Structural, Optical and Spectral Studies of Sm3+ Doped K3Gd(PO4)(2) Bulk and Nanophosphors Synthesized by Different Methods

Undoped and trivalent samarium (0.5-2.5 mol%) doped K3Gd(PO4)(2) phosphors were synthesized by solid state method (SSM), combustion method (CM) and citrate gel combustion method (CGCM), respectively. The resulting phosphors were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectroscopy. The XRD pattern signifies that the synthesized phosphors crystallize in the monoclinic phase with space group P2(1/m). The DR spectra of the phosphors synthesized reveal that the synthesis methods modify the band gap energy from 5.2 to 5.29 eV. At excitation wavelength 402 nm, the maximum PL emission intensity was found in the phosphors synthesized by combustion methods because of its smaller particle size, improved crystallinity and compositional homogeneity. The optimum concentration of Sm3+ ion was estimated to be 2 mol% for all the synthesis methods. On increasing Sm3+ concentration, the emission intensity of Gd3+ ion decreases shows an energy transfer process between Gd3+ ion (sensitizer) and Sm3+ ion (activator). The non-exponential decay curves of K3Gd(PO4)(2) phosphors with different Sm3+ ions concentrations were found and the data is well fitted with the Inokuti-Hirayama (I-H) model. The energy transfer parameters such as critical distance for the transfer processes were determined for the samples synthesized by three different methods and the maximum value of critical distance at 2 mol% was calculated to be 9.52 (angstrom) for combustion method. The Commission Internationale de L'Eclairage chromatic coordinates and color correlated temperature were also determined for the prepared samples.