Press Dependent Electronic And Optical Properties Of Rare Earth Materials

The yellow phosphorescent body Ba₂Mg（PO₄）₂:Eu²⁺,the self-activated phosphorescent body Sr₂VO₄Cl and Sr₅（VO₄）₃Cl,the green phosphorescent body Mg₂Sn O₄:Mn²⁺,and the near infrared phosphorescent body Li Sc Si₂O₆:Cr³⁺exhibits the advantages of high broadband absorption and luminescence efficiency,and has important applications in pressure warning,photoelectric devices and traffic safety signs fields.Applying pressure can improve the electronic and photoelectric properties of the fluorescent materials,which is an effective optical and photoelectric property control method.In this paper,the performance of the fluorescent materials was improved by pressure control.It is found that the band structure,density of states,charge density difference,static dielectric constant and static refractive index of these fluorescent materials change obviously with the increase of pressure,and the absorption spectrum appears blue shift with the increase of pressure.These fluorescent materials have potential applications in pressure warning and sensor.The details are as follows:The first chapter introduce the luminescence principle and classification of fluorescent materials,the research status of pressure regulation,and the research content of this paper.The second chapter introduce the first principles,density functional theory and software for calculation.In Chapter 3,in order to explore whether yellow phosphorescent body Ba₂Mg（PO₄）₂:Eu²⁺has the potential of pressure warning sensing performance,this chapter co-regulates the electronic structure and optical properties of the phosphorescent body by doping Eu²⁺and applying pressure.The sites occupied by Eu²⁺can be determined by calculating binding energy.It is found that with the increase of pressure,the band gap will increase,the charge transfer will be affected and the electron gain and loss in the structure will be improved.Through the study of optical properties,it is found that the increase of Eu²⁺doping concentration will enhance the polarization ability and phototransition intensity of phosphorescent body.The peak of dielectric function,absorption coefficient and static refractive index increase with the increase of pressure,resulting in the blue shift of emission peak.In Chapter 4,in order to regulate the absorption and emission bands of self-activated phosphorescent body,the influence of pressure on the electronic structure and optical properties of Sr₂VO₄Cl and Sr₅（VO₄）₃Cl self-activated phosphorescent was studied in this chapter.It is found that pressure regulates the band gap value,the band gap of Sr₂VO₄Cl decrease from 3.696 e V to 0.317 e V,the band gap of Sr₅（VO₄）₃Cl decrease from 3.805 e V to 2.358 e V.The absorption spectrum of Sr₂VO₄Cl and Sr₅（VO₄）₃Cl appear blue shift as pressure increasing,and a new absorption peak appears in the absorption spectrum.Pressure regulate the electron layout of valence and conduction bands.These results prove that Sr₂VO₄Cl and Sr₅（VO₄）₃Cl is a pressure-sensitive material and suitable for pressure sensors.In Chapter 5,in order to improve the electronic and optical properties of green phosphorescent body,the electronic structure and optical properties of Mg₂Sn O₄:Mn²⁺are regulated by doping Mn²⁺and applying pressure in this chapter.The sites occupied by Mn²⁺can be determined by calculating binding energy.The study of electronic structure shows that doping Mn²⁺causes the band gap of Mg₂Sn O₄:Mn²⁺decrease from 1.892 e V to 0.Doping Mn²⁺causes the main contribution of the top valence band changing from O-2p orbital to Mn-3d orbital,and the main contribution of the bottom of the conduction band adding Sn-5s orbital under pressure.When Mn²⁺doping concentration is 0.33,the absorption coefficient in the visible region reaches the maximum value,and the Mg₂Sn O₄:Mn²⁺appears blue shift in the energy range of 15-30 e V under pressure.In Chapter 6,in order to enhance the photoelectric performance of near infrared phosphorescent body Li Sc Si₂O₆:Cr³⁺,the electronic structure and optical properties of Li Sc Si₂O₆:Cr³⁺phosphorescent body are co-regulated by doping Cr³⁺and applying pressure in this chapter.The results show that doping Cr³⁺lead to band hybridization and reduce the band gap become 0.When doping concentration is 0.125,the optical transition intensity of Li Sc Si₂O₆:Cr³⁺is the largest.However,the band gap increases firstly and then decreases under pressure,and the absorption coefficient has a strong photoelectric response to the low energy region.The maximum value of Li Sc Si₂O₆:Cr³⁺absorption coefficient increases with increasing pressure and reaches its maximum value at 80 GPa,meanwhile blue shift of absorption coefficient occurs in the energy range of 16.41-29.11 e V.Doping Cr³⁺causes Cr-3d orbital become main contributer in the top of valence band and the bottom of conduction band,while Si-3p orbital contributes to the bottom of conduction band after applying pressure.