Luminescent Properties Of Borate Phosphors With High Quantum Efficiency

White LEDs(light emitting diode)has been widely researched because of their long life,environmental friendly and other advantages.At present,the commercial white LEDs are mainly made of blue LED chips and yellow phosphors.With the continuous development of lighting technology,LED phosphors with various types of matrices have been developed,including aluminate series,silicate series,tungsten/molybdate series,nitrogen(oxygen)compounds series,etc.These matrices have more or less disadvantages,such as poor chemical stability,high synthesis cost and complex preparation process.Therefore,it is important to develop new phosphors which can be used in white LED with the advantages of low synthesis temperature,good chemical stability and excellent luminescent performance.In this paper,a series of rare earth doped orthoborate luminescent materials were synthesized by high-temperature solid-state reaction method.This paper focuses on the energy transfer and the luminescent properties of co-doped rare earth doped orthoborate phosphors.(1)Na Ba_0.99-xBO₃:0.01Ce³⁺,x Tb³⁺(x=0,0.01,0.03,0.05,0.07 and 0.09)phosphors were synthesized by high temperature solid-state reaction method.The crystal structure,luminescent properties,fluorescence lifetime and energy transfer mechanism of the samples were studied in detail.In Na Ba BO₃matrix,the main emission peak of Ce³⁺ions is 415nm and the main emission peak of Tb³⁺ions is 545 nm,which belong to d-f transition and ⁵d₄-⁷f₅transition,respectively.When Ce³⁺and Tb³⁺ions are co-doped,the energy transfer between them is through dipole-dipole interaction.The critical distance of concentration quenching is calculated as R_c=12.46?,and the highest luminous intensity of phosphor is obtained when the doping concentration of Tb³⁺ions is 3%.Under 355 nm excitation,the internal quantum efficiency of Na Ba_0.96BO₃:0.01Ce³⁺,0.03Tb³⁺phosphor is as high as 57%.At the same time,the tunable emission from blue to blue-green can be realized by changing the doping concentration of Tb³⁺ions under the excitation of near UV light.A white LED lamp is fabricated by combining Na Ba_0.96BO₃:0.01Ce³⁺,0.03Tb³⁺blue green phosphor and Ca Al Si N₃:Eu²⁺commercial red phosphor with a 365 nm near UV LED chip.The color temperature and color rendering index are 6473 K and 81.4,respectively.(2)Na Ba_0.99-xBO₃:0.01Ce³⁺,x Mn²⁺(x=0,0.01,0.03,0.05,0.07,0.09,0.11,0.13 and0.15)phosphors were synthesized by high temperature solid-state reaction method.Their crystal structure,luminescent properties and energy transfer were studied.The luminescent intensity of Ce³⁺ions decreased with the increase of the doping concentration of Mn²⁺ions,and the best doping concentration was 11%.The main emission peaks of Na Ba_0.99-xBO₃:0.01Ce³⁺,x Mn²⁺phosphors are at 415 nm and 645 nm under the excitation of 355 nm near UV.By observing the fluorescence decay curves of Na Ba_0.99-xBO₃:0.01Ce³⁺,x Mn²⁺can be found that the fluorescence lifetime decreases with the increase of the concentration of doped Mn²⁺ions.The phenomenon of energy transfer from Ce³⁺ions to Mn²⁺ions is observed,the mechanism of energy transfer between Ce³⁺ions and Mn²⁺ions is through dipole-dipole interaction,and the critical distance of concentration quenching is calculated as R_c=19.78?.By changing the doping concentration ratio of Ce³⁺/Mn²⁺ions,the luminescent region of Na Ba_0.99-xBO₃:0.01Ce³⁺,x Mn²⁺can be from(0.161,0.071)to(0.339,0.178).(3)Na_0.99-xMg BO₃:0.01Ce³⁺,x Tb³⁺(x=0,0.02,0.04,0.06,0.08,0.10,0.12 and 0.16)phosphors were prepared by solid-state reaction method.The luminescent properties,energy transfer and fluorescence lifetime of the samples were studied.The main characteristic peaks of the emission spectra are consist of Ce³⁺ions and Tb³⁺ions,located at 460 nm and 486 nm,542 nm,581 nm,622 nm,respectively.With the increase of the doping concentration of Tb³⁺ions,the emission intensity of Ce³⁺ions decreases.The emission intensity of Tb³⁺ions increases first and then decreases,when the doping concentration of Tb³⁺is 6%the highest luminous intensity of phosphor is obtained.The fluorescence lifetime of Na_0.99-xMg BO₃:0.01Ce³⁺,x Tb³⁺phosphors decreased with the increase of doping concentration of Tb³⁺ions.The energy transfer mechanism from Ce³⁺ions to Tb³⁺ions is through dipole-quadrupole interaction,and the critical distance of concentration quenching is calculated as R_c=13.19?.By changing the doping concentration of Tb³⁺ions,the chromaticity coordinates of phosphors can be from(0.187,0.241)to(0.263,0.369).