Soares M R N, Ferro M, Costa F M, Monteiro T
Departamento de Física & I3N, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
Nanoscale. 2015 Dec 21;7(47):19958-69. doi: 10.1039/c5nr04052c. Epub 2015 Oct 15.
Lanthanide doped inorganic nanoparticles with upconversion luminescence are of utmost importance for biomedical applications, solid state lighting and photovoltaics. In this work we studied the downshifted luminescence, upconversion luminescence (UCL) and blackbody radiation of tetragonal yttrium stabilized zirconia co-doped with Tm(3+) and Yb(3+) single crystals and nanoparticles produced by laser floating zone and laser ablation in liquids, respectively. The photoluminescence (PL) and PL excitation (PLE) were investigated at room temperature (RT). PL spectra exhibit the characteristic lines in UV, blue/green, red and NIR regions of the Tm(3+) (4f(12)) under resonant excitation into the high energy (2S+1)LJ multiplets. Under NIR excitation (980 nm), the samples placed in air display an intense NIR at ∼800 nm due to the (1)G4→(3)H5/(3)H4→(3)H6 transitions. Additionally, red, blue/green and ultraviolet UCL is observed arising from higher excited (1)G4 and (1)D2 multiplets. The power excitation dependence of the UCL intensity indicated that 2-3 low energy absorbed photons are involved in the UCL for low power levels, while for high powers, the identified saturation is dependent on the material size with a enhanced effect on the NPs. The temperature dependence of the UCL was investigated for single crystals and targets used in the ablation. An overall increase of the integrated intensity was found to occur between 12 K and the RT. The thermally activated process is described by activation energies of 10 meV and 30 meV for single crystals and targets, respectively. For the NPs, the UCL was found to be strongly sensitive to pressure conditions. Under vacuum conditions, instead of the narrow lines of the Tm(3+), a wide blackbody radiation was detected, responsible for the change in the emission colour from blue to orange. This phenomenon is totally reversible when the NPs are placed at ambient pressure. The UCL/blackbody radiation in the nanosized material exhibits non-contact pressure colour-based sensor characteristics. Moreover, tuning the color of the blackbody radiation in the nanoparticles by harvesting the low energy photons into the visible spectral region was found to be possible by adjusting the excitation power, paving the way for further developments of these nanoparticles for lighting and photovoltaic applications.
具有上转换发光的镧系掺杂无机纳米粒子在生物医学应用、固态照明和光伏领域具有极其重要的意义。在这项工作中，我们研究了分别通过激光悬浮区法和液体中的激光烧蚀法制备的共掺杂Tm(3+)和Yb(3+)的四方钇稳定氧化锆单晶和纳米粒子的向下转换发光、上转换发光（UCL）和黑体辐射。在室温（RT）下研究了光致发光（PL）和PL激发（PLE）。PL光谱在共振激发到高能(2S+1)LJ多重态时，在Tm(3+)（4f(12)）的紫外、蓝/绿、红和近红外区域呈现特征谱线。在近红外激发（980 nm）下，置于空气中的样品由于(1)G4→(3)H5/(3)H4→(3)H6跃迁在~800 nm处显示出强烈的近红外光。此外，还观察到由更高激发的(1)G4和(1)D2多重态产生的红色、蓝/绿色和紫外UCL。UCL强度的功率激发依赖性表明，对于低功率水平，2 - 3个低能量吸收光子参与了UCL过程，而对于高功率，确定的饱和现象取决于材料尺寸，对纳米粒子有增强作用。研究了单晶和用于烧蚀的靶材的UCL的温度依赖性。发现在12 K和室温之间积分强度总体增加。单晶和靶材的热激活过程分别由10 meV和30 meV的激活能描述。对于纳米粒子，发现UCL对压力条件非常敏感。在真空条件下，检测到的不是Tm(3+)的窄谱线，而是宽的黑体辐射，这导致发射颜色从蓝色变为橙色。当纳米粒子置于环境压力下时，这种现象是完全可逆的。纳米材料中的UCL/黑体辐射表现出基于非接触压力颜色的传感器特性。此外，通过调整激发功率，发现有可能将纳米粒子中的黑体辐射颜色调整到可见光光谱区域，通过收集低能量光子实现，为这些纳米粒子在照明和光伏应用中的进一步发展铺平了道路。
