Study On Lasing Characteristics Of Organic Semiconductor Materials

In 1996,the research group of A.J.Heeger at University of California,Santa Barbara,demonstrated the first optically pumped solid-state conjugated polymer laser which aroused the interest in the field of organic semiconductor laser.Since then,many organic semiconducting materials have been investigated in devices with different types of configurations,such as microcavities,distributed feedback lasers,etc.Many materials are not affected by concentration quenching.Thus,stimulated emission could be obtained from neat films,leading to much lower laser thresholds.Amplified spontaneous emission?ASE?stability remains one of the important challenges for the realization of commercial organic lasers.Organic materials have weak molecular interactions and show poor stability.The material performance is very vulnerable to oxygen,water vapor,and the temperature of the surrounding environment.Therefore,encapsulation problems must be solved before practical application of organic optoelectronic devices,in order to prevent the material degradation.Study on new kinds of materials with lower threshold and better ASE stability under optical pumping is an important issue in the field of organic lasers.Another important issue in organic laser field is the design of a reasonable device structure to achieve laser.With this objective,the following work is carried out:Firstly,we studied the stimulated emission characteristics of benzimidazole derivatives BBPI doped in polystyrene matrices.The BBPI:PS film shows a high photoluminescence quantum efficiency of 67.9% and a deep blue emissive spectrum?440nm?with a narrow FWHM of 15.1 nm.A low threshold of 30?J/cm2 has been demonstrated by optical pumping experiment with a stripe shape excitation beam.A net gain of 9.37 cm-1 were obtained,the stimulated emission cross-section is about 1.8?10-16cm2,which demonstrated BBPI could be a promising candidate as the gain medium for blue lasers.Secondly,we studied the ASE stability of meso aromatic substituted BODIPY derivatives-Ph BOD,Na BOD and En BOD incorporated into polystyrene matrices.The three materials exhibit good optical properties and possess low ASE threshold and relatively high photostability,ambient stability and thermal stability.These materials exhibit good photostability when pumping at high repetition rate and pump energy.To test the ASE environmental stability,film samples preserved in air at room temperature without encapsulation for three months.The films still show ASE properties with little changed threshold.To test the ASE thermal stability,the sample is placed on the hot stage and continues to heat up to 100?.ASE properties of the three materials were measured under this high temperature environment.It is found that Ph BOD shows the best ASE thermal stability among them.By theoretical calculation and analysis,the optimized ground-state structure parameters of Ph BOD,Na BOD and En BOD have been obtained using the Gaussian 09 program.We suggest that ASE stability of materials related to chemical stability and the degree of conjugation of molecular structure.A large conjugation degree of each group in the molecule and a symmetrical Mulliken charge distribution would lead to a better ASE stability of the materials.Finally,we designed and prepared high reflective metal electrode by using the structure of metal /dielectric/metal.It can be found that Ag?100nm?/YF₃?175nm?/Ag?12nm?has a reflectance of above 95% in the wide spectral range between 450 nm to 660 nm.The highest reflectance reaches more than 98%.It shows that the structure can effectively improve the reflectance of the metal electrode in the visible region.We designed and prepared high reflective anode with a DBR structure of?TiO₂/SiO₂?^10/WO₃?46nm?/Ag?11nm?/WO₃?20nm?,its reflectance can exceed 99% at around 530 nm.This anode has the characteristics of high reflectivity and high work function simultaneously,which can be applied to the organic light-emitting devices and electrically pumped organic lasers.