Photoluminescence Extraction Efficiency Research Articles

Two-dimensional photonic crystals increasing vertical light emission from Si nanocrystal-rich thin layers.

We have fabricated two-dimensional photonic crystals (PhCs) on the surface of Si nanocrystal-rich SiO2 layers with the goal to maximize the photoluminescence extraction efficiency in the normal direction. The fabricated periodic structures consist of columns ordered into square and hexagonal pattern with lattice constants computed such that the red photoluminescence of Si nanocrystals (SiNCs) could couple to leaky modes of the PhCs and could be efficiently extracted to surrounding air. Samples having different lattice constants and heights of columns were investigated in order to find the configuration with the best performance. Spectral overlap of the leaky modes with the luminescence spectrum of SiNCs was verified experimentally by measuring photonic band diagrams of the leaky modes employing angle-resolved spectroscopy and also theoretically by computing the reflectance spectra. The extraction enhancement within different spatial angles was evaluated by means of micro-photoluminescence spectroscopy. More than 18-fold extraction enhancement was achieved for light propagating in the normal direction and up to 22% increase in overall intensity was obtained at the spatial collection angle of 14°.

The variation of the enhanced PL efficiency of Y2O3:Eu3+ phosphor films with the height to the ZrO2 nanoparticle-assisted 2D PCL by reverse nano-imprint lithography

We developed a zirconium oxide (ZrO2) nanoparticle-assisted photonic structure for improving the light extraction efficiency of Y2O3:Eu3+ phosphor films by reverse nano-imprint lithography approach. The structural effect of a two-dimensional (2D) ZrO2 nanoparticle photonic crystal (PC) pattern on the extraction efficiency of photoluminescence (PL) from the underlying Y2O3:Eu3+ phosphor film was investigated. The 2D photonic crystal structure was fabricated using a reverse nano-imprint process with a ZrO2 nanoparticle solution as a nano-imprint resin and a patterned trimethylolpropane propoxylate triacrylate (TPT)/polydimethylsiloxane (PDMS) stamp as a mold. We controlled height of ZrO2 nanoparticle patterns in the range 190–370nm by varying the height of master mold. This simple process results in 6.9 times improvement of extraction efficiency for a 2D ZrO2 nanoparticle-assisted photonic crystal pattern (h=∼370nm) compared to the conventional Y2O3:Eu3+ thin-film phosphors.

Fabrication of Al<SUB>2</SUB>O<SUB>3</SUB> Coated 2D TiO<SUB>2</SUB> Nanoparticle Photonic Crystal Layers by Reverse Nano-Imprint Lithography and Plasma Enhanced Atomic Layer Deposition

This paper reports simple process to enhance the extraction efficiency of photoluminescence (PL) from Eu-doped yttrium oxide (Y2O3:Eu3+) thin-film phosphor (TFP). Two-dimensional (2D) photonic crystal layer (PCL) was fabricated on Y2O3:Eu3+ phosphor films by reverse nano-imprint method using TiO2 nanoparticle solution as a nano-imprint resin and a 2D hole-patterned PDMS stamp. Atomic scale controlled Al2O3 deposition was performed onto this 2D nanoparticle PCL for the optimization of the photonic crystal pattern size and stabilization of TiO2 nanoparticle column structure. As a result, the light extraction efficiency of the Y2O3:Eu3+ phosphor film was improved by 2.0 times compared to the conventional Y2O3:Eu3+ phosphor film.

Tuning a nano-pillar array for enhancing the photoluminescence extraction efficiency of GaN-based light-emitting diodes

We demonstrate the fabrication of hexagonal nano-pillar arrays at the surface of GaN-based light-emitting diodes (LEDs) by nanosphere lithography. By varying the oxygen plasma etching time, we could tune the size and shape of the pillar. The nano-pillar has a truncated cone shape. The nano-pillar array serves as a gradual effective refractive index matcher, which reduces the reflection and increases light cone. It is found that the patterned surface absorbs more pumping light. To compare extraction efficiencies of LEDs, it is necessary to normalize the photoluminescence power spectrum with total absorption rate under fixed pumping power, then we could obtain the correct enhancement factor of the photoluminescence extraction efficiency and optimized structure. The highest enhancement factor of the extraction efficiency is 10.6.

