Random Laser Research Based On Polymers Doped With CdSe/ZnS Quantum Dots

Compared with traditional laser,the random laser has a similar working principle,but the laser mode is determined by multiple scattering,and random lasing does not require a resonant cavity.The multiple scattering increases the optical path length of the photon in the gain medium.When the gain of the photon is greater than the loss in a certain mode,the random lasing is achieved.The CdSe/ZnS quantum dots(QDs)with a type-I band alignment use ZnS shell to inorganic passivate CdSe core,which improves the optical properties and photochemical stability.As a functional material,polymer is usually used to form a waveguide structure doped with a gain medium.The polymer doped with CdSe/ZnS QDs is beneficial for random laser emission with low laser threshold,high color purity,and good environmental stability.In this paper,the enhancement effect of surface plasmon resonance of Ag nanoislands on random laser is studied based on polymethyl methacrylate(PMMA)doped with CdSe/ZnS QDs.And the laser characteristics of SiO₂ anchor CdSe/ZnS QDs flexible random lasers is studied based on polydimethylsiloxane(PDMS).Based on the surface plasmon resonance effect of metal nanoparticles,the random lasing action from PMMA doped with CdSe/ZnS quantum dots plasmonically enhanced by Ag nanoislands were studied.When the Ag nanoislands are not introduced in the system,there is no discrete spikes in the emission spectrum,and only the amplified spontaneous emission(ASE)phenomenon is observed.The full width at half maximum(FWHM)of the spectrum was about10 nm,and the threshold is about 2.0 mJ/cm2.However,when the Ag nanoislands structure is introduced in the system,a random laser phenomenon with an FWHM of about 0.2 nm can be observed in the emission spectrum.And the threshold of the random laser is only about 1.6mJ/cm2 due to the existence of the surface plasmon resonance effect of the Ag nanoislands and the light confinement effect of the PMMA active waveguide layer.By changing the distribution density of the Ag nanoisland structure in the system,the influence of the surface plasmon resonance effect of the Ag nanoislands on the random laser emission is further determined.The change of Ag nanoislands distribution density can adjust the emission intensity and oscillation mode of random lasers,which provides an idea for designing tunable random lasers.Finally,by changing the pump stripe length,it is determined that there is a critical pumping area for random laser emission.And the stability of random laser emission is studied.It can be observed that the intensity decreased by only 20% and the FWHM is still less than 1 nm after 1.4 * 10⁵ laser pulse pumping.The random laser emission characteristics from PDMS doped with CdSe/ZnS QDs anchored by SiO₂ is studied.The SiO₂-QDs structure was prepared,which avoid the Stark effect and fluorescence quenching caused by quantum dot clusters,so that the luminous efficiency of quantum dots will not be reduced.By changing the concentration of SiO₂ nanoparticles in the system,it is determined that there is the minimum threshold value(¹.2 mJ/cm2)of the random laser emission when the concentration of SiO₂ nanoparticles is 1.2 mg/mL.Subsequently,the influence of the particle size of SiO₂ nanoparticles on the random laser emission is investigated,and it can be find that the feedback depth is the strongest in the system when the particle size of SiO₂ nanoparticles was 550 nm.Next,under the condition that the optimal concentration and particle size of the SiO₂ nanoparticles,the peak wavelength and the number of modes of the random laser emission can be adjusted by changing the pump stripe length.And the angle dependence of the random laser emission is studied.It can be find that the emission of random lasing is strongly restricted to an angle range of ±10°.Finally,the controllability of random laser emission under PDMS film stretching was explored.Due to the flexibility and ductility of PDMS films,this random laser has potential application in the integrated optics,micro-nano optoelectronics,display imaging and wearable device.