Preparation And Fluorescence Properties Of Praseodymium And Samarium Doped Molybdate Red Phosphors For White

Phosphor-converted white light-emitting diodes (pc-WLEDs) as so-called thefourth generation solid-state light source show mangy advantages such as longlifetime, high luminescent efficiency, low power consumption, environmentfriendliness, compactness, etc and are gradually replacing conventional incandescentand fluorescent lamps. However, the current red-emitting phosphor used for WLEDshows a rather low efficiency under near-UV light excitation、inadequate lifetime andinstability. To solve these problems, it is important to explore novel and superior redphosphors for WLEDs. In this study, we paid attention to the synthesis of novel redphosphors for WLEDs application via blue or near-UV LEDs. Molybdate is animportant light-emitting substral material with excellent physical and chemicalproperties. Therefore, using ZnMoO4as host matrix and Pr3+/Sm3+as activators,ZnMoO4/ZnMoO4:Pr3+/ZnMoO4:Sm3+/ZnMoO4:Sm3+, Pr3+phosphors weresynthesized successfully via a co-precipitation route at800℃for2h. XRD patternand FL spectra were used to measure the property of the luminescence material, theresults were as follows:Pure ZnMoO4is a self-activated phosphor, its intrinsic emission band is due tothe radioactive annihilation of self-trapped excitons localized on MoO42-complexes.FL spectra of ZnMoO4showed that its maximum excitation and emission wavelengthlocated at290nm and403nm, respectively. The excitation spectra of ZnMoO4:2%Pr3+phosphor displayed four absorpption peaks which originated from3H4�'3P2(450nm)、3H4�'1I6(465nm)、3H4�'3P1(473nm)、3H4�'3P0(489nm) transitions of Pr3+,respectively.Its maximum excitation wavelength located at450nm, indicating thatZnMoO4:2%Pr3+phosphor can be effectively excited by450nm blue light LED chips.Under excitation of450nm blue light, its emission spectra showed four remarkableemission peaks which located at603nm、616nm、661nm、693nm corresponding to1D2�'3H4、3P0�'3H6、3P0�'3F2、3P0�'3F3transition of Pr3+, respectively. The weak3P0�'3H6transition is induced by the lack of inversion symmetry at the Pr3+ions sites.Both the higher intervalence charge transfer (IVCT) state and the lower structural symmetry are responsible for the strong deep red emission corresponding to thehypersensitive3P0�'3F2transition.ZnMoO4:2%Sm3+phosphor can be effectively excited by405nm near-ultravioletlight and emits four emission bands which located at561nm、598(606nm)、647nm、709nm corresponding to4G5/2�'6H5/2、4G5/2�'6H7/2、4G5/2�'6H9/2、4G5/2�'6H11/2transitions of Sm3+, respectively. Among these transitions, the4G5/2�'6H9/2transitionof Sm3+was dominated, which indicates that Sm3+occupies a site without inversionsymmetry in ZnMoO4. ZnMoO4:Sm3+/Pr3+phosphor upon405nm near-ultravioletlight excitation emits strong red-emitting luminescence at621and648nm which areattributed to3P0�'3H6and3P0�'3F2transitions of Pr3+, respectively. An effectiveenergy transfer from Sm3+to Pr3+in the ZnMoO4:Sm3+/Pr3+system occurred. Thus,this study showed that red phosphors, ZnMoO4:Pr3+/ZnMoO4:Sm3+/ZnMoO4:Sm3+,Pr3+are advantageous for the fabrication of white LEDs via blue or near-UV LEDs.