Size-Dependent Upconversion Luminescence in Er3+/Yb3+-Codoped Nanocrystalline Yttria: Saturation and Thermal Effects

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• 作者：Xue Bai ; Hongwei Song ; Guohui Pan ; Yanqiang Lei ; Tie Wang ; Xingguang Ren ; Shaozhe Lu ; Biao Dong ; Qilin Dai ; Libo Fan
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：September 13, 2007
• 年：2007
• 卷：111
• 期：36
• 页码：13611 - 13617
• 全文大小：366K
• 年卷期：v.111,no.36(September 13, 2007)
• ISSN：1932-7455

文摘

In this paper, the upconversion luminescent properties of Y₂O₃:Er³⁺(1%)/Yb³⁺(4%) nanoparticles with differentsizes (13-55 nm) and its corresponding bulk material as a function of excitation power were studied under978-nm excitation. Red (⁴F_9/2 ⁴I_15/2), green (²H_11/2, ⁴S_3/2 ⁴I_15/2), and blue (²H_9/2 ⁴I_15/2) transitions wereobserved. The results indicated that the relative intensity of the blue as well as the red to the green increasedgradually with decreasing particle size. As a function of excitation power, the slope in the ln-ln plot for thered emission changed between 2.0 and 1.0 and gradually decreased with increasing particle size, which wasattributed to competition between linear decay and upconversion processes for the depletion of the intermediateexcited states. As the particle size decreased to 13 nm, a three-photon populating process occurred for thegreen emission. As the excitation power varied in different paths, gradually increasing or gradually decreasing,a hysteresis loop appeared in the power dependence of emission intensity, which was mainly caused by alocal thermal effect induced by laser irradiation. The intensity ratio of ²H_11/2 ⁴I_15/2 to ⁴S_3/2 ⁴I_15/2 (R_HS)varied complicatedly with excitation power, which was theoretically explained considering the thermaldistribution and relaxation processes. Two novel cross-relaxation paths were proposed on the basis of thevariation of R_HS under excitation at different wavelengths, 488 and 978 nm.