单、双掺钒酸钇晶体的Raman光谱与能量转移研究

Research on Raman Spectra and Energy Transfer in Tm^(3+),Ho^(3+) Single and Co-Doped YVO_4 Crystals

文章采用双光栅单色仪(HRD-1),氩离子激光器的488.0 nm波长激发,分别测得室温下,激发光平行、垂直晶体c轴入射时,Tm3+,Ho3+单掺和双掺钒酸钇晶体的拉曼光谱,对检测结果进行分析并探讨了对能量转移的影响。观测到对Ho3+∶YVO4,激发光垂直c轴时的散射光强明显强于激发光平行c轴时的散射光强;由于488.0 nm波长靠近Ho3+的一个吸收峰,吸收和散射相互竞争,使475 cm-1被削弱,且外模振动展宽;测得样品最大声子能量集中在880 cm-1附近。主要是(VO4)3-的A1g呼吸模引起的,表明与YAG基质一样,也是一种具有高声子能量的晶体。用808 nm激发,锁相放大器,PbS探头接收,测得双掺Tm3+∶Ho3+∶YVO4的2.09μm荧光强度是单掺Tm3+∶YVO41.85μm的4/5,意味着Tm3+对Ho3+的敏化效率高达80%,因为Tm3+∶YVO4的荧光谱与Ho3+吸收谱重合甚少,由辐射跃迁导致的能量转移可能性不大,因此Tm3+离子之间的交叉弛豫以及Tm3+的3F4与Ho3+的5I7之间近共振的能量转移主要是依靠声子辅助的无辐射跃迁。

Raman spectra of Tm^3＋ ： YVO4, Ho^3＋ ： YVO4 and Tm^3＋ ： Ho^3＋ ： YVO4 crystals were measured at room temperature by HRD-1 double grating monochromator, with the excitation laser beam were parallel and perpendicular to c axis, respectively. For the Ho^3＋ ： YVO4, it was found that the Raman spectrum excited by laser beam perpendicular to axis c is stronger than that by parallel excitation, and because 488 nm laser was very close to the absorption peak of Ho^3＋ , the competition between absorption and scattering results in the 475 cm^-1 Raman mode weakening and external mode widening. It was also found that the most probable phonon energy focused on the 880 cm^-1, which was brought about by the breathe mode of （VO4）^3- . Like YAG, YVO4 is a kind of crystal with high phonon energy too. Comparing the luminescence of Tm^3＋ ： YVO4 with that of Tm^3＋： Ho^3＋ ： YVO4, it was found that the intensity of Ho^3＋ 2. 09μm is about 4/5 of that of Tm^3＋ 1.85 μm, which means the sensitization efficiency of Tm^3＋ to Ho^3＋ was as high as up to 80%, and since the overlap between the luminescence of Tm^3＋ with the absorption of Ho^3＋ is quite small, the radiative energy transfer between them was very less possible, and most probability, this process was via the nonradiative, phonon-aided cross-relaxation between Tm^3＋ and near resonance energy transfer between Tm^3＋ and Ho^3＋.