Fig xA Emission spectra of as prepared Pb
An important criterion for specifying the property of the phosphor is its color that KY02111 can be described in terms of CIE chromaticity coordinates. So, for studying the emission color of Pb2+ co-doped YVO4:5Dy3+ phosphors, we have determined the CIE coordinates of 1 at.% Pb2+ co-doped YVO4:5Dy3+ phosphor as (0.347, 0.364), (0.362, 0.411) and (0.388, 0.424), respectively for as-prepared, 500 and 900 °C annealed sample under 280 nm excitation. And for undoped YVO4:5Dy3+ phosphor CIE chromaticity lies in bluish white with CIE coordinates (0.331, 0.323) under 280 nm excitation. We see that on co-doping Pb2+ ions into YVO4:5Dy3+ color changes from bluish white to white region on contrary to that observed on co-doping Bi3+ ions  and then shift towards yellow region as we move from 500 to 900 °C annealed sample (Fig. 14). The emission color of 900 °C annealed 7 at.% Pb2+ co-doped YVO4:5Dy3+ phosphor under 280 nm is found to be in pure yellow region with CIE co-ordinate (0.397, 0.410). This is related to the slight increase in the value of asymmetric ratio owing to the dominance of yellow light emission over blue emission on heat treatment. This shows that annealing temperature is also responsible for tuning the color of the phosphors. We also find that the emission color remain the same even on changing the excitation wavelengths from 280 nm. However, multicolor tunable emission was accomplished by just using different excitation wavelength in Bi3+ co-doped YVO4:5Dy3+ phosphors . Under 300 nm excitation, the emission color of 1 at.% Pb2+ co-doped phosphor also fall in white region with CIE coordinates (0.342, 0.371) . The well fitting of CIE coordinates in white region on co-doping of Pb2+ into YVO4:5Dy3+ could serve as a good source of white light in the application of white LEDs.