Luminescence,Temperature Sensing And Gas Sensing Properties Of Pr³⁺ Doped Perovskite-Type Oxides

Praseodymium ions(Pr³⁺)-doped perovskite-type oxides has stimulated enormous interest in the last years due to their excellent photoluminescence?PL?properties and the considerable application potentials on luminescent devices and sensing devices.In-depth understanding the underlying PL mechanisms of Pr³⁺-doped oxides remains as the biggest challenge in this field.Such understanding is crucial for optimization or modulation of the PL properties hence generation of novel sensing and multifunctional-device applications based on Pr³⁺-doped oxides.In this present work,a series of Pr³⁺-doped perovskite-type niobates and titanates have been successfully produced.The PL properties have been studied in depth,based on the mechanisms of intervalence charge transfer.The influence of doping content,host,temperature,post-annealing,atmosphere,etc.on the PL properties has been investigated systematically.Importantly,ultrahigh sensitive optical temperarture sensing and gas sensing properties of these Pr³⁺-doped perovskite-type oxides have been also explored.Firstly,Pr³⁺-doped perovskite-type oxides,including SrTiO₃:Pr³⁺,Ba_0.7Sr_0.3TiO₃:Pr³⁺,K_0.5Na_0.5NbO₃:Pr³⁺,have been produced by using hydrothermal method and solid-state reaction method,respectively.The influence of doping content,host,post-annealing,etc.on the PL properties has been investigated systematically.By tuning the relative intensity of blue-green and red emission peaks of Pr³⁺,the emission color can be modified in a controlled manner.For instance,white emission of SrTiO₃:Pr³⁺ has been achieved.Secondly,the influence of temperature on the PL properties of Ba_0.7Sr_0.3TiO₃:0.5%Pr³⁺ and KNN:0.5%Pr³⁺ has been investigated systematically.The dependence of the intensity of ¹D₂-³H₄ red emissions and 3P0-3H4 blue-green emissions on temperature has been revealed.Based on this new founding,a new temperature sensing method using the intensity ratio of the two emissions has been proposed.The temperature sensing sensitivities employing the PL of Ba_0.7Sr_0.3TiO₃ and K_0.5Na_0.5NbO₃:Pr³⁺ are respectively as high as 6165/T2 and 7997/T2,which are significantly higher than all reported results based on the emission intensity ratio of rare-earth-doped materials.Furthermore,the sensing mechanism has been interpreted using the intervalence charge transfer mechanism.In addition,Pr³⁺ was confirmed to enhance ferroelectric property of K_0.5Na_0.5NbO₃.By in situ polarization under low voltage,it is found that such polarization can influence only the absolute PL intensity of K_0.5Na_0.5NbO₃:Pr³⁺,not the intensity ratio of the ¹D₂-³H₄ and 3P0-3H4 emissions.Therefore,the low-voltage polarization can not disturb the temperature sensing of K_0.5Na_0.5NbO₃:Pr³⁺.Finally,by annealing in oxygen and argon,the influence of post-annealing on the PL properties of KNN:0.5%Pr³⁺ has been explored.The results have been analyzed by the mechanism of inter-valence band charge transfer.It is revealed that oxygen gas can strongly vary the PL properties of the K_0.5Na_0.5NbO₃:Pr³⁺ post-annealed in argon.The oxygen sensing properties of K_0.5Na_0.5NbO₃:Pr³⁺ have been studied,indicating that K_0.5Na_0.5NbO₃:Pr³⁺ can act as a new optical gas sensing material.Highly-sensitive sensing can be realized by monitoring the intensity ratio of the ¹D₂-³H₄ red emissions to the 3P0-3H4 blue-green emissions at 98 centigrade and the intensity variation of the ¹D₂-³H₄ red emissions at 165 centigrade.PL properties of a series of Pr³⁺-doped perovskite-type oxides have been systematically studied.Meanwhile,new optical temperature sensing and gas sensing methods based on these Pr³⁺-doped oxides have been proposed.This work may provide a solid base for multifunctional device application of Pr³⁺-doped oxides.