还原制备Pr_(2)O_(3)粉体及其结构和光学性能研究

Structure and Optical Property of Pr_(2)O_(3)Powder Prepared by Reduction

镨的倍半氧化物(Pr_(2)O_(3))是合成荧光粉和激光增益介质的重要原料,由于其易发生镨的变价并在空气中吸水而受到的关注较少。本研究采用不同表征手段研究在空气和在氩氢混合气氛下Pr6O11还原为Pr_(2)O_(3)的过程机理以及两种粉体的物相、微观形貌、粒度及价态等,并进一步分析以上两种氧化镨的发光特性与镨的价态关系。结果表明:两种气氛下氧化镨的相变过程显著不同,还原性的Ar/H_(2)气氛可以加快Pr6O11的还原过程,在800℃即可得到Pr_(2)O_(3)。含Pr^(3+)的Pr_(2)O_(3)除了导带到价带跃迁导致的紫外吸收外,还存在因f→f跃迁引发的可见光波段的吸收,而Pr6O11对波长超过320 nm的紫外–可见光有较强吸收,这与Pr4+和氧之间电荷转移有关。Pr_(2)O_(3)的荧光发射光谱中的宽谱带显示Pr^(3+)的4f5d轨道的最低能级在1S0之下,同时含Pr^(4+)的Pr6O11在404 nm处的荧光强度降低63%,这归因于Pr^(3+)/Pr^(4+)之间的能量耗散。这种荧光性能的差异可用于含谱的高氧离子迁移率陶瓷或晶体中Pr的价态分析。本工作研究的Pr6O11到Pr_(2)O_(3)在不同气氛下的转变过程及相关机理性能,有望推动Pr_(2)O_(3)在不同领域的应用。

As an important raw material for synthesis of phosphor and laser gain medium,the sesquioxide of praseodymium(Pr_(2)O_(3))receives few attentions due to its susceptibility to change of valence and hygroscopicity in air.Here,the reduction process from Pr6O11 to Pr_(2)O_(3)and corresponding mechanism in air and Ar/H2 atmosphere as well as the crystal phases,morphologies,particle sizes and valence states of the two kinds of oxides were investigated.Furthermore,the photoluminescent properties of praseodymium oxide were analyzed in relation to the valence state of praseodymium.The results show that phase transition of Pr6O11 significantly varied in different atmospheres.Reduction of Pr6O11 is accelerated in Ar/H2 atmosphere and Pr_(2)O_(3)can be obtained at 800℃.In addition to adsorption in ultraviolet region resulted from transition from valence to conductive band,the Pr_(2)O_(3)containing Pr^(3+)also shows the absorption in visible light band caused by the f→f transition.Pr6O11 shows strong absorption to UV-Vis wavelengths over 320 nm,which is related to the charge transfer between Pr^(4+)and oxygen ion.Wide band in the fluorescence emission spectrum of Pr_(2)O_(3)indicates that the lowest energy level of 4f5d orbital of Pr^(3+)is below 1S0.Fluorescence intensity of Pr6O11 containing Pr^(4+)decreases 63%compared to that of Pr_(2)O_(3)at 404 nm,which can be attributed to the energy dissipation between Pr^(3+)and Pr^(4+).This difference in fluorescence property can be used to analyze Pr valence in ceramics or crystals with high oxygen ion mobility.This research demonstrated that the transformation process and the related property from Pr6O11 to Pr_(2)O_(3)in different atmosphere may promote the application of Pr_(2)O_(3).