Effect of Tm3+ Ions on the White Light Emission of Dy3+–Tm3+ Codoped SrMg2La2W2O12 Phosphors

Dy3+–Tm3+ ions codoped SrMg2La2W2O12 (strontium magnesium lanthanum tungstate) phosphors were synthesized by conventional high-temperature solid-state reaction method. X-ray analysis of the end products revealed the well-crystallized phases with orthorhombic structure. The functional groups present in the phosphors were studied by the Fourier transform infrared measurements. To know the potential applicability of these phosphors for white light emission, the excitation and emission spectra were recorded. The excitation spectra exhibited an intense broad band at 313 nm, pertaining to the O → W ligand-to-metal charge-transfer state (LMCT) of the host. With the excitation of LMCT band (313 nm), the decay curves of singly doped SrMg2La2W2O12:Dy phosphors exhibited single exponential, where as the codoped SrMg2La2W2O12:DyTm phosphors exhibited double exponential nature. The luminescence colors of these phosphors were estimated from Commission Internationale de L'Eclairage (CIE) coordinates using the photoluminescence data. The color of singly doped SrMg2La2W2O12:Dy phosphor has been tuned by codoping with Tm3+ ions. It has been noticed that the CIE chromaticity coordinates (x,y) determined from the luminescence spectrum of singly Dy3+ doped SrMg2La2W2O12 phosphor shifted toward the white light region, when codoped with Tm3+ ions. The increase in correlated color temperatures (Tcct) has been noticed with the increase of Tm3+ ions concentration in SrMg2La2W2O12:DyTm phosphors.