Comparative Investigation on Structural and Optical Properties of a Yellow-Emitting Zn 3(Vo4)2: Ce3+ Phosphor for Applications in White Light Emitting Devices
White light emitting diodes (wLEDs) is considered as the next generation of white light sources after fluorescent lamps due to their merits of long term operational lifetime, high quantum efficiency, energy savings, compactness and environmental friendliness. Presently, cerium-doped yttrium aluminium garnet, Y3Al5O12:Ce3+ phosphor is used to convert blue light emissions from InGaN to white light. However, the emitted white light has low color rendering property due to weak red emission intensity in its spectrum. To improve on the color rendering property, a phosphor can be tuned to emit red-shifted light in its emission spectrum. In the present study, Zn3 (VO4)2:Ce3+ phosphor has been tuned to emit light at long wavelength by varying the Ce3+ activator concentration. Zn3-x (VO4)2:Cex3+ (x = 0, 0.03, 0.05, 0.1) phosphor powder were synthesized by citrate gel combustion and microwave synthesis methods, respectively. The structural and luminescence properties of Zn3(VO4)2 phosphor samples with different concentrations of Ce3+ were investigated using x-ray diffractometry (XRD) and photoluminescence (PL) spectroscopy techniques. The XRD patterns confirmed the presence of diffraction peaks belonging to the Zn3 (VO4)2 orthorhombic phase (JCPDS card number 73-1300). The PL spectra were found to consist of broad excitation band (300-400nm) and emission band (400-800 nm) due to the allowed 4f14f05d1 transitions of Ce3+ ion. The findings confirmed that Zn3 (VO4)2:Ce3+ phosphor can strongly absorb near UV/blue light and convert them into visible light (due to the broad emission spectrum). The PL emission peak positions red-shifted from 556 to 577 nm with increase in Ce3+ concentration. Due to the broad PL emission spectrum (bandwidth of 180 nm) and the red-shifting of the maximum wavelength peak positions, the color rendering property of Zn3 (VO4)2:Ce3+ phosphor is expected to be better than that of Y3Al5O12:Ce3+ phosphor with maximum peak position at 560 nm and bandwidth of 116.1 nm. Low magnification SEM images for the Zn3(VO4)2 phosphor samples exhibited highly crystalline, pure and large micro-rods and ribbon-like particles produced by the gel combustion and microwave synthesis routes, respectively. SEM images of Ce3+-doped samples revealed the presence of small microspheres with rough surfaces.