Luminescent And Temperature Sensing Properties Of Rare Earth Doped Vanadate Phosphors

Due to its excellent properties,including low synthesis temperature,stable chemical properties and good thermal stability,vanadate has received extensive research and attention.A variety of phosphors with different luminescent properties can be obtained by combining vanadate with rare earth ions.At present,high performance phosphors for white LED and phosphors for optical temperature measurement are two hot topics.The main work of this paper is to investigate the luminescent and temperature sensing properties of rare earth doped vanadate phosphors.The research contents are summarized as follows:（1）Luminescent properties of Na₂GdMg₂（VO₄）₃:Eu³⁺red phosphors for NUV excited pc-WLED:Herein,a series of novel Na₂GdMg₂（VO₄）₃:Eu³⁺(NGMVO:Eu³⁺)red phosphors were elaborated by conventional solid-state reaction process.Their structural features,luminescent properties,energy transfer were researched at length.X-ray diffraction（XRD）patterns indicate that NGMVO:Eu³⁺crystallized in single cubic garnet structure.Under the excitation of near ultraviolet light at 356 nm,the emission spectra of NGMVO host could be divided in two parts that resulted from ³T₂→¹A₁ and ³T₁→¹A₁ transitions of VO₄^3-.While NGMVO:Eu³⁺phosphors show intense sharp red emission peaks including 590,610,652 and 706 nm that originated from ⁵D₀→⁷F_J（J=1-4）transitions of Eu³⁺,respectively.The optimal concentration of Eu³⁺is 0.7.Importantly,NGMVO:0.7Eu³⁺sample presents high energy transfer efficiency（89%）and high external quantum efficiency（48.3%）.Besides,its emission intensity remains 79%at 420 K compared with that at 300 K,proving the good thermal stability of phosphors.All above results suggest that NGMVO:Eu³⁺red phosphors have latent applications in white light emitting diodes.（2）Up-conversion and optical thermometry of Na₂YMg₂（VO₄）₃:Er³⁺,Yb³⁺phosphors:Na₂YMg₂（VO₄）₃:Er³⁺,Yb³⁺phosphors are reported for UC luminescent material as optical thermometry relied on FIR and fluorescence lifetime.Their structures,UC luminescent properties and temperature sensing properties have been systematically investigated.Heavy doping of Er³⁺and Yb³⁺ions with maximal content of 59%is realized,which is beneficial to obtain highly efficient UC luminescence.Excited by 980 nm laser,Er³⁺and Er³⁺,Yb³⁺doped phosphors give 525,550 and 660 nm emissions,which are originated from ²H_11/2,⁴S_3/2 and ⁴F_9/2→⁴I_15/2transitions of Er³⁺ions,respectively.The reasonable UC mechanism is discussed in detail.What’s more,the UC emissions of all samples dominate in green area from thermally coupled ²H_11/2/⁴S_3/2 levels of Er³⁺ions,which is helpful to obtain better temperature sensing performances.And the maximal relative sensitivities of FIR and fluorescence lifetime methods reach 1.104%K^-1（303 K）and 0.087%K^-1（412 K）,respectively.All results manifest that Na₂YMg₂（VO₄）₃:Er³⁺,Yb³⁺phosphors are good potential alternative for optical temperature sensors.（3）Up-conversion and optical thermometry of Na₂GdMg₂（VO₄）₃:Er³⁺,Yb³⁺phosphors:Na₂GdMg₂（VO₄）₃:Er³⁺,Yb³⁺phosphors were prepared by high-temperature solid-state method for optical thermometry.According to XRD,scanning electron microscopy（SEM）,diffuse reflection spectra（DRS）,UC emission spectra,power dependent UC spectra,fluorescent decay curves and temperature dependent emission spectra,their crystal structures,UC luminescent characteristics and temperature sensing performances based on fluorescence intensity ratio technology were studied in detail.Heavy doping（59%）of Er³⁺and Yb³⁺ions is achieved.There are three characteristic luminescence peaks at 525,550 and 660 nm in the UC emission spectra of Er³⁺single-doped and Er³⁺,Yb³⁺co-doped samples excited by 980 nm laser,which are attributed to ²H_11/2,⁴S_3/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺ions.UC emission area is dominated by green lights and greatly enhanced UC emission over 389 times is realized by introducing Yb³⁺ions.In addition,the fluorescence intensity ratio technology of thermally coupled energy levels(²H_11/2/⁴S_3/2)of Er³⁺is used to achieve a wide range of temperature measurement.When the temperature is 303 K,the relative sensitivity reaches maximal value of 0.976%K^-1.All the experimental results show that Er³⁺,Yb³⁺co-doped Na₂GdMg₂（VO₄）₃phosphors might act as optical temperature sensing materials with good stability.