Low‐Threshold Lasing from Copper‐Doped CdSe Colloidal Quantum Wells (original) (raw)
Related papers
Nature Communications, 2020
Colloidal semiconductor quantum wells have emerged as a promising material platform for use in solution-processable lasers. However, applications relying on their optical gain suffer from nonradiative Auger decay due to multi-excitonic nature of light amplification in II-VI semiconductor nanocrystals. Here, we show sub-single exciton level of optical gain threshold in specially engineered CdSe/CdS@CdZnS core/crown@gradient-alloyed shell quantum wells. This sub-single exciton ensemble-averaged gain threshold of ( N g )≈ 0.84 (per particle) resulting from impeded Auger recombination, along with a large absorption cross-section of quantum wells, enables us to observe the amplified spontaneous emission starting at an ultralow pump fluence of ~ 800 nJ cm −2 , at least three-folds better than previously reported values among all colloidal nanocrystals. Finally, using these gradient shelled quantum wells, we demonstrate a vertical cavity surface-emitting laser operating at a low lasing thr...
ACS Nano, 2015
Here, we systematically investigated the spontaneous and stimulated emission performances of solution-processed atomically flat quasi-2D nanoplatelets (NPLs) as a function of their lateral size using colloidal CdSe core NPLs. We found that the photoluminescence quantum efficiency of these NPLs decreases with increasing lateral size while their photoluminescence decay rate accelerates. This strongly suggests that nonradiative channels prevail in the NPL ensembles having extended lateral size, which is well-explained by the increasing number of the defected NPL subpopulation.
Doping of bulk semiconductors has revealed widespread success in optoelectronic applications. In the past few decades, substantial effort has been engaged for doping at the nanoscale. Recently, doped colloidal quantum dots (CQDs) have been demonstrated to be promising materials for luminescent solar concentrators (LSCs) as they can be engineered for providing highly tunable and Stokes-shifted emission in the solar spectrum. However, existing doped CQDs that are aimed for full solar spectrum LSCs suffer from moderately low quantum efficiency, intrinsically small absorption cross-section, and gradually increasing absorption profiles coinciding with the emission spectrum, which together fundamentally limit their effective usage. Here, the authors show the first account of copper doping into atomically flat colloidal quantum wells (CQWs). In addition to Stokes-shifted and tunable dopantinduced photoluminescence emission, the copper doping into CQWs enables near-unity quantum efficiencies (up to ≈97%), accompanied by substantially high absorption cross-section and inherently step-like absorption profile, compared to those of the doped CQDs. Based on these exceptional properties, the authors have demonstrated by both experimental analysis and numerical modeling that these newly synthesized doped CQWs are excellent candidates for LSCs. These findings may open new directions for deployment of doped CQWs in LSCs for advanced solar light harvesting technologies.
Low-Threshold Stimulated Emission Using Colloidal Quantum Wells
Nano Letters, 2014
applications, including biolabeling 2 and light-emitting devices 3 . By contrast, the use of colloidal nanocrystals for optical amplification 4 and lasing 5 has been limited by the high input power densities that have been required. In this work, we show that colloidal nanoplatelets (NPLs) produce amplified spontaneous emission (ASE) with pump-fluence thresholds as low 6 µJ/cm 2 and gain as high as 600 cm -1 , both a 4-fold improvement over the best reported values for colloidal nanocrystals; in addition, gain saturation occurs at pump fluences two orders of magnitude higher than the ASE threshold. We attribute this exceptional performance to large optical cross-sections, slow Auger recombination rates, and the narrow emission linewidth of the NPL ensemble. The NPLs bring the advantages of quantum wells as an optical gain medium to a colloidal system, opening up the possibility of producing high-efficiency, solution-processed lasers.
