The purpose of this paper is to present a new spectroscopic experimental technique to study the contributions of the different cross-relaxation mechanisms observed in Dy3+ doped TeO2-GeO2-ZnO ...glasses, based on the luminescence decay curves from 4F9/2 → 6H13/2 (at 573 nm) transition of Dy3+ ions under spatial and temporal simultaneous UV (6H15/2 → 6P7/2) and IR (6H15/2 → 6F3/2,6H15/2 → 6H7/2 and 6H15/2 → 6H9/2) excitations, for which the results are reported. The spectroscopic characterization was carried out through Raman, optical absorption, luminescence decay time profiles, and energy transfer as a function of Dy3+ ions content (0.5–5%). Emission spectra measurements indicated that concentration quenching is active in the samples. The lifetime decay of emission at 573 nm (4F9/2 level) was studied under excitation at 355 nm. At lower concentration of Dy3+, the temporal behavior of the emission at 573 nm is exponential, however, it becomes non-exponential as the concentration increases. The emission decay curves at 573 nm were fitted to Inokuti-Hirayama model and an energy transfer process dominated by an electric dipole-dipole interaction was deduced. A shortened lifetime was observed as the dysprosium ion content increased, which is attributed to non-radiative energy transfer between Dy3+ ions through the cross-relaxation mechanism. The analysis of the 4F9/2 → 6H13/2 (573 nm) emission decays, obtained under simultaneous excitation at 355 nm and at different infrared excitations 6H15/2 → 6F3/2 (905 nm), 6H15/2 → 6H7/2 (1100 nm) and 6H15/2 → 6H9/2 (1285 nm), allowed the determination of the dominant process in the cross-relaxation mechanism at high and low concentrations of Dy3+. It was possible to infer that in the glass with low concentration of Dy3+ the mechanism occurs predominantly by 4F9/2 + 6H15/2 → 6F11/2 + 6F3/2 channel, and for high concentration of Dy3+, the channels 4F 9/2 + 6H15/2 → 6F11/2 + 6F3/2, F9/2 + 6H15/2 → 6F5/2 + 6F9/2 +5H7/2, and 4F9/2 + 6H15/2 → 6F3/2 + 6F11/2 + 5H9/2 have a similar contribution to the Dy3+-Dy3+ resonant energy transfer.
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Recently, mixed-former glasses have attracted a large attention due to the appropriate combinations of the chemical, physical and optical properties of each glass former. In this scenario, the ...optical properties of fluoroborate glasses doped with rare earth ions is of importance due to their good transparency window from ultra-violet to near-infrared region, good rare-earth solubility, long excited state lifetime of such ions, and high mechanical strength. In this work, we had studied the optical properties of the Tb3+ doped fluoroborate glasses, focusing on the concentration dependent behavior of luminescence dynamics of 5D3 and 5D4 exited states of this ion. The blue-to-green intensity ratio, lifetime of the emitting levels under various excitation wavelengths, cross-relaxation rate, ion-ion critical distance and emission gain bandwidth are calculated.
Analytical models of rare-earth-doped fiber lasers were proposed in the past as very efficient yet reliable alternative to comprehensive numerical models. Cross-relaxation in thulium-doped fiber ...lasers has a great impact on their efficiency through a two-for-one process but it has not been addressed in analytical models so far. Here, the analytical model of thulium-doped fiber laser is proposed that respects the cross-relaxation mechanism of a type: <inline-formula><tex-math notation="LaTeX">^{3}</tex-math></inline-formula>H<inline-formula><tex-math notation="LaTeX">_{4}\rightarrow ^{3}</tex-math></inline-formula>F<inline-formula><tex-math notation="LaTeX">_{4}</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">^{3}</tex-math></inline-formula>H<inline-formula><tex-math notation="LaTeX">_{6}\rightarrow ^{3}</tex-math></inline-formula>F<inline-formula><tex-math notation="LaTeX">_{4}</tex-math></inline-formula>. The model is based on a two-level model and enables to express the threshold power and slope efficiency in a closed form. The effect of intrinsic losses is modeled by a physically motivated semi-empirical formula. The model is compared with the numerical one and with experimental data. Its application limits are discussed. An approximate method for checking validity conditions of the model is proposed.
