Research On Laser Gain In Colloidal Semiconductor Nanocrystals

Colloidal semiconductor nanocrystals have an extremely small size.When they are smaller than the Bohr radius of excitons,they produce quantum confinement effects,so that their forbidden band width increases with the decrease of size,so that their absorption and absorption can be adjusted by changing the size,emission wavelength.In addition,colloidal semiconductor nanocrystals can be further optimized by combining heterostructures to meet the needs of different application scenarios,such as increasing the absorption cross section,reducing non-radiative recombination,and improving luminous efficiency.Colloidal semiconductor nanocrystals can also be easily mass-produced by solution method,with low production cost and easy industrial production and processing.Due to its narrow luminescence peak,discrete atomic energy levels,and tunable spectral range,it has significant advantages in lasers due to its low gain threshold,spectral stability,and tunability.The micronano laser based on colloidal semiconductor nanocrystals has good application prospects in the fields of laser display light source,integrated optical circuit on-chip light source,biomarker and other fields.However,since laser gain in semiconductor nanocrystals is generally a multi-exciton process,multi-exciton interactions under narrow-scale confinement can cause strong non-radiative Auger recombination,thereby raising the threshold of optical gain in them.Compared with zero-dimensional quantum dots and one-dimensional quantum rods,two-dimensional colloidal quantum wells have larger exciton binding energy and gain cross-section,lower Auger velocity,and narrower luminous linewidth,making them a more superior buff material.In addition,colloidal atomic layer deposition(c-ALD)can easily grow and control the thickness and chemical composition of the shell layer,achieving precise control of the atomic layer grown in each layer.However,the colloidal quantum wells thus obtained have low luminous efficiency and cannot meet the requirements of light-emitting devices.We have developed a simple UV light treatment method,which increases the luminous efficiency by 79 times and reduces the gain threshold by 37.5%.Our UV-treated quantum well solution is used as a gain medium in a cylindrical optical resonator to realize liquid laser of whispering gallery mode laser.This provides a new idea for the application of colloidal semiconductor quantum wells in light-emitting devices.Traditional semiconductor nanocrystalline luminescent materials generally contain heavy metals such as lead and cadmium,which limits their application in consumer electronics.However,the most commonly used indium phosphide quantum dots are extremely difficult to generate optical gain due to problems such as interface defects.In order to achieve optical gain and lasing in environmentally friendly quantum dots,we synthesized high-efficiency ZnSe(Te)/ZnS quantum dot materials,and achieved optical gain and lasing in the entire blue spectral range by adjusting the Te content.In addition,Te doping can regulate the energy band alignment of the quantum dot core-shell heterostructure,suppress the non-radiative Auger recombination,and lower the laser threshold.The optical gain of quantum dot materials was analyzed and studied by using transient absorption spectroscopy technology,and it was the first time to prove the optical gain in heavy metal-free quantum dots.Quantum dot materials were encapsulated into a Fabry-Pérot cavity,pumped by quasi-continuous light,and a blue laser was observed,with a threshold of 12.5 μJ cm-2,which is the lowest threshold of blue lasers reported based on nanocrystals and the first time in Realization of blue laser in heavy metal-free quantum dot materials.All these prove that the ZnSe(Te)/ZnS quantum dot material is an ideal blue light gain material,which provides a new idea for the realization of an efficient and environmentally friendly blue light gain medium.