Research On Near Infrared Characteristics Of Nd³⁺/Cr³⁺ Doped Tungstate/Zirconate Phosphors

Near infrared light（NIR）is widely used in face recognition,food safety detection,remote sensing measurement and control,solar cells,biological nitrogen fixation,geological exploration and other fields.Due to the unique optical properties,rare earth elements（RE）are used as activator ions of NIR luminescent materials.Among them,Nd³⁺has attracted the attention of many researchers.However,most of the near-infrared luminescent materials doped with Nd³⁺ions show weak absorption intensity,narrow excitation spectrum range and low intensity,which limits their practical application.At the same time,the luminescence of Cr³⁺originates from the transition of the external 3d energy level and is sensitive to the crystal field and electron-phonon coupling.Based on the above problems,this paper aims to find the suitable sensitizer and matrix to improve the near infrared luminescence intensity of Nd³⁺and Cr³⁺ions.Specific work content:We mainly studied the Mn⁴⁺/Nd³⁺co-doped K_0.5La_0.5Sr Mg WO₆phosphor which was prepared by high temperature solid-state method.The emission spectrum of K_0.5La_0.5Sr Mg WO₆:Mn⁴⁺,Nd³⁺samples shows the broad-spectrum emission in the range of 850-1150 nm,and the center of the emission peak is at 697 nm.The Mn⁴⁺in K_0.5La_0.5Sr Mg WO₆matrix not only has high internal quantum efficiency（97.3%）,but also the excitation spectrum covers the wide band range from ultraviolet light to visible light.Under 468 nm light excitation,it is found that at the optimum Mn⁴⁺and Nd³⁺doping concentration,the NIR light intensity at 1064 nm of Nd³⁺is about 54.7times than that at the optimum Nd³⁺doping concentration.The significant enhancement of Nd³⁺emission intensity is caused by the energy transfer of Mn⁴⁺to Nd³⁺.In addition,Reisfeld and Inokuti-Horayama model are used to research the samples,and it is found that the resonant energy transfer from Mn⁴⁺to Nd³⁺in Mn⁴⁺,Nd³⁺co-doped samples is mainly realized through the dipole-dipole interaction.We mainly studied the Cr³⁺/Ce⁴⁺co-doped Li₂MgZrO₄phosphor which was prepared by high temperature solid-state method.The emission spectrum of Li₂MgZrO₄:Cr³⁺,Ce⁴⁺samples shows the broad-spectrum emission in the range of650-850 nm,and the center of the emission peak is at 740 nm.Due to the same radius of Mg²⁺,Zr⁴⁺and to make charge conservation,it is speculated that Cr³⁺ions replace Mg²⁺ions and Zr⁴⁺ions in Li₂MgZrO₄,which provides a way to broaden the near infrared emission band.The concentration quenching of Cr³⁺in Li₂MgZrO₄samples are determined to be due to the electric dipole-dipole interaction by using Dexter theory.Ce⁴⁺is introduced as a medium to adjust the crystal field environment of Li₂MgZrO₄,and the near infrared luminescence of Cr³⁺is enhanced by changing the crystal field environment.The optimum doping concentration of Cr³⁺and Ce⁴⁺are determined to be 1%and 3%,respectively.