Oxyfluoride glass-ceramics (GCs) containing LaF₃ or α-NaLuF₄ nanocrystals, co-doped with 2 mol% Yb³⁺ and 0.5 mol% Er³⁺, are considered as core materials for the implementation of optical fiber photoluminescence (PL) thermometers. A dual-channel ratiometric thermometry approach combining green (UC, ²H_11/2 → ⁴I_15/2 vs ⁴S_3/2 → ⁴I_15/2) and infrared emissions (IR, ⁴I_13/2(m´) → ⁴I_15/2 vs ⁴I_13/2(m) → ⁴I_15/2) allows the extension of the sensing temperature range above the UC luminescence quenching (at ≈ 650 K) by over 100 K (LaF₃) or 150 K (α-NaLuF₄). The IR channel, working near λ= 1.55 mm, operates at the wavelength of minimum propagation losses of optical fibers, facilitating long-distance propagation of luminescence signals. The UC channel in LaF₃-GC shows a maximum absolute sensitivity S_A = 102 × 10^-4 K^-1 at 602 K in glass and S_A = 71 × 10^-4 K^-1 at 591 K in GC with thermal resolution δ = 1.5–3 K. The α-NaLuF₄-glass and -GC reach UC S_A = 90 × 10^-4 K^-1 at 698 K. The IR channel in both GCs, based on PL intensity ratios at 1498 nm and 1610 nm, exhibits S_A ≈ 30-10 × 10^-4 K^-1 for the 300-800 K range.

Published in Advanced Optical Materials vol 14, pg e01720, 2026

Lanthanide-doped Ca₃(NbGa)₅O₁₂-type disordered single crystals are promising media for high power lasers with ultrashort pulse durations. In this work, planar optical waveguides in lithium-modified Yb:Ca₃(NbGa)₅O₁₂ single crystals have been fabricated by O or F room temperature irradiation using 20 MeV of energy and a fluence of 1×10¹⁵ at/cm². The produced waveguides show 7 dark modes  in the O  case and 6 dark modes in the F one, monitored at λ= 632.8 nm. Light confinement is induced by a ≈ 4% drop of the refractive index at ≈ 4-4.5 µm of depth which is primary associated to electronic damage for both irradiations. The irradiation induces some crystal coloration that is largely eliminated by air annealing in the 150-300 ºC temperature range. A post implantation thermal annealing reduces the waveguide propagation losses at λ= 632.8 nm of F-implanted samples up to 1.8 dB/cm.

The cationic charge increase on the tetrahedral garnet site shifts the ytterbium level energy towards higher values.

Crystallographic information on the cationic interactions that may broaden the Yb³⁺ optical bands in garnets for sustaining shorter femtosecond laser pulses is provided. It is shown that the energy of the Yb^{3+ 2}F_7/2(0)↔²F_5/2(0´)  optical absorption (0↔0´ OA) measured at a cryogenic temperature (T= 6 K) in Ca₃(NbGa□)₅O₁₂ (CNGG) type disordered single crystal garnets is sensitive to the electric charge of cations incorporated in the 24d tetrahedral site while very little sensitive to the substitutions made on the 16a octahedral one.

Li⁺ and Ge⁴⁺ fill exclusively tetrahedral garnet site with a strong reduction of the cationic vacancy density monitored in the Li case by positron annihilation lifetime spectroscopy (PALS). Ti⁴⁺ sits exclusively in the octahedral garnet site with no effect on the crystal cationic vacancy density, while Mg²⁺ is distributed in the three garnet sites with preference for the tetrahedral one and a moderate reduction of the crystal vacancy density.

Yb³⁺ 0↔0´ OA bands observed at λ = 973 nm, 971.9 nm, 971.3 nm, 971.1 nm and 969.6 nm are correlated with the presence in the nearest to Yb³⁺ tetrahedral garnet sites of a vacancy (electric charge Q=0), Li⁺, Mg²⁺, Ga³⁺ and Ge⁴⁺, respectively. However, the incorporation of Ti⁴⁺ in the octahedral site substituting mainly Ga³⁺ has not observable effect on the Yb³⁺ 0↔0´ OA.

