Structural, Optical and Spectral Studies of Sm~(3+) Doped K_3Gd(PO_4)_2 Bulk and Nanophosphors Synthesized by Different Methods

摘要

Undoped and trivalent samarium (0.5-2.5 mol%) doped K_3Gd(PO_4)_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 Sm~(3+) ion was estimated to be 2 mol% for all the synthesis methods. On increasing Sm~(3+) concentration, the emission intensity of Gd~(3+) ion decreases shows an energy transfer process between Gd~(3+) ion (sensitizer) and Sm~(3+) ion (activator). The non-exponential decay curves of K_3Gd(PO_4)_2 phosphors with different Sm~(3+) 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 (A) for combustion method. The Commission Internationale de L'Eclairage chromatic coordinates and color correlated temperature were also determined for the prepared samples.