Studies On Broadband Near-infrared Phosphors For NIR Pc-LED

Near infrared phosphor conversion LED(NIR pc-LED)is a new type of solid-state near-infrared light source for test and illumination.It is mainly used for integrated near infrared spectroscopy equipment,miniaturization of medical imaging equipment and reducing the interference of functional near infrared imaging equipment to experimental subjects.Therefore,it has great application prospects in agriculture,food,petroleum,pharmaceutical,medical and other fields.At the same time,compared with the traditional broadband emission near-infrared light source,NIR pc-LED has many advantages,such as high efficiency,small size,continuous spectrum,long life,anti-seismic,low cost and so on.The 450 nm blue light generated by the high efficiency blue LED chip is absorbed by the broadband near infrared phosphor coated on chip,and then converted into broadband near infrared emission.This structure and working mode are inspired by white LED(WLED).At present,the transition metal Cr3+doped broadband NIR phosphors have higher NIR emission efficiency,but there is still room for improvement in efficiency,emission range and thermal stability.Therefore,it is of great theoretical and practical value to actively explore new broadband near-infrared luminescent materials and study the luminescent characteristics of Cr³⁺in different matrix materials.In this paper,the broadband near-infrared luminescence properties of Cr³⁺ions in diopside matrix(Ca Mg Si₂O₆)and?-phase matrix(X₄Zr₃O₁₂,X=Sc,Y,Lu)were investigated:(1)Cr³⁺doped Ca Mg Si₂O₆ broadband near-infrared phosphors was prepared by high temperature solid-state method.The emission spectra shows that under the excitation of 455 nm blue light,with the increase of Cr doping concentration,the emission FWHM extends from 139 nm to 206 nm,and the emission range extends from 650-1100 nm to 650-1350 nm.The emission peak value are all around 800 nm.There is reabsorption effect in the luminescence process.The low reabsorption emission spectra were recorded by dispersed the near infrared phosphor on the glass slide.The broad band emission corresponds to the overlap of two emission peaks,and the properties of the two emission centers vary with the Cr doping concentration.The temperature characteristics of Ca Mg Si₂O₆:Cr are good.The thermal quenching temperature reaches 653 K with lower Cr³⁺doping samples,and 508 K with higher Cr³⁺doping samples.The NIR pc-LED fabricated by Ca Mg Si₂O₆:0.5%Cr and Ca Mg Si₂O₆:4% Cr can achieve near-infrared light output of 11.55 m W and 4.16m W at 100mA current,respectively.(2)A series of Cr³⁺doped?-phase broadband near-infrared luminescent materials(X₄Zr₃O₁₂,X=Sc,Y,Lu)were synthesized by high temperature solid-state method.For the synthesized?-phase broadband near infrared luminescent materials,the crystal field environment of Cr³⁺is affected by the change of corresponding trivalent cations.The crystal field parameters of these three materials were calculated by spectral data.The crystal field strength parameter D_q increase with the decrease of the bond length of octahedron in corresponding materials.And the NIR emission position and FWHM increase with the increase of the bond length of octahedron.At the same time,due to the ligand oxygen ion participating in the bond formation,the nephelauxetic effect leads to the difference of the Racah parameters of the three materials(the Racah parameter B of Sc₄Zr₃O₁₂:Cr,Y₄Zr₃O₁₂:Cr,Lu₄Zr₃O₁₂:Cr rises in turn),which interferes with the corresponding relationship between D_q/B parameters and the average bond length of Cr ion.