溴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 CuBr semiconductor microcrystallines doped borosilicate glass

王貞華(Jen-Hua Wang)

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

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。由TEM之分析照片中顯示出大量的奈米晶體以半徑約為4∼15nm的暗色球體出現。我們使用Q-switch Nd：YAG laser提供線性極化脈衝(pulse width∼6ns)作為光源，在波長為355nm與532nm的條件下，進行其非線性吸收與光激發發光觀察之實驗。
此類奈米晶體之非線性吸收現象，可歸因於雙光子吸收及自由載子的吸收。以Z-scan實驗法進行測量後，可求得其雙光子吸收係數β與自由載子吸收截面σ等重要數據。
在室溫下，以波長355nm的雷射光照射於已鑲入鹵化銅之玻璃時，會出現光激發發光現象。以裝置有光電倍增管之分光儀測量此光激發發光現象，掃描波長350nm到800nm之間，可得一波峰位於520nm(2.38 eV)附近之寬波段光譜，其波峰強度與激發光源的強度成正比。因此我們推論此光激發發光可能導因於電子經載體吸附後，在電洞進行再結合所產生的效應。

關鍵字

溴化銅 ； 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 (ηω ≈ 3.49 eV) 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 β and the free carrier absorption (FCA) cross section σ 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
dI/dz =αI – βI2 – σNI , where N is the instantaneous free carrier density given by dN/dt =αI/ћω + βI2/2ћω. Under the weak absorption limit (i.e. the fluence is less than the critical fluence Fc defined as Fc ≈ 2ћω/σ(1-e-αL)), 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 β and σ 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 F0 is 30 mJ/cm2. This emission becomes very bright when F0 30 mJ/cm2. We also measure these PL spectra 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 (2.38 eV). 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 recombination associated with traps or defects from impurities in the cuprous halide nanocrystals and their glassy surroundings.

並列關鍵字

CuBr ； Nonlinear absorption ； photoluminescence ； microcrystallines

參考文獻

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