Solid-State Synthesis And Luminescent Properties Of Eu³⁺-Doped Tungstates And Molybdates Red Phosphors

In the 21st century, white light emitting diode (WLED) is a remarkable lighting source with environmental-friendliness and energy-saving because of its many advantages, such as high efficiency, long lifetime and without environmental hazards. Therefore, it is promising for the market applications. The main approach to obtain WLED is phosphor-converted. However, the current red-emitting phosphor used for WLED shows a rather low efficiency under near-UV light excitation. To solve these problems, it is important to explore novel and superior red phosphors for WLED.In this paper, series of red-emitting phosphors containing (Ca, M)WO4:Eu³⁺ (M = Mg, Zn), (Ca, M)WO4:Eu³⁺ (M = Li, Na, K), Ca(WO4)1-y(MoO4)y:Eu³⁺ and (Ca, M)(WO4)1-z (MoO4)z:Eu³⁺ (M = Mg, Zn) were prepared by conventional solid state reactions. When a trivalent Eu³⁺ ion was incorporated into a host lattice and substituted for a divalent Ca2+ ion, charge balancing was necessarily required. The doped modes applied in this work were as followings: Firstly, Ca2+ ions were supposed to be replaced by Eu³⁺ ions in the molar ratio of 1:1, in which the host had to capture O2 in the air to neutralize the charge generated by Eu³⁺ substitution for Ca2+. Secondly, Ca2+ ions were replaced by Eu³⁺ ions in the molar ratio of 2:3, with charge compensation provided by a calcium vacancy (V"Ca ). Finally, two Ca2+ ions were replaced by one Eu³⁺ and one M+, and M+ (M = Li, Na, K) acted as a charge compensator.In order to study the effects of different doped ions and different charge compensation mechanisms on the crystal structure and luminescent properties of samples, XRD, FTIR, SEM, excitation and emission spectra were carried out. XRD and FTIR patterns showed that all the phosphors are isostructural and share a tetragonal scheelite structure of space group I41/a(88). SEM micrographs confirmed that the charge compensation is beneficial to improve the crystallization of the phosphor. The excitation and emission spectra of all the phosphors exhibited superior red emission around 615 nm to the commercial red phosphor Y2O2S:Eu³⁺ with 395 nm light excitation. In particular, the phosphors with efficient charge compensation exhibit a strongly enhanced red emission of Eu³⁺. In a word, the effective charge compensations are effective approaches to improve the crystallization of the phosphor and enhance red emission of Eu³⁺.In this basic investigation, the influences of different doped ions and different charge compensation mechanisms on the crystal structure and luminescent properties of Eu³⁺ doped tungstates and molybdates were studied, which was expected to give the valuable reference to explore novel red phosphors for WLED.