Amplified Spontaneous Emission and Lasing in Colloidal Nanoplatelets
ACS Nano, 2014
Colloidal nanoplatelets (NPLs) have recently emerged as favorable light-emitting materials, which also show great potential as optical gain media due to their remarkable optical properties. In this work, we systematically investigate the optical gain performance of CdSe core and CdSe/CdS core/crown NPLs having different CdS crown size with one-and two-photon absorption pumping. The core/crown NPLs exhibit enhanced gain performance as compared to the core-only NPLs due to increased absorption cross section and the efficient interexciton funneling, which is from the CdS crown to the CdSe core. One-and two-photon absorption pumped amplified spontaneous emission thresholds are found as low as 41 μJ/cm 2 and 4.48 mJ/cm 2 , respectively. These thresholds surpass the best reported optical gain performance of the state-of-the-art colloidal nanocrystals (i.e., quantum dots, nanorods, etc.) emitting in the same spectral range as the NPLs. Moreover, gain coefficient of the NPLs is measured as high as 650 cm À1 , which is 4-fold larger than the best reported gain coefficient of the colloidal quantum dots. Finally, we demonstrate a two-photon absorption pumped vertical cavity surface emitting laser of the NPLs with a lasing threshold as low as 2.49 mJ/cm 2 . These excellent results are attributed to the superior properties of the NPLs as optical gain media.
ExcitonâExciton Interaction and Optical Gain in Colloidal CdSe/CdS Dot/Rod Nanocrystals
Advanced Materials, 2009
Semiconductor colloidal nanocrystals have been proposed as optically-active media for solution-processable optoelectronic devices, because they combine inexpensive, wet-chemistry synthesis with high photoluminescence quantum yield, large oscillator strength and size tuneability of optical transitions. Key to the success of nanocrystal-based devices is the possibility to design and consistently synthesize nanocrystals with desired properties. Size uniformity can be usually controlled within less than 5% uncertainty; surface capping, passivation and core/shell structures can lead to photoluminescence quantum yields exceeding 50%, optical gain and lasing. A new frontier in nanocrystal design has appeared with heterostructures allowing spatial separation of electron and hole wavefunctions, like in type-II CdSe/CdTe core/shell nanocrystals, through staggered conduction and valence band offsets. Charge separation inside nanocrystals is useful in photodetector and photovoltaic devices, quantum optics and low-threshold lasers. Exciton nonlinearities also depend on the degree of separation of electron and hole wavefunction. In type-II heterostructures, it has been demonstrated that charge separation can lead to a large repulsive exciton-exciton interaction. The resulting blueshift of the exciton-to-biexciton transition suppresses to a large extent resonant re-absorption of stimulated emission from single-exciton states, allowing net optical gain and lasing at excitations corresponding to less than one electron-hole pair per nanocrystal. In this regime, losses inherent to multiexciton recombinations are avoided, resulting in optical gain with a much longer lifetime, an essential step towards the demonstration of lasing under continuous wave operation.
ACS Nano, 2015
While over the last years the syntheses of colloidal quantum dots (CQDs) with core/shell structures were continuously improved to obtain highly efficient emission, it has remained a challenge to use them as active materials in laser devices. Here, we report on a successful demonstration of random lasing at room temperature in films of CdSe/CdS CQDs with different core/shell band alignments and extra thick shells. Even though the lasing process is based on random scattering, we find systematic dependencies of the laser thresholds on film morphology and excitation spot size. This systematics suggests that random lasing experiments are a valuable tool for testing nanocrystal materials, providing a direct and simple feedback for the further development of colloidal gain materials towards lasing in continuous wave operation.
Nanoscale Research Letters, 2007
Picosecond time-resolved photoluminescence measurements were performed on CdSe core and CdSe/ZnS core/shell colloidal quantum dots (QDs). Photoluminescence (PL) emission is observed to originate from intrinsic (1 U and (1 L bright states with lifetimes of 60 and 450 ps, respectively, and from a long living component with nanosecond lifetimes. The latter is attribuited to the emission from surface states (ss) approximately 16 and 13 meV below the (1 L state for core and core/shell QDs, respectively. We show that in the temperature range between 15 and 70 K the three recombination processes compete and they are thermally populated through different pathways ((1 L f (1 U and ss f (1 L ).