The Fabrication And Application Of PbSe Colloidal Quantum Dots Light Emitting Diodes

Semiconductor quantum dots have some unique properties, such as quantum confinement effect, surface effect, dielectric confinement effect, etc. At the same time, quantum dots have the advantages of broad absorption spectra, high quantum yields, narrow emission spectra and high stability. Therefore, it has very broad application prospects in the field of biology, optoelectronic device, luminescent device, detection and so on. According to the high cost, complex processing technology and difficulty to adjust the emission wavelength of traditional near infrared light source, we employed near infrared PbSe quantum dots as conversion materials and GaN light emitting diode as exciting light sources to create a new sort of near infrared light source for the first time. Then, we utilized this kind of light source to detect a few combustible and explosive gases. We made some innovative progress, the details are as follows:1. Fabrication and characterization of a near infrared light emitting diode based on PbSe quantum dots.The near infrared quantum dot light emitting diodes actuated by electricity have plenty of nonradiative recombination which effect the luminous efficiency of devises. The efficiency of near infrared quantum dot light emitting diodes is much lower than visible quantum dot light emitting diodes. Therefore, we dispersed PbSe quantum dots into UV glue and considered the mixture as light conversion materials. Combining with a GaN light emitting diode,we fabricated a new sort of near infrared light source with single wavelength. The characterization result shows that: the best external quantum efficiency of the the devices reached 2.52%; the device is stable; we can change the wavelength just by changing the size of quantum dots.2. Taking the single wavelength PbSe quantum dot light emitting diode as the detection light source to detect acetylene gas.The chemical reaction between the surface of the quantum dot and some gases would change thefluorescence spectra of PbSe quantum dots, such as fluorescence quenching and fluorescence intensity decreased. Therefore, most of the gas detection using quantum dots is based on this characteristic of quantum dots. However, the detection sensitivity of this method is not high. In the meantime, there are some problems to put this technology for actual applications. A new type of method we developed for gas detection using quantum dots is utilising PbSe quantum dots near infrared light source as detection light source to detect acetylene gas by direct absorption spectroscopy. The detection limit of the detection system is 20 ppm and the detection precision is 2%.3. Utilizing PbSe quantum dots light emitting diode with multi wavelength to detect a variety of gas simultaneously.We integrated three sized PbSe quantum dots(their diameters are 4.6、5.1、6.1nm) into a GaN light emitting diode to fabricate a near-infrared light source which could emit three wavelengths(1526 、 1676 and 1948nm). Then we employed direct absorption spectroscopy to detect methane, acetylene and ammonia simultaneously with the help of this light source. The detection limits of three kinds of gases are 100, 20 and 20 ppm, with the precision of 2%. The system achieved the goal of detecting multigas.4. Using the PbSe quantum dots light emitting diode with multi wavelength which could be modulated separately as detection light source to detect two gases through the method of differential optical absorption spectroscopy.We chose a GaN light emitting diode with three chips as excitation light source. The three chips could be modulated by frequency controller respectively because they have separate electrodes. After the PbSe quantum dots with three sizes(corresponding diameters are 2.53、4.83、6.88nm) were integrated into the three chips, we successfully fabricated a near-infrared light source with three wavelengths which can be modulated respectively. We utilized this light source to detect acetylene and ammonia at the same time employing differential optical absorption spectroscopy method which could eliminate the error caused by instability of the light source to obtain higher accuracy and sensitivity. For simplify the detection system, the spectrometer was replaced by the photodetector. The detection limit of two gases is 25 and 30 ppm and the detection error is less than 2%.