Electronic structure calculations of intrinsic and extrinsic hydrogen point defects inKH2PO4

Abstract

We report first-principles total-energy density-functional theory electronic structure calculations for the neutral and charge states of H intrinsic ͑Frenkel pair͒ and extrinsic ͑H vacancy or interstitial͒ point defects in KH 2 PO 4 . The relaxed atomic structures, the formation energy, the ionization energy, and electron and hole affinities for the various defects have been calculated. For the Frenkel pair, the additional hole leads to a decrease of the OuO bond length between the two O atoms next to the H vacancy, while the effect of the additional electron is small. For the H vacancy, the added hole is trapped and shared by the two O atoms adjacent to the vacancy, reducing dramatically the OuO bond length, thus forming a molecular-type polaron. We find that the positively charged H vacancy introduces states in the gap, in contrast with its neutral state, confirming the experimental suggestion that it is a relevant absorbing center. The negatively charged H vacancy leads to an increase of the two O atoms close to the H vacancy, and does not induce states in the gap. The H interstitial does not interact with the host atoms in the neutral state. However, the addition of an electron leads to the ejection of a H host atom and the subsequent formation of a H 2 interstitial molecule and a H vacancy, in agreement with experimental suggestions. In the positively charged state the H interstitial binds to its nearest-neighbor O atom forming a hydroxyl bond. The H interstitial in both positive and negative charge states induces no defect states in the band gap, in contrast with its neutral state. The calculations provide insights into the role of the charged and neutral defects on the transient optical absorption under irradiation by high-intensity laser beam.

Performance of rapid-grown KDP crystals with continuous filtration

“…It was found that typical damage pinpoints were caused by defects, which efficiently absorbed laser energy, leading to a temperature rise and subsequent 'micro-explosion' [5][6][7] . Various types of bulk defect, such as metallic impurities [8][9][10] , electronic defects [11][12][13] , organic materials, bacteria [14,15] , dislocation [16] and insoluble impurities, have been reported. In 1999, the continuous filtration Correspondence to: Y. Zhao, No.…”

Transmittance increase after laser conditioning reveals absorption properties variation in DKDP crystals

“…So in some parts of area, the point defects stay close together and the concentration in this area is in an order of 10 −2 [24], which is quite higher than the average concentration. First principle calculation for hydrogen point defects in KDP has found that the band gap for the neutral interstitial H and positive charged H vacancy are greatly reduced to 2.6 and 2.5eV [13,14], which is smaller than photon energy of 355nm laser. Therefore, this defect cluster can be the major factor of inducing laser damage.…”

“…Recent work based on the electron paramagnetic resonance and resonance Raman scattering experiments provided direct evidence of the [HPO4]¯ hole center and the hydrogen interstitial H 0 electron center [12]. First principle calculation for hydrogen point defects in KDP have found that the band gap for the neutral interstitial H and positive charged H vacancy were greatly reduced to 2.6 and 2.5eV [13,14]. It suggested that thermal point defects played an important role on the lowering LIDT of KDP crystal.…”

Novel optical properties of n-alkylammonium dihydrogen phosphates under ultraviolet excitation and first principle study

“…However, when a series of CnADP (n = 6-14) is put under 254 and 365 nm ultraviolet (UV) lamps, it is observed clearly that the samples emit white light, and even the afterglow as long as 4 min emerged from 254 nm UV excitation stopped. In order to obtain more information about these novel optical phenomena, we synthesized a series of CnADP (n = [6][7][8][9][10][11][12][13][14] in the present work, and then give some reasonable explanation through combining a few optical spectrums and first principle study.…”