Low‐Threshold Lasing from Copper‐Doped CdSe Colloidal Quantum Wells

Abstract

Transition metal doped colloidal nanomaterials (TMDCNMs) have recently attracted attention as promising nano‐emitters due to dopant‐induced properties. However, despite ample investigations on the steady‐state and dynamic spectroscopy of TMDCNMs, experimental understandings of their performance in stimulated emission regimes are still elusive. Here, the optical gain properties of copper‐doped CdSe colloidal quantum wells (CQWs) are systemically studied with a wide range of dopant concentration for the first time. This work demonstrates that the amplified spontaneous emission (ASE) threshold in copper‐doped CQWs is a competing result between the biexciton formation, which is preferred to achieve population inversion, and the hole trapping which stymies the population inversion. An optimum amount of copper dopants enables the lowest ASE threshold of ≈7 µJ cm−2, about 8‐fold reduction from that in undoped CQWs (≈58 µJ cm−2) under sub‐nanosecond pulse excitation. Finally, a copper‐doped CQW film embedded in a vertical cavity surface‐emitting laser (VCSEL) structure yields an ultralow lasing threshold of 4.1 µJ cm−2. Exploiting optical gain from TMDCNMs may help to further boost the performance of colloidal‐based lasers.

Ultralow‐Threshold and High‐Quality Whispering‐Gallery‐Mode Lasing from Colloidal Core/Hybrid‐Shell Quantum Wells

“…[7][8][9] As such, a broad range of solution-processable materials, such as organic dye molecules and colloidal semiconductor nanostructures, with low-cost production and easy incorporation into various cavities, have been the core gain media of intense research for lasing demonstration at or close to room temperature. [1,3,4,6,[8][9][10][11][12][13] Among all these solution-processable gain materials, 2D colloidal nano platelets (NPLs) with pure quantum confinement from the vertical direction, [14,15] also referred to as semiconductor quantum wells, have become the most promising alternative owing to the suppressed nonradiative Auger recombination (AR) rates relative to their 0D quantum dots and 1D nanorods counterparts and their long-term stable lasing performance compared to traditional organic dyes which suffer from…”

“…[21,22] Driven by their remarkable gain properties, numerous works have been conducted on the demonstration of core/alloyed shell NPLs-based lasers. [23][24][25][26][27] To date, the majority of works using NPLs as a gain medium have adopted several optical feedback configurations including Fabry−Pérot cavity, [10,11,23,25,[28][29][30] photonic-crystal cavity, [26,31] distributed feedback cavity, [24] as well as random lasing cavity. [32] However, NPLs-whispering gallery mode (WGM) lasers with ultrahigh quality (Q) factor and extremely small mode volume, [33,34] in which the closed feedback loop is formed via total internal reflection in the boundaries of high refractive index cavity, are rarely studied.…”

“…[ 7–9 ] As such, a broad range of solution‐processable materials, such as organic dye molecules and colloidal semiconductor nanostructures, with low‐cost production and easy incorporation into various cavities, have been the core gain media of intense research for lasing demonstration at or close to room temperature. [ 1,3,4,6,8–13 ] Among all these solution‐processable gain materials, 2D colloidal nanoplatelets (NPLs) with pure quantum confinement from the vertical direction, [ 14,15 ] also referred to as semiconductor quantum wells, have become the most promising alternative owing to the suppressed nonradiative Auger recombination (AR) rates relative to their 0D quantum dots and 1D nanorods counterparts and their long‐term stable lasing performance compared to traditional organic dyes which suffer from severe irreversible photobleaching. [ 12,16 ] In addition, thanks to the persistent efforts made by researchers, various approaches including thickness tunability, [ 14 ] ligand exchange, [ 17,18 ] and heterostructure‐engineering [ 19,20 ] have been reported to manipulate the excitonic characteristics of the final NPLs products with emission covering the whole visible spectral regime.…”

Ligand Exchange and Impurity Doping in 2D CdSe Nanoplatelet Thin Films and Their Applications

“…[43] However, the same amount of cadmium actate dihydrate was used in all synthesis of undoped and doped NPL, implying that the addition of dopant ions slightly changes the aspect ratio of NPLs as demonstrated in our previous reports. [41,44] Inductively coupled plasma-mass spectrometry (ICP-MS) was conducted to measure the doping concentration of Cu-and Ag-doped CdSe NPLs, showing 1.05 weight % (Cu/Cd) and 0.85 weight % (Ag/Cd), respectively (Figure 1b). The NPL solutions were spin-coated onto pre-cleaned and (3-Mercaptopropyl)trimethoxysilane (MPTS)-treated substrates to form NPL thin films.…”

Visualizing Nonlinear Phononics in Layered ReSe2

“…To glean insight into the time-domain information on coherent intralayer atomic motions in layered ReSe 2 , the oscillated Δ R / R 0 signal in Figure b has been converted into time-dependent spectral amplitudes (chronograms) by sliding window FT (SWFT), which yields instantaneous frequencies and amplitudes of the coherent atomic vibrations (see Methods for details). − From the contour plot of SWFT in Figure a, two distinct time-dependent phonon frequency behaviors have been resolved: those phonon modes that contain the contribution from out-of-plane atomic motions (i.e., the mixed vibrations, Se vibrations, and the out-of-plane vibration of Re atoms at ∼4.84 THz) exhibit a clear frequency beat which is absent in the in-plane vibration of Re atoms at 3–4 THz (the classification of atomic vibrational directions in layered ReSe 2 is detailed discussed previously ,,,, ). One may also notice that there is an amplitude collapse and revival for the in-plane vibration of Re atoms at 3–4 THz, which is the result of the classical oscillation overlap among these three in-plane coherent atomic motions with similar frequencies (i.e., ∼3.39 THz, ∼3.58 THz, and ∼3.77 THz), as previously observed in layered graphite .…”