Enhanced light extraction from Y2O3: Eu3 + phosphor films via vacuum nano-imprint lithography using spin-on dielectric materials

This paper reports a simple process to enhance the extraction efficiency of photoluminescence from Eu-doped yttrium oxide (Y2O3: Eu3+) thin-film phosphor. The two-dimensional (2D) SiO2 photonic crystal layer was fabricated by vacuum nano-imprint method using a conventional spin-on dielectric solution as a nano-imprint resin and a 2D patterned Si stamp. The applied pressure and temperature of the patterning and annealing process facilitates the conversion of the spin-on dielectric solution into a SiO2 hemisphere structure resulting in high definition transfer of the 2D reverse pattern of the Si mold. The light extraction efficiency of the Y2O3: Eu3+ thin-film phosphor assisted by 2D SiO2 photonic crystal layer was approximately 1.72 times higher than that of the conventional Y2O3: Eu3+ thin-film phosphor.

Enhanced photoluminescence extraction efficiency from a diamond photonic crystal via leaky modes

Two-dimensional photonic crystal can be exploited as the top part of a light source in order to increase its extraction efficiency. Here, we report on the room-temperature intrinsic photoluminescence (PL) behavior of a nanocrystalline diamond (NCD) layer with diamond columns prepared on the top and periodically ordered into the lattice with square symmetry. Angle-resolved far-field measurements in the Γ–X crystal direction of broadband visible PL revealed up to six-fold enhancement of extraction efficiency as compared to a smooth NCD layer. A photonic band diagram above the lightcone derived from these measurements is in agreement with the diagram obtained from transmission measurements and simulation, suggesting that the enhancement is primarily due to light's coupling to leaky modes.

Fabrication of 2D photonic crystal assisted Y 2O 3:Eu 3+ thin-film phosphors by direct nano-imprinting

The effect of a two-dimensional Y 2O 3:Eu 3+ photonic crystal (PC) pattern on the extraction efficiency of photoluminescence from the underlying Y 2O 3:Eu 3+ thin-film phosphor was investigated. The photonic crystal structure was fabricated using a direct nano-imprint process with a Pechini-type Y 2O 3:Eu 3+ sol as the nano-imprint resin and a patterned polydimethylsiloxane (PDMS) stamp as the mold. The elevated pressure and temperature of the nano-imprinting process converts the Y 2O 3:Eu 3+ sol into a Y 2O 3:Eu 3+ gel resulting in high definition transfer of the 2D patterns of the master template into the gel on top of the Y 2O 3:Eu 3+ thin-film phosphor layer. The extraction efficiency of the 2D Y 2O 3:Eu 3+ gel PC-assisted Y 2O 3:Eu 3+ thin-film phosphor was approximately 3.7 times higher than a non-PC Y 2O 3:Eu 3+ gel coated Y 2O 3:Eu 3+ thin-film phosphor.

Effect of the extinction coefficient on the extraction efficiency of ZnS:Mn thin-film phosphors grown on two-dimensional nanorod substrates

We have studied the effects of varying the extinction coefficient of two-dimensional (2D) nanorod-assisted ZnS:Mn thin-film phosphors on their photoluminescence extraction efficiency. The finite-difference time-domain method was employed for the design and analysis of 2D nanorod-assisted thin-film phosphors. Using a nanorod pattern with a depth of 200 nm, a lattice constant of 600 nm, and a radius of 180 nm, the extraction efficiency of a transparent ZnS:Mn thin-film phosphor is predicted theoretically to increase by a factor of more than ∼9.1. Experiments have shown that incorporation of the 2D SiO2 nanorod layer only improves the light extraction efficiency over that of a conventional ZnS:Mn thin-film phosphor by a factor of ∼4.0. We discuss the reasons for this mismatch between the theoretical and experimental extraction efficiencies, in order to further improve the extraction efficiency of ZnS-based thin-film phosphors.

Effect of nonradiative recombination on light emitting properties of two-dimensional photonic crystal slab structures

InGaAsP-based two-dimensional photonic crystal light emitting structures are fabricated by employing wafer fusion and characterized optically. The structure does not contain defect regions and the whole area of the photonic crystal is used for light generation and extraction. The effect of nonradiative recombination is studied as a function of pump power. The relative contribution of surface recombination can be as low as 10% as pump power increases since carrier recombination is dominated by Auger recombination. In spite of the large surface-to-volume ratio of the photonic crystal pattern, over four-fold enhancement of photoluminescence extraction efficiency is observed.

Excitons in microcavities: Cavity polariton photoluminescence

We present an extensive set of absorption and PL measurements on semiconductor microcavities in the strong-coupling regime. We observe strong coupling from 110 K to room temperature. We look at the behaviour of the photoluminescence for different exciton-photon detuning. We discuss this data using two different pictures, the first is a non-interacting (uncoupled) picture of an exciton in a cavity filter. The second model is that of a cavity polariton and this explains the observed dynamics in the strong-coupling regime. We show how the opposing needs of strong coupling and high photoluminescence extraction efficiency can be reconciled.