Research On Luminescence Properties Of Vanadate Up-conversion Materials Under 1550 Nm Infrared Excitation

Rare earth doped up-conversion luminescence materials have attracted the attention of domestic and foreign researchers due to its excellent luminescent properties.In most studies up-conversion luminescence,researchers mostly use 980 nm laser as the excitation source,while the use of 1550 nm laser as the excitation source is less reported.By contrast,1550 nm infrared has less damage to the eye and has a deeper depth of biological tissue imaging.More importantly,under 1550nm excitation,Er³⁺ions can be directly excited to form up-conversion luminescence,which is an up-conversion excitation light source with application potential.In this work,rare earth doped La VO₄and Lu VO₄up-conversion materials were selected as the research object.We focus on the up-conversion luminescence properties under 1550 nm excitation.The specific research work is as follows:（1）LaVO₄:Er³⁺phosphors were synthesized by solid-state method.XRD data shows that the doped product maintains the monoclinic phase structure of the La VO₄host,and the introduction of Er³⁺ions regulated the lattice parameters.Under 1550 nm excitation,the material exhibits emission peaks at 523 nm,552 nm and 666 nm,which is attributed to the three-photon process.The 818 nm near-infrared emission was observed,which is attributed to two-photon process.It is found that the doping concentration of Er³⁺ions had an effect on the luminescence properties.Under low doping conditions,the up-conversion luminescence is mainly realized by the direct light absorption of Er³⁺.As the Er³⁺ions concentration further increases,the spacing of Er³⁺ions decrease.The increased sensitization effect of Er³⁺ions improved the probability of ETU process,which resulted in the enhanced luminescence.（2）Er³⁺,Yb³⁺co-doped LaVO₄phosphors were synthesized by solid-state method.Under 1550 nm excitation,the red and green emissions were observed,which belong to the three-photon processes.It is different from the luminescence under 1550 nm excitation,but the green emission is dominated luminescence under 980 nm excitation.And all luminescence processes are two-photon processes.Under 1550 nm excitation,the strong near-infrared emission was also observed,which is attributed to two-photon process.But the near-infrared emission was not observed under 980 nm excitation.Under 1550 nm excitation,the introduction of Yb³⁺enhances the luminescence intensity of the material,indicating that Yb³⁺can play an intermediate sensitization role to improve the energy transfer efficiency of Er³⁺.Then,up-conversion luminescence mechanism and the transition process were discussed in detail.The chromaticity diagram shows that the color of the phosphors gradually changes from yellow to green with the increase of Yb³⁺concentration under 1550 nm excitation,indicating that the regulation of the color of can be realized by adjusting the Yb³⁺concentration.But the effect of color regulation is not obvious under 980nm excitation.The results of temperature sensing characteristics showed that the La VO₄:Er³⁺,Yb³⁺sample has realized the temperature measurement function under the excitation of 1550 nm and 980 nm,respectively.The temperature sensitivity is Sr_（1550nm）=0.34%K^-1@296K and Sr_（980nm）=1.01%K^-1@296K,respectively.（3）The LuVO₄:0.2Er³⁺/0.05Yb³⁺material was synthesized by the solid-state method.The XRD refinement results showed that the doped product maintained the tetragonal structure of Lu VO₄host,and the lattice parameters and volume become larger.Under 1550nm excitation,the sample showed green emissions at 524 nm and 553 nm and red emission at 660 nm,both of which belong to three-photon processes.And strong near-infrared emission at 801 nm was observed,which belongs to the two-photon process.The up-conversion luminescence properties were compared under 980 nm excitation.It is found that the luminescence process of Lu VO₄system is similar to that of La VO₄system,but its luminescence intensity is slightly lower than that of La VO₄system.The monoclinic La VO₄system has lower symmetry than the tetragonal Lu VO₄system,which enhances the transition probability of Er³⁺.The temperature sensing characteristics shows that the temperature sensitivity of Lu VO₄:Er³⁺/Yb³⁺material is Sr_（1550nm）=0.27%K^-1@306K and Sr_（980nm）=0.82%K^-1@296K,respectively.In summary,under 1550 nm excitation,the up-conversion luminescence of Er³⁺/Yb³⁺doped La VO₄and Lu VO₄materials were both achieved and the samples exhibited red,green and near-infrared emissions of Er³⁺ions.The introduction of Yb³⁺improves the energy transfer efficiency and enhances the up-conversion luminescence intensity.Compared to Lu VO₄system materials,the La VO₄system material has excellent luminescence intensity,which has application prospect in the fields of color regulation and temperature sensing,indicating that it is an up-conversion optical material with research value and application potential.