Anti‐Stokes cooling in semiconductor nanocrystal quantum dots: A feasibility study

Abstract

Multicolor luminescent films have great potential for use in optoelectronics, solid‐state light‐emitting materials, and optical devices. This work describes a systematic investigation of the ordered assembly of two‐ (blue/green, blue/orange, red/blue, red/green) and three‐color (blue/red/green) light‐emitting ultrathin films (UTFs) by using different photofunctional anions [bis(N‐methylacridinium)@polyvinylsulfonate ion pairs and anionic derivatives of poly(p‐phenylene), poly(phenylenevinylene), and poly(thiophene)] and Mg‐Al‐layered double hydroxide nanosheets as building blocks. The rational combination of luminescent components affords precise control of the emission wavelengths and intensity, and multicolored luminescent UTFs can be precisely tailored covering most of the visible spectral region. The assembly process of the UTFs and their luminescence properties, as monitored by UV–vis absorption and fluorescence spectroscopy, resulted in a gradual change in luminescence color in the selected light‐emitting spectral region upon increasing the number of deposition cycles. X‐ray diffraction demonstrates that the UTFs are periodic layered structures involving heterogeneous superlattices associated with individual photoactive anion–LDH units. These UTFs also exhibit well‐defined multicolor polarized fluorescence with high polarization anisotropy, and the emissive color changes with polarization direction. Therefore, this work provides a way of fabricating heterogeneous UTFs with tunable‐color luminescence as well as polarized multicolor emission, which have potential applications in the areas of light displays and optoelectronic devices.

Anti-stokes emission in whispering gallery mode microcavities with semiconductor quantum dots

“…We also found that the integrated intensity of anti-Stokes PL has an almost linear dependence on the excitation intensity under weak or moderate excitation (< 200 W/cm 2 ). This dependence is very similar to the behavior of ASPL in colloidal QDs where the progressive transition from Stokes to anti-Stokes PL can be observed when adjusting the excitation wavelength to below the band-gap region [7]. A similar effect was recently reported in small (2 µm diameter) microspheres with a thin shell of semiconductor QDs, and explained by the multiphononassisted excitation of an electron from the ground state to the excited state through the mediation of the QDs shallow trap levels [8].…”

Semiconductor nanowires self-assembled from colloidal CdTe nanocrystal building blocks: optical properties and application perspectives

“…56 This type of emission process involves the emission of higher energy photons than those that are absorbed. The absorption of vibrational energy distinguishes anti Stokes PL from other up conversion effects like two photon or two step excited luminescence.…”

Structural and Electrical Properties of Electrodeposited Single Junction of Cuprous (I) Oxide-Copper

“…The current of metal-semiconductor-metal solar cell as a function of the voltage can be expressed as follows [1,4,[6][7][8][9][10][11][12]:…”

“…The solar cell materials have been the subject of intense research for many years due to their unusual optical and electrical properties [1][2][3][4][5][6][7][8][9][10][11][12]. On the basis of theoretical studies it may be proven that, photovoltaic technology has advanced considerably, resulting in singlejunction solar cells with a record efficiency of 28.3% and multi-junction cells with an efficiency (under concentrated illumination) of 43.5% [2].…”