Electron paramagnetic resonance study of Ag⁰atoms and Ag²⁺ions in  -BaB₂O₄nonlinear optical crystals

Abstract

Silver ions have been diffused into single crystals of β-BaB2O4 (commonly referred to as BBO). The crystals were wrapped in silver foil and then held in air at 760°C for periods of time ranging from 1 to 7 h. This treatment resulted in Ag+ ions occupying both Ba2+ sites and interstitial sites within the crystal. After the diffusion, the crystal was irradiated at room temperature with 60 kV x-rays. Three distinct paramagnetic defects, one holelike and two electronlike, were produced by the x-rays and observed with electron paramagnetic resonance (EPR) at temperatures between 15 and 80 K. The Ag+ ions substituting for Ba2+ ions trapped radiation-induced holes and became paramagnetic Ag2+ ions. At the same time, interstitial Ag+ ions trapped electrons and became paramagnetic Ag0 atoms. There are two distinct versions of these latter centres. The EPR spectra of the Ag0 atoms show resolved hyperfine from the 107,109Ag isotopes, as well as from a neighbouring nucleus (possibly a Na+ impurity substituting for a Ba2+ ion). All the radiation-induced EPR signals were stable at room temperature for hours.

Growth and optical properties of Nd 3+ -doped Ba 2 Na 3 [B 3 O 6 ] 2 F crystals

“…This evidences that PLE bands for 300-450 nm emission, located in the 200-215, 220-250, and 250-295 nm ranges belong to different luminescence centers [18][19][20][21][22][23]. Here, one can observe different energy states for sodium ions depending on their position in the structure: in the case of cation antisite defect (Na + → Ba 2+ ) or Na + in channel positions, with formation of Ba and Ɉ vacancies [11][12][13]16]. We suppose that upon introduction of Re 3+ (Nd 3+ ) ions into ȼȼɈ and Ba 2 Na 3 [B 3 O 6 ] 2 F structure, the charge compensation for RE ions can be realized both by formation of barium vacancies (2 Re 3+ →2 Ba 2+ + V Ba ) and Ba 2+ replacing with Na + (Re 3+ → Ba 2+ , Na + → Ba 2+ ).…”

“…When sodium content in the sample was 0.02 wt. % and higher, the authors of [16] observed the peaks of thermostimulated luminescence (TSL) at 123, 200 and 240ºɋ with emission maximum near Ȝ = 400 nm. At lower sodium content the TSL peaks at 80-90ºɋ had demonstrate emission near 360 nm [17,18].…”

“…Intense broad band near 330 nm in RL spectrum (Fig.5) is likely related to native defects in the Ba 2 Na 3 [B 3 O 6 ] 2 F crystal lattice. These can be vacancies of barium or oxygen which produce deep levels in the forbidden zone [11][12][13]16].…”

“…16 and 0.22/2.73=0.08, respectively [6]. The aim of this work is to study the optical properties of Ba 2 Na 3 [B 3 O 6 ] 2 F crystals which are pure and doped with neodymium ions Nd 3+ .…”

Observation of paramagnetic point defects in BBO (β-BaB2O4) crystals

“…Also, Bravo et al [6] have used EPR to characterize spectra due to Nd 3þ ions in doped BBO crystals. In another EPR study, Hong et al [7] investigated the post-growth diffusion of Ag þ ions into BBO crystals. These ions occupy Ba 2þ sites and interstitial sites, and ionizing radiation at room temperature converts them into Ag 2þ and Ag 0 centers, respectively, as they trap holes and electrons.…”