Y_(6)TeO_(12):Eu^(3+)红色荧光粉的制备与发光特性研究

Preparation and Luminescent Properties of Red-emitting Y_(6)TeO_(12):Eu^(3+)Phosphor

利用高温固相法在1200℃制备了一系列红色荧光粉(Y_(1-x))_(6)TeO_(12):xEu^(3+)(x=0.1~0.5)材料。对样品进行了X射线衍射、形貌特征、激发和发射光谱、浓度猝灭、热稳定性、荧光衰减曲线以及发光二极管封装与光色电性能等方面的分析与探究。结果表明:该红色荧光粉样品能被近紫外光(393 nm处)和蓝光(464 nm处)有效激发,在632 nm处表现出较强的红光发射。根据荧光强度与掺杂浓度的变化趋势,确定出最佳Eu3+掺杂量为x=0.3,更多的掺杂量引起浓度猝灭。进一步分析激活剂Eu^(3+)间能量传递类型,得出电偶极-电偶极作用导致了浓度猝灭。(Y_(0.7))_(6)TeO_(12):0.3Eu^(3+)在150℃时积分发光强度是室温的76.5%,热激活能为0.1969 eV。该样品的荧光寿命为813μs,色坐标值为(0.6376,0.3431),并基于板上芯片工艺进行了发光二极管封装,对光色电性能进行了表征。(Y_(1-x))_(6)TeO_(12):xEu^(3+)荧光粉表现出了良好的发光特性、发光热稳定性及色纯度,在白光发光二极管中具有潜在的应用价值。

The industry of white light-emitting diodes,next-generation illumination sources,has become an interesting field for their superior advantages such as energy savings,high efficiency,long operating lifetime as well as environmental friendliness.By far,the most effective white light-emitting diode is a combination of a near-ultraviolet chip and yellow-emitting phosphors.However,this type of phosphor converted white light-emitting diode has some disadvantages,it suffers from the weakness of low color rending index and high correlated color temperature because of the deficiency of red component.Thus,to overcome this problem,a large number of red phosphors,especially the trivalent Eu3+doped phosphor,have been widely studied.Eu3+ion is an important red activator in most of the commercial red phosphors,which can provide an efficient and narrow band emission due to characteristic 4f-4f transitions.Especially,Eu^(3+)ions can be used to prove the point group symmetry of the substituted site in the host.When Eu3+ions occupy noncentrosymmetric lattice sites,Eu3+can emit intense red emission,benefiting to improve the overall efficiency of the white light-emitting diodes.So the host can affect the intensity of emission peaks of Eu3+ion.Tellurate exhibits excellent properties in the optical,physical,and chemical fields.Given the low phonon energy of tellurate,this material can avoid the competitive non-radiative decay for the Eu3+ions doped.Therefore,tellurate is suitable for hosting matrices used in phosphors.We report herein,the preparation and luminescent properties of red-emitting(Y_(1-x))_(6)TeO_(12):xEu^(3+)phosphor.The(Y_(1-x))_(6)TeO_(12):xEu^(3+)phosphors were prepared through the high-temperature solid-state reaction at 1200°C for 20 h.The(Y_(1-x))_(6)TeO_(12):xEu^(3+)phosphors were prepared in this way for seven different concentrations of Eu3+(x=0.1,0.2,0.3,0.4 and 0.5).The samples(Y_(1-x))_(6)TeO_(12):xEu^(3+)were analyzed in detail by XRD,excitation and emission spectra,concentration quenching,thermal stability,luminescent decay curves,quantum efficiency,and color coordinates.To identify the detailed crystal structure information of(Y_(1-x))_(6)TeO_(12):xEu^(3+)phosphors,the Rietveld refinement was performed using the Generalized Structure and Analysis System.The absence of an impurity phase in the present doping concentration ranges(0.1≤x≤0.5)confirmed that incorporation of Eu3+ions did not show any notable change in Y6TeO12 phase.The refinement results were clear that the as-obtained(Y_(1-x))_(6)TeO_(12):xEu^(3+)phosphors were of trigonal structure with R3(No.146)space group.Further representative particle distribution and scanning electron microscopy of the(Y0.7)6TeO12:0.3Eu3+phosphors were carried out and the results indicate that average grain size is 4.61μm with diameter ranging from 2μm to 8μm.The band gap energy Eg of(Y0.7)6TeO12:0.3Eu3+obtained from diffuse reflectance spectra is 3.25 eV.The excitation and emission spectra of(Y_(1-x))_(6)TeO_(12):xEu^(3+)phosphors show that the prepared phosphor can be excited by ultraviolet light(393 nm)or blue light(464 nm),and exhibits a strong red light emission band at 632 nm corresponding to 5D0→7F2 electric dipole transition of Eu3+ions.The intensity ratio R of 5D0→7F2 to 5D0→7F1 transition(R=I(5D0→7F2)/I(5D0→7F1))is a good way to measure the symmetry of Eu3+sites.The intensity ratio value R is calculated to be 6.338.It is higher than some reported Eu3+-doped phosphors.Usually,with the increase of magnitude of R,the ideal value of the color chromaticity is closer.The dependence of integrated intensity on Eu3+contents reveals the optimum doping concentration is x=0.3,beyond which concentration quenching was observed.Concentration quenching for the prepared(Y_(1-x))_(6)TeO_(12):xEu^(3+)phosphors confirmed that the electric dipole-electric dipole interaction was responsible for energy transfer,resulting in the concentration quenching.The integrated emission intensity of prepared phosphor(Y0.7)6TeO12:0.3Eu3+at 150℃is as high as 76.5%of that at ambient temperature.The thermal activation energy was obtained as 0.1969 eV,which ensures a good thermal stability.This demonstrates its possible application in solid state lighting or optical thermometry.The decay characteristics of(Y_(1-x))_(6)TeO_(12):xEu^(3+)phosphors were studied to understand the average lifetime of an activator ion in an excited state.The decay curves of the prepared(Y_(1-x))_(6)TeO_(12):xEu^(3+)phosphors were monitored under 393 nm excitation wavelength and 632 nm emission wavelength.At doping concentrations of Eu3+,the luminescence lifetimes are 1114μs,907μs,813μs,661μs and 583μs,respectively.The lifetime decreases with an increase in Eu3+dopant concentration.This type of observation is results when the distance between the dopant Eu3+ion decreases and this leads to nonradiative transitions.Based on the datum of emission spectrum of(Y0.7)6TeO12:0.3Eu3+,the chromaticity coordinates are determined to be(0.6376,0.3431),close to the National Television System Committee value(0.67,0.33).To further evaluate the potential applications of the(Y0.7)6TeO12:0.3Eu3+phosphor,the prototype light-emitting diodes fabricated by coating the phosphors on the near-UV chips emit a bright light.The strong emission band(360~440 nm)originates from the near-UV chip and other sharp emission bands attribute to the Eu3+4f-4f transitions.The phosphor exhibits favorable luminescent properties,thermal stability of luminescence with good chromaticity coordinate,which have potential application in white light-emitting diodes.