Study On The Luminescence And Temperature Sensing Properties Of Rare Earth Doped Multi-Color Upconversion Materials

Rare earth doped upconversion luminescence materials,with the advantages of excellent photochemical stability,long fluorescence lifetime,no photoblinking and photobleaching,etc.,gradually show great application potential in many fields,such as coding and decoding,anti-counterfeiting,fluorescent labeling,temperature sensor,and bio-imaging.In this work,a series of micro/nano molybdate and oxysulfide based upconversion luminescence materials materials are successfully prepared by doping rare earth ions involving Yb3+,Er3+,Tm3+,Ho3+.The crystal phase change,energy transfer process and temperature sensing characteristics of the samples are studied in detail.By adjusting the doping type and concentration of rare earth ions,the efficient multi-color upconversion luminescence materials is realized and the sensitivity of temperature sensing is improved.The specific research contents and results are as follows:(1)Rare earth doped Gd2Mo4O15 upconversion luminescence materials materials are prepared by high temperature solid state method.By introducing an appropriate amount of small radius rare earth ions,such as Y3+ and Yb3+,the regulation of Gd2Mo4O15 from triclinic phase to monoclinic phase is realized.Compared to the triclinic phase,the infrequent monoclinic counterpart(space group P21/c)shows better upconversion luminescence materials and temperature sensing properties.In particular,in the case of 40%Yb3+,0.5%Er3+and 0.5%Tm3+ tri-doping,the luminescence quantum yield is as high as 3.9%.Based on the thermally coupled levels of Er3+ and Tm3+,the double-model temperature sensing is realized in the range of the green light that most sensitive to the human eye and the biological first window,with the maximum sensitivity of 12.44×10-3 K-1 and 0.36×10-3 K-1,respectively.The results show that Gd2Mo4O15: 40%Yb3+,0.5%Er3+,0.5%Tm3+ is a potential material for the temperature sensing with self-calibration.(2)A series of KYb(MoO4)2: Ln3+(Ln = Tm,Er,Ho)upconversion luminescence materials materials are prepared by high temperature solid state method.Under 980 nm excitation,by optimizing the doping concentration of rare earth ions,three primary colors of blue,green and red upconversion luminescence materials are obtained in the single doping system of Tm3+,Er3+ and Ho3+.Multiple emission colors can be obtained by mixing the three primary color samples of KYb(Mo O4)2: 1.0%Tm3+,KYb(Mo O4)2: 4.0%Er3+ and KYb(Mo O4)2:2.0%Ho3+ in a certain proportion,and application of mixtures in the field of anti-counterfeiting is verified.In addition,the stable white light emission is realized by introducing Tm3+ ion into KYb(Mo O4)2: 2.0%Ho3+.The CIE coordinates(x = 0.3325,y =0.3327)are the closest to the equal white light illumination when the excitation power density is 45.55 m W/mm2.The temperature sensing performances of KYb(Mo O4)2: 2.0%Tm3+,2.0%Ho3+ sample are studied.When the temperature is 673 K,the absolute sensitivity of I694/I801 for Tm3+ ions reaches the maximum value of 0.25×10-3 K-1.(3)Gd2O2S: Yb3+,Er3+ nanoparticles are synthesized by the homogeneous co-precipitation method combining with the solid-gas sulfidation technology.Scanning electron microscope pictures show that Gd2O2S: Yb3+,Er3+ nanoparticles are spherical shape and narrow size distribution with a mean particle diameter of ≈65 nm.Under the excitation of1530 nm,the integral emission intensity ratio of red to green of the Gd2O2S: Yb3+,Er3+sample is enhanced by 3.8-fold compared with the Gd2O2S: Er3+ sample without Yb3+ doping.The enhancement mechanisms of red emission component are discussed in detail based on the luminescence spectra and fluorescence decay curves at excitations of 380,808,980,and 1530 nm.The results suggest that the enhancement of red emission is induced by the cross relaxation process from Er3+ to Yb3+ via 4S3/2(Er3+)+ 2F7/2(Yb3+)→ 4I13/2(Er3+)+ 2F5/2(Yb3+)and 4I11/2(Er3+)+ 2F7/2(Yb3+)→ 4I15/2(Er3+)+ 2F5/2(Yb3+),and combined with the back energy process from Yb3+ to Er3+ through 4I13/2(Er3+)+ 2F5/2(Yb3+)→ 4F9/2(Er3+)+ 2F7/2(Yb3+).Furthermore,the temperature sensing performance of the Gd2O2S: Yb3+,Er3+nanoparticles under 1530 nm excitation is studied and the maximum absolute sensitivity of the sample reaches 7.90×10-3 K-1 at 453 K.