Upconversion Luminescence And Optical Thermometry Of Rare Earth Doped β-Ca₃（PO₄）₂ Type Materials

Temperature is one of the most fundamental physical quantities and is extremely important in scientific research,industrial production,and life sciences.Therefore,precise temperature measurement is a crucial aspect of scientific research.Compared to temperature measurement techniques,such as thermocouples,rare-earth doped upconversion luminescent materials offer non-contact measurement with fewer measurement constraints.Moreover,they can reduce the influence of non-temperature parameters such as excitation power and fluorescence loss,making it a highly promising temperature measurement method.β-Ca₃（PO₄）₂-type phosphors exhibit excellent luminescent properties,good stability,and have more environmentally friendly synthesis methods.Its unique crystal structure makes it easy to adjust the structure and luminescent properties.Moreover,β-Ca₃（PO₄）₂-type materials are structurally and compositionally very similar to natural bone tissue,making them highly biocompatible.However,research on upconversion luminescence ofβ-Ca₃（PO₄）₂-type phosphors has been rare compared to downconversion luminescence in recent years.Therefore,we believe thatβ-Ca₃（PO₄）₂-type phosphors with upconversion luminescent will have broad application prospects in various fields,including temperature sensing,biological imaging,biosensing,laser anti-counterfeiting,laser display,infrared detection,and others.This paper focuses on the typical matrix material Ca₉Y（PO₄）₇,which has aβ-Ca₃（PO₄）₂structure,and uses rare-earth ion doping to achieve upconversion luminescence.The electronic structure of the material is calculated,and the crystal structure and luminescent properties are studied.Temperature sensing is also investigated using thermally and non-thermally coupled energy levels.The main contents of this paper are as follows:1.Upconversion luminescence and optical temperature sensing study of Er³⁺-Yb³⁺doped Ca₉Y（PO₄）₇.Ca₉Y（PO₄）₇:Er³⁺,Yb³⁺phosphors were prepared using high-temperature solid-state method.The crystal structure,electronic structure,and upconversion emission properties of the matrix material and doping material were studied to investigate the temperature sensing characteristics of the thermally and non-thermally coupled energy levels of LIR.Under 980 nm excitation,the Ca₉Y（PO₄）₇:Er³⁺,Yb³⁺sample exhibited three upconversion emission bands（with peak wavelengths at 527 nm,553 nm,and 651 nm）,corresponding to the transitions of²H_11/2→⁴I_15/2,⁴S_3/2→⁴I_15/2,and ⁴F_9/2→⁴I_15/2,respectively.The temperature sensing sensitivities of LIR based on the thermally coupled energy levels ²H_11/2-⁴S_3/2(I_{527 nm}/I_{553 nm})and the non-thermally coupled energy levels ²H_11/2-⁴F_9/2(I_{527 nm}/I_{651 nm})were calculated.In the temperature range of 323～853 K,the S_a-max and S_r-max of LIR(I_{527 nm}/I_{553 nm})were0.00894 K^-1（750 K）and 1.41%K^-1（327 K）,respectively,while the S_a-max and S_r-max of LIR(I_{527 nm}/I_{651 nm})were 0.0022 K^-1（853 K）and 0.51%K^-1（523 K）,respectively.The temperature sensing performance of LIR(I_{527 nm}/I_{553 nm})was better in the temperature range of 323～550 K,while the temperature sensing performance of LIR(I_{527 nm}/I_{651 nm})was better in the temperature range of 550～853 K.2.Upconversion luminescence and non-thermally coupled energy levels optical temperature sensing study of Tm³⁺-Yb³⁺doped Ca₉Y（PO₄）₇.Ca₉Y（PO₄）₇:Tm³⁺,Yb³⁺upconversion phosphors were prepared,and their crystal structure and upconversion emission properties were studied.The electronic structure of the material was also calculated using first-principles.Under 980 nm excitation,three upconversion emission bands were observed,corresponding to the transitions of ¹G₄→³H₆,¹G₄→³F₄,and³F₃→³H₆,with peak wavelengths of 471 nm,644 nm,and 695 nm,respectively.LIR(I_{695 nm}/I_{471 nm})and LIR(I_{695 nm}/I_{644 nm})based on the non-thermally coupled