Study On The Effect Of Mn,Ho And Bi Ions Doping Concentrations On The Optical Properties Of CaZnOs-based Mechanoluminescence Materials

Recently,the researches of mechanoluminescence(ML)and the related fields have attracted much attention.ML refers to the light emission generated when the materials are stimulated by mechanical force.ML has a great potential for advanced optoelectronics which can trigger many important technologies(such as new light sources,pressure visualization sensors,and mechatronics,etc).In particularly,the strain-induced piezoelectric potential stimulates the emission of photons without additional energy such as external light and electrical excitation,which provides an important promissing for manufacturing of intelligent devices.In the past few years,doped ZnS,CaZnOS,SrAl₂O₄,and Li Nb O3 mechanoluminescence materials have aroused great interest.Among them,the semiconductor material CaZnOS is an excellent luminescence matrix material.The photoluminescence(down-conversion and upconversion luminescence),afterglow-luminescence,and mechanoluminescence phenomena are activated by doping with lanthanides or transition metal elements,resulting in important applications in many aspects,so it becomes a hot topic of research recently.Because it has nearultraviolet excitation,wide range of visible light emission,long phosphorescence,X-ray excited fluorescence,and excellent ML luminescence,the luminescent material matrix used herein is the a CaZnOS-based semiconductor.CaZnOS crystals doped with different luminescent ions can display effective and tunable ML wavelengths with spectrum range from purple to nearinfrared,which can solve the limitation of ML emission color in the development of ML technology.In this paper,the experimental preparation of the CaZnOS-based material,its structure characterization and luminescent characteristics are described in detail.The results are as follows:1.Preparations of ML materials doped with different luminescent ionsBased on the previous works(Advanced materials,201807062;201907747),the research objects screened in this article were ZnS-CaZnOS: Mn²⁺,CaZnOS: Ho³⁺,and CaZnOS: Bi³⁺ML materials.These three categories prepared by high-temperature solid-state reaction process.When preparing ZnS-CaZnOS: Mn²⁺,fix ZnS and Ca CO3 with the molar ratio of 1: 0.5,guarantee the two phases of ZnS and CaZnOS coexist,then change the amount of MnCO₃ as one of the raw materials,adjust the doping concentration of Mn²⁺ to tune the luminous color and luminous brightness of the material;at the same time,we also synthesized CaZnOS: Ho³⁺ML material with green luminescence performance,explored to change the amount of doped raw material holmium nitrate hexahydrate,control the doping concentration of Ho³⁺ ions,and optimize the material formula for the best luminescence characteristics;Synthesize CaZnOS:Bi³⁺ ML with blue luminescent properties,explored the effect of changing the doping concentration of bismuth nitrate on the luminescent characteristics,including wavelength and ML intensity,optimize the luminescent characteristics,and obtain the best material formula.2.Characterizations for the synthesized mechanoluminescent powdersSystematic measurements of the structural phases and luminescent characteristics of the three different systems synthesized.Characterization methods include powder X-ray diffraction,scanning electron microscope(SEM),EDS chemical element analysis,UV-visible diffuse reflection,up-conversion luminescence,fluorescence spectrometer(PL),fluorescence microscopy,X-ray fluorescence,and mechanoluminescence(ML).The mechanoluminescence and fluorescence spectra of three different systems of powders were analyzed.Fixed the amount of ZnS and Ca CO3 as starting materials,and changed the doping concentration of Mn²⁺ ions to 0.1%,0.2%,0.4%,0.8%,1%,2%,4%,and 8%.Under the 393 nm wavelength excitation,photoluminescence peak red-shifted 9nm for ZnS-CaZnOS:Mn²⁺ composite from lower concentration to a higher concentrations,while mechanoluminescence peak has a red-shift with the value of 35 nm.When the concentration of raw material MnCO₃ keeps 0.8%,the mechanoluminescence shows the strongest intensity;Under the 451 nm wavelength excitation,CaZnOS: Ho³⁺ sample shows a green color photoluminescence with the wavelength of 559 nm,and the doping concentration of Ho(NO₃)3.6H2 O is changed to 2%,4%,6%,10% and 16%.The ML emission wavelength of all the samples keep at 559 nm without changes.CaZnOS: Ho(6%)has the strongest ML luminescent intensity;in order to abtain blue emission,we chose the doped ion of Bi³⁺ by using the raw materials as Bi(NO₃)3.5H2 O,following the similar process for Ho³⁺ doped samples,we synthesized CaZnOS: Bi³⁺ samples doped with different concentrations,the photoluminescent peak of sample is 473 nm under the 283 nm wavelength excitation,while ML emission wavelength is 485 nm,showing the blue PL and ML emission characteristics.3.Application Scenarios investigationThe above-synthesized powders were used for electronic signature handwriting collection and imaging.By selecting the ML powders with premium luminescent performance,a stressvisualized mechanoluminescence sensor thin-film device is prepared to simulate the effect in the smart electronic signature.By capturing photographs of the handwriting "vis","shenzhen" and hand-drawn drawings(lychee-fruit pattern)through the camera CCD unit,and then we use the software of Photoshop to eliminate picture noise,and finally through Matlab software,we complete the three-dimensional image processing of the above-handwritten photographs to achieve the intensity distribution analysis of the photographs.This methods not only can record the 2D writing patterns,but also can record the strength of pressure distribution for writing habits.The dual informations of writing personality are mapped by the ML photographs.Compared with the traditional method for handwriting images,the security of ML E-signatures is greatly enhanced.