发光颜色可调Cs_(3)Gd_(1-x-y)Lu_(y)Ge_(3)O_(9):xBi^(3+)固溶体荧光粉的制备和发光性质研究

Preparation and Luminescence Properties of Color-tunable Emission Cs_(3)Gd_(1-x-y)Lu_(y)Ge_(3)O_(9):xBi^(3+)Solid Solution Phosphor

采用传统的高温固相法合成了一系列Cs_(3)Gd_(1-x)Ge_(3)O_(9):xBi^(3+)(0.02≤x≤0.1)蓝色荧光粉,并通过Lu^(3+)替代Cs_(3)Gd_(1-x)Ge_(3)O_(9)基质中的Gd^(3+),调控激活剂Bi^(3+)周围局部环境,制备了一系列发光颜色可调的Cs3Gd0.96-yLuyGe_(3)O_(9):0.04Bi^(3+)(0.1≤y≤0.9)固溶体荧光粉。X射线衍射、稳态/瞬态荧光光谱、变温光谱对荧光粉样品的物相结构、发光特性、荧光寿命、热稳定性进行了详细表征。结果表明,我们成功合成了一系列纯相的Cs_(3)Gd_(1-x-y)Lu_(y)Ge_(3)O_(9):xBi^(3+)化合物。在紫外光330 nm激发下,Cs_(3)Gd_(1-x)Ge_(3)O_(9):xBi^(3+)荧光粉的发射峰位于452 nm,呈现蓝光发射,该宽带发射峰源于Bi^(3+)的^(3)P_(1)→^(1)S_(0)跃迁,Bi^(3+)掺杂浓度为0.04 mol时,Cs_(3)Gd_(1-x)Ge_(3)O_(9):xBi^(3+)荧光粉的荧光强度达到最大值。在最优Bi^(3+)掺杂浓度下,通过Lu^(3+)替代基质中的Gd^(3+),发现合成的一系列Cs_(3)Gd_(0.96-y)Lu_(y)Ge_(3)O_(9):0.04Bi^(3+)(0.1≤y≤0.9)固溶体荧光粉发射峰逐渐发生红移,随着Lu^(3+)掺杂浓度的逐渐增加,发射峰从x=0.1 mol时的453 nm逐渐红移至x=0.9 mol时的483 nm,相应的半峰宽从88 nm展宽至116 nm,色坐标从蓝色区域(0.1685,0.1602)过渡到青色区域(0.2179,0.3007)。样品光谱行为的变化主要是因为晶体场劈裂程度增大和斯托斯克位移增大。探究了x=0.04 mol、y=0.5 mol样品的发光热稳定性,当温度升高到423 K时样品的发光强度保持在初始值的55%。所得到的一系列发光颜色可调的固溶体荧光粉在全光谱照明、植物照明等领域具有潜在的应用。

Phosphor-converted White Light-Emitting Diodes(pc-WLEDs)have energy-saving,environmental protection and other excellent performance.At present,the commercial WLEDs are composed of blue LED chip combined with Y3Al5O12:Ce^(3+)yellow phosphor.However,due to the lack of red components in the emission spectrum,the white light generated by this method has a low color rendering index(CRI<75)and a high correlation color temperature(CCT>4500 K),which cannot satisfy the needs of indoor lighting.Researchers at home and abroad have proposed an improved method to generate white light by excitation of red,green and blue phosphors by a near-ultraviolet LED chip.Although this method can produce warm white light for indoor illumination,there is a significant cyan gap in the cyan region of the visible spectrum(480~520 nm),which makes it challenging to achieve full spectral illumination.Therefore,it is desirable to obtain a cyan luminescent material that can achieve full spectrum illumination by mixing phosphors.It is well known that rare-earths Eu^(2+)and Ce^(3+)have been widely used as activator ions in inorganic phosphors.However,Eu^(2+)/Ce^(3+)activated phosphors have spectral overlap in the visible region,resulting in low luminescence efficiency and color drift of the synthesized devices.Compared with rare earth ions,Bi^(3+)hardly absorbs in the visible region,so Bi^(3+)activated phosphors can effectively avoid the spectral reabsorption problem encountered by rare earth Eu^(2+)/Ce^(3+).At the same time,the outermost electrons 6s and 6p of Bi^(3+)are exposed and sensitive to the changes of crystal field environment,so Bi^(3+)is considered as an activator ion that can realize the color-tunable of phosphors luminescence.Therefore,the abundant optical properties of bismuth ions have attracted extensive attention.In this paper,a series of Cs_(3)Gd_(1-x)Ge_(3)O_(9):xBi^(3+)(0.02≤x≤0.1)blue phosphors were synthesized by the traditional high-temperature solid-state method.The local environment around Bi^(3+)is regulated by replacing Gd^(3+)in the matrix with Lu^(3+).A series of Cs_(3)Gd_(0.96-y)Lu_(y)Ge_(3)O_(9):0.04Bi^(3+)(0.1≤y≤0.9)solid solution phosphors with color-tunable were prepared.The phase structure,luminescence properties,fluorescence lifetime,and thermal stability of the phosphors were characterized by X-ray diffraction,steady-state/transient fluorescence spectra and variable temperature spectra.The results showed that a series of pure phase Cs_(3)Gd_(0.96-y)Lu_(y)Ge_(3)O_(9):0.04Bi^(3+)compounds were successfully synthesized.Under the excitation of the ultraviolet light wavelength of 330 nm,the emission peak of Cs_(3)Gd_(1-x)Ge_(3)O_(9):xBi^(3+)phosphor is located at 452 nm,showing blue emission.The broadband emission peak originates from the ^(3)P_(1)→^(1)S_(0) transition of Bi^(3+).When the Bi^(3+)doping concentration is 0.04 mol,the luminescence intensity of Cs_(3)Gd_(1-x)Ge_(3)O_(9):xBi^(3+)phosphor reaches the maximum value.Under the optimal Bi^(3+)doping concentration,by substituting Lu^(3+)for Gd^(3+),the emission peak of Cs_(3)Gd_(0.96-y)Lu_(y)Ge_(3)O_(9):0.04Bi^(3+)gradually redshifted.With the gradual increase of Lu^(3+)doping concentration,the emission peak gradually redshifted from 453 nm at x=0.1 mol to 483 nm at x=0.9 mol,the corresponding half-peak width is widened from 88 nm to 116 nm,and the color coordinates transition from the blue region(0.1685,0.1602)to the cyan region(0.2179,0.3007).The change of spectral behavior is attributed to the increase of crystal field splitting degree and stokes shift displacement.The luminescence thermal stability of x=0.04 mol and y=0.5 mol samples was investigated,and the luminescence intensity of the samples remained 55%of the initial value when the temperature was raised to 423 K.A series of solid solution phosphors with adjustable luminescence color obtained have potential applications in the fields of full spectrum lighting and plant lighting.