spectrum of (Sr1-x, Zn-x)(Al-1.98, B-0.02)O-4:Eu2+ phosphor (x <= 0.7) well overlapped with the 460 nm blue emissions. Consequently, it was concluded that the new blue sites successfully played the role of sensitizer for the energy transfer, which is responsible for the enhancement of the luminescence intensity. Finally, the optimized phosphor (Sr-0.6, Zn-0.4)(0.9)(Al-1.98, B-0.02)O-4:Eu-0.1(2+) showed 185% improved emission intensity compared with that of the Sr-0.9(Al-1.98, B-0.02)O-4:Eu-0.1(2+) phosphor under ultraviolet (lambda(ex) = 393 nm) excitation.