Study On The Preparation And Properties Of Er³⁺/Yb³⁺ Doped Double Perovskite A₂MgWO₆ （A=Ca,Sr,Ba） Upconversion Phosphors

Lanthanide-doped upconversion luminescent materials have been widely used in the field of temperature sensing,optical anti-counterfeiting,solar cells,nano-bioprobe,and so on,owing to their distinctive optical properties within the ultraviolet,visible,and near-infrared regions.At present,the problems of impoverished temperature sensing performance and single-mode luminescence limit the applications of most upconversion luminescence material in the fields of temperature sensing and optical anti-counterfeiting.The preparation of upconversion materials with excellent temperature sensing and luminescence performance plays a key role in practical applications.Therefore,in this paper,the double perovskite tungstate A₂MgWO₆（A=Ca,Sr,Ba）matrix materials with low phonon energy,straightforward preparation process,and good physical and chemical stability were selected,and a series of phosphors with excellent performance were prepared by doping Er³⁺,Yb³⁺or Eu³⁺lanthanide ions.The structural composition and luminescent properties of the materials were studied in detail,and their multifunctional applications in the fields of precise temperature measurement and anti-counterfeiting security were explored.The main works and consequences are listed below:（1）A series of Er³⁺/Yb³⁺doped Ca₂MgWO₆（CMW）,Sr₂MgWO₆（SMW）,and Ba₂MgWO₆（BMW）upconversion phosphors were synthesized by high-temperature solid-phase method.The three phosphors had a similar structure,and the[Er O₆]octahedron where Er³⁺ions were located in the BMW phosphors had the lowest distortion degree.The SEM results showed that the particle sizes of the synthesized phosphor powder decreased gradually from CMW to BMW.The XPS and ICP test results indicated that low concentrations Er³⁺/Yb³⁺were successfully doped into the A₂MgWO₆ double perovskite hosts,and the actual doping amounts of Er³⁺/Yb³⁺were basically the same,which were approximate close to stoichiometric proportion（0.3mol%）.Comparing the up-conversion luminescence properties of the phosphors,the luminescence of CMW was the strongest,followed by SMW,and BMW was the weakest.The synergistic effect of the particle sizes of phosphor powders,the actual doping concentration of Er³⁺/Yb³⁺ions,the degree of lattice distortion,and the ²H_11/2,⁴S_3/2,⁴F_9/2→⁴I_15/2energy level transitions of Er³⁺ions,etc,led to the difference in the upconversion luminescence of phosphors,in which the degree of lattice distortion had the greatest influence on the luminescence.Larger changes in FIR value could result in larger absolute sensitivity（S_A）values.The maximum absolute sensitivity of CMW phosphors was 72.14×10^-4 K^-1（398 K）,SMW was 135.32×10^-4 K^-1（398 K）,BMW was 7.41×10^-4 K^-1（323 K）.（2）Taking the CMW matrix as the representative,by co-doped Eu³⁺in the up-conversion Ca₂MgWO₆:Er³⁺/Yb³⁺phosphor,the effective improvement of the temperature sensing sensitivity factor and the multi-mode anti-counterfeiting were simultaneously achieved.The maximum S_A based on the ²H_11/2/⁴S_3/2 couples of Er³⁺increased from 81.83×10^-4 K^-1 at 423 K to 88.12×10^-4 K^-1 at 398 K,which was attributed to the energy transfer between Er³⁺and Eu³⁺which increases the fluorescence intensity ratio values.Taking advantage of the down-conversion luminescence characteristics of Eu³⁺ion,phosphors showed color tunability under 980 and 365 nm excitations.Meanwhile,the white ink prepared by using Ca₂MgWO₆:Er³⁺/Yb³⁺/Eu³⁺phosphor powder was printed on a piece of ordinary paper to form the anti-counterfeiting pattern by screen printing technology,which realized dual-mode anti-counterfeiting function.Therefore,the novel phosphors have potential applications in noncontact temperature sensing and optical anti-counterfeiting security fields.