Abstract
We address optical amplification properties of quantum nanoparticles of the cadmium selenide/cadmium sulfide (CdSe/CdS) material system with different dimensionality of spatial confinement. CdSe/CdS core/shell quantum dots (QDs), core/shell quantum rods (QRs) and 5 monolayer thick core/crown nanoplatelets (NPLs) at ambient temperature are considered, exhibiting 0D, 1D and 2D spatial confinement dimensionality of the electronic system, respectively. Continuous films of all these nanoparticles are synthesised, and amplified spontaneous emission (ASE) spectra are measured under femtosecond pumping at wavelengths of 400 nm and 800 nm, respectively. The lowest threshold is found for NPLs and the highest for QDs, demonstrating the influence of the rod-like and plate-like CdS structures. To emphasize this effect, ASE is demonstrated also in CdSe/CdS QRs and NPLs under nanosecond pumping at 355 nm in the same material films. The amplification has been achieved without use of any feedback structure, emphazising the efficiency of the antenna effect. The pumping threshold fluences for NPLs and QRs are observed to be similar, but no ASE is observed in QDs up to the damage threshold of the nanoparticle layers. The length variation investigation with nanosecond pumping resulted in the gain coefficients of 29 cm−1 and 37 cm−1 for QRs and NPLs, respectively.
Highlights
Be demonstrated that by close packaging of quantum dots (QDs) into solid state films, it is possible to obtain the concentrations that are sufficiently high for the optical gain to successfully compete with the Auger decay[16]
While the use of highly expensive femtosecond laser systems is still appropriate for basic studies of the optical properties and their ability to provide optical gain, it would be desirable for practical applications to control and pump optical devices on the basis of quantum materials with low-cost nanosecond pump sources
Low-threshold lasing in CdSe/ZnS QDs embedded into a thin layer of PMMA has been demonstrated under nanosecond pumping at 355 nm using a distributed feedback structure in order to benefit from low gain[18]
Summary
Parva Chhantyal[1,3], Suraj Naskar[2,3], Tobias Birr 1,3, Tim Fischer[1,3], Franziska Lübkemann[2,3], Boris N. Small NPLs, due to their 2D spatial extension, have been demonstrated to exhibit an even larger absorption cross-section as compared to QRs and QDs22 This enables achieving higher gain and ASE without any resonator structure using lower pump power laser sources. Optical gain is demonstrated in the same QRs and NPLs material films under nanosecond pumping without the use of any feedback structure, paving the way for practical applications of quantum confined materials as versatile light sources. The CdSe/CdS core/shell QDs, core/shell QRs and core/crown 5 monolayer NPLs at ambient temperature exhibit 0D, 1D and 2D spatial confinement dimensionality of the electronic system, respectively Continuous films of these nanoparticles are synthesized, and ASE spectra are measured under femtosecond pumping at wavelengths of 400 nm and 800 nm, respectively, as well as nanosecond pumping in the ultraviolet spectral range at 355 nm. No ASE is observed in QDs up to the damage threshold of the nanoparticle layers around ≈22 mJcm−2
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