Design,Synthesis And Property Of The Transition Metal Ions Doped Li₂ZnGe₃O₈ Near Infrared Luminescent Materials

In this paper,serials of transition metal ions doped(Cr³⁺,Mn²⁺)Li₂ZnGe₃O₈ near infrared luminescent materials are synthesized using a high-temperature solid-state method.The luminescent properties can be tuned by different doping,different substitutions and controlling the ratio of cations in host,and the reason of tunable luminescent properties are analyzed,as follows.?1?Transition metal ion Cr³⁺doped Li₂Zn Ge₃O₈ deep-red luminescent materials are synthesized,the excitation spectrum is characterized by a broad band from 250 nm to 640 nm,and the emission peak located at 713nm.The change of luminescent properties were researched when Zn²⁺and Ge⁴⁺are substituted by Cr³⁺in host,respectively.The emission spectra both have a red shift along with the increase of Cr³⁺ions in Li₂Zn Ge_3-xO₈:xCr³⁺and Li₂Zn_1-xGe₃O₈:xCr³⁺phosphors.Herein,the red shift distance of the latter is larger than the former,which is related to the different occupation of Cr³⁺ ions.In order to obtained near infrared light and to analyze the luminescent regulation by controlling the ratio of cations in host,the Mg²⁺/Ca²⁺/Sr²⁺/Ba²⁺ions were introduced in Li₂Zn GeO₈:xCr³⁺phosphors.The luminescent materials has realized the control from deep red to near-infrared light by increasing the doping ionic(Ca²⁺,Sr²⁺,and Ba²⁺)radii.Herein,the emission spectra have a blue shift and then present an obvious red shift by controlling the Zn/Mg ratio.A common effect between the crystal field splitting and the nephelauxetic effect makes it possible to blue shift,and the red shift can be ascribed to the reduced site symmetry around some Cr³⁺ions caused by the disorder.In addition,the emission spectra have a red shift when Zn²⁺is substituted by bigger ions(Ca²⁺,Sr²⁺,Ba²⁺),which is also a common effect between the crystal field splitting and the nephelauxetic effect.To further broaden the excitation and emission range of Li₂Zn Ge₃O₈:xCr³⁺phosphors,the Mn²⁺ions were introduced in Li₂ZnGe₃O₈:xCr³⁺.The spectra of Mn²⁺and Cr³⁺ions have a superposition,as a result,the near infrared materials with broad excitation and emission were got.Especially,it can be find that Mn²⁺ions have an near infrared emission in Li₂ZnGe₃O₈ host.?2?Transition metal ion Mn²⁺doped Li₂ZnGe₃O₈ near infrared luminescent materials are synthesized,and the excitation spectrum is characterized by a broad band from 250 nm to 640 nm centered at 475 nm.Besides,the emission spectra present a broad band from 650 to 900 nm with the main peak at 832nm,which is a typical wide near infrared emission.The effects of Mn²⁺doping concentration on synthesis temperature and luminescence properties were investigated.Herein,the luminescence mechanism,thermal stability and morphology of the materials were described in detail.In view of the similar ionic radius between Mg²⁺and Zn²⁺,a series of Li₂Zn_1-xMg_xGe₃O₈:xMn²⁺ phosphors,with different spectral widths,were obtained by introducing the Mg²⁺ion.Preliminary control of matrix components was researched on Li₂ZnGe₃O₈:Mn²⁺ phosphor realizing the expansion of emission spectra to short wave direction,especially,there is a transformation from the[ZnO6]unit to[MgO4]or[ZnO4]in the LZG crystal,which generates defects leading to the obvious broadening of the emission spectra.?3?For Li₂ZnGe₃O₈ host,[ZnO4]shows the tetrahedral coordination mode,[ZnO6]and [GeO6]all show octahedral coordination modes.By controlling the occupation sites of the Mn²⁺emitters,the phosphor can be tuned in the green to NIR regions.The effect of matrix composition?Li/Zn?Zn/Ca?Zn/Sr?Zn/Ba?on luminescent properties within Li₂Zn Ge₃O₈:Mn²⁺materials are investigated.Through increasing the Zn²⁺concentration in host,the green emission is enhanced continuously and the NIR emission?Zn O6 site?is restrained.We have obtained a width-tunable NIR phosphor related to the defects when Zn²⁺was substituted by smaller ions in Li₂Zn_1-yMg_yGe₃O₈:Mn²⁺.Herein,when Zn²⁺is substituted by bigger ions from Ca²⁺to Sr²⁺and Ba²⁺,the local environment of Mn²⁺ around ZnO6 is influenced which leads to part of the Mn²⁺emitters occupying the Ge⁴⁺ site,and it has the most enhanced effect on the Mn²⁺red emission.Finally,series of Mn²⁺ doped near infrared phosphors were obtained,and the excitation spectra cover the ultraviolet and visible light regions.The results have a very significant significance to the research on tuning the fluorescence properties of the materials by different doping,different substitutions and controlling the ratio of cations in host,which provides a selective space for"biological window"near infrared materials.