Explorational Study On Novel Mechanoluminescent Materials

Mechanoluminescent（ML）materials are mechano-optical converters that can emit light under an external mechanical stimulus including compress.However,at present,the number of ML materials is limited,the emissions of reported of ML meaterials are mainly concentrated in the visible region,which restrains the application area.If the ML emission can be extented to the near infrared（NIR）region,it can be expected to be used in in vivo biomechanical imaging with the aid of penetration capability of near infrared light.Therefore,this work starts from finding new type of ML host,developing NIR ML phosphor and exploring the way to optimize the ML properties.The main research results are as follows:1 A series of visible mechanoluminescent materials were sdutied.（1）The ML properties of MGa₂O₄:Cr³⁺（M=Zn,Mg）were studies.The ML peaks of MgGa₂O₄:Cr³⁺and ZnGa₂O₄:Cr³⁺were located near 710 nm.ZnGa₂O₄:0.5%Cr³⁺was selected as the case for enchanced ML properties.The results showed that both afterglow and ML properties of the sample were obviously improved by conntrolling the substitution of Ga by Ge.The enhancement of the thermoluminescence（Th L）curve of sample ZGGO:0.5%Cr³⁺and the widening of the Th L curve in the high temperature part revealed that the introduction of Ge increased the concentration of deep defects in the sample,thus optimizing the afterglow and ML properties.（2）A novel Mn²⁺-doped wide band gap semiconductor,BaZnOS,demonstrates intense elastico-mechanoluminescence（EML）under pressure and friction.Orange-to-red EML emission peaks（586,610 nm）were observed after application of different mechanical stimuli,which differs from the photoluminescence（PL）peak,which is fixed at 634 nm.Besides,the intensity of ML emission peaks is proportional to the applied compressive stress.The special phenomenon indicates that BaZnOS:Mn²⁺can be employed as a stress sensor that not only records the stress magnitude and distribution,but also identifies the stress type.（3）The ML characteristics of CaZnOS:RE³⁺(RE³⁺including Pr³⁺,Sm³⁺,Eu³⁺,Tb³⁺,Dy³⁺and Ho³⁺)were also explored,and it is found that this series of samples show bright luminous upon load.2 A series of near infrared mechanoluminescent materials were sdutied.（1）A series of NIR ML phosphors were discovered by doping rare earth ions RE³⁺（RE=Nd,Yb,Tm）into CaZnOS.Specially,the NIR ML peaks of CaZnOS:Nd³⁺were 910,1094and 1390 nm,which firstly covers the the first and second tissue-penetrating bioimaging window.At the same time,the CaZnOS:Nd³⁺has the advantages of high luminous efficiency,low ML threshold and repeatability.More remarkably,the CaZnOS:Nd³⁺can penetrate tissue as deep as>22 mm to enable biomechanical detection.Additionally,we recorded the NIR ML from the sintered cylindrical samples when the samples were bitten by the human teeth.Indeed,we observed a distinct NIR ML signal when the sample was bitten by the teeth with the mouth open.When the mouth was closed but the sample was still bitten by the teeth,the NIR ML signal could still be detected.Hence,the biocompatible CaZnOS:Nd³⁺is a new potential ultrasensitive biomechanical probe and expands ML application horizons into in vivo bioimaging.（2）NIR ML phenomena were also found in Tm³⁺,Yb³⁺doped CaZnOS phosphors,the ML spectra are consistent with the photoluminescence spectra.The main NIR-ML peaks of Tm³⁺and Yb³⁺are 785 nm,814 nm and 980 nm.3 Ultra wide Vis-NIR ML,with emission peaks at 550 nm,675 nm,855 nm,978 nm,1540 nm,was achieved in CaZnOS:Er³⁺.Strong green glow can be seen by naked eyes in dim environment under mechanical stimuli.It is also found that the crystallinity of the sample was obviously improved by adding Li₂CO₃ as flux,thus increasing the ML performance up to three times.So far,the combination of RE ions and CaZnOS has realized ML output from blue,green,yellow,red relying on the rich energy level of RE ions,thus realizing the ultra-wide ML from single matrix for the first time.