Search

LaOCl doped with 0–10 mol% Cr was synthesized by thermal decomposition of chlorides. X-ray diffraction (XRD) analysis revealed that incorporation of chromium results in a decrease of the lattice parameter a and a simultaneous increase of the lattice parameter c. The local structure of chromium ions was studied with X-ray photoelectron (XPS), X-ray absorption (XANES), multifrequency electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy techniques. It was determined that synthesis in oxidizing atmosphere promotes the incorporation of chromium ions predominantly in the 5+ oxidation state. Changes of chromium oxidation state and local environment occur after a subsequent treatment in reducing atmosphere. Spin-Hamiltonian (SH) parameters for a Cr5+ and two types of Cr3+ centers in LaOCl were determined from the EPR spectra simulations. [ABSTRACT FROM AUTHOR]

In this study, we report broadband near-infrared persistent luminescence of a novel MgGeO 3 : Cr3+ material. The luminescence can be excited by the ultraviolet radiation and detected for more than 16 h. Optical and electron paramagnetic resonance spectroscopy experiments suggest that the observed bands appear as a result of interaction between Cr3+ luminescence centre and oxygen-impurity complexes and oxygen vacancy related trapping states. Thermally stimulated luminescence analysis revealed that the states are closely overlapping and lie relatively deep in the band gap with the activation energy exceeding 0.9 eV. The experimental data strongly suggest that the main detrapping route for the trapped charge carriers in the MgGeO 3 : Cr3+ material is athermal tunnelling directly to the luminescence centres. • MgGeO 3 :Cr3+ phosphor has been reported for the first time. • Near-infrared long persistent luminescence lasting over 16 h has been observed. • Persistent luminescence process is governed by athermal tunnelling. [ABSTRACT FROM AUTHOR]

Manganese doped polycrystalline CaAl 4 O 7 samples with doping concentrations in 0.1–2.0 mol% range were synthesized using the solid-state synthesis method. Photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopy techniques were applied to characterize the local structure and properties of Mn ions in CaAl 4 O 7. With excitation of 406 nm, Mn2+ exhibited a wide emission band centered at 572 nm with luminescence decay time 6.5–8.3 ms. The results of EPR and X-ray diffraction (XRD) analyses evidenced preferential incorporation of Mn2+ in the seven-fold coordinated site of Ca2+. • Mn2+-doped CaAl 4 O 7 exhibits photoluminescence (PL) centered at 572 nm. • Luminescence decay time of Mn2+ ions was in the 6.5–8.3 ms range. • EPR and XRD analyses suggest that Mn2+ ions are incorporated in the Ca2+ sites. • The colour tuneability of Mn-doped CaAl 4 O 7 PL has been demonstrated. [ABSTRACT FROM AUTHOR]

Materials with long persistent luminescence (PersL) have caused widespread interest among scientists and industry for decades. Currently, there is widely available information on the long persistent luminescence materials with emission in the blue and green spectral range, while the number of publications on the afterglow in the red and near-infrared spectral range is considerably lower. In the course of this work MgGeO 3 material doped with 0.1 mol% Mn2+ was produced using solid-state reaction synthesis in ambient and reducing atmospheres. The material exhibits a broad luminescence band with a peak around 680 nm, excited by either X-rays or UV. After cessation of irradiation, the afterglow up to 6 h when excited by UV and 15 h in the case of excitation by X-rays can be observed. Decay kinetics of the samples indicate that persistent luminescence in this material is a complex process that includes several different traps. Different thermally stimulated luminescence (TSL) techniques, such as T stop – T max and Hoogenstraaten's methods were employed to draw conclusions about the nature of the traps and properties of the material. It was concluded that multiple traps with activation energy between 0.60 and 1.55 eV are present in the samples, furthermore the synthesis in reducing atmosphere promotes creation of additional closely overlapping deep traps, which, based on electron paramagnetic resonance (EPR) measurements, most likely are related to oxygen vacancies. • MgGeO 3 :Mn2+ material in ambient and reducing atmospheres has been synthesized. • Red long persistent luminescence lasting up to 15 h has been observed. • Multiple TSL methods have been employed to draw conclusions about the nature of the traps and trap depth. • Several traps with activation energy between 0.60 and 1.55 eV are present in the samples. • The synthesis in reducing atmosphere promotes creation of additional closely overlapping deep traps. [ABSTRACT FROM AUTHOR]