泡生法生长Ho3+,Yb3+双掺KGd(WO4)2晶体及其光谱性能

钨酸钆钾(KGd(WO4)2,简称KGW)是一种新型的激光基质材料。以Yb3 作为Ho3 的敏化剂,采用泡生法生长出了单斜晶系的Ho∶Yb∶KGW晶体。通过X射线衍射仪(XRD)分析确认所生长的晶体为-βHo∶Yb∶KGW。热重与差热分析(TG-DTA)测试结果表明,晶体的熔点为1072.31℃,相变温度为1043.09℃。测试了晶体的吸收光谱,对吸收峰值归属进行了确认,计算了相应的光谱参数。Yb3 在981 nm处吸收峰较强,半峰全宽(FWHM)为14 nm。从荧光光谱可以看出,在1022 nm附近,Yb3 发射主峰的半峰全宽达16 nm,对应的是Yb3 的2F5/2和2F7/2的能级之间的跃迁;Ho3 在1985 nm处的荧光发射峰半峰全宽为45 nm左右,发射截面积为1.79×10-20cm2。     

Ho3+/Yb3+/Ce3+三掺钽酸锂上转换绿光的研究

在三掺Ce3+的Ho3+/Yb3+/LiTaO3多晶粉中,发现增强上转换绿光并同时抑制上转换红光的新途径,能有效提高上转换发光的单色性.XRD衍射谱结果表明制备粉体仍为三方晶系.980 nm LD激发下,上转换绿光发光强度随Ce3+掺杂浓度增加而增强,并在Ce3+掺杂摩尔分数达15％时,上转换绿光发光效率达到最大,并同时抑制了上转换红光.Ce3+将2F7/2能级上的能量传递给H03+的516能级来增加上转换绿光.并在高掺Ce3+时,新的交叉弛豫过程使Ce3将2 F7/2能级上的能量传递给H03+的5F4/5S2能级,增强了上转换绿光并同时抑制了上转换红光.     

Yb:Er:Tm:LiTaO3的上转换发白光性能研究

980 nm脉冲激光激发下,首次通过高温固相法制备Yb(10%):Er(1%):Tm(1%):LiTaO3(摩尔分数)多晶粉并实现室温上转换白光.X射线粉末衍射测试结果表明,Yb:Er:Tm:LiTaO3中的掺杂离子并没有改变晶格结构,以取代的方式存在于钽酸锂晶格中.结合功率曲线测试结果和上转换机制研究发现,产生上转换蓝光的Tm3+离子1G4态的布居主要来自双光子同时吸收过程.而单光子上转换输出的红光,则由Tm3+和Er3+离子之间的交叉弛豫过程产生,即3F2/3(Tm3+)+4I15/2(Er3+)→3H6(Tm3+)+4I9/2(Er3+).上转换绿光来源于Yb/Er离子对的二次能量传递.     

Ho3+,Yb3+双掺KGd(WO4)2激光晶体的光谱性能

钨酸钆钾是一种新型的激光基质材料.以Yb3 作为Ho3 的敏化剂,采用顶部籽晶提拉法生长出了单斜晶系的HoYbKGW晶体.测试了晶体的红外光谱和拉曼光谱,并对出现的峰值进行了振动归属.分析了晶体的吸收光谱,计算了相应的光谱参数.从荧光光谱可以看出,在1022 nm附近,Yb3 发射主峰的发射线宽达14 nm,对应的是Yb3 的2F5/2和2 F7/2的最低能态之间的跃迁;Ho3 在1985 nm处的荧光发射峰半高宽为45 nm左右,发射截面积为σemp=1.79×10-20cm2.测试了晶体的上转换荧光谱,得到了较强的上转换红光,并分析了相应的上转换机制.     

Theoretical calculation and experiment of microwave electromagnetic property of Ni(C) nanocapsules

With the combination of the dielectric loss of the carbon layer with the magnetic loss of the ferromagnetic metal core,carbon-coated nickel Ni(C) nanoparticles are expected to be the promising microwave absorbers. Microwave electromagnetic parameters and reflection loss in a frequency range of 2 GHz–18 GHz for paraffin-Ni(C) composites are investigated.The values of relative complex permittivity and permeability, the dielectric and magnetic loss tangent of paraffin-Ni(C) composites are measured, respectively, when the weight ratios of Ni(C) nanoparticles are equal to 10 wt%, 40 wt%, 50 wt%,70 wt%, and 80 wt% in paraffin-Ni(C) composites. The results reveal that Ni(C) nanoparticles exhibit a peak of magnetic loss at about 13 GHz, suggesting that magnetic loss and a natural resonance could be found at that frequency. Based on the measured complex permittivity and permeability, the reflection losses of paraffin-Ni(C) composites with different weight ratios of Ni(C) nanoparticles and coating thickness values are simulated according to the transmission line theory. An excellent microwave absorption is obtained. To be proved by the experimental results, the reflection loss of composite with a coating thickness of 2 mm is measured by the Arch method. The results indicate that the maximum reflection loss reaches-26.73 d B at 12.7 GHz, and below-10 d B, the bandwidth is about 4 GHz. The fact that the measured absorption position is consistent with the calculated results suggests that a good electromagnetic match and a strong microwave absorption can be established in Ni(C) nanoparticles. The excellent Ni(C) microwave absorber is prepared by choosing an optimum layer number and the weight ratio of Ni(C) nanoparticles in paraffin-Ni(C) composites.     

Upconversion Properties of LiNbO_3 Single Crystals Co-doped with Ho and Yb

The IR-to-visible upconversion fluorescent crystals, Yb:Ho:LiNbO3, with a constant Ho3+ concentration (0.1 mol%) and different doping concentrations of Yb3+ (0.5, 1.5, 2.0, 2.5, 3.0 mol%) are synthesized by Czochralski method in air atmosphere. X-ray diffraction shows that the obtained crystal is a single phase of LiNbO3 and the rare-earth ions occupied the Li+ or Nb5+ sites instead of the interstitial sites. Under 980 nm excitation, green and red emission bands due to the Ho3+ (5S2, 5F4)/5I8 and Ho3+ 5F5/5I8 energy transitions are observed in these samples, respectively. Power dependence studies on these samples with different Yb3+ dopant concentrations indicate that the red and green emissions are based on a two-photon process. The intensities of the red and green upconversion fluorescence increase with Yb3+ ions of 0~2.0 mol% because of an increased Yb3+ sensitization, but decrease at higher concentrations owing to the back-energy transfer between the Yb3+ and Ho3+ ions.