Polarized emission of CdSe nanocrystals in magnetic field: the role of phonon-assisted recombination of the dark exciton

Abstract

Optical phonon-assisted emission of dark excitons controls the intensity and maximum position of σ− and σ+ polarized photoluminescence of CdSe nanocrystals.

Photoluminescence Kinetics of Dark and Bright Excitons in Atomically Thin MoS2

“…We believe that the possible dependence of the dark-bright exciton splitting on strain can explain the huge dispersion of the data on the fine exciton spectrum in 2D MoS 2 , published in literature. [4,[41][42][43] It can also be noted that the characteristic lifetimes for dark excitons are not as long as in quantum dots or in epitaxial 2D GaN/AlN systems, [48,81] where they can approach tens and hundreds of ns at LTs. This fact, which is probably associated with the different energy splitting between the dark and bright excitons, along with the strong oscillator strength in the TMDs, requires a comprehensive study along with the dependence of the fine spectrum of the exciton states on strain.…”

“…It can also be noted that the characteristic lifetimes for dark excitons are not as long as in quantum dots or in epitaxial 2D GaN/AlN systems, [ 48,81 ] where they can approach tens and hundreds of ns at LTs. This fact, which is probably associated with the different energy splitting between the dark and bright excitons, along with the strong oscillator strength in the TMDs, requires a comprehensive study along with the dependence of the fine spectrum of the exciton states on strain.…”

“…In both MoS2 monolayers under study, the characteristic times of the spin and momentum forbidden states increase with a temperature rise, which can be interpreted in terms of an increase in the population of dark states as observed in various nanostructures. [40,[63][64][65][66] In the first approximation, the longer characteristic time L in each doublet, comprising optically allowed and forbidden by spin or momentum states, can be described via their recombination rate at low temperature [64] :…”

“…At LTs (<100 K), it can be interpreted in terms of an increase in the population of dark states as observed in various nanostructures. [48,[78][79][80][81] In the first approximation, the longer characteristic time τ L in each doublet, comprising optically allowed and forbidden by spin or momentum states, can be described via their recombination rate at LT. [79] τ…”

“…At LTs (<100 K), it can be interpreted in terms of an increase in the population of dark states as observed in various nanostructures. [ 48,78–81 ] In the first approximation, the longer characteristic time τ L in each doublet, comprising optically allowed and forbidden by spin or momentum states, can be described via their recombination rate at LT. [ 79 ] where k B is the Boltzmann constant, T is temperature, Γ A and Γ F are the respective recombination rates of the allowed and forbidden states, and Δ E is the energy of acoustic phonons, which matches the dark–bright exciton splitting Δ AF (here, it is assumed that thermalization of exciton states is via the interaction with the phonons). When k B T > Δ E , the second term in Equation () decreases, and the recombination rate tends to the half‐sum of Γ A and Γ F at LT.…”