Luminescence Properties Of Zn₂GeO₄:Mn²⁺:Bi³⁺ Long Afterglow Nanophosphors And Sr₂MgSi₂O₇:Tb³⁺ Nanoparticles

The nanoluminescent materials doped with transition metals and rare earth ions can cover all wavelength bands from ultraviolet to visible and infrared,which have the advantages of strong light absorption capability,high conversion efficiency and good color purity,Luminescent materials have a wide range of applications in many fields such as lighting,display,and detection.Therefore,exploring and studying the luminescence properties and internal mechanism of new doped transition metal and rare earth ion optical materials have important scientific significance and application value.The main content of this article is as follows:First,Zn₂GeO₄:Mn²⁺and Zn₂GeO₄:Mn²⁺:Bi³⁺long afterglow phosphors were prepared by high temperature solid-state reaction.The crystal structure and surface morphology of the samples were characterized by XRD and SEM.The results show that the diffraction peaks of the prepared Zn₂GeO₄ matrix are basically consistent with those of the standard card.There are no new diffraction peaks after Mn²⁺or Bi³⁺doped.However,with the increase of Mn²⁺and Bi³⁺doping concentration,the XRD diffraction peak is slightly blue-shifted,which indicates that the introduction of Mn²⁺and Bi³⁺ions will slightly change the crystal structure of Zn₂GeO₄;the SEM photos show that the two series of nano-phosphors are spherical structures.The average particle size is around 50 nm.Under the excitation of 325 nm,the fluorescence emission and afterglow emission center wavelengths of Zn₂GeO₄:Mn²⁺and Zn₂GeO₄:Mn²⁺:Bi³⁺samples are all around 530 nm,and all come from the ⁴T_1g?G??⁶A_1g?S?transition of Mn²⁺ions.After the excitation light source is turned off,the Zn₂GeO₄:0.2Mn²⁺phosphor has a measurable afterglow time of about 60 minutes,The visible duration of the naked eye in the darkroom environment is 180 minutes;After co-doping with 0.2 mol%Bi³⁺ions,the measured afterglow time of the sample is 150 min,which is about 2.5 times longer than that of the single-doped 0.2 mol%Mn²⁺ions,and the visible time in the darkroom environment is 360 minutes for the naked eye,It is twice as long as the afterglow of single doped Mn²⁺ions sample.The afterglow attenuation of both series of samples satisfies the double exponential equation.The reasons for the improved afterglow performance of Zn₂GeO₄:0.2Mn²⁺samples by Bi³⁺doping are as follows:?1?Incorporation of trivalent tellurium ions can cause new lattice distortions and increase the number of defect levels with appropriate depth;?2?Bi³⁺ions can transfer energy to Mn²⁺ions.Secondly,Sr₂MgSi₂O₇:Tb³⁺nanopowders were prepared by the same method.XRD and SEM characterization results show that Tb³⁺ion doping had no obvious effect on the crystal structure of Sr₂MgSi₂O₇ host,but with the increase of Tb³⁺doping concentration,the particle size of Sr₂MgSi₂O₇ sample increased significantly.Excited by different pump light at 245 and373 nm,The central wavelength of the emission peak of Sr₂MgSi₂O₇:Tb³⁺phosphor have no change,and They are located at 382,415,437,490,545,585 and 624 nm,corresponding to the characteristic peak of the f-f transition of Tb³⁺ion.Although 245 nm is the optimal pump wavelength for the Sr₂MgSi₂O₇:Tb³⁺nanopowder,the deep UV LED chip is expensive.Although the green emission of the Sr₂MgSi₂O₇:Tb³⁺phosphor will be reduced when using373 nm excitation,it can greatly reduce the price of the LED chip used as a pump source.At the same time,the effect of erbium doping concentration on the luminescence intensity of the sample was studied.When the optimal concentration of doped Tb³⁺is 1.6 mol%,the green light emission at 545 nm is the strongest.The reason for the concentration annihilation was due to the cesium ion electric dipole-galvanic couple.Caused by the interaction between the poles.