Reliance on low tissue penetrating UV or visible light limits clinical applicability of phototherapy, necessitating use of deep tissue penetrating near-infrared (NIR) to visible light transducers ...like upconversion nanoparticles (UCNPs). While typical UCNPs produce multiple simultaneous emissions for unidirectional control of biological processes, programmable control requires orthogonal non-overlapping light emissions. These can be obtained through doping nanocrystals with multiple activator ions. However, this requires tedious synthesis and produces complicated multi-shell nanoparticles with a lack of control over emission profiles due to activator crosstalk. Herein, we explore cross-relaxation (CR), a non-radiative recombination pathway typically perceived as deleterious, to manipulate energy migration within the same lanthanide activator ion (Er
) towards orthogonal red and green emissions, simply by adjusting excitation wavelength from 980 to 808 nm. These UCNPs allow programmable activation of two synergistic light-gated ion channels VChR1 and Jaws in the same cell to manipulate membrane polarization, demonstrated here for cardiac pacing.
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•La2MgTiO6 synthesized by the co-precipitation method was crystallized in an orthorhombic phase with space group Pbnm.•Luminescent spectra of Nd3+ at the site of low symmetry (Cs), ...were observed in all samples excited at 266 nm and 808 nm.•The decay times of the 4F3/2 luminescence strongly depend on the Nd3+ concentration, temperature and excitation wavelength.•The energy transfer between Nd3+-Nd3+ ions is governed by dipole-dipole interaction analyszd by the Inokuti-Hirayama model.•The maximum relative sensibility is 0.8 %K−1 at 248 K for thermally coupled 4F5/2 → 4I9/2 and 4F3/2 → 4I9/2transitions.
La2MgTiO6: Nd3+ samples synthesized by the coprecipitation method crystallized in an orthorhombic phase with space-group Pbnm (62). The SEM images of the sample showed heterogeneous morphology and the average crystallite size was 0.7 μm. Luminescent spectra, typical for Nd3+ ions at low symmetry site (Cs), were observed in all samples excited at 266 nm and 808 nm. The highest emission intensity was obtained for the sample doped with 3% Nd3+. The emission lifetimes at 77 K and 300 K shorten with increasing Nd3+ concentration due to cross-relaxation processes. Noticeably, the lengthening of the decay times at 300 K, as compared to 77 K, resulted from the thermalization of the higher Stark component of the 4F3/2 level. In addition, the experimental data were analysed using the Inokuti – Hirayama model; the energy transfer between Nd3+ ions was predominantly regulated by the dipole–dipole interaction. The critical transfer distance R0, critical concentration C0, energy transfer parameter Cda, and energy transfer probability Wda were found to be 4.9 Å, 2×1021 ions∙cm−3, 5.67×10-41 cm6∙s-1, and 4004 s-1, respectively. Furthermore, the temperature–dependent luminescence exhibited good thermal stability with temperature quenching at 450 K. The temperature sensing ability of the sample doped with 5 % Nd3+, based on the emission of two thermally coupled 4F5/2 and 4F3/2 levels, was investigated. The highest value of the relative sensitivity was 0.81 and 0.83 % K-1 at 248 K and 275 K, respectively.
