【摘要】 采用燃烧法制备了不同尺寸和不同掺杂浓度的Y2O3∶Ho/Yb纳米晶,并系统地研究了颗粒尺寸对Y2O3∶Ho/Yb纳米晶发光性质的影响。研究发现,随着尺寸的减小,发射强度和荧光分支比均发生了显著变化,Ho3+的整体发射强度降低,但5F5→5I8的红光发射比5S2(5F4)→5I8的绿光发射的荧光分支比增强。尺寸减小,表面原子更易吸附空气中的水和二氧化碳,引入一些较大的振动模式,从而增大了无辐射跃迁的速率,荧光分支比随尺寸的变化被归因于表面效应引起的无辐射弛豫过程5S2(5F4)→5F5和5I6→5I7的增强。更多还原

【Abstract】 Y₂O₃∶Ho/Yb nanocrystals have been prepared by combustion method. The nano-crystals size was estimated by X-ray diffraction. Green emissions near 549 nm and red emissions near 668 nm were observed under 488 nm and 980 nm excitation, which were associated with （）⁵S₂（（）⁵F₄）→（）⁵I₈ and （）⁵F₅→（）⁵I₈ transitions of Ho³⁺ that required two-step energy transfer （ET） from Yb³⁺ ions. The intensity ratio of red light to green light varied obviously with the nanocrystals size, which should be due to surface defects. The smaller the size was, the weaker the emission intensity became. As the same time, the ratio of red light intensity to green light intensity increased obviously with the decrease of particle size. As the particle size decreased, a great number of surface defects were involved. These defects, which acted as nonradiative transition channels, led the decrease of the emission intensity. On the other hand, the surface of the powders absorbed the CO₂ and the H₂O in the air. So large vibrational modes could be produced, which offered the probability for depopulating of the excited states nonradiatively. Thus, the nonradiative relaxation rates from （）⁵S₂（（）⁵F₄） to （）⁵F₅ became much faster. As a result the ratio of red light intensity to green light intensity decreased. Two nonradiative relaxations processes, （）⁵S₂（（）⁵F₄）→（）⁵F₅ and （）⁵I₆→（）⁵I₇, are involved in upconversion luminescence, but only （）⁵S₂（（）⁵F₄）→（）⁵F₅ in downconversion. So the increase of emission intensity ratio is more prominent in upconversion luminescence than downconversion luminescence.更多还原