energy levels of³F₃ and ¹G₄,exhibited good temperature sensing performance.They had S_a-max values of0.0113 K^-1（823 K）and 0.0807 K^-1（823 K）,and S_r-max values of 1.07%K^-1（473 K）and 1.04%K^-1（523 K）,respectively,in the temperature range of 323～823 K.Compared to the LIR based on the Tm³⁺thermally coupled energy level,the LIR based on the non-thermally coupled energy level showed better temperature sensing performance.3.Upconversion luminescence and non-thermal coupling levels optical temperature sensing based on Ho³⁺-Yb³⁺doped Ca₉Y（PO₄）₇.Ca₉Y（PO₄）₇:Ho³⁺,Yb³⁺upconversion fluorescence powder was successfully synthesized using high-temperature solid-phase method.The upconversion luminescence of Ho³⁺was observed for the first time in Ca₉Y（PO₄）₇ matrix material.The electronic structure of the material was calculated,and the crystal structure and upconversion luminescence characteristics were analyzed.The temperature sensing performance based on the non-thermal coupling level LIR of Ho³⁺was studied.Three upconversion emission bands were observed under 980 nm excitation,originating from ⁵F₄/⁵S₂→⁵I₈,⁵F₅→⁵I₈,and ⁵F₄/⁵S₂→⁵I₇ transitions,with peak positions at 549 nm,648 nm,and 750 nm,respectively.However,⁵F₄/⁵S₂→⁵I₇transition exhibited anomalous thermal quenching.The temperature sensing performance of LIR(I_{750 nm}/I_{549 nm}),LIR(I_{648 nm}/I_{549 nm}),and LIR(I_{750 nm}/I_{648 nm})was studied.In the temperature range of 323～823 K,the S_a-max values of the three were 0.013 K^-1（853 K）,0.0062 K^-1（853 K）,and 0.0033 K^-1（853 K）,respectively.The S_r-max values were 1.29%K^-1（623 K）,0.36%K^-1（523 K）,and 0.88%K^-1（723 K）,respectively.LIR(I_{648 nm}/I_{549 nm})showed higher sensitivity in the temperature range of 323～523 K,while LIR(I_{750 nm}/I_{549 nm})had better performance in the temperature range of 573～853 K.These results indicate that Ca₉Y（PO₄）₇:Ho³⁺,Yb³⁺has good temperature sensing performance in the temperature range of 323～823 K.4.Temperature sensing based on dual rare-earth emitting centers doped in Ca₉Y（PO₄）₇.The upconversion luminescence and temperature sensing characteristics of dual rare-earth ions luminescent center in Ca₉Y（PO₄）₇,including Tm³⁺-Er³⁺,Tm³⁺-Ho³⁺,and Ho³⁺-Er³⁺,were studied.As a comparison,we also investigated the temperature sensing properties of two mixture samples,Mix _Tm,Er,which is a mixture of Tm³⁺-Yb³⁺and Er³⁺-Yb³⁺doped samples,and the sample Mix _Tm,Ho,which is a mixture of Tm³⁺-Yb³⁺and Ho³⁺-Yb³⁺doped samples.Compared to samples with single-emitting center of Er³⁺,Tm³⁺or Ho³⁺,the dual-emitting centers samples showed improved temperature sensing sensitivity.For the Ca₉Y（PO₄）₇:Tm³⁺,Er³⁺,Yb³⁺sample,Tm³⁺and Er³⁺exhibited their respective upconversion characteristic emissions.LIR（I_G/I_B）,LIR（I_G/I_R）,and LIR（I_R/I_B）were used for temperature sensing,with S_a-max and S_r-max of 0.0032 K^-1 and 1.34%K^-1,respectively.However,the temperature sensing performance of Mix _Tm,Er samples was weak.For Ca₉Y（PO₄）₇:Tm³⁺,Ho³⁺,Yb³⁺samples,Tm³⁺and Ho³⁺exhibit respective upconversion characteristic emissions.LIR（I_D/I_B）,LIR（I_D/I_G）,and LIR（I_D/I_R）all demonstrated temperature sensing properties,with S_a-max of 0.015 K^-1 and S_r-maxof 5.3%K^-1.Compared to the single-emitting center sample,the dual-emitting centers sample improved the temperature sensing performance to a certain extent.The mixed sample Mix _Tm,Hofurther improved the temperature sensing performance,with S_a-max and S_r-max of 0.020 K^-1 and7.03%K^-1,respectively.Although the upconversion emission spectra of Ca₉Y（PO₄）₇:Ho³⁺,Er³⁺,Yb³⁺show significant overlap between Ho³⁺and Er³⁺,LIR(I_{527 nm}/I_{553 nm})and LIR(I_{527 nm}/I_{654 nm})could still achieve temperature sensing.Their S_a-max and S_r-max were0.0035 K^-1,0.0008 K^-1and 0.64%K^-1,0.37%K^-1,respectively.Although LIR(I_{527 nm}/I_{553 nm})performed better,the temperature sensing performance was not improved compared to samples co-doped with Ho³⁺-Yb³⁺and Er³⁺-Yb³⁺.