Ba₂LaF₇ Up-conversion Luminescence Properties And Heat-sensitive Properties Of Ba₂LaF₇ Glass-ceramics

Upconversion（UC）luminescence materials with rare earth doped have been the focus of research all over the world.The reason is that these materials have important potential applications in the bio-medical imaging,anti-counterfeiting,temperature sensors,solar energy management,data storage,and 3D volumetric displays.Rare earth ion co-doped upconversion luminescence materials applied in temperature sensors has attracted much attention because of the dependence of spectral properties and temperature.Compared to traditional thermometers such as glass thermometers,thermocouple thermometers,semiconductor thermometers,spectral temperature sensors have the advantages of non-contact and high sensitivity.The sensitivity of optical temperature sensors greatly depends on the luminescence efficiencies of rare earth ions.However,the rare earth ions emission efficiency is relative low because of their special 4f electronic transition structure.Therefore,it has important research significance in studying optical properties of rare earth ions doped materials,and how to improve luminescent efficiency of rare earth ions doped materials.This paper has discussed the Ba₂La F₇:Yb³⁺/Er³⁺glass ceramics and the Ba₂LaF₇:Yb³⁺/Tm³⁺glass ceramics for optical thermometrystudied and the surface plasmon resonance enhanced spontaneous up-conversion in glass ceramics containing Ba₂LaF₇ nanocrystals.（1）The optical thermometry properties of Er³⁺in Ba₂La F₇ glass ceramics were studied,and the upconversion luminescence of Er³⁺was enhanced by increasing annealing temperature.The FIR of the two green UC emissions peaked at 523 nm and 541 nm,originating from the transitions from ²H_11/2/⁴S_3/2 to ⁴I_15/2,was recorded for optical thermometry in the temperature range from 298 K to 573 K.The sensitivity of Er³⁺/Yb³⁺co-doped Ba₂LaF₇ glass ceramics reached 0.43%K^-1 at 298 K,Moreover,the thermal effect induced by laser was also investigated and the sample temperature varied from 336 K to 407 K with increasing pump power density from 1.01W/cm² to 9.59 W/cm².The results indicate that the Yb³⁺/Er³⁺ions co-doped Ba₂LaF₇glass ceramics with good temperature sensitivity are potential candidates for integrating heaters and thermometers.（2）The spontaneous UC emissions intensity of Er³⁺was drastically improved with the Ag nanoparticles（NPs）emerged in Ba₂La F₇ glass-ceramic for the contribution of the surface plasmon resonance and some of the energy transfer from Ag NPs to Er³⁺.Meanwhile,the stimulated emission as a random lasing action was achieved in this hybrid material.It is found that the incorporation of Ag NPs was advantageous in reducing the threshold of the lasing action.Therefore,the new class of hybrid glasses allows for fiber-based devices to be developed for photonic applications or as a useful tool for tailoring light-nanoparticles interactions study.（3）The optical thermometry properties of Tm³⁺in Ba₂LaF₇ glass ceramics were studied.It is found that Yb³⁺can be used not only as a sensitizer but also as a nucleation agent.The number of crystal nucleus gradually increases with increasing concentration of Yb³⁺.The temperature sensing performances for optimized sample were recorded and the maximum sensitivity were about 0.00046 K^-1 at 573 K.Moreover,a laser induced thermal effect was also investigated and the host temperature varied from 315 K to 350 K with increasing pump power from 749 mW to1665 mW.The results indicated that the Yb³⁺/Tm³⁺ions co-doped Ba₂LaF₇ glass ceramics were an ideal candidate for optical thermometer and optical heaters.