Synthesis,luminescence Mechanism And Temperature Sensitivity Of Pr³⁺/Eu³⁺activated Oxides-based Phosphors

In recent years,rare earth doped inorganic phosphors have been widely used in solar cells,light-emitting diodes,biological imaging,display technology,fluorescent anti-counterfeiting,optical thermometry and other fields due to their good chemical and thermal stability.To date,rare earth inorganic phosphors still have some basic problems such as low luminous intensity,efficiency and relative sensitivity in the fields of display and optical thermometry.To overcome the above problems,Pr³⁺/Eu³⁺activated oxides-based phosphors with high luminous intensity and efficiency or high relative sensitivity for applications in the fields of display and optical thermometry were synthesized via fluxes assisted solid phase methods or novel sol-gel methods.With the help of various characterization methods,the intrinsic relationship between structure,composition and properties of materials was established.The results are as follows:(1)CaTiO₃:Pr³⁺red phosphors were synthesized by NaF flux assisted solid state method.The results show that all samples have orthorhombic perovskite phase and no impurity phase is found.The morphology of typical sample CaTiO₃:0.6%Pr³⁺+2%NaF is mainly spherical,and the particle size is about 670 nm.When the concentration of Pr³⁺is 0.6 mol%,concentration quenching occurs and the critical distance is?26.09?.The mechanism of concentration quenching is dipole-dipole interaction.A certain amount of NaF flux can improve the photoluminescence intensity of CaTiO₃:Pr³⁺.In addition,based on intervalence charge transfer(IVCT)state,the temperature sensitive fluorescence intensity ratio(FIR)values of³P₁?³H₆/¹D₂?³H₄ are constructed.The relative sensitivity of typical samples is as high as 4624/T² K^-1,and the maximum absolute sensitivity(S_a)and relative sensitivity(S_r)are?0.015 K^-1@523K and?5.2%K^-1@298K,respectively.It is expected to be used in the field of optical thermometry.(2)CaTiO₃:Pr³⁺red phosphors were synthesized by H₃BO₃ flux assisted solid state method.The results show that the typical sample CaTiO₃:0.6%Pr³⁺+3.4%H₃BO₃ has orthorhombic perovskite phase,its optical band gap is?3.59 e V,and its CIE chromaticity coordinates are very close to the ideal red light.The long afterglow performance of CaTiO₃:0.6%Pr³⁺+3.4%H₃BO₃ is better than that of CaTiO₃:0.6%Pr³⁺.Besides,based on IVCT state,the temperature sensitive FIR values of TE/¹D₂?³H₄are constructed,and the relative sensitivity of typical sample is as high as6837/T² K^-1.The maximum S_a is?0.0258 K^-1@473 K,the maximum S_r is7.69%K^-1@298 K.and the temperature resolution is 0.26-0.65 K,which has great potential in the field of optical thermometry.The thermochromism phenomenon is studied by using the temperature sensitive characteristics.The color difference is obvious at different temperatures,and the qualitative thermometry can be realized quickly.In addition,in successive 3 cycles,the color difference of typical samples changes little at the same temperature,which indicates that it has good reversibility and repeatability.(3)The novel Pr³⁺doped Sr SnO₃/SnO₂ phosphors were prepared by solid state reaction.The results show that the typical sample Sr SnO₃+SnO₂:0.16%Pr³⁺has a spherical multiphase structure with an average particle size of 421 nm.The enhanced PL intensity is attributed to the presence of SnO₂ phase,which promotes the improvement of Sr SnO₃ crystallinity and energy transfer efficiency from the host to Pr³⁺.The energy transfer between Pr³⁺-Pr³⁺in Sr SnO₃:Pr³⁺and Sr SnO₃+SnO₂:Pr³⁺is electric dipole-quadrupole and electric dipole-dipole interaction,respectively.In addition,based on IVCT state,the temperature sensitive FIR values of TE/³P₀?³H₄are constructed,and the relative sensitivity of the typical sample Sr SnO₃+SnO₂:0.16%Pr³⁺is as high as 5258/T² K^-1.At 303 K,the maximum S_r is 5.73%K^-1,which may provide some insight into optical thermometry strategy with high sensitivity.(4)Layered Eu³⁺doped?-Al₂O₃ phosphors were prepared by microwave/starch assisted sol-gel method.The results show that the solid solubility of Eu³⁺in the host of?-Al₂O₃ is?2 mol%,and the concentration quenching type is electric dipole-dipole interaction.The luminescence intensity of typical sample decreases to 68%of initial intensity at 423 K,and its activation energy is about 0.259 e V,which shows good thermal stability.Moreover,temperature sensitive FIR values are constructed by using the integrated intensity ratio of ⁵D₀?⁷F₄ and ⁵D₀?⁷F₀,₁,₂ to explore its temperature sensing.At?374 K,the maximum S_rof typical sample is0.103%K^-1,which is expected to be used in the field of optical thermometry.(5)SnO₂:Eu³⁺phosphors were prepared by albumin-assisted sol-gel method.The results show that the typical sample SnO₂:2%Eu³⁺has an irregular lamellar structure with tetragonal rutile phase;When the concentration of Eu³⁺exceeds 2.0%,the impurity Eu₂Sn₂O₇ appears.Eu³⁺ions can gather at the grain boundary and inhibit the growth of SnO₂particles.When the concentration of Eu³⁺is 2.0%,the concentration quenching phenomenon occurs,and is attributed to the electric dipole-quadrupole interaction.Furthermore,the temperature sensitive FIR values of TE/⁵D₀?⁷F₁ are constructed based on the non-thermal coupling energy level optical thermometry strategy.The high relative sensitivity of typical sample is 2854/T² K^-1,which is better than the theoretical value of 2446/T²K^-1 based on the thermal coupling energy level of Eu³⁺.The maximum S_aof the typical sample is?0.88 K^-1@373 K and the maximum S_r is?3.21%K^-1@298 K,which has potential for optical thermometry.