碘化銅奈米晶粒玻璃複合材料製成及其非線性吸光及光激發發光現象

Nonlinear absorption and photoluminescence in CuI semiconductor microcrystallines doped borosilicate glass

周文元(Wen-Yuan Jou)

指導教授 ： 文在川

高雄醫學大學/生命科學院/醫藥暨應用化學研究所/碩士(2005年)

摘要

我們以熔融與熱處理法將鹵化銅奈米晶體鑲嵌入硼酸矽玻璃中。大量的暗色球形奈米晶體可以被TEM觀察到，而其半徑約為4∼15nm。我們使用Q-switch Nd：YAG laser提供線性極化脈衝(pulse width∼6ns)，在波長為355nm及532 nm的狀況下做為光源以進行其非線性吸收與光激發發光測定之實驗。
半導體內部非線性吸收的現象，以自由載子吸收及雙光子吸收為主，我們利用Z-scan的實驗方法，計算出自由載子的吸收截面σ及雙光子吸收係數β等數據。
在室溫下之鹵化銅鑲入之玻璃以波長355nm的雷射光將其激發時，會出現光激發發光現象。此發光光譜經由分光儀測得，為一非常寬的波帶其波峰處於520nm(≈2.38 eV)。同時我們觀察到，520 nm波峰的強度，與入射光強成正比。所以我們猜想光激發發光的主要路徑，可能是電子經載體吸附後在與電洞結合。

關鍵字

碘化銅 ； 奈米晶粒 ； 非線性吸光 ； 光激發發光

並列摘要

Cuprous halides nanocrystals embedded in borosilicate glass are prepared by a melt and heat-treatment method. A large amount of these nanocrystals appear as dark ball shape with radius roughly ranging from 4 to 15 nm according to the TEM analysis. A Q-switched Nd:YAG laser delivery linearly polarized pulses at 355 nm wavelength ( ) with ~6 ns pulse width is employed as light source for the nonlinear absorption and the photoluminescence (PL) experiments.
The two photon absorption (TPA) coefficient and the free carrier absorption (FCA) cross section above the band gaps of these quantum dots are suggested to be attributed to the TPA, the linearly generated FCA, and the TPA generated FCA. The propagation equation is , where N is the instantaneous free carrier density given by = . Under the weak absorption limit (i.e. the fluence is less than the critical fluence defined as ), our experimental data of inverse transmission (1/T) as a function of incident fluence can be properly fitted with a formula derived from the above equations, while we obtain the values of and that are comparable to the literature values.
Upon excitation with 355 nm laser pulses in those cuprous halide doped glasses at room temperature, PL is observed, as we know, for the first time as the incident fluence is . This emission becomes very bright when . We also measure these PL specta at room temperature with a 0.5-m monochromator equiped by a PMT. The signal intensity is obtained with direct digital scanning from 350~800 nm. These spectra consist of a very broad band and centered at the visible region of about 520 nm ( ). Similar spectrum centered around 515 nm is also observed at low excitation irradiance. The intensity of PL at 520 nm is measured vs. the input intensity, and the results display that this emitted energy increases linearly with irradiance. We therefore suggested that the PL could be due to the radiative recombonation associated with traps or defects from impurities in the cuprous halide nanocrystals and their glassy surroundings.

並列關鍵字

CuI ； microcrystallines ； Nonlinear absorption ； photoluminescence

參考文獻

[1] A. I. Ekimov, A. L. Efros "Nonlinear optics of semiconductor-doped glasses" Phys. Stat. Sol. (b) 150, 1988, 627.

[2] P. Gilliot, B. Honerlage, R. Levy, J. B. Grun "Nonlinearities of CuCl microcrystals" Phys. Stat. Sol. (b) 159, 1990, 259-265.

[3] L. G. Zimin, S. V. Gaponenko, V. Yu. Lebed, I. E. Malinovskii, I. N. Germanenko, E. E. Podorova, V. A. Tsekhomskii "Nonlinear optical absorption in I-VII and II-VI microcrytallites under quantum confinement of elementary excitations" Phys. Stat. Sol. (b) 159, 1990, 267-273.

[4] F. Henneberger, U. Woggon, J. Puls, Ch. Spiegelberg "Exciton-related optical nonlinearities in semiconductors and semiconductor microcrystallites" Appl. Phys. B 46, 1988, 19-25.

[5] M. Kull, J. L. Coutaz "Intensity dependent absorption and luminescence in semiconductor doped glasses" J. Opt. Soc. Am. B 7, 1990, 1463-1472.