“…7 (b), the E g were measured with the help of reflectance spectra plotting graphs of (K x hν) n versus (hv) (with n = 2, which is appropriate for a direct band gap material such as ZnAl 2 O 4 ). The extrapolation of linear region of this plot to (K x hν) 2 = 0…”
Section: Reflectance and Band Gap Analysis (Uv-vis Spectroscopy)mentioning
confidence: 99%
“…Over the past decades, spinel compounds have attracted interest in many researchers around the globe due to their properties such as high chemical and thermal stability, high mechanical resistance, low sintering temperature and high quantum yields [1,2]. Spinels are class of binary transition metal oxides of the form AB 2 O 4 with varied structures and owing to their unique properties, they have found potential applications in the area of material science and technology [3,4].…”
ZnAl 2 O 4 nano-powders have been successfully prepared via citrate sol-gel technique. All powder samples were annealed at 600 o C for 1, 2, and 3 h. Thermogravimetric analysis (TGA) confirmed that the minimum annealing temperature of crystallization is ~ 400 °C. Fourier Transform Infrared (FTIR) results showed a series of absorption peaks in the range of 810-4000 cm-1. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) results showed that the prepared nano-crystals consists of the mixture of both cubic (ZnAl 2 O 4) and hexagonal (ZnO) structures. Ultra violet visible (UV-vis) spectroscopy revealed that the annealing time (AT) influences the band gap of the prepared phosphor materials. When the 2 samples were excited at 275 nm, two emission peaks at 428 nm (violet) and 561 nm (green-yellow) were observed and they are attributed to the defects levels within the ZnO and ZnAl 2 O 4 band gaps. The Commission Internationale de l'Elcairage (CIE) colour coordinates confirmed that all the prepared samples exhibit the violet emission and varying the AT does not influence the emission colour.
“…7 (b), the E g were measured with the help of reflectance spectra plotting graphs of (K x hν) n versus (hv) (with n = 2, which is appropriate for a direct band gap material such as ZnAl 2 O 4 ). The extrapolation of linear region of this plot to (K x hν) 2 = 0…”
Section: Reflectance and Band Gap Analysis (Uv-vis Spectroscopy)mentioning
confidence: 99%
“…Over the past decades, spinel compounds have attracted interest in many researchers around the globe due to their properties such as high chemical and thermal stability, high mechanical resistance, low sintering temperature and high quantum yields [1,2]. Spinels are class of binary transition metal oxides of the form AB 2 O 4 with varied structures and owing to their unique properties, they have found potential applications in the area of material science and technology [3,4].…”
ZnAl 2 O 4 nano-powders have been successfully prepared via citrate sol-gel technique. All powder samples were annealed at 600 o C for 1, 2, and 3 h. Thermogravimetric analysis (TGA) confirmed that the minimum annealing temperature of crystallization is ~ 400 °C. Fourier Transform Infrared (FTIR) results showed a series of absorption peaks in the range of 810-4000 cm-1. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) results showed that the prepared nano-crystals consists of the mixture of both cubic (ZnAl 2 O 4) and hexagonal (ZnO) structures. Ultra violet visible (UV-vis) spectroscopy revealed that the annealing time (AT) influences the band gap of the prepared phosphor materials. When the 2 samples were excited at 275 nm, two emission peaks at 428 nm (violet) and 561 nm (green-yellow) were observed and they are attributed to the defects levels within the ZnO and ZnAl 2 O 4 band gaps. The Commission Internationale de l'Elcairage (CIE) colour coordinates confirmed that all the prepared samples exhibit the violet emission and varying the AT does not influence the emission colour.
“…Fluorescence is the term used to describe a substance’s spontaneous light emission when it is exposed to stimulating electromagnetic radiation. Phosphorescence refers to a material’s ability to absorb light and delay its immediate reemission. − The emission intensity (efficiency) of the phosphor will be low if the concentration of an activator ion exceeds a specific value. The increased delocalization of the excitation or cross relaxation (exchange contact) between luminous centers, which is known as the concentration quenching effect, is the cause of this phenomenon .…”
Currently, the world is facing an energy crisis. One
of the techniques
to fulfill the energy demand is to increase the utilization of solar
energy. For harvesting solar energy in large amounts, it is essential
to develop efficient solar cells. Notably, solar cells (photovoltaic
cells) produce electricity from solar energy. The biggest hurdles,
however, are the capability and reliability of solar cells. Poor energy
density and the spectrum in the bandgap of semiconductor phosphors
do not match the energy allocation of the photons in solar spectra
lines. These issues and cell efficacy must be addressed before photovoltaic
cells can be developed as a viable source of electrical power. The
amount of energy generated per unit area depends linearly on cell
efficiency. Hence, it makes sense to increase the efficiency rather
than enhancing the space for solar cell installation. One well-known
method for converting a high-energy photon into two or more lower-energy
photons is “downconversion”, which makes use of the
wide solar spectrum required for solar cells. The design maximizes
the use of the entire sunlight spectrum, improving the efficiency
of various solar cell types. This review article surveys how spectrum
converters, especially lanthanide-based downconverters and downshifters
will be developed. This review focuses on the current materials and
methods used to enable the downconversion and downshifting processes
in solar cells and some of the challenges in developing solar cells.
“…[1][2][3][4] Spinel as a kind of nanomaterials is an ideal host lattice for transition metal and rare earth ions to generate luminescence, on account of its facecentered cubic (FCC) structure. [5][6][7][8] ZnAl 2 O 4 with typical spinel structure has been used as a phosphor host material doped with various metal and rare earth ions in previous literatures. 7 8 And with the properties of excellent chemical and optical stability, high mechanical resistance, low sintering temperature and high quantum yield, ZnAl 2 O 4 spinel can be used as host material of optical coating, thin film electroluminescence displays, stress imaging device, etc.…”
Section: Introductionmentioning
confidence: 99%
“…[5][6][7][8] ZnAl 2 O 4 with typical spinel structure has been used as a phosphor host material doped with various metal and rare earth ions in previous literatures. 7 8 And with the properties of excellent chemical and optical stability, high mechanical resistance, low sintering temperature and high quantum yield, ZnAl 2 O 4 spinel can be used as host material of optical coating, thin film electroluminescence displays, stress imaging device, etc. 9 10 Meanwhile, Nd 3+ -doped inorganic nanomaterials also have been widely studied because of their unique near infrared (NIR) emission, which have significant applications in biological and optical fields.…”
ZnAl 2 O 4 nanofibers and nanoparticles were in situ synthesized by electrospinning technique. Utilizing poly (vinyl pyrrolidone) (PVP) with different degree of polymerization, SEM (scanning electron microscope) results indicate that ZnAl 2 O 4 nanostructures exhibit different morphologies under the same electrospun parameters. When PVP with high molecular weight (Mw = 1,300,000) was used, the ultra-long ZnAl 2 O 4 nanofibers were obtained with an average diameter of ∼200 nm. However, while PVP with low molecular weight (K-30) was used, the ZnAl 2 O 4 changed into particle-shape with an average size of ∼100 nm. Utilizing Nd 3+ ions as the optical activator, three emission peaks centered at 905 nm, 1064 nm and 1335 nm were detected respectively in the photoluminescence (PL) spectra of ZnAl 2 O 4 :Nd 3+ nanostructures under 808 nm laser excitation. It is noticed that both the excitation wavelength (808 nm) and the emission wavelength (905 nm and 1064 nm) are located in the 700-1100 nm optical window of cells and tissues. And the cytotoxicity investigation indicates ZnAl 2 O 4 :Nd 3+ nanostructures are biocompatible with human cells, which endow their potential application as biological markers, etc.
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