Study On The Photoelectric Properties Of Lanthanide Doped Pyrophosphate Luminescent Materials Based On First Principles Calculations

Rare earth metal doped luminescent materials play an important or even indispensable role in lighting,display,photovoltaic,biological imaging,medical,anti-counterfeiting,sensing and many other applications.With the development of society and scientific techniques,finding new luminescent materials has become the main objective of luminescent material research.However,traditional research methods are based on intensive experiments to find new luminescent materials,which has very big drawbacks in terms of cost and time.For example,the influence of dopant ion content on the crystal phase and photon luminescence performance is complicated,the emission band and luminescence center are difficult to determine,and many related energy transfer mechanisms cannot be explained.In this work,we take lanthanide(Ln)-doped pyrophosphate materials,hot and typical phosphors,as a representative.Using screened hybrid density functional theory(HSE06),the electronic structure,character of electronic transition and energy level scheme are systematically investigated.The specific research contents are as follows:Firstly,the substitutions of Sr in Sr₂P₂O₇ by equivalent and non-equivalent doping of rare earth lanthanide element Ln^2+/3+are systematically studied.The equivalent doping is realized by substituting one Sr²⁺cation with a Ln²⁺cation;The non-equivalent doping is performed via substituting one Sr²⁺cation with one Ln³⁺cation and one Sr²⁺in the vicinity of the Ln³⁺cation replaced with a Na⁺cation.The electronic structure,character of electronic transition and energy level scheme of Ln^2+/3+-doped Sr₂P₂O₇ are investigated.It is found that,owing to the doping of Ln^2+/3+ions,some extra Ln 4f and 5d states are introduced in the host Sr₂P₂O₇ band gap,causing a change in the electronic structures and the luminescence properties.The specific locations of the Ln 4f and 5d states and the possibility of electronic transitions,especially the 4f?5d,are systematically studied.The energy level scheme is constructed from the calculated electronic structures,and it fits well with the experimental scheme.This gives a whole picture of the Ln doping effect on the materials.It can be applied to all Ln-doped fluorescent materials and to aid in the discovery of new bright scintillator materials.Secondly,the electronic structures and photoelectrical properties of the ground and excited states of M₂P₂O₇:Eu²⁺(M=Ca,Sr,Ba)have been systematically investigated.The most stable structure of M₂P₂O₇ is obtained by fitting V-E curve.The calculated ground state energy band structure shows that all the host materials own direct band gap.Ca₂P₂O₇:Eu²⁺and Sr₂P₂O₇:Eu²⁺can be used as bright luminescence materials,which is consistent with the experiments.Their electron transition energies of 4f?5d are also consistent with the experimental values.The reason why Mg₂P₂O₇:Eu²⁺and Ba₂P₂O₇:Eu²⁺cannot be used as luminescence materials is obtained by comparing energy level schemes.Further,the luminescence mechanism of M₂P₂O₇:Eu²⁺,Mn²⁺is investigated.The energy transfer mechanism of Eu,Mn co-doping is confirmed.The origin of the bright blue and orange emission peaks,and the small effect of the incorporation of Mn²⁺on the M₂P₂O₇:Eu²⁺luminescence are well explained.