1.College of Physics and Optoelectronic Engineering, Harbin Engineering University, Harbin 150001, China 2.College of Science, Heilongjiang University of Science and Technology, Harbin 150027, China 3.Key Laboratory of Photoelectric Bandgap Materials, Ministry of Education, Harbin Normal University, Harbin 150025, China
Abstract:Single ion doped single phase white emitting phosphors have some special advantages and great potential applications in the field of high quality LED lighting. This type of phosphors can effectively solve the problem of uneven particle dispersion and sedimentation in the white light scheme obtained by UV chip plus trichromatic phosphor, and solve the problems of the luminescence and reabsorption between phosphors and the regulation of trichromatic ratio. A comparison of the single-ion doping luminescent material with the multi-ion doping system shows that the single-ion doping luminescent material is simpler in both preparation process and luminescence color adjustment, which can achieve higher color rendering index, more easily controlled color temperature and closer to the color coordinates of white light. According to the principle of colorimetry and luminescence, light of two or more wavelengths may be combined to obtain white light emission. Under the UV excitation, the Sm3+ ions emit relatively strong green, yellow, orange and red light at 580–670 nm. Under UV excitation, the broadband spectrum of ${\rm{WO}}_{4}^{2-} $ self-activated emission covers almost the whole visible region, but the blue-green light is strong in the short wavelength region and the yellow-orange-red light is weak in the long wavelength region. When Sm3+ ions are doped into tungstate, Sm3+ ions’ luminescence can effectively supplement the weak luminescence intensity of tungstate in the long-wave region, and white light can be obtained. Under the excitation of 250 nm, the phosphor emits cold white light, and warm white light under the excitation of 403 nm. The experimental results show that Sm3+ ions have a significant effect on the correlated color temperature adjustment of self-activated luminescence of NLW phosphors. All the prepared samples are crystallized into the tetragonal crystal phase structures and that their morphologies present rhombic sheet. By analyzing the experimental data, the type of energy transfer between Sm3+ ions is determined to be electrical dipole–electrical dipole interaction. The NLW: xSm3+ phosphor has high stability and can be effectively excited by ultraviolet/near-ultraviolet light, which can be used as a potential candidate of single matrix single-ion doped white phosphors. Keywords:NaLa(WO4)2: Sm3+/ photoluminescence/ white light phosphors
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3.1.样品XRD结构分析
NLW:x Sm3+(x = 1%, 2%, 3%, 4%和5%)系列样品的XRD谱如图1(a)所示. 可见所有样品的衍射峰均与粉末衍射标准联合委员会(JCPDS)的标准PDF卡片#79-1118相符, 未发现其他衍射杂峰, 说明所得样品均为纯的四方相晶系(I41/a(88)). 衍射峰尖锐、强度高, 表明合成的荧光粉结晶度良好. 虽然掺杂了Sm3+离子, 但NLW样品的晶格没有发生显著变化. 如图1(b)所示, 由于Sm3+离子半径小于La3+离子半径, 随着Sm3+浓度增加, 晶格常数变小, (112)衍射峰总体趋势是向大角度移动, 较直观表明Sm3+成功掺杂进入NLW的晶格. 利用通用结构分析系统(GSAS)对样品NLW:2%Sm3+的XRD进行Rietveld精修, 如图1(c)所示, × 谱线和蓝色实线分别为实验数据和计算值, 可见该样品所有衍射峰均满足反射条件和宿主的结构细化图. 晶体的结构如图1(d)所示, 当Sm3+被引入NLW基质中时, 由于离子半径接近, 更可能占据的是Na+或者La3+格位. 图 1 晶体结构信息 (a) NLW:x Sm3+荧光粉的XRD谱; (b) (112)峰位置随Sm3+浓度变化偏移; (c) NLW:2%Sm3+ XRD谱的Rietveld精修; (d) NLW:x Sm3+晶体结构图 Figure1. Crystal structure information: (a) XRD patterns of NLW:x Sm3+ phosphors; (b) offset of the (112) peak position with the Sm3+ concentration; (c) rietveld refinement of XRD pattern of NLW:2%Sm3+; (d) the crystal structure of NLW:x Sm3+.