*Editorial* **Optoelectronic Materials, Devices, and Applications**

**Pingjuan Niu 1,\*, Li Pei 2, Yunhui Mei 1, Hua Bai <sup>1</sup> and Jia Shi <sup>1</sup>**


This Special Issue entitled "Optoelectronic Materials, Devices, and Applications" is devoted to gathering a broad array of research papers on the latest advances in the development of optoelectronic materials and devices of semiconductors, fiber optics, power electronics, microwaves, and terahertz. Each of the included papers highlights the latest principles, methods, and potential applications of optoelectronics. The primary aim of this Special Issue is to promote cross-disciplinary research in optoelectronics.

In total, ten papers are included in this Special Issue. New advances in optoelectronic materials have been reported for crystals, electrodes, and bonding materials. First, Zakrzewski et al. analyzed the photothermal piezoelectric spectroscopy of Cd1−xBexTe, a new material with potential for use in X-ray and γ-ray detectors [1]. Next, Han et al. investigated the characteristics of a copper foil three-electrode planar spark gap high-voltage switch integrated with EFI [2]. Ding et al. showed in their study a reliable way to improve the electrochemical migration resistance of nanosilver paste as a bonding material [3]. New advances in optoelectronic devices have also been reported for LEDs and photonic crystal waveguides. Bai et al., for example, proposed a new method for the measurement of adhesive force between a single μLED and a substrate based on the use of an atomic force microscope [4]. Zhang et al. analyzed the strain relaxation effect on the peak wavelength of blue InGaN/GaN multi-quantum well micro-LEDs [5]. In addition, Shi et al. proposed an all-dielectric terahertz photonic crystal waveguide with a lilac-shaped defect operating in a 6G terahertz communication window [6]. New applications of optoelectronic materials and devices have additionally been reported for piezoelectric sensors, crystal materials, synthetic aperture radar (SAR), and optical coherence tomography (OCT). Wang et al. established a collision model of wheat grains impacting a force plate with a piezoelectric sensor and investigated the influence of the elastic recovery coefficient on the sensor's detection accuracy during the collision process [7]. Next, He et al. demonstrated the application of a BaGa4Se7 crystal in a tunable and compact mid-infrared optical parametric oscillator with a repetition rate of up to 250 Hz [8]. Wang et al. proposed a new feature learning method for the automatic target recognition of SAR images [9]. Finally, Shi et al. reviewed the quantitative assessment methods used for early enamel caries with OCT [10].

It is our sincere hope that these advances will provide new inspiration for the development and application of optoelectronic materials and devices.

**Acknowledgments:** We would like to give our thanks to all of the authors and peer reviewers who contributed to this Special Issue entitled "Optoelectronic Materials, Devices, and Applications".

**Conflicts of Interest:** The authors declare no conflict of interest.

**Citation:** Niu, P.; Pei, L.; Mei, Y.; Bai, H.; Shi, J. Optoelectronic Materials, Devices, and Applications. *Appl. Sci.* **2023**, *13*, 7514. https://doi.org/ 10.3390/app13137514

Received: 19 June 2023 Accepted: 21 June 2023 Published: 25 June 2023

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