Boon S. Ooi

Air-Stable Surface-Passivated Perovskite Quantum Dots for Ultra-Robust, Single- and Two-Photon-Induced Amplified Spontaneous Emission

We demonstrate ultra-air- and photostable CsPbBr3 quantum dots (QDs) by using an inorganic-organic hybrid ion pair as the capping ligand. This passivation approach to perovskite QDs yields high photoluminescence quantum yield with unprecedented operational stability in ambient conditions (60 ± 5% lab humidity) and high pump fluences, thus overcoming one of the greatest challenges impeding the development of perovskite-based applications. Due to the robustness of passivated perovskite QDs, we were able to induce ultrastable amplified spontaneous emission (ASE) in solution processed QD films not only through one photon but also through two-photon absorption processes. The latter has not been observed before in the family of perovskite materials. More importantly, passivated perovskite QD films showed remarkable photostability under continuous pulsed laser excitation in ambient conditions for at least 34 h (corresponds to 1.2 × 10(8) laser shots), substantially exceeding the stability of other colloidal QD systems in which ASE has been observed.

InGaN/GaN disk-in-nanowire white light emitting diodes on (001) silicon

High density (∼1011 cm−2) GaN nanowires and InGaN/GaN disk-in-nanowire heterostructures have been grown on (001) silicon substrates by plasma-assisted molecular beam epitaxy. The nanowires exhibit excellent uniformity in length and diameter and a broad emission is obtained by incorporating InGaN disks of varying composition along the length of the nanowires. Monolithic lighting emitting diodes were fabricated with appropriate n- and p-doping of contact layers. White light emission with chromaticity coordinates of x=0.29 and y=0.37 and a correlated color temperature of 5500–6500 K at an injection current of 50 A/cm2 is measured. The measured external quantum efficiency of the devices do not exhibit any rollover (droop) up to an injection current density of 400 A/cm2.

Luminescence of Eu3+ and Tb3+ doped Zn2SiO4 nanometer powder phosphors

Abstract We report, for the first time to the best of our knowledge, the luminescent properties of Tb 3+ and Eu 3+ doped Zn 2 SiO 4 phosphors prepared by a sol–gel process. The phosphors have shown prominent luminescence in green and red, respectively, due to the electronic transitions of 5 D 0 → 7 F 2 (Eu 3+ ) and 5 D 4 → 7 F 5 (Tb 3+ ). Structural characterization of these luminescent materials was carried out with XRD and TEM. Luminescence spectra were analyzed by measuring the excitation, photoluminescence spectra and lifetimes of the emission transitions of Eu 3+ ( 5 D 0 → 7 F J , J =1–5) and Tb 3+ ( 5 D 4 → 7 F J , J =1–6). Our experimental results have shown that these phosphors have comparable luminescence properties as those currently used in TVs and CRTs.

Monolithic Electrically Injected Nanowire Array Edge-Emitting Laser on (001) Silicon

A silicon-based laser, preferably electrically pumped, has long been a scientific and engineering goal. We demonstrate here, for the first time, an edge-emitting InGaN/GaN disk-in-nanowire array electrically pumped laser emitting in the green (λ = 533 nm) on (001) silicon substrate. The devices display excellent dc and dynamic characteristics with values of threshold current density, differential gain, T0 and small signal modulation bandwidth equal to 1.76 kA/cm(2), 3 × 10(-17) cm(2), 232 K, and 5.8 GHz respectively under continuous wave operation. Preliminary reliability measurements indicate a lifetime of 7000 h. The emission wavelength can be tuned by varying the alloy composition in the quantum disks. The monolithic nanowire laser on (001)Si can therefore address wide-ranging applications such as solid state lighting, displays, plastic fiber communication, medical diagnostics, and silicon photonics.

Improvement of organic light-emitting diodes performance by the insertion of a Si3N4 layer

Abstract The interface between the organic layer and the metallic layer of an organic light-emitting diode (OLED) is crucial to the stability and performance of the device. A uniform thin silicon nitride film, used as an anode modification layer, has been deposited on ITO coated glass by plasma enhanced chemical vapor deposition used as an anode modification layer. This thin film improves the interface of the electrode and the organic layer, prevents the diffusion of the metallic ions from the ITO anode to the organic layer and restrains the surface noisy leakage current. The device performance has thus been improved. The maximum electroluminescence (EL) efficiency of the device with the silicon nitride film is of several times higher than that of the device without it.

The recombination mechanisms leading to amplified spontaneous emission at the true-green wavelength in CH3NH3PbBr3 perovskites

We investigated the mechanisms of radiative recombination in a CH3NH3PbBr3 hybrid perovskite material using low-temperature, power-dependent (77 K), and temperature-dependent photoluminescence (PL) measurements. Two bound-excitonic radiative transitions related to grain size inhomogeneity were identified. Both transitions led to PL spectra broadening as a result of concurrent blue and red shifts of these excitonic peaks. The red-shifted bound-excitonic peak dominated at high PL excitation led to a true-green wavelength of 553 nm for CH3NH3PbBr3 powders that are encapsulated in polydimethylsiloxane. Amplified spontaneous emission was eventually achieved for an excitation threshold energy of approximately 350 μJ/cm2. Our results provide a platform for potential extension towards a true-green light-emitting device for solid-state lighting and display applications.

Quantum Dashes on InP Substrate for Broadband Emitter Applications

We report on the development of InAs/InGaAlAs quantum-dash-in-well structure on InP substrate for wideband emitter applications. A spectral width as broad as 58 meV observed from both photoluminescence and surface photovoltage spectroscopy on the sample indicating the formation of highly inhomogeneous InAs-dash structure that results from the quasi-continuous interband transition. The two-section superluminescent diodes (SLDs), with integrated photon absorber slab as lasing suppression section, fabricated on the InAs dash-in-well structure exhibits the close-to-Gaussian emission with a bandwidth (full-width at half-maximum) of up to 140 nm at ~ 1.6 mum peak wavelength. The SLD produces a low spectrum ripple of 0.3 dB and an integrated power of ~ 2 mW measured at 20degC under 8 kA/cm2. The oxide stripe laser exhibits wide lasing wavelength coverage of up to 76 nm at ~ 1.64 mum center wavelength and an output optical power of ~ 400 mW from simultaneous multiple confined states lasing at room temperature. This rule changing broadband lasing signature, different from the conventional interband diode laser, is achieved from the quasi-continuous interband transition formed by the inhomogeneous quantum-dash nanostructure.

Going beyond 4 Gbps data rate by employing RGB laser diodes for visible light communication

With increasing interest in visible light communication, the laser diode (LD) provides an attractive alternative, with higher efficiency, shorter linewidth and larger bandwidth for high-speed visible light communication (VLC). Previously, more than 3 Gbps data rate was demonstrated using LED. By using LDs and spectral-efficient orthogonal frequency division multiplexing encoding scheme, significantly higher data rates has been achieved in this work. Using 16-QAM modulation scheme, in conjunction with red, blue and green LDs, data rates of 4.4 Gbps, 4 Gbps and 4 Gbps, with the corresponding BER/SNR/EVM of 3.3 × 10⁻³/15.3/17.9, 1.4 × 10⁻³/16.3/15.4 and 2.8 × 10⁻³/15.5/16.7were obtained over transmission distance of ~20 cm. We also simultaneously demonstrated white light emission using red, blue and green LDs, after passing through a commercially available diffuser element. Our work highlighted that a tradeoff exists in operating the blue LDs at optimum bias condition while maintaining good color temperature. The best results were obtained when encoding red LDs which gave both the strongest received signal amplitude and white light with CCT value of 5835K.

Room-temperature broadband emission of an InGaAs/GaAs quantum dots laser.

We report the first demonstration to our knowledge of an ultrabroad emission laser using InGaAs/GaAs quantum dots by cycled monolayer deposition. The device exhibits a lasing wavelength coverage of approximately 40 nm at an approximately 1160 nm center wavelength at room temperature. The broadband signature results from the superposition of quantized lasing states from highly inhomogeneous dots.

2.3 Gbit/s underwater wireless optical communications using directly modulated 520 nm laser diode

We experimentally demonstrate a record high-speed underwater wireless optical communication (UWOC) over 7 m distance using on-off keying non-return-to-zero (OOK-NRZ) modulation scheme. The communication link uses a commercial TO-9 packaged pigtailed 520 nm laser diode (LD) with 1.2 GHz bandwidth as the optical transmitter and an avalanche photodiode (APD) module as the receiver. At 2.3 Gbit/s transmission, the measured bit error rate of the received data is 2.23×10(-4), well below the forward error correction (FEC) threshold of 2×10(-3) required for error-free operation. The high bandwidth of the LD coupled with high sensitivity APD and optimized operating conditions is the key enabling factor in obtaining high bit rate transmission in our proposed system. To the best of our knowledge, this result presents the highest data rate ever achieved in UWOC systems thus far.