Up And Down Conversion Luminescence And Optical Temperature Measurement Of Ca₂MgWO₆ Phosphors

Double perovskite structure materials have been widely studied because of their excellent properties such as simple synthesis method,good physical/chemical stability,various crystal structures and moderate phonon energy.Among them,Ca₂MgWO₆ is a typical double perovskite structure compound.The[WO₆]group emits light under the excitation of ultraviolet light and can be used as a sensitizer for the luminescence center.At the same time,Ca₂MgWO₆ has moderate phonon energy(850 cm^-1),which is a good host for optical temperature measurement.This article will focus on the preparation,application and optical properties of Ca₂MgWO₆phosphors,mainly including the following three aspects:（1）Bi³⁺ions doped double perovskite Ca₂MgWO₆ phosphor for yellow light emission.In order to develop new single-phase phosphor materials,a series of Ca₂MgWO₆:y Bi³⁺phosphors were successfully synthesized by high temperature solid-state method.The structure,morphology and optical properties of the phosphors were described by X-ray diffraction,scanning electron microscopy and photoluminescence.The crystal lattice and morphology of the samples were adjusted by adding fluxes.And the emission intensity of Bi³⁺ions was increased by 21.4%.In addition,the characteristics emission of the[WO₆]group was explored.Under excitation at 297 nm,[WO₆]group possesses a broad emission band（350-550 nm）from W⁶⁺→O^2-transfer.Under 336 nm excitation,Ca₂MgWO₆:y Bi³⁺phosphors exhibit an ultra-wide emission band（400-800 nm）of Bi³⁺ions.At the same time,Ca₂MgWO₆:y Bi³⁺phosphors have high quantum efficiency and absorption,and their maximum values reach 42.1%and 90.7%,respectively.All results show that Ca₂MgWO₆:y Bi³⁺phosphors have potential applications in solid state lighting.（2）A three-mode self-referenced optical thermometry based on up-conversion luminescence of Ca₂MgWO₆:Er³⁺,Yb³⁺phosphors.To develop new up-conversion luminescent materials for optical thermometry,a sequence of Ca₂MgWO₆:x Er³⁺,y Yb³⁺phosphor samples were synthesized via high temperature solid-state reaction method.Their structure,morphology and luminescent performances were completely explored via X-ray diffraction,scanning electron microscopy and photoluminescence.Excited by 980 nm laser,all phosphor samples emit intense up-conversion luminescence of Er³⁺at 531,549 and 661 nm.Besides,these emissions were greatly enhanced with addition of Yb³⁺ions.Benefiting from the different temperature dependence of three emission peaks,a dual-mode temperature sensor based on fluorescence intensity ratio(²H_11/2/⁴S_3/2 and ²H_11/2/⁴F_9/2)is realized by using single luminescent center(Er³⁺).Meanwhile,the fluorescence lifetime of ⁴S_3/2 state of Er³⁺ions was used as the third temperature detection signal.More importantly,the phosphors exhibit superior thermal stability that will be helpful to obtain high precision temperature measurement.All results show that Ca₂MgWO₆:Er³⁺,Yb³⁺samples could have potential applications for self-referenced optical thermometry.（3）Dual-mode optical temperature measurement based on Ca₂MgWO₆:Ho³⁺,Yb³⁺phosphor up/down conversion luminescence.Ho³⁺,Yb³⁺ions doped Ca₂MgWO₆phosphors were prepared by high temperature solid-state method.The crystal structure of sample was studied in detail by X-ray diffraction.The luminescence mechanism of Ca₂MgWO₆:Ho³⁺,Yb³⁺phosphors was studied in detail.Under 980 nm and 451 nm excitation,the phosphors have three characteristic emission peaks at 543,653 and 756 nm,which are generated by the transitions of⁵F₄,⁵S₂→⁵I₈,⁵F₅→⁵I₈ and ⁵F₄,⁵S₂→⁵I₇,respectively.At the same time,dual-mode of fluorescence intensity ratio thermometry is realized in a single luminescent center(Ho³⁺).The relative sensitivity of these two modes reached 0.82%K^-1（303 K）and2.45%K^-1（573 K）,respectively.The above results indicate that Ca₂MgWO₆:Ho³⁺,Yb³⁺phosphors have potential applications in the field of optical temperature sensing.