NaYF4 微晶与纳米晶中晶相对Tb3+ -Er3+ 耦合对下转换的影响

实验研究了晶相对下转换的影响。Tb³⁺ -Er³⁺ 耦合对将一个紫外光子(Tb³⁺ 的⁷F₆→⁵L₁)294 nm 剪裁成800 nm (Er³⁺ 的⁴I_9/2→⁴I_15/2) 和467 nm (Tb³⁺ 的⁵D₄→⁷F₆) 两个都能被GaAs 太阳能电池吸收的低能光子。采用水热法制备了NaYF₄六角相微晶和立方相纳米晶粒子,六角相由于具有热力学稳定性和有序的排列结构而更有利于量子剪裁过程的发生,相反在立方相结构中没有发现量子剪裁现象。分别采用294 nm 和355 nm波长的光对六角相NaYF₄进行激发,从发射光谱可以看出,下转换的实现是通过一个交叉弛豫过程完成的。实验结果表明,与熔融法相比,用水热法制备的NaYF₄ 的量子产率明显降低。

Effect of Crystal Phase on The Down-conversion for Tb3+-Er3+ Couples in NaYF4 Micro- and Nano-crystals

The influence of crystal phases on the downconversion quantum processes is studied experimentally.One high-energy ultraviolet photon(Tb3+ :7F6 →5L1,294 nm) is quantumly cut into two lower energy photons: one in the near-infrared region(Er3+ :4I9/2→ 4I15/2,800 nm) and the other in the blue region(Tb3+:5D4 →7F6,467 nm),both of which can be efficiently absorbed by GaAs solar cells.The hexagonal microcrystal and cubic nanoparticles NaYF4∶Tb3+,Er3+ were prepared by hydrothermal method.The thermodynamically stable and ordered hexagonal phase is favorable for the quantumcutting processes,however,the dowconversion can not be observed in our cubic phase samples.Using different excitation wavelengths of 294 and 355 nm to excite the hexagonal phase NaYF4∶Tb3+,Er3+,the spectra indicate that the cross-relaxation(Tb3+:5L1,Er3+:4I15/2) →(Tb3+:5D4,Er3+:4I9/2) is required for down conversion.It is shown that the quantum yields in the medium prepared by hydrothermal method are lower compared with that by melting method.