Superposed picosecond luminescence kinetics in lithium niobate revealed by means of broadband fs-fluorescence upconversion spectroscopy
Superposed picosecond luminescence kinetics in lithium niobate revealed by means of broadband fs-fluorescence upconversion spectroscopy
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DOI：
10.1038/s41598-020-68376-6
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发表时间：
2020-07-09
影响因子：
4.6
通讯作者：
Imlau, M.
中科院分区：
文献类型：
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作者：
Krampf, A.;Messerschmidt, S.;Imlau, M.
小极化子的各种表现形式强烈地影响着氧化物晶体铌酸锂（LiNbO3，LN）的线性和非线性光学性质。虽然近几十年来已广泛研究了LN中的相关瞬态吸收现象，但仍然缺少描述锂酸盐单晶的蓝绿色（光）发光的声音显微照片。特别是，几乎没有什么是已知的：（i）发光建立和（ii）其室温衰减。我们在这里提出的结果，我们系统的实验研究，使用名义上未掺杂和Mg掺杂LN晶体与不同的Mg浓度。利用飞秒荧光上转换光谱技术（FLUPS）对皮秒发光进行了探测，并将其扩展到氧化物晶体的反射几何检测中。揭示了皮秒时间尺度上两种不同的发光衰减分量。虽然每个样品中存在短的指数衰减，但较长的非指数衰减显然取决于晶体组成。由于瞬态吸收光谱不包括成对的小极化子湮灭的发光的微观原因，这两个衰减组件的自陷激子（STE）的运输和衰减的背景下进行了讨论。
Various manifestations of small polarons strongly affect the linear and nonlinear optical properties of the oxide crystal lithium niobate (LiNbO3, LN). While related transient absorption phenomena in LN have been extensively studied in recent decades, a sound microscopic picture describing the blue-green (photo)luminescence of lithium niobate single crystals is still missing. In particular, almost nothing is known about: (i) the luminescence build-up and (ii) its room temperature decay. We present here the results of our systematic experimental study using nominally undoped and Mg-doped LN crystals with different Mg concentration. Picosecond luminescence was detected by means of femtosecond fluorescence upconversion spectroscopy (FLUPS) extended to the inspection of oxide crystals in reflection geometry. Two distinct luminescence decay components on the picosecond time scale are revealed. While a short exponential decay is present in each sample, a longer non-exponential decay clearly depends on the crystal composition. Since transient absorption spectroscopy excludes geminate small polaron annihilation as microscopic cause of the luminescence, both decay components are discussed in the context of self-trapped exciton (STE) transport and decay.