NIR emission of lanthanides for ultrasensitive luminescence manometry-Er3+-activated optical sensor of high pressure

Pressure-Induced Remarkable Spectral Red-Shift in Mn2+ -Activated NaY9 (SiO4 )6 O2 Red-Emitting Phosphors for High-Sensitive Optical Manometry

To settle the low sensitivity of luminescent manometers, the Mn2+ -activated NaY9 (SiO4 )6 O2 red-emitting phosphors with splendid pressure sensing performances are developed. Excited by 408 nm, the resulting products emit bright red emission originating from 4 T1 (4 G) → 6 A1 transition of Mn2+ , in which the optimal concentration of the activator ion is ≈1 mol%. Moreover, the admirable thermal stability of the developed phosphors is studied and confirmed by the temperature-dependent emission spectra, based on which the activation energy is derived to be 0.275 eV. By analyzing the pressure-dependent Raman spectra, the structural stability of the synthesized compounds at extreme conditions is verified. Furthermore, the designed phosphors exhibit remarkable spectral red-shift at elevated pressure. Especially, as pressure increases from 0.75 to 7.16 GPa, the emission band centroid shifts from 617.2 to 663.4 nm, resulting in a high sensitivity (dλ/dP) of 7.00 nm GPa-1 , whereas the full width at half maximum (FWHM) increases from 83.0 to 110.6 nm, leading to the ultra-high sensitivity (dFWHM/dP) of 10.13 nm GPa-1 . These achievements manifest that the designed red-emitting phosphors are appropriate for ultrasensitive optical manometry. More importantly, the developed manometer is a current global leader in sensitivity, when operating in the band-width mode, that is, FWHM.

Mechanoluminescence and Photoluminescence Heterojunction for Superior Multimode Sensing Platform of Friction, Force, Pressure, and Temperature in Fibers and 3D-Printed Polymers

Endowing a single material with various types of luminescence, that is, exhibiting a simultaneous optical response to different stimuli, is vital in various fields. A photoluminescence (PL)- and mechanoluminescence (ML)-based multifunctional sensing platform is built by combining heterojunctioned ZnS/CaZnOS:Mn2+ mechano-photonic materials using a 3D-printing technique and fiber spinning. ML-active particles are embedded in micrometer-sized cellulose fibers for flexible optical devices capable of emitting light driven by mechanical force. Individually modified 3D-printed hard units that exhibit intense ML in response to mechanical deformation, such as impact and friction, are also fabricated. Importantly, they also allow low-pressure sensing up to ≈100 bar, a range previously inaccessible by any other optical sensing technique. Moreover, the developed optical manometer based on the PL of the materials demonstrates a superior high-pressure sensitivity of ≈6.20 nm GPa-1 . Using this sensing platform, four modes of temperature detection can be achieved: excitation-band spectral shifts, emission-band spectral shifts, bandwidth broadening, and lifetime shortening. This work supports the possibility of mass production of ML-active mechanical and optoelectronic parts integrated with scientific and industrial tools and apparatus.

Evolution of the full energy structure of Mn4+ in fluoride phosphors under high pressure conditions

This paper analyzes the photoluminescence excitation and emission spectra of fluoride phosphors doped with Mn⁴⁺: KNaSiF₆:Mn⁴⁺, Rb₂GeF₆:Mn⁴⁺, and Na₃HTiF₈:Mn⁴⁺ under high pressure conditions. From the optical spectra, the pressure-dependent energies of optically active ⁴T₂, ⁴T₁, and ²E crystal field subterms of Mn⁴⁺ have been determined in the 0-30 GPa pressure range. A strong blueshift of the ⁴T₂ and ⁴T₁ subterms was found, as expected from the Tanabe-Sugano diagram for Mn⁴⁺ (d³). At the same time, the ²E emitting state exhibited a redshift under pressure - an effect opposite to the prediction of the Tanabe-Sugano diagram. This is a manifestation of the pressure-driven nephelauxetic effect, governed by pressure induced changes of Racah parameters, which demonstrates the necessity of taking into account the Racah parameters for a correct description of Mn⁴⁺ emission under pressure. The high pressure experimental data allowed to determine the pressure dependence of crystal field strength parameter Dq and Racah parameters B and C. Finally, obtaining the pressure dependence of Dq and Racah parameters allowed to calculate the full energy structure of the d³ configuration of Mn⁴⁺ in KNaSiF₆, Rb₂GeF₆, and Na₃HTiF₈ in the pressure range of 0-30 GPa. The calculations reproduced the redshift of the ²E emitting state under pressure, as well as gave the pressure shift direction and magnitude for all crystal field subterms of Mn⁴⁺ up to 50 000 cm^-1 (i.e. the equivalent of the Tanabe-Sugano diagram for high-pressure experiments). The approach presented in this paper can be easily extended for calculating the energy structure of materials doped with isoelectronic Cr³⁺ as well as other transition metal ions.

A dual-ratiometric optical thermometry based on Sr2LaF7:Er3+ crystal-implanted pliable fibers

Sr2(La1-xErx)F7/polyacrylonitrile composite fibers with special pliability and excellent crystal dispersibility have been fabricated, which provide the smaller size and appropriate temperature sensitivity. Up-conversion emission shows quadratic dependence of the photoluminescence...