An Er3+ doped Ba2MgWO6 double perovskite: a phosphor for low-temperature thermometry

Interstitial Oxygen-Driven Far-Red/Near-Infrared Emission and Efficiency Enhancement via Heterovalent Cation Substitution in Ca3WO6 Phosphors

In this work, Ca3WO6 (CWO) phosphors were successfully synthesized using a high-temperature solid-state method, exhibiting an anomalous far-red/near-infrared (FR-NIR) emission centered at 685 nm. The origin of this FR-NIR emission is confirmed through Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), density functional theory (DFT) calculations, and heterovalent cationic substitution (Y3+/Na+ → Ca2+). These analyses indicate that interstitial oxygen (Oi) defects within the lattice are primarily responsible for the FR-NIR emission. The heterovalent substitution of Y3+ for Ca2+ increases the concentration of Oi, significantly enhancing the FR-NIR emission intensity. This results in an increase in the internal quantum efficiency (IQE) increasing from 12.8 to 90.9%, realizing an efficient FR-NIR emission from self-activated phosphors. Furthermore, CWO phosphors demonstrate a unique dual-band emission characterized by a blue emission at 435 nm and an FR-NIR emission at 685 nm. This dual-band emission endows CWO phosphors with multifunctional applications in plant growth lighting, nondestructive testing, and night vision fields.

A highly sensitive ratiometric optical thermometer based on a Sr2MgWO6 double perovskite doped with Dy3+ exploiting thermally coupled and uncoupled levels

The increasing demand for highly sensitive optical thermometers operating within a wide temperature range necessitates the development of new phosphors. In this work, the potential temperature sensing performance of a novel yellow-emitting phosphor, Sr2MgWO6 double perovskite, doped with varying concentrations of Dy3+ was investigated for the first time. Increasing the concentration of Dy3+ from 0% to 7% shifted the color of luminescence from blue to yellowish-orange within the CIE1931 color space. The energy transfer efficiency from (WO6)6- to Dy3+ also increased significantly to 98.4%. Moreover, the sample doped with 3% Dy3+ showed the highest emission intensity, with a concentration beyond this threshold inducing concentration quenching. This phenomenon was primarily governed by dipole-dipole interactions. The highest quantum yield was found to be 30.7% for the sample doped with 3% Dy3+. Upon 266 nm wavelength excitation, the temperature sensing ability of the samples doped with 3%, 5%, and 7% Dy3+ was examined based on the fluorescence intensity ratio between the thermally coupled and uncoupled levels. It showed that the relative thermal sensitivity of Sr can be tuned by changing the Dy3+ concentration. Sr-max = 3.24% K-1 was obtained for the sample doped with 3% Dy3+ at 193 K within the 80-273 K operating range for thermally uncoupled levels. For thermally coupled levels, the Sr-max value reached 1.35% K-1 at 333 K for the sample doped with 7% Dy3+ in the range of 293-593 K. These results demonstrate the enormous potential of the studied materials for thermal sensing applications.

Effect of A-Cation Radius on the Structure, Luminescence, and Temperature Sensing of Double Perovskites A2MgWO6 Doped with Dy3+ (A = Ca, Sr, Ba)

Herein, we report a case of A2MgWO6 (A = Ca, Sr, Ba) doped with 2%Dy3+, 2%Li+, in which the influences of the cation substitution are exhibited through the crystal structure, the charge transfer band (O2--W6+), the emission spectrum, the color of the luminescence, and the luminescent decay time. The substitution of Ca2+ and Sr2+ ions for larger ions (Ba2+) led to the crystal structure alteration from cubic to monoclinic and tetragonal, respectively. These structure changes also lowered the crystallography symmetry site of Dy3+, tuned the color of the emitted light from the whitish to yellowish region, and caused a blue shift of the CTB. Furthermore, a significant decline in the lifetime of the 4F9/2 → 6H13/2,15/2 transitions was noticed, from 748, 199, to 146 μs corresponding to Ba, Sr, Ca sample owing to the reduction in the local symmetry of Dy3+. Moreover, the thermal sensing properties of 2%Dy3+-doped samples were investigated based on the fluorescence intensity ratio technique in the range of 80-325 K. Under 266 nm excitation wavelength, the maximum relative sensitivity of the investigated samples was remarkably enhanced from 2.26%/K, 3.04%/K, to 4.38%/K corresponding to Ba, Ca, and Sr samples, respectively. In addition to providing a comprehensive understanding of the effects of compositional modifications on the optical properties, the results also present a viable pathway to manipulate the temperature sensing performance.