Crystallite Morphology-Dependent Optical Temperature-Sensing Properties of Eu3+-Doped NaGd(WO4)2 Phosphor

NaGd(WO4)(2): Eu3+ phosphors by using sodium citrate (Na(3)Cit, Na3C6H5O7) as chelating agent were synthesized via hydrothermal method. The structure and morphology were characterized and analyzed by the X-ray diffraction and field emission scanning electron microscopy. Adding Na(3)Cit into the reaction solution can considerably influence the crystallite morphologies of the samples. The temperature dependent photoluminescence spectra of NaGd(WO4)(2): Eu3+ phosphors with different ratios of Cit(3-)/Re3+ have been measured. It was found that, in the NaGd(WO4)(2): Eu3+ phosphors, the optical temperature sensing can be achieved by following three temperature dependent parameters: the ratio of luminous intensity of thermally coupled energy levels (D-5(0) and D-5(1)); the emission intensities of Eu3+ 5D0-F-7(2) transition; the Huang-Rhys factor of Eu3+ 7F0-D-5(2) transition absorption. And the temperature sensing sensitivities of all three methods increased with increase of the ratios of Cit(3-)/Re3+. This is mainly due to that the number of crystal defects increases with increase of the concentration of Cit(3-), and the vibration modes and number of phonons increase, so the intensity of electron-phonon coupling increases.