Research On Synthesis And Properties Of Bi³⁺ Ions Doped Multifunctional Materials

It is well known that the luminescence of Bi³⁺ions at room temperature is usually attributed to the ³P₁?¹S₀transition,rather than the strongly forbidden ³P₀?¹S₀and³P₂?¹S₀transitions.When the temperature is low enough,the ³P₀?¹S₀transition can occur due to the relaxation process between ³P₁and ³P₀.Bi³⁺ion has a special electronic structure[Xe]4f¹⁴5d¹⁰6s².The exposed 6S electrons of Bi³⁺ions are very sensitive to the crystal field environment.In general,different doping sites in the same matrix make the luminescence sites of Bi³⁺ions different.Compared with rare earth ions,Bi³⁺ions have a wide absorption range in the ultraviolet region,but no absorption in the visible region.This avoids the re absorption of rare earth ions in the visible region.Therefore,in recent years,Bi³⁺doped materials are widely used in anti-counterfeiting,information encryption and colorful lighting.In this paper,the energy transformation between Bi³⁺ions and rare earth/transition metal ions and the internal relationship between Bi³⁺ions and matrix material structure are explored.It is applied to the field of temperature sensing,anti-counterfeiting and plant growth lamps.(1)Herein,a new ratio-metric luminescent thermometer Gd₂ZnTiO₆(GZTO):Bi³⁺,Mn⁴⁺is designed,which exhibits both red and blue luminescence under 375 nm excitation.Based on the different thermal sensitivity of Mn⁴⁺and Bi³⁺ions and the energy transfer from Bi³⁺to Mn⁴⁺ions,the luminescent thermometer reveals excellent thermal sensitivity(Sr=2.4%K^-1,Sa=16.8%K^-1)and a wide temperature measurement range(313–473 K).Both of them are superior to the most reported materials.In addition,the luminescence intensity of two ions matches the light absorption bands of photosynthetic pigment well,which indicates that GZTO:Bi³⁺,Mn⁴⁺phosphors also have a great prospect as a plant growth lamp.(2)Herein,a series of K₃Lu_1-xSi₂O₇:x Tb³⁺/x Bi³⁺phosphors with persistent luminescence or multimode luminescence have been successfully synthesized by high temperature solid state reaction method.For the first time,their structural and luminescent properties have been explored in detail and applied to anti-counterfeiting.Under the exaction from 280 nm to 375 nm,KLSO:Bi³⁺phosphors can exhibit multiple emission bands whose peaks locate at 375 nm,410 nm and 493 nm respectively,which is attributed to the ³P₁?¹S₀transitions of Bi³⁺ions in different lattice sties(Lu³⁺,K1⁺and K2⁺)from K₃Lu Si₂O₇(KLSO).In addition,the high concentration doping of Tb³⁺ions is realized in matrix KLSO for the first time.Due to the presence of appropriate traps in KLSO:Tb³⁺,Tb³⁺ions can show green persistent luminescence when the KLSO:Tb³⁺phosphors leave stimulation of 275nm.On the basis of these properties,the samples were used to print luminescent images through a screen printing process on the film.The luminescent image is showing different color patterns under different stimulations.All the results demonstrate the material KLSO:Tb³⁺/Bi³⁺which deserves to be injected more attention has potential for applications in anti-counterfeiting and information encryption.