Modelocked femtosecond lasers require of luminescent ions with large emission bandwidth and tunability. This requirement is difficult to fulfill with lanthanides due to the inner nature of the 4f orbital. The concept of «disordered single crystals» which  is based on multiple (isovalent or heterovalent) cationic substitutions on the same lattice site has gained attention to solve the problem but results are still limited. In our recent publication in Journal of Alloys and Compounds 961 (2023) 171092 (doi 10.1016/j.jallcom.2023.171092) we show that the random orientation of the Bi3+ non-bonded 6s2 lone pair induces a large band broadening of the Yb3+ emission in monoclinic KY1-x-yBixYby(WO4)2 single crystals. The  growth of these crystals and their laser capabilities are demonstrated within the activity of our THINLAS project.

 

 

 

Most common thermometric luminescent  nanoprobres contain alkaline and/or halogen ions which poisson currently used catalysts, for instance the well known NaYF4 host based compounds. Our IMPETUSS project (PID2021-128090OB-C21) aims the development of eficient luminescence nanoprobes compatible with standardly catalyzed reactions. In this direction we develloped alkaline and halogen-free β´Gd2(MoO4)2 nanoprobes doped with Yb3+, Er3+ and Tm3+. We defined three different ratiometric  channels to determine  temperature from 20 to 600ºC with optimised sensitivity. See Journal of Alloys and Compounds 913 (2022) 165180 doi 10.1016/j.jallcom.2022.165180.

 

Our recent publication in Journal of Materials Chemistry A 2023, 11, 19854 (doi 10.1039/d3ta03654e) in collaboration with the Institute of Chemical Technology (UPV-CSIC) in Valencia (among others) adresses the problem found in Tandem Catalysis of having»spatially proximate but thermally distant» catalysts contained in a single reactor.  An elegant solution arose through the specific heating of the hot catalyst by magnetic susception. A thermal gradient of 50 ºC between the hot and cold catalysts was infered by  luminescence lifetime thermometry by using Eu3+-doped and Cr3+-doped nanoprobes. A probe of concept was demostrated by direct production of propene from ethene, via sequential olefin dimerization and metathesis reactions.

In February 2024 Dr. Xiumei Han incorporated to the REALM group as responsible of the Top Seeded Solution Crystal Growth laboratory.

Also in February 2024  Illán Calvo Llorente  incorporated to the REAL group  hired by THINLAS project.

We wish both of you all success during your stays.

 

On July 14th 2021 Jorge Omar Álvarez Pérez obtained his PhD degree from the Autonomous University of Madrid  with the work entitled «Caracterización física y láser de monocristales de granates desordenados tipo Ca3(NbGa)5O12 dopados con Yb3+»  (Physical and laser characterization of Ca3(NbGa)5O12 disordered single crystals doped with Yb3+). The work was awared with the «cum laude» maximum qualificatlon.

The work “A roadmap for laser optimization of Yb:Ca₃(NbGa)₅O₁₂–CNGG–type single crystal garnet”  published  in Journal of Materials Chemistry C vol 9, pgs 4628-4642, 2021 https://pubs.rsc.org/en/Content/ArticleLanding/2021/TC/D0TC05718E#!divAbstract

completes a trilogy of new physical knowledge and laser performance progress of this disordered cubic crystal garnet with applications in ultrashort laser pulse oscillators.

Following the path of our original proposal of CNGG Na+ modification for charge compensation of Yb3+ doping, in a first work we introduced a crystallographic model to describe the Yb3+ optical bandwidth. In a second work we disclosed the presence of a small amount of Yb3+ in centrosymmetric octahedral position with dominant magnetic dipole transitions. In the present work we describe how to minimize the crystal coloration,  the limits for Na incorporation and the relevant parameters helping for laser performance optimization.

Na and Li codoping of Yb:CNGG is found to provide the broadest tuning range along with best laser preformances.