Anticounterfeiting is a vitally important issue in modern society. At present, the most commonly used luminescent anticounterfeiting technique is based on static photoluminescence (PL), which is ...easily counterfeited by certain substitutes. In this work, we report for the first time a dynamic PL material, Na2CaGe2O6:Tb3+. Irradiated by a portable ultraviolet (254 nm) lamp, the PL color of the material due to Tb3+ changes from the initial red to yellow and, finally, green. The investigation reveals that the dynamic PL is due to the presence of appropriate traps and the cross-relaxation effect of Tb3+ in Na2CaGe2O6. By employing this unique dynamic PL material, high-level dynamic luminescent anticounterfeiting and encryption devices can be fabricated. The dynamic PL features of the devices are easily detected using a cheap portable lamp, and at present, it is impossible for the features to be faked by any substitutes. In a virtual military scenario, the results demonstrate that the encryption device is safe and that a spy will be detected. Accordingly, this dynamic PL material could inspire more ingenious security designs.
In accordance with the growing popularity of luminescence thermometry in the single-band-ratiometric approach configuration, we developed the first blue-emitting case based on LaF3:Pr3+. By using ...excitations matched to ground- and excited-state absorption, strong thermally activated quenching and enhancement of the band associated with the 3P0 → 3H4 electronic transition were obtained, respectively. Due to the differences in the thermal dependences of the luminescence intensity signals for different Pr3+ concentrations being controlled by the thermally activated cross-relaxation depopulation process, independencies of the calibration curves for the Pr3+ content were obtained. Concentration-independent high relative sensitivities of the temperature reading, reaching even 5–6% K−1 with 0.5 K temperature determination uncertainty, confirm the high applicative potential of the developed blue-emitting Pr3+ ion-based luminescent thermometer.
In this paper, new upconversion (UC) phosphors for Yb3+–Er3+- and Yb3+–Ho3+-doped Gd9.33(SiO4)6O2 (GSO) were designed via a solid-state reaction method. The phase purity of the samples was examined ...using XRD patterns. In Yb3+–Er3+ -doped GSO, the characteristic emission peaks of Er3+ appear upon 980 nm excitation, and the optimum Er3+ concentration was found to be 1 mol%. Different changes in the intensity of green and red emissions with Er3+ concentration appeared, and were interpreted by cross-relaxation between Er3+ ions. In Yb3+–Ho3+-doped GSO, three emission peaks of Ho3+ were observed, and the power-dependent UC luminescence was studied. For studying the temperature-sensing properties, different strategies were employed, including thermally coupled levels and non-thermally coupled levels. High sensitivities were obtained in the phosphors, and GSO:Yb3+,Er3+ showed the highest sensitivities. The above investigation results indicated that the developed GSO:Yb3+–Er3+/Ho3+ phosphors could have potential applications in optical thermometry.
Lead phosphate glasses singly-doped with selected Ln3+ ions (Ln = Pr, Tm) were prepared by traditional melt-quenching method. The effect of concentration of optical active dopants in glass ...composition on spectroscopic properties of lead phosphate glasses were systematically investigated based on excitation, visible and near-infrared emission spectra as well as luminescence decay analysis. It was found that the luminescence intensity decreases with increasing content of Pr3+ and Tm3+ ions due to the concentration quenching. Also, the luminescence lifetimes of 1D2, 1G4 (Pr3+) and 1D2, 3H4 (Tm3+) states decrease with increasing concentration of both ions. Based on luminescence decay analysis and calculations using theoretical Inokuti-Hirayama model it was confirmed that non-radiative processes like cross-relaxation among the donor systems are dominate and influence direct donor-acceptor energy transfer in lead phosphate glasses. Moreover, the obtained results suggest clearly lower self-quenching emission in lead phosphate glasses doped with Pr3+ than Tm3+ ions.
•Lead phosphate glasses singly doped with Pr3+ and Tm3+ were obtained.•Luminescence spectra of Ln3+ (Ln = Pr and Tm) and their decays were examined.•The quenching of the visible and near-infrared luminescence were observed when concentration of Pr3+ and Tm3+ ions increase.•The luminescence lifetimes decrease with increasing concentration of Ln3+ ions.•The luminescence quenching via non-radiative energy transfer processes was explained by theoretical Inokuti-Hirayama model.
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