Synthesis And Spectral Characteristics Of Eu³⁺ And Tb³⁺ Doped MMoO₄ (M=Ca, Zn, Ba) Phosphors

In comparison with traditional light sources for lighting, White LED is promising for the market applications because it has more prominently performance. Therefore, the phosphor for White LED is a novel topic of increasing interest. In this paper, CaMoO₄:Eu³⁺, ZnMoO₄:Tb³⁺ and BaMoO₄:Eu³⁺ phosphor powders were prepared with a high-temperature solid-state reaction method and their crystal structure and luminescent properties were investigated.A high-efficient red luminescence material was synthesized by the Eu³⁺ ions doped in CaMoO₄. The study indicated that the Eu³⁺ ions was doped in CaMoO₄ lattice and occupied the sites of the Ca²⁺ ions. The excitation spectrum consisted of one broad band and some narrow peaks, in which the broad band located at the range of 220～320nm. The greater two narrow bands are located at 394nm and 464nm, respectively. Farther analyzing spectrum, the excitation broad band of sample was attributed to the Mo6+—O2- charge transfer transition, but not to Eu³⁺—O2- charge transfer transition. The spectral characteristic and influence of various Eu³⁺ ions concentrations on the luminescent intensity of CaMoO₄:Eu³⁺ were investigated.The ZnMoO₄:Tb³⁺ phosphor was prepared by high temperature solid-state reaction method and its crystal structure and luminescent properties are investigated in this paper. The X-ray diffraction patterns (XRD) showed that the phosphor calcinated at 800℃can obtain pure ZnMoO₄ phase. The excitation spectrum consisted of one broad band and some narrow peaks, in which the broad band belong to Mo6+—O2- charge transfer transitions (CT) and all of narrow peaks are attributed to 4f—4f transitions on Tb³⁺. The strongest excitation peak is located at 377nm correspond to magnetic dipole transitions. The blue shift of a charge transfer transition (CT) broad band could be observed in the excitation spectra of various Tb³⁺ doping concentrations. The effect of Tb³⁺ concentration on the emission spectrum intensity of ZnMoO₄:Tb³⁺ was investigated, and the results show that the emission spectrum intensity increased with increasing Tb³⁺ concentration, and reached the maximum value at x=0.15, then decreased. Fluorescence lifetimes of the Tb³⁺ in ZnMoO₄ are measured, it show fluorescence lifetimes is about 0.506ms. The spectrum characteristics suggest that ZnMoO₄:Tb³⁺ is a promising green-emitting phosphor for LED applications. The BaMoO₄:Eu³⁺ phosphors were synthesized by solid-state method and were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectra. XRD analysis confirmed the formation of BaMoO₄ at 800℃and exhibited a tetragonal crystal structure. SEM studies show particles are regular in shape and size and grain size is in the range from 1μm to 2μm .The excitation spectrum of sample showed one broad band and some peaks are located behind 350nm. The former was attributed to the charge transfer transition of Eu³⁺—O2-, and the later were belonged to the f—f transitions of Eu³⁺ ions. The emission spectrum shows four peaks at 591nm, 615nm, 654nm and 702nm. The dominant peak is located at 615nm due to the 5D0—7F2 electric dipole transition of Eu³⁺. The effect of Eu³⁺ concentration on the emission spectrum intensity of BaMoO₄:Eu³⁺ phosphor was investigated, and the results showed that the emission spectrum intensity reached the maximum value at 20mol% Eu³⁺, and then decreased, which had a phenomenon of concentration quenching.