Fake and shoddy products,such as fake certificates,drugs and money,cause great harm to the interests of individuals,enterprises and even the state.Anti-counterfeiting technology,as an effective means to combat counterfeit and shoddy products,has become an indispensable part of people's daily life.Technologies such as watermarking,bar code,holography,and luminescence have been widely used in anti-counterfeiting technology to ensure public safety.Among them,luminescence technology has become one of the best choices for anti-counterfeiting technology due to its advantages such as visual visibility,color diversity,and ease of implementation.However,most luminous materials can only display a single luminous color at a specific excitation and have a low security level,increasing the risk of counterfeiting and limiting their application in advanced anti-counterfeiting.Therefore,it is very important to develop solid luminescent materials with multi-mode excitation and multi-luminescent colors.Compared with Eu2+,Ce3+and other rare earth ions,Bi3+ions have attracted wide attention due to their environmental friendliness,abundant reserves and low price.The electron configuration of Bi3+is[Xe]4f145d106s2,and the electron shell is 6s2.Due to the 3P1→1S0 non-radiative transition of Bi3+,the emission range of Bi3+doped phosphor can extend from the ultraviolet region to the infrared region.Therefore,Bi3+is widely regarded as an activator that can achieve luminous color regulation.It has been reported that gallate has stable physical and chemical properties,so in this work,aluminate Sr2LaAlO5 was selected as the matrix host.Sr2LaAlO5 has a simple crystal structure,and both Sr and La have suitable ionic coordination number and ionic radius,which provides the possibility for successful doping of Bi3+.So far,Sr2LaAlO5 phosphors doped with rare earth ions have been reported successively.However,to the best of our knowledge,Bi3+doped Sr2LaAlO5 phosphors have not been reported.At present,one of the most commonly used methods of luminescence regulation is through cation substitution,because cation substitution can have a great impact on the local environment around the luminescence center,and it is possible to achieve the tuning of the emission spectrum.Since Sr2LaAlO5 and Ba2LaAlO5 belong to the I4/mcm tetramonal system,Sr and Ba cation substitution on the basis of Sr2LaAlO5 is expected to achieve the luminescence regulation of Bi3+.In this paper,Sr2LaAlO5∶xBi3+blue phosphors and Sr2-yBavLaAlO5∶0.02Bi3+solid solution phosphors were successfully realized.The phase structure,luminescence characteristics and luminescence efficiency of phosphors were experimentally characterized by X-ray diffraction,photoluminescence spectrum,photoluminescence excitation spectrum,fluorescence microscopy and quantum yield measurements.The effect of equivalent cation substitution on luminescence characteristics was analyzed in detail,and the corresponding mechanism was proposed.When Sr2+is gradually replaced by Ba2+,it can be observed that the luminous color of Sr2-vBayLaAlO5∶0.02Bi3+solid solution phosphors is regularly redshifted in the blue-green region,which is caused by the crystal field splitting and nephelauxetic effect.In addition,the luminescence redshift of Sr2LaAlO5:0.02Bi3+phosphor gradually increased with the excitation wavelength,indicating that Bi3+ions occupied different cation sites and formed multiple luminescence centers.Finally,a series of Sr2-yBayLaAlO5∶0.02Bi3+solid solution phosphors have been synthesized in this work due to the multi-excitation and multi-emission characteristics of solid solution phosphors,which can be used as potential candidate materials in anti-counterfeiting applications.
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