Tunable Luminescence And Temperature Sensing Properties Of Double Doped Phosphors

Matrixes with similar crystal structure types are easy to construct solid solution phosphors.Compared with other phosphors,solid solution phosphors have great advantages in adjustability.Therefore,exploring solid solution phosphors has become a major research hotspot.In this paper,we mainly establish a double doped dual-emitting system based on the solid solution,and realized the tunable color of phosphors through strategies such as energy transfer between two doped ions,changing the crystal field environment,and excitation driven;The temperature sensing performance of phosphors were analyzed by optical thermometry based on fluorescence intensity ratio technology.In addition,as an extension of our research work,we also explored rare earth doped self-activated phosphors with dual luminescence system,the specific research contents are as follows:（1）Most rare earth doped phosphors need to be prepared in a reducing atmosphere,such as phosphors doped by Eu²⁺and Ce³⁺ions with d-f transition.In contrast,the doping ion Bi³⁺selected in this paper has more advantages.A new type of solid solution Sr_3-xGd_xAl O_4+xF_1-x designed by the two Cs₃Co Cl₅-type compounds Sr₃Al O₄F and Gd Sr₂Al O₅ well promotes the luminescence of Bi³⁺ion.In the dual luminescence system constructed with sensitizer Bi³⁺and activator Eu³⁺,by adjusting the concentration of Bi³⁺/Eu³⁺,the phosphor can be tuned from blue to red,which is due to the energy transfer caused by dipole–dipole interaction between Bi³⁺and Eu³⁺.Surprisingly,by means of excitation-driven,the emission peak position of Bi³⁺ions can also be moved from～425nm to～437 nm,and red shift occurs,so as to realize the tuning of the fluorescence from orange red to blue.We speculate that this is induced by the presence of multiple emission centers of Bi³⁺,and different absorption strength of Bi³⁺and Eu³⁺.In addition,Bi³⁺and Eu³⁺ions have different thermal responses to temperature.They are thermally quenched by energy level cross relaxation（ELCR）and multi-phonon deexcitation（MPD）,respectively.The maximum relative sensitivity（Sr）of optical thermometry based on fluorescence intensity ratio（FIR）is approximately 1.17%K^-1 at 323 K,which is higher than that of previously reported Bi³⁺and Eu³⁺co-doped phosphors.At 523 K,we also obtained a high absolute sensitivity（Sa）of 0.0064 K^-1.Therefore,the prepared solid solution phosphors have great application prospects in the field of temperature monitoring.（2）The spectral tuning of Bi³⁺is a great challenge that limits its commercial application.Herein,by regulating the value of x in the new solid solution Sr_2+xLa_1-xGa O_5-xF_x,the luminescence of Bi³⁺is well promoted.Through an excitation-driven strategy,the emission peak position of Bi³⁺is redshifted,and the luminescence of trivalent bismuth is successfully adjusted,which can also be applied to anti-blue lighting.On this basis,we constructed a Bi³⁺–Eu³⁺dual luminescence system,and,regardless of changes in the Bi³⁺/Eu³⁺concentration or excitation wavelength,a single matrix white-light-emitting phosphor was realized.Through calculations,the activation energy of the phosphor doped with 2.5%Eu³⁺was found to be 0.257 e V,which is higher than the activation energy of some common compounds.This indicates that the phosphor has good application prospects in the field of solid-state lighting.It is worth noting that based on the different thermal response behaviors of Bi³⁺and Eu³⁺,when the Eu³⁺content is fixed at 1%,the maximum relative sensitivity of the optical thermometer based on its fluorescence intensity ratio is about 1.46%K^-1 at 383 K,which is higher than most co-doped phosphors previously reported.An absolute sensitivity of 0.00139 K^-1 was also obtained at 403 K.Therefore,the thermal sensitivity of Bi³⁺and Er³⁺ions co doped in solid solution was also studied.The results show that the prepared solid solution phosphor has great potential in temperature sensing.（3）As an extension of our research work,we also explored the luminescent properties of single-doped self-activated dual-luminescent phosphors.Most praseodymium-doped red-emitting phosphors need high-temperature synthesis conditions with a reducing atmosphere.The niobate matrix lattice sites chosen in this paper provide a sufficient electron-rich site environment for praseodymium,and praseodymium can be reduced in the air,which is safe and environment friendly.By establishing the energy transfer of[Nb O₆]group→Pr³⁺and finely modifying the doping concentration of Pr³⁺ions,we constructed a dual luminescence system of dopant Pr³⁺self-activated host.Thereby,optical temperature measurement based on fluorescence intensity ratio（FIR）technology of Pr³⁺ions and[Nb O₆]groups was carried out using nonthermal coupling pairs,through the Boltzmann fitting and integral calculation,the maximum Sr and Sa values were 2.25%K^-1 and 0.0049 K^-1 at 403 K and 443 K,respectively,the Sr value is four times that obtained from the thermal coupling of Pr³⁺ions,which exceeded most values previously reported for the fluorescence powder.Accordingly,we also studied the thermal sensitivity of Er³⁺ions and Eu³⁺ions mono-doped Ca Nb₂O₆ substrates.Results reveal that Ca Nb₂O₆:Er³⁺/Eu³⁺phosphors also have excellent temperature measurement sensitivity.