Red-light photodetectors without filters are in urgent need for narrowband applications such as full-color imaging and multi-output visible light communication (VLC). However, their development is hindered by the lack of small-band-gap and narrowband response materials. Without wavelength filters, a new type of photodetector with a simple single-layer architecture is developed, based on a stable small-band-gap squarylium dye and characterized by a detectivity peak at 680 nm and full width at half maximum of 80 nm. The device, which exhibits high stability in air and humid conditions, shows a significantly low dark current of ß2 nA·cm −2 at −2 V and high specific detectivity of 3.2 × 10 12 Jones. The response current ratio of the device to red, green, and blue lights with a luminous flux amplitude ratio of 3:6:1 (standard ratio for white light) is 100:12:1.1. These properties indicate that the squarylium dye red-light photodetectors are promising for VLC and other narrowband optoelectronic applications.

Organic-inorganic hybrid photodetectors attract considerable attention because they can combine the advantages of both organic and inorganic systems. Here, a perovskite compound with a broad absorption spectrum and high power conversion efficiency is used as a photosensitive layer in an organic/inorganic hybrid heterojunction photodetector with a high and fast response. The high sensitivity exceeding 104 is obtained at bias of 0–4 V. Using a tandem organic light-emitting diode (OLED) as the light source, we fabricated an optocoupler device. The optocoupler achieved a maximum photoresponsivity of 1.0 A W−1 at 341.3 μWcm−2 at an input voltage of 6 V. The device also exhibits rapid response times of τrise ~ 20 μs and τfall ~ 17 μs; as well as a high current transfer ratio (CTR) of 28.2%. After applying an amplification circuit, the CTR of the optocoupler increases to 263.3%, which is comparable with that of commercial inorganic optocouplers. The developed hybrid optocoupler thus shows great promise for use in photonics.

This paper considers an augmented double autoregressive (DAR) model, which allows null volatility coefficients to circumvent the over-parameterization problem in the DAR model. Since the volatility coefficients might be on the boundary, the statistical inference methods based on the Gaussian quasi-maximum likelihood estimation (GQMLE) become non-standard, and their asymptotics require the data to have a finite sixth moment, which narrows applicable scope in studying heavy-tailed data. To overcome this deficiency, this paper develops a systematic statistical inference procedure based on the self-weighted GQMLE for the augmented DAR model. Except for the Lagrange multiplier test statistic, the Wald, quasi-likelihood ratio and portmanteau test statistics are all shown to have non-standard asymptotics. The entire procedure is valid as long as the data is stationary, and its usefulness is illustrated by simulation studies and one real example.where u, φ i ∈ R, ω > 0, α i > 0, {η t } is a sequence of independent and identically distributed (i.i.d.) random variables with zero mean and unit variance, and η t is independent of {y s ; s < t}. Model (1.1) was first termed by Ling (2004), and it is a subclass of ARMA-ARCH models in Weiss (1984) and of nonlinear AR models in Cline and Pu (2004), but it is different from Engle's ARCH model if some φ i = 0.

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