Spectroscopic Properties And Luminescence Mechanisms Of Rare Earth Doped（Ba,Sr）TiO₃Nanopowders

The research on luminescence properities of rare earth doped materials is one of hot topics in the optoelectronic materials science due to its broad application prospect in optoelectronic device, such as optical fiber communication, optical fibre amplifier, laser technology etc. In this paper, The spectroscopic properties of3mol%Ho3+,(1,3,5,7mol%) Er3+doped and (Yb3+, Er3+) co-doped BST nanocrystals were studied. The luminescence mechanism and concentration quenching mechanism were also investigated.BST nanocrystals doped with different kinds of rare earth and different concentrations were fabricated by the sol-gel method. XRD patterns show that all the samples are crystallized perovskite polycrystalline structures. The Crystalline size are estimated to be100nm.Based on the Judd-Ofelt (J-O) theory, the intensity parameters Ω2,Ω4,Ω6of3mol%Ho3+doped BST nanocrystals were determined,0.229×10-20,0.515×10-20and0.761×10-20cm2, respectively, and then the values of the oscillator strength, radiative transition probabilities and branching ratios of Ho3+were calculated. Under514nm laser excitation, the emission bands centered at about545nm,650nm,706nm and753nm were detected, corresponding to (5F4,5S2)â†'5I8,5F5â†'5I8,5I4â†'5I8and (5F4,5S2)â†'5I7transition. The stimulated emission cross-sections of the emission bands centered at about545nm,650nm,706nm and753nm were calculated.The intensity parameters, the spontaneous radiative transition probabilities, the branching ratios, and the radiative lifetimes of different concentration Er3+-doped BST nanocrystals were calculated based on the J-O theory. The measured lifetime of2H11/2level is found to be116.31μs, and the fluorescence quantum efficiency of the2H11/2level is calculated to be38.77%. Under the excitation at514nm laser, there are five emission bands centered at522nm,545nm,654nm,801nm and851nm corresponding to the2H11/2â†'4I15/2,4S3/2â†'4I15/2,4F9/2â†'4I15/2,4I9/2â†'4I15/2and4S3/2â†'4I13/2transition. The Stokes luminescence mechanism and the quenching mechanism were also discussed.The purple and green unconversionluminescence properties of Er3+doped and(Yb3+, Er3+) co-doped BST nanocrystals were studied. The purple and green upconverted luminescence properties of Er3+doped BST nanocrystals were investigated by785nm laser excitation. The upconversion emission bands centered at407nm,523nm and547nm corresponde to2H9/2â†'4I15/2,2H11/2â†'4I15/2and4S3/2â†'4I15/2transitions, respectively. Under the excitation at800nm, blue and green upconversion luminescence in (Yb3+, Er3+) co-doped BST nanocrystals were observed. The blue and green bands centered at468nm and537nm, are corresponding to the4F3/2â†'4I15/2and4S3/24I15/2transition, The upconversion mechanism and the quenching mechanism were also discussed.