Excitonic effects in oxyhalide scintillating host compounds

Abstract

Electronic and elastic properties of yttrium gallium garnet under pressure from ab initio studiesAb-initio calculations based on density functional theory have been performed to study the electronic, optical, mechanical, and vibrational properties of scintillator host compounds YOX (X ¼ F, Cl, Br, and I). Semiempirical dispersion correction schemes are used to find the effect of van der Waals forces on these layered compounds and we found this effect to be negligible except for YOBr. Calculations of phonons and elastic constants showed that all the compounds studied here are both dynamically and mechanically stable. YOF and YOI are found to be indirect band gap insulators while YOCl and YOBr are direct band gap insulators. The band gap is found to decrease as we move from fluorine to iodine, while the calculated refractive index shows the opposite trend. As the band gap decreases on going down the periodic table from YOF to YOI, the luminescence increases. The excitonic binding energy calculated, within the effective mass approximation, is found to be more for YOF than the remaining compounds, suggesting that the excitonic effect to be more in YOF than the other compounds. The optical properties are calculated within the Time-Dependent Density Functional Theory (TDDFT) and compared with results obtained within the random phase approximation. The TDDFT calculations, using the newly developed bootstrap exchange-correlation kernel, showed significant excitonic effects in all the compounds studied here. V C 2014 AIP Publishing LLC. [http://dx.

The photoluminescence of isolated and paired Bi3+ ions in layered LnOCl crystals: a first-principles study

“…S1 (ESI†). The corresponding direct bandgaps of LnOCl (Ln = Y, Gd, La) are 4.86, 4.74 and 3.96 eV, close to other theoretical values of 4.9 eV in the YOCl 53 and 4.07 eV in the LaOCl crystal. 54 To improve the bandgap underestimated by the GGA method, the hybrid functional method is applied, which mixes a portion of Hartree–Fock exchange α to a local or semilocal density exchange functional.…”

High-contrast multi-surface imaging of latent fingerprints using color-tunable YOF:Tb3+,Eu3+ ultrafine nanophosphors with high quantum yield

“…The optical band gap for YOF:0.01Eu 3+ nanophosphor was found to be 4.1 eV which is approximately near the energy band gap of pristine YOF. 48 However, the introduction of Tb 3+ ions produced a sudden drop in the optical band gap values for the other three samples and they returned a value of 2.67 eV, which can be solely attributed to the absorption edge in the visible region due to Tb 4+ ions. 43…”

Time-dependent density-functional theory for periodic solids: assessment of excitonic exchange–correlation kernels

“…LRC-type kernels have been used in a number of applications to calculate optical properties of materials [121][122][123][124][125][126][127][128][129]. A critical assessment of LRC-type kernels was recently carried out [98,99] (for numerical details, please consult these references).…”