SrZn2Si2O7:Eu2+, Mn2+: a single-phased emission tunable nanophosphor suitable for white light emitting diodes

A series of emission-tunable nanophosphors with nominal composition of Sr0.96Zn2-xSi2O7:0.04Eu(2+), xMn(2+) (0 <= x <= 0.15) were designed and synthesized by solgel technique for application in white-light-emitting diodes. The structural, morphological, and optical properties were investigated using comprehensive characterization methods, such as x-ray diffraction, scanning and transmission electron microscopy, energy-dispersive x-ray spectroscopy, and photoluminescence spectroscopy. The results indicate that the calcination temperature has strong effect on the crystalinity and morphology. Moreover, the calcination temperature can change grain size and microstrain. SrZn2Si2O7:Eu2+, Mn2+ phosphors show two emission bands excited by near ultraviolet light: blue (around 480 nm) and orange-yellow (around 595 nm) emissions. These emissions are photophysically originated from 4f(6)5d(1)(D-2) -> 4f(7)(S-8(7/2)) transition of Eu2+ sensitizer ions and T-4(1) -> ((4)G) -> (6)A(1)(S-6) transition of Mn2+ activator ions, respectively. The phosphors can generate various lights with different color coordinates and relative color temperatures by properly tuning the relative ratio of the Eu2+ to Mn2+ ions through the principle of energy transfer. The energy transfer from Eu2+ to Mn2+ in SrZn2Si2O7 host matrix was confirmed by several experimental results, such as the luminescence spectra, energy transfer efficiency, and decay curve of the phosphors. Furthermore, the mechanism of this phenomenon was demonstrated as resonant type via a dipole-quadrupole reaction and the critical distance between Eu2+ and Mn2+ ions was calculated at about 10.7 angstrom. Eventually, when the dopant content of Mn2+ is 0.09, the color coordinate of the phosphor (x = 0.345, y = 0.301) is close to the normal white light and can be considered as a suitable UV-converting phosphor for white light-emitting diodes. (C) 2013 Optical Society of America