NaLaMgWO6:Mn4+/Pr3+/Bi3+ bifunctional phosphors for optical thermometer and plant growth illumination matching phytochrome PR and PFR

Sr/Ba substitution induced higher thermal stability far red-emitting Ba1-ySryLaLiWO6:Mn4+ phosphors for plant growth applications

A series of red-emitting BaLaLiWO₆:Mn⁴⁺ (BLLW:Mn⁴⁺) phosphors were successfully synthesized by a high-temperature solid-state reaction method. The crystal structure and luminescence properties of the obtained samples were systematically investigated. The emission spectra exhibited a deep red emission band peaking at 716 nm with a full width at half-maximum (FWHM) of 44 nm under 340 nm excitation. The optimal Mn⁴⁺ molar concentration was about 1.2%. In addition, the luminescence mechanism was analyzed using a Tanabe Sugano energy level diagram. With the substitution of Sr for Ba, there was a red shift in the emission spectrum and a blue shift in the excitation spectrum. The emission intensity of BLLW:1.2%Mn⁴⁺ at 150 °C was about 22% of the initial value at room temperature. In contrast, the emission intensity of SrLaLiWO₆:1.2