Growth And Properties Of Rare Earth Ion Tb³⁺ Doped Laser Crystals

Visible light band lasers have major application requirements in display,communication,biomedicine,optical sensing,spectroscopy,high-end manufacturing and other fields.Compared with the complex frequency doubling method to realize visible laser output,pumping rare earth ions directly to realize visible laser output has attracted increasing attention of researchers.And yellow light plays an important role in the fields of sodium beacon lasers,scientific research and remote sensing,which has attracted the attention of researchers.The advantage of Tb³⁺to directly generate yellow light is obvious through the complex frequency combination method.The most critical problem in the study of Tb³⁺ions is the excited state absorption（ESA）of its ⁵D₄energy level,which severely restricts the laser output in the visible band.In addition,the weak ground-state absorption of Tb³⁺ions from the ⁷F₆to ⁵D₄energy levels means that the crystal length needs to be increased to several centimeters to obtain effective pump energy absorption.The excessively long crystal also increases the difficulty of crystal growth.Aiming at the ESA of Tb³⁺ions and the weak absorption from the ground state energy levels ⁷F₆to ⁵D₄,this work proposes the selection of fluoride with a higher energy level of 4f⁷5d¹and co-doping sensitizing ions to solve these two key problems accordingly.In addition,since visible light fluorescence plays an important role in color rendering,LED,etc.,then this work uses a mature 980 nm LD pump source replace the unmature 486 nm LD sources to achieve visible-band luminescence through cooperative up-conversion luminescence through co-doping Yb³⁺/Tb³⁺.The main results are shown as follows:1.A series of crystals including Tb:CaF₂,Tb,Y:CaF₂and Tb,Pr:CaF₂,Tb,Dy:CaF₂crystals with different doped concentrations were grown by temperature gradient technique.The effects of codoping Y³⁺ions and sensitizing ions Pr³⁺ions and Dy³⁺ions on the spectral properties of Tb:CaF₂crystals were systematically studied.It shows that the spectral quality of Tb ions in CaF₂is great,and the spectral quality can be effectively improved by codoping Y³⁺ions.In addition,the problem of weak absorption of Tb³⁺ions was improved by co-doping sensitizing Pr³⁺ions,and the emission cross section of the crystal was also calculated.For the Tb³⁺/Pr³⁺co-doped crystal,the emission cross section of the green light band at 545 nm corresponding to the ⁵D₄→⁷F₅level transition is 5.56×10^-22cm²,and the emission cross section of the yellow light band at 587 nm corresponding to ⁵D₄→⁷F₄is 8.78×10^-23cm²,respectively.When Dy³⁺ions are used as sensitizing ions,there exist energy transfer between Tb³⁺ions and Dy³⁺ions.By pumping with xenon lamps in different bands,the doping concentration ratio is optimized,and the best concentration ratio scheme is found.2.High-quality 10 at%Tb,x at%Na:SrF₂（x=0,3,5）and 10 at%Tb,y at%Y:SrF₂（y=0,5,10）crystal were grown by the temperature gradient technique,and crystal growth,crystal structure,spectrum and laser properties were studied in detail.For Tb:SrF₂crystal,the emission cross-section of the green light band at 545 nm is0.68×10^-21cm²,and the emission cross-section of the yellow light band at 583 nm is0.096×10^-21cm².While codoping with Y³⁺ions and Na⁺ions,the emission cross-section is 0.68×10^-21cm²and 0.72×10^-21cm²for the 545 nm,and 0.15×10^-21cm²and 0.14×10^-21cm²for the 583 nm,respectively.Using 2ω-OPSL 488 nm pumping source,a green laser output in 545 nm with a maximum power of 259 m W and a laser slope efficiency of 35.2%was achieved in a 10%Tb,10%Y:SrF₂crystal.To the best of our knowledge,this is the highest power laser output in the terbium doped alkaline earth fluoride crystal.3.Tb,Re（Re=Lu,Gd）:BaF₂ crystals were grown by temperature gradient technique.It was found that codoping Gd³⁺ions will enhance the emission cross-section of green light,but will greatly reduce the emission cross-section of yellow light.When codoping Lu³⁺ions at a low concentration,the emission cross section of yellow light will be improved.The emission cross sections of Tb³⁺ions in the visible range in 15%Tb:BaF₂,15%Tb,3%Lu:BaF₂,15%Tb,5%Lu:BaF₂,15%Tb,3%Gd:BaF₂,15%Tb,5%Gd:BaF₂crystals were calculated.The emission cross sections for green ligth at 544 nm are 0.86×10^-21cm²,0.85×10^-21cm²,0.76×10^-21cm²,0.91×10^-21cm²,and0.93×10^-21cm²,respectively.The emission cross sections at 587 nm for yellow light are 0.064×10^-21cm²,0.071×10^-21cm²,0.054×10^-21cm²,0.020×10^-21cm²,and0.039×10^-21cm²,respectively.4.In addition,the micro-pull-down method with the advantage of short growth period and low cost is used to grow a series of Yb³⁺/Tb³⁺ions co-doped YAG crystals.And the energy conversion law between its ions was studied to seek the best concentration ratio,so as to achieve cooperative up-conversion luminescence.These results indicate that by adjusting the concentration ratio of Yb³⁺ions and Tb³⁺ions,the output of visible light can be achieved through cooperative up-conversion luminescence,which has potential applications in color rendering,LED,etc.