Luminescence Properties Of Defects Research Articles

Novel perovskite quantum dots and hydroxyapatite nanocomposites: Enhanced thermal stability, improved emission intensity, and color-tunable luminescence

All-inorganic perovskite (CsPbX3, X = Cl, Br, and I) quantum dots (PQDs) are new stars of semiconductor optoelectronic materials with superior optical properties. However, due to the ionic nature of crystal structure, the stability of PQDs is relatively poor, which seriously hinders their practical application. Herein, the strontium hydroxyapatite (SrHAp) with mesoporous structure and defect-luminescence properties has been introduced as inorganic matrix material to modify the surface of CsPbBr3 QDs. A series of novel CsPbBr3@SrHAp nanocomposites have been prepared by a simple room-temperature synthesis approach for the first time. The CsPbBr3@SrHAp nanocomposites not only enhance the green light emission of the CsPbBr3 QDs, but also realize the color-tunable luminescence from blue through cyan and eventually toward green emission by simply adjusting the relative composition of CsPbBr3@SrHAp. Meanwhile, the thermal stability of CsPbBr3 QDs in the nanocomposites is dramatically improved by incorporating the SrHAp matrix. Furthermore, the as-obtained LED device by combining the CsPbBr3@SrHAp nanocomposite and 365 nm LED chip can exhibit dazzling green light emission, which indicates potential prospects and applicability of the nanocomposites for lighting and display devices.

Luminescence properties of defects in nanocrystalline ZnO

Formation of intrinsic acceptor defects in ZnO is rare due to the low formation energy of donors. Understanding this phenomenon is of interest for the fabrication of high quality light emitting diodes. Herein, we examine the temperature dependent formation of defects in nanocrystalline ZnO through a combination of X-ray excited optical luminescence (XEOL) together with X-ray absorption near edge structures (XANES) and electron spin resonance (ESR). Certain defects are shown to form under low temperature and are unstable above 700 °C. These defects have high g-values characteristic of acceptors and short spin-lattice relaxation times. XEOL measurements show that acceptor defects with a characteristic red luminescence are also formed under these conditions. Low g-value (donor) defects forming at temperatures >700 °C are shown to have spin-lattice relaxation characteristic of nonradiative recombination centers.

Luminescence Properties Related to Defects in Y2O3:Ho3+ Nanocrystal

In this paper, Y2O3:Ho3+ nanocrystals have been prepared by a solution combustion synthesis method. The luminescence properties of defects and Ho3+ ions in yttria nanocrystal have been studied under 325 nm laser excitation. The emissions which were corresponding to 5F4-5I8, 5S2-5I8 and 5G4-5I6 trasitions of Ho3+ were measured. It was observed that the characteristic emissions of Ho3+ were gradually submerged in the broad cingulum emissions with the decrease of the nanoparticle size. The research results indicated that the broad cingulum emissions originated from the defects of nanocrystals. With the decrease of size, surface atoms which have a lot of defects increase relatively. Those surface defects can easily absorb the energy of excitation photons producing the broad spectra emissions. The electron paramagnetic resonance experiments have been performed to definitely reveal the defects information. The electron paramagnetic resonance signal has a slight shift towards the direction of weak magnetic field with the decrease of nanocrystal size, which means that the corresponding g factor becomes bigger in smaller size sample.

Luminescence properties of defects in GaN

Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The point defects include native isolated defects (vacancies, interstitial, and antisites), intentional or unintentional impurities, as well as complexes involving different combinations of the isolated defects. Further improvements in device performance and longevity hinge on an in-depth understanding of point defects and their reduction. In this review a comprehensive and critical analysis of point defects in GaN, particularly their manifestation in luminescence, is presented. In addition to a comprehensive analysis of native point defects, the signatures of intentionally and unintentionally introduced impurities are addressed. The review discusses in detail the characteristics and the origin of the major luminescence bands including the ultraviolet, blue, green, yellow, and red bands in undoped GaN. The effects of important group-II impurities, such as Zn and Mg on the photoluminescence of GaN, are treated in detail. Similarly, but to a lesser extent, the effects of other impurities, such as C, Si, H, O, Be, Mn, Cd, etc., on the luminescence properties of GaN are also reviewed. Further, atypical luminescence lines which are tentatively attributed to the surface and structural defects are discussed. The effect of surfaces and surface preparation, particularly wet and dry etching, exposure to UV light in vacuum or controlled gas ambient, annealing, and ion implantation on the characteristics of the defect-related emissions is described.