Upconversion cooling of Er-doped low-phonon fluorescent solids

We report on a novel mechanism for laser cooling of fluorescent solids based on infrared-to-visible upconversion often found in rare-earth-doped low-phonon materials. This type of optical cooling presents some advantages with regards to conventional anti-Stokes cooling. Among them, it allows to obtain cooling in a broader range of frequencies around the barycenter of the infrared emitting band.Comment: 4 pages, 1 figur

Random lasing in Nd:LuVO4 crystal powder

Room temperature random lasing action is demonstrated for the first time in a low concentrated neodymium doped vanadate crystal powder. Laser threshold and emission efficiency are comparable to the ones obtained in stoichiometric borate crystal powders. The present investigation provides a complete picture of the random lasing characteristics of Nd-doped vanadate powder both in the spectral and temporal domain, together with a simplified model which accounts for the most relevant features of the random laser. © 2011 Optical Society of America.Peer Reviewe

Energy Test of an Efficient Random Laser Emission Collecting System

The problem of light collection in random lasers (RLs) is addressed. As the radiation emitted by this system is Lambertian due to its spatial incoherence, a device based on an ellipsoidal revolution mirror is designed, developed, and tested in order to optimize the harvesting of the radiation emitted by the RL. The system provides a simple injection procedure of the emitted energy at the entrance of a multimode optical fiber. The results obtained show that the device has a net energy efficiency of 35%, close to the theoretically expected one. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported LicenseThis work was supported by the Basque Government PIBA2018-24, Spanish Government MINECO under Project No. MAT2017-87035-C2-2-P (AEI/FEDER, UE), and Basque Country University (UPV/EHU) PPG17/07 and GIU17/01

Role of Eu2+ and Dy3+ Concentration in the Persistent Luminescence of Sr2MgSi2O7 Glass-Ceramics

In this study, glass-ceramics based on Sr2MgSi2O7 phosphor co-doped with Eu/Dy were obtained from the sintering and crystallisation of glass powders. The glasses were melted in a gas furnace to simulate an industrial process, and the dopant concentration was varied to optimise the luminescence persistence times. The doped parent glasses showed red emission under UV light excitation due to the doping of Eu3+ ions, while the corresponding glass-ceramics showed persistent blue emission corresponding to the presence of Eu2+ in the crystalline environment. The dopant concentration had a strong impact on the sintering/crystallisation kinetics affecting the final glass-ceramic microstructure. The microstructures and morphology of the crystals responsible for the blue emission were observed by scanning electron microscopy–cathodoluminescence. The composition of the crystallised phases and the distribution of rare-earth (RE) ions in the crystals and in the residual glassy phase were determined by X-ray diffraction and energy dispersive X-ray analysis. The emission and persistence of phosphorescence were studied by photoluminescence.This research was funded by MICINN under projects PID2020-115419GB-C-21/C-22/AEI/ 10.13039/501100011033 and PID2019-107439GB-I00 and by the project PIE-CSIC 201960E016. And The APC was funded by PID2020-115419GB-C-21/C-22/AEI/ 10.13039/501100011033

Structure and luminescent properties of Sm/Dy-doped Sr2MgSi2O7 glass-ceramics

Sm3+-doped and Sm3+/Dy3+ codoped SiO2–SrO–MgO glasses were prepared by conventional melt quenching and Sr2MgSi2O7 based glass–ceramics from sintering and crystallization of the glass powders. The thermal, structural, and optical properties of the glasses and glass–ceramics were investigated as a function of the dopant concentration. The optical characterization includes the photoluminescence spectra and the lifetimes of the 4G5/2 (Sm3+) and 4F9/2 (Dy3+) excited states. In Sm3+ single-doped samples, the emission intensity increases up to a concentration of 0.3 mol% Sm3+ ions and then decreases due to nonradiative energy transfer processes. The emission spectra in the glass–ceramics show a more resolved structure and higher intensity compared to the glass samples, suggesting a different and crystalline environment for the Sm3+ ions. The non-radiative processes also influence the experimental decays of the glass samples which deviate from a single exponential with lifetimes decreasing as Sm3+ concentration increases. The emission and excitation spectra of the codoped samples do not show significant energy transfer between Sm3+ and Dy3+ ions. Different emitting colors can be obtained in the codoped glasses by changing the excitation wavelength. The studied glass–ceramics could be applied as enamels on ceramic or metallic substrates.Funding from MICINN under projects PID2020-115419GB-C-21/C-22/AEI/ 10.13039/501100011033, PID2019-107439GB-I00 and PIE-CSIC 201960E016 is acknowledged

Femtosecond laser direct inscription of 3D photonic devices in Er/Yb-doped oxyfluoride nano-glass ceramics

[EN]The fabrication of optical waveguides by direct femtosecond laser irradiation in Er3+/Yb3+ oxyfluoride nano-glass ceramics is investigated. Following the strategy of single line irradiation, a wide range of laser parameters can be used to obtain single-mode waveguides with nearly-gaussian modal profiles, in the visible and near-infrared. Measured propagation loss is 1.6 dB/cm for the optimum parameters (0.34 μJ/pulse and 20 μm/s scanning velocity), with no annealing after irradiation, and the induced refractive index contrast is Δn∼0.006 (at 800 nm). The multi-scan technique is used to gain control of the refractive index profiles thus producing multimodal structures. The active behavior of the waveguides is induced under ∼800 nm seeding and the co-propagating guidance of the erbium emission is demonstrated. The integration of photonic elements such as Y-splitters, both in 2D and 3D, as well as Mach-Zehnder interferometers, is also shown. Results demonstrate the optimum behavior of Er3+/Yb3+ oxyfluoride nano-glass ceramics as a host material for the integration of complex active photonic devices by femtosecond laser irradiation in the low repetition rate regime.Ministerio de Economía y Competitividad (FIS2017-87970R, MAT2017-87035-C2-1-P/-2-P); Consejería de Educación, Junta de Castilla y León (SA287P18); Euskal Herriko Unibertsitatea (GIU17/014); Eusko Jaurlaritza (PIBA2018-24)

Non-Linear Optical Properties of Er3+–Yb3+-Doped NaGdF4 Nanostructured Glass–Ceramics

Transparent oxyfluoride glass–ceramics containing NaGdF4 nanocrystals were prepared by melt-quenching and doped with Er3+ (0.5 mol%) and different amounts of Yb3+ (0–2 mol%). The selected dopant concentration the crystallization thermal treatments were chosen to obtain the most efficient visible up-conversion emissions, together with near infrared emissions. The crystal size increased with dopant content and treatment time. NaGdF4 NCs with a size ranging 9–30 nm were obtained after heat treatments at Tg + 20–80 °C as confirmed by X-ray diffraction and high-resolution transmission electron microscopy. Energy dispersive X-ray analysis shows the incorporation of rare earth ions into the NaGdF4 nanocrystals. Near-infrared emission spectra, together with the up-conversion emissions were measured. The optical characterization of the glass–ceramics clearly shows that Er3+ and Yb3+ ions are incorporated in the crystalline phase. Moreover, visible up-conversion emissions could be tuned by controlling the nanocrystals size through appropriated heat treatment, making possible a correlation between structural and optical properties.This research was funded by Spanish National projects MAT2017-87035-C2-1-P/2-P (AEI/FEDER, UE), Basque Country University PPG17/07 and GIU17/014 and Basque Government PIBA2018-24. This study is part of the dissemination activities of project FunGlass. This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 739566. This study was also created in the frame of the project Centre for Functional and Surface Functionalized Glass (CEGLASS), ITMS code is 313011R453, operational program Research and innovation, co-funded from European Regional Development Fund

Er3+-doped fluorotellurite thin film glasses with improved photoluminescence emission at 1.53 µm

7 págs.; 5 figs.; 4 tabs.Transparent oxyfluoride tellurite thin film glasses have been produced at room temperature by pulsed laser deposition in O2 atmosphere from an Er-doped TeO2–ZnO–ZnF2 bulk glass. Thin film glasses present high refractive index (n≥1.95) and good transparency (T≥80%) in the visible (λ>400 nm) and near infrared range. However, their photoluminescence (PL) performance at 1.5 μm is poor. Thermal annealing at moderate temperatures (T≤315 °C), well below glass crystallization, increases the PL intensity by more than one order of magnitude as well as the PL lifetime up to τ≈3.3 ms. Film glasses present a larger fraction of TeO3 trigonal pyramids than the bulk glass and a very large OH− content. The structure and composition of film glasses do not change upon annealing and thus the activation of the PL response is related to the improvement of the surface morphology and the significant decrease of their OH− content. & 2015ElsevierB.V.This work has been supported by the Spanish Government (Projects MAT2009-14282-C02-01, MAT2009-14282-C02-02, TEC 2012-38901-C02-01, MAT2013-48246-C2-2-P and FIS2013-48087-C2-1-P).Peer Reviewe

Active mid-IR emissions from rare-earth doped tellurite glass ceramics for bioapplications

16th International Conference on Transparent Optical Networks, Graz (Grazer Messe), Austria, July 6th - 10th, 2014.Promising bio based applications such as bloodless surgery, non-invasive blood constituents monitoring or high sensitivity tracing of green house gases could be designed starting form optically active materials working within the 2.0-2.3 μm wavelength window. For this purpose, room temperature operated high power devices are entering the market of which rare-earth (RE) doped devices hold a prominent place. But such devices are based today on 3+ rare-earth doping of thulium and holmium. Though Er has an active 2.0 μm transition to achieve broad emission bandwidth, it is usually quenched in an amorphous matrix and hence rarely reported in glasses or any other 3+ as the active ion backbone would leverage efforts and investments done in the telecom industry to non-telecom applications which would allow a quick progression. This work successfully reports the engineering of the base glass matrix to produce the key 2.0 μm emission. This was obtained by specific selection of precursors and custom-designed heat treatment of an Er doped fluorotellurite glass.This work has been supported by the Spanish Ministry of Economy and Competitiveness (Projects TEC2011-22422, FIS2011-27968 and TEC2012-38901-C02-01)Peer Reviewe

Er/Yb co-doped LiYF4 transparent oxyfluoride glass-ceramics with up-conversion optical properties

Transparent oxyfluoride glass-ceramics doped with rare earth ions (RE3+) are promising materials for photoluminescence up- and down-conversion. In this study, glass compositions within the system 40SiO2–25Al2O3–18Li2O–7LiF–10YF3 (mol.%) doped with ErF3 and codoped with ErF3/YbF3 were prepared by melt-quenching method and subjected to thermal treatment at temperatures above glass transition (Tg + 35 °C) for long dwell times to obtain the corresponding glass-ceramics. The formation of LiYF4 and LiAlSiO4 nanocrystals was confirmed by XRD analysis after thermal treatment at 540 °C for 20 h. The increase in the treatment time up to 80 h resulted in the enhancement of the UC luminescence yield and the decrease of the Red to Green ratio (R/G) emission intensity. Due to the nano-sized crystals, the glass-ceramic products were transparent (%T) in near-infrared (NIR) and visible spectral region with %T remaining approximately 85% and 75%, respectively, after 20 h treatment. However, the visible window transparency reduced, with %T dropping to around 50% after 80 h due to the increase in crystal size and crystalline fraction. The influence of Yb3+ co-doping on the up-conversion (UC) luminescence has been investigated in the glass-ceramics and compared to the parent glasses, confirming that Yb3+ ions were also a key factor for facilitating up-conversion via energy transfer (ET), leading to a greater luminescence yield than for Er3+ single doped glass-ceramics and tuning of R/G intensities.This work was supported by a part of the European Union’s Horizon 2020 research and innovation program [grant number 739566]; the MICINN [grant number PID2020-115419GBC-21/C-22/AEI/10.13039/501100011033]; and the project VEGA 1/0476/22