GdVO_4∶Eu^(3+)的激发光谱特性研究

Excitation Spectrum Properties of GdVO_4∶Eu^(3+)

测量了GdVO4 ∶Eu3 +在室温下的光致发光光谱 ;研究了不同掺杂方式和烧结气氛对多晶GdVO4 ∶Eu3 +发光性质的影响 ,探讨了GdVO4 ∶Eu3+的激发光谱在 2 0 0～ 35 0nm范围内激发带的来源和GdVO4 ∶Eu3+中的能量传递。在 2 0 0～ 35 0nm范围内的激发带可解释为来自于钒酸根团的配体O到V的电荷迁移跃迁吸收 ;硝酸溶液使部分正GdVO4 形成多钒酸盐 ,还原气氛使GdVO4 产生O空位和部分V变价 ,影响了钒酸根团间的电荷迁移跃迁吸收和钒酸根团间、钒酸根团与Eu3 +间的能量传递 ,产生激发谱带蓝移和激发带间强度比例变化。GdVO4 中VO3 -4 的π轨道能使得VO3 -4 和稀土离子 (Gd3+、Eu3+)的电子波函数有效地重叠 ,从而VO3 -4 和稀土离子可通过交换作用有效地传递能量。GdVO4 ∶Eu3+在 2 0 0nm处的吸收很弱 ,在此位置也没有Gd3 +或Eu3+的 4fn -15d的吸收和明显的 4fn 高能级吸收 ,而激发却十分有效 ,可解释为由于存在VO3 -4 与Gd3 +或Eu3+的 4fn 高能级间有效的能量传递所致 ;由于Gd3 +的特征发射恰好在基质的强激发带 ,且Gd3+的特征发射没有出现 ,可存在Gd3 +→VO3-4 →Eu3 +的能量传递。Gd3+的6GJ、6PJ能级间隔与Eu3 +的7F1、5D0 能级间隔相近 ,处于6GJ态的Gd3 +可通过共振能量传递激发Eu3 +到5D0 态 ,这可导致Gd3 +?

The excitation and diffusion reflection spectra of GdVO 4∶Eu 3+ were measured at room temperature. The influences of the doping method and sintering atmosphere on the excitation spectrum of GdVO 4∶Eu 3+ were studied. The blue shift and intensity proportion change of the excitation bands, which are due to the effects of acid and deduced sintering atmosphere, are interpreted, the source of the bands at 200～350nm and the possible energy transfer of GdVO 4∶Eu 3+ were discussed. The polycrystalline GdVO 4∶Eu 3+ was prepared by the high temperature solid reaction. Using X ray diffraction (XRD) data, the lattice parameters a =7 22 and c =6 38 were calculated by the least square method, calculation gives the estimation density D X of XRD and D X=5 34 (g/cm 3). The excitation band of GdVO 4∶Eu 3+ in the range of 200～350nm can be fitted by five Gauss peaks very nicely. They can be interpreted as the absorption of the charge transfer transition of the vanadate group:V 5+ O -2 n n →V 4+ O -2 n+1 n. The acid nitric solution causes some of VO 3- 4 to form the multi vanadate group, such as V 2O 4- 7 and V 3O 3- 9 etc. This is equivalent to decreasing the negative charge around V 5+ and the near vanadate groups will feel stronger potential field, which causes the absorption band of the charge transfer of these vanadate groups to shift toward higher energy. As for V +5 m m O -2n n —Eu 3+ , if m increases, the interaction of V +5m m O -2n n —Eu 3+ will decrease and Eu 3+ will be closer to the near vanadate group on the other side, which benefits to the energy transfer between the vanadate group and Eu 3+ , causes the change of the intensity proportion of the excitation peaks of 220～350nm. In GdVO 4, the wave functions of the rare earth ion (Gd 3+ , Eu 3+ ) and VO 3- 4 overlap effectively through the π orbital of VO 3- 4 , VO 3- 4 will have a maximum electron cloud density in the direction of the rare earth ion, by which the energy can be transferred effectively from VO 3- 4 to the rare earth ion by exchange interaction. Near 200nm, the absorption of GdO 4∶Eu 3+ is very weak and there has no absorption of 4f n -1 5d and no obvious absorption of 4f n of Eu 3+ or Gd 3+ , which can be interpreted by the effective energy transfer between VO 3- 4 and the high 4f n energy levels of Gd 3+ or Eu 3+ . The characteristic emissions of Gd 3+ peak at the strong excitation band of GdVO 4, suggests that there existed the energy transfer of Gd 3+ →VO 3- 4→Eu 3+ . At the same time, the energy level difference of 6G J and 6P J of Gd 3+ is close to that of 7F 1 and 5D 0 of Eu 3+ , a Gd 3+ in 6G J state can excite Eu 3+ into 5D 0 state by resonance energy transfer, which results in the energy transfer of Gd 3+ →Eu 3+ .