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Color point tuning is an important challenge for improving the practical applications of various displays, especially there are very limited white color single hosts that emits in the white spectrum. In this paper, the possibility of color tuning by substituting part of host lattice cation (Sr 2+ ions) by Ca 2+ or Ba 2+ ions in an efficient strontium aluminate phosphor, Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ , is reported and found to be very promising for displays. A detail study by replacing part of Sr 2+ with Ca 2+ or Ba 2+ has been investigated. X-ray diffraction study showed that crystal structure of Sr 4 Al 14 O 25 is preserved up to 20 mol of Ca 2+ ion exchange while it is limited to 10 mol of Ba 2+ ions exchange. Substantial shift in the emission band and color were observed by substitution of Sr 2+ by Ca 2+ or Ba 2+ ions. A bluish-white emission and afterglow was observed at higher Ca 2+ ions substitution. Further, partial Ca 2+ substitutions (up to 0.8 mol) resulted in enhanced afterglow of Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ phosphor. However, Ba 2+ substitution decreased the fluorescence as well afterglow of the Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ phosphor significantly. The enhanced phosphorescence by partial Ca 2+ substitution is explained on the basis of increased density of shallow traps associated with higher solubility of Dy 3+ ions in to the host lattice due to equivalent size of Ca 2+ and Dy 3+ ions. Thus, Ca 2+ substitution in the Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ phosphor is a promising method for tuning the emission color and improving the afterglow intensity of the phosphor. |
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