Cr³⁺/Ni²⁺ Doped Gallate Broadband Emitting Near-infrared Fluorescent Materials And Their Applications

Near-infrared(NIR)spectroscopy determination,which has great potential in food analysis,biosensing,biomedical imaging,iris/facial recognition and night vision,has received extensive attentions because of non-contact,non-invasive,high sensitivity and rapid response.NIR luminescent materials can be applied to different fields according to emission band ranges characteristics.The NIR optical window Ⅰ(NIR-Ⅰ,650-1000 nm)can penetrate food deeply with less heating effect and interact with the overtones of molecular vibrations in chemical composition of food,which can be designed as light sources of spectrometers for food analysis.The NIR optical window Ⅱ(NIR-Ⅱ,1000-1450 nm)offers lower auto fluorescence,less tissue scattering and deeper penetration into biological samples,making it possible to obtain a large imaging depth and have a promising biomedical imaging application prospect.Broadband NIR emitters have emerged as vital core light sources for NIR spectroscopy applications.With the increasing demand for food analysis,quality control and health monitoring,broadband NIR light sources have been greatly developed with advantages of reliability,rapid and noninvasiveness.Phosphor converted light-emitting diode(pc-LED)has attracted attention due to low energy consumption,long-lifetime,fast response and small volume.In this paper,Cr3+/Ni2+ activated broadband NIR gallate phosphors were investigated.The crystal structure,morphology and luminescence properties were discussed in detail.The broadband NIR-LED devices were fabricated by using the phosphors combined with blue LED chips,the applications of which were explored preliminarily.The main contents of this paper are concluded as follows:1.Multiple crystallographic sites occupancy strategy to broaden the emission spectrum.The lumin:scence properties of broadband NIR phosphor Mg3Ga2GeO8:Gr3+was investigated and a non-destructive analytical method for quantitative food analysis was established.The detailed crystal structure of Mg3Ga2GeO8:Cr3+ was investigated by powder XRD Rietveld refinements,HRTEM image and corresponding SAED.Luminescence mechanism based on different Cr3+ ions positions was investigated according to Gaussian peak fitting.A NIR-LED light source was fabricated by packing the phosphor with a blue LED chip.A non-destructive analytical method for food quality control was established preliminarily by penetrating fruits using as-fabricated NIR-LED to obtain transmission spectra.This work exploits a new and specific application for ultra-broadband NIR phosphors.2.Improving thermal quenching performance based on activator ion lattice site occupation to construct dual-function near-infrared luminescent material.A series of dual-functional Crr-doped magnetoplumbite structure LaMgGa11O19 phosphors were prepared via traditional solid state method.In LaMgGa11O19 host,a strategy to obtain dual-emitting centers with enlarged emission band and completely different thermal-quenching behaviors by the sites selection of Cr3+ has been developed,achieving a material with both food analysis and temperature sensing functions.The phosphor exhibits broadband NIR emission in the range of 650-1200 nm.Based on this,food composition analysis is performed.Meanwhile,the emission intensity peaking at 730 nm and 918 nm displays reverse tendency with rising temperature.The ratiometric optical thermometric characteristic based on luminescence of the two emitting centers was investigated,indicating potential application in optical thermometric sensing.3.Design and synthesis of the continuous solid solution by energy transfer enhancement luminescent intensity strategy.Cr3+/Ni2+co-doped NIR-Ⅱ phosphors Zn1+ySnyGa2-2yO4 with high energy transfer efficiency for the application of optical imaging were investigated.The phosphors show broad emission in the range of 1100-1600 nm in the second NIR window under the excitation of 450 nm.Due to energy transfer from Cr3+ to Ni2+,the emission intensity of Ni2+could be substantially enhanced more than 50 times when excited at 450 nm.The energy transfer mechanism was inferred from the excitation,emission spectra and decay lifetimes curve,confirming that the main process is the electric dipole-dipole interaction.Finally,the phosphor was fabricated as NIR-LED light source combined with blue LED chip in one package to transilluminate biological tissue.The obtained near-infrared photos can well distinguish biological tissues in different states,suggesting the great application prospect in advanced optical imaging.