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Absolute Photoluminescence Quantum Yield of Phosphors
Published in Ru-Shi Liu, Xiao-Jun Wang, Phosphor Handbook, 2022
The photoluminescence (PL) quantum yield ΦPL for a molecule or material is defined as the ratio of the number of emitted photons PN(Em) to the number of absorbed photons PN(Abs). This is one of the most fundamental and important photophysical parameters for luminescent materials. ΦPL=PN(Em)PN(Abs)
Borate Phosphor
Published in S. K. Omanwar, R. P. Sonekar, N. S. Bajaj, Borate Phosphors, 2022
There is always a delay between the moment the material has absorbed the higher-energy photon and the moment the secondary lower-energy photon is re-emitted. This delay is defined by the lifetime of excitation states, or simply by how long atoms or molecules are able to stay in excited high-energy conditions. Delay time can vary many orders of magnitude for different materials. Based on practical observations, two types of photoluminescence were historically established: ‘fluorescence’ and ‘phosphorescence’.
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Published in Vidya Nand Singh, Chemical Methods for Processing Nanomaterials, 2021
Alejandro Fajardo Peralta, Jose Valenzuela-Benavides, Nestor Perea-Lopez, Mauricio Terrones
A key aspect boosting research on S-L TMDs is the availability of ad hoc characterization techniques. Starting with optical methods, we can mention photoluminescence (PL) spectroscopy—it uses an excitation beam with photon energy higher than the bandgap of the material of interest. Monolayer TMDs are direct bandgap semiconductors; hence, the photon emission is intense regardless of the infinitesimal thickness of the film [35, 3, 2] Raman spectroscopy is another optical technique—it probes the vibrational modes of the crystals using laser excitation, a monochromator, and a detector to monitor the energy losses of the excitation beam. The Raman shift peaks appear at energies commensurate with the vibrational modes of the lattice, and serve as a fingerprint of the material [36, 37]. For TMDs, PL and Raman represent excellent non-destructive techniques with high sensitivity to the material type and the number of layers [38, 39].
Radiation tolerance and defect dynamics of ALD-grown HfTiO x -based MOS capacitors
Published in Radiation Effects and Defects in Solids, 2023
R. Sai Prasad Goud, Mangababu Akkanaboina, Arshiya Anjum, K. Ravi Kumar, A. P. Gnana Prakash, S.V.S. Nageswara Rao, A. P. Pathak
Photoluminescence spectroscopy is a widely used technique for estimating/quantifying the defects present in thin films. Hence, for the pristine sample (Figure 2(a)) and gamma-irradiated thin films (Figure 2(b–e)), PL measurements are carried out using an excitation wavelength of 360 nm. We have noticed oxygen defects at 2.4, 2.7, 2.9 and 3.1 eV. The relative area under individual peaks of each sample is tabulated in Table 1. Among them 2.9, 2.7 and 3.1 eV are assigned to Vo+, Vo2+ and Vo0, respectively (62,63). Figure 2(f) shows the variation of the relative percentage area of each defect as a function of irradiated dose. This relative area is calculated as the ratio of the corresponding peak to the total area under the curve. As the irradiation dose is increasing, the major defect 2.7 eV (Vo + 2) is diminishing compared to other defects. There is an overall increase in the concentration of Vo+ and Vo0 defects as a function of dose. A new defect at 2.4 eV is observed at the dose of 500 krad which increases further with the dose.
Characterization and experimental investigation of rheological behavior of oxide nanolubricants
Published in Particulate Science and Technology, 2021
Harsh Gupta, Santosh Kumar Rai, Piyush Kuchhal, Gagan Anand
Photoluminescence occurs when a sample excited by absorbing photons emits photons at different wavelength when returning to its original energy level. This is a nondestructive process in which light directed on to a sample absorbs energy, this is termed as photo excitation. Luminescence is one of the ways by which the absorbed energy is dissipated, i.e., through the emission of light. In the case of photo excitation, the luminescence is termed as photoluminescence. This is a valuable tool to characterize nanoparticles. The device used to conduct this test in this experiment is PerkinElmer LS 45 Fluorescence Spectrometer (PerkinElmer, Waltham, MA). It uses a Xenon source for excitation. The data of dissipated energy for different wavelength was obtained from the Win Lab software. The range of wavelengths for this device is from 200 to 800 nm.
Ferroelectric and optical properties of ‘Ba-doped’ new double perovskites
Published in Phase Transitions, 2018
B. N. Parida, Niranjan Panda, R . Padhee, R. K. Parida
The dielectric (capacitance, dissipative factor) impedance and inductance parameters of the sintered pellet were measured as a function of frequency (1 kHz to 1 MHz) at different temperatures (25–500 °C) using a computer-controlled phase sensitive meter (PSM LCR 4NL (Model: 1735, UK)) with a laboratory-designed and fabricated sample holder and furnace. A chromel–alumel thermocouple and KUSAM MECO 108 digital millivoltmeter were used to record the temperatures. The polarization (hysteresis loop) of the material on the poled sample (electric field = 6 kV/cm, time = 8 h) was obtained at different temperatures using hysteresis loop tracer (M/S Marine India, New Delhi). The optical band gap of the material was calculated using UV-Visible (UV-Vis) spectroscopy technique (Shimadzu-2600 double beam spectrophotometer) by measuring the absorption and diffuse reflection spectra. In addition to UV-Vis spectroscopy, photoluminescence spectra has been carried to study the electronic configuration of the material. For this using the spectrofluorometer of JASCO FP:8300 (Japan), emission spectra of the studied sample was carried out.