材料物理性能：1. INTRODUCTION

1、Site-occupancy of Eu2+- and Eu3+-doped MgZn2(PO4)2 phosphors,1. INTRODUCTION,M3(PO4)2 (M= Zn, Mg, Ca, Sr, Ba) have rich phases. Zn3(PO4)2: -Phase, CN=4, -Phase, CN=4, 5 above 1200 K -phase“: only by small replacing of Zn2+ by M2+, (Zn, Mg, Mn, Co, Fe, Ca, Sr, and Ba); no pure -phase,phase has monocl

2、inic structure with space group P21/. Two sites in lattices, five-coordinated MI, and six-coordinated MII. Among M2+ ions Mg2+ is the only one substituting 1/3 and stabilizing the -Zn3(PO4), i.e., MgZn2(PO4)2,Research motivation In -Zn3(PO4), distribution of MI and MII has been studied and have diff

3、erent conclusion. luminescence of Eu2+ can be greatly influenced by different crystal field. Eu3+ is a well-known a structural probe ion. The microstructures of Eu3+- and Eu2+- in the lattices were discussed on the base of the luminescence and crystal structure, i.e., occupying sites by Eu3+- and Eu

4、2+ among MgZn2(PO4)2 lattices,2 Results,Fig. 1 XRD patterns,Table 1 The calculated unit cell parameters,Fig. 2 emission spectra MgZn2(PO4)2:xEu2,The critical transfer distance (Rc) is 21.88 It is bigger than the usually reported phosphates or silicates, KCaPO4:Eu2+ (18.05 ), NaSrPO4:Eu2+ (15.2 ), Li

5、SrPO4:Eu2+(15.04), Li4SrCa(SiO4)2:Eu2+ (9.95 ). This is due to the rigid host by tetrahedral PO4 and spectral overlap between the absorption and emission bands,MgZn2(PO4)2:Eu2,Fig. 3 excitation by monitoring 450 and 525 nm,Fig. 4 decay curves in MgZn2(PO4)2:0.03Eu2,Two separated Eu2+ centers (Eu1: 4

6、50 and Eu2: 525). With increase of doping, Eu1-450nm bands get higher intensities,The effective excitation in the UV region is from 200 to 450 nm. There exists excitation in VUV, however it is weak indicating energy transfer from the host to the Eu2+ center is weak,Observation in MgZn2(PO4)2:Eu3,the

7、 excitation in both UV and VUV are strong. Effective energy transfer takes place from the host to Eu3+ ions,Fig. 5 excitation spectra (em=595 nm,Fig. 6 emission spectra (ex=254 nm,origin-red color with CIE of (x=0.59, y=0.38). The emission are dominated by 5D07F1. Eu3+ occupies only one crystallogra

8、phic site,Fig. 7 excitation for 7F05D0,Fig.8 site-selective emission spectra,Fig.9 5D07F1 (595 nm) luminescence decay,Eu3+ occupies only one crystallographic site,Fig. 10 The temperature-dependent luminescence intensities,Thermal stabilities,3. Discussions,CF strength Dq is,450 nm from Eu2+ occupyin

9、g loose Mg with larger Mg-O length (MII site); low-energy 525 nm to Eu2+ occupying compact Zn with shorter Zn-O bond. Eu2+ occupying on Zn2+ are dominated,ZnO5 are strongly disorderd, MgO6 are highly ordered,I(5D07F2)/I(5D07F1)= 0.47 indicates Eu3+ substitute the Mg2+ sites, which are almost regular

10、 MgO6 octahedral,4 Conclusions,MgZn2(PO4)2:Eu2+ presents green luminescence. Eu2+ occupy Mg2+ and Zn2+, and occupancy on Zn2+ is dominated. Excitation of MgZn2(PO4)2:Eu2+ in near-UV region is effective; weaker in VUV region. It could be an effective phosphor for W-LEDs, and is limited for PDP application. MgZn2(PO4)2:Eu3+-origin-red color , Only one Eu3+-distribution on Mg2+ sites in MgZn2(PO4)2 lattices. MgZn2(PO4)2:Eu3+ has effective excitation in both near-UV and VUV region. It has potential application for both W-LEDs and PDP display,5. thermal s