SPECTRAL VARIATION AND CHARACTERISTICS OF LOW VALENCY RARE EARTH IONS IN COMPLEX OXIDESⅢ.EFFECT OF THE CRYSTAL ENVIRONMENT AND CHEMICAL FACTORS ON LUMINESCENCE PROPERTIES OF EUROPIUM (Ⅱ) ION

摘要

Inthis paper,the influence of crystal-field on the Luminescence properties of Eu2+ in complex oxidesare studied theoretically by using purely electrostatic model,the dependence of the 4f65d levels on Eu-Obond distance is given.Quantum chemistry calculation shows that the splitting extent of 4f65d energy band incubic or in octahedral fields will be inversely proportional to R5,where R is the distance of Eu2+ to oxygenligand.The value of R affects slightly the location of the centre of 4f65d energy band.According to the exper-imental spectrum data,we have discussed the influence of the host chemical composition,the replaced sites ofEu2+ and degree of covalency of Eu-O bond on luminescence properties of Eu2+.Some regularity offluorescence spectrum was observed.In alkali-alkaline earth-phosphates,the splitting extent of 4f65d band （△E） becomes smaller as theEu-O bond distance （R） increases.In Na3-x（PO4）1-x（SO4）x and Na2-xCaSi1-xPxO4 hosts,d-d emissionpeak of Eu2+ will shift to shorter wavelength with the increase of x’s value.The crystal structure data show that Eu2+ in K2Mg2（SO4）3 is affected more strongly by crystal-fieldand covalancy than in KMgF3,so K2Mg2（SO4）3:Eu2+ emits blue light (Eemm=400nm) and KMgF3:Eu2+produces ultraviolet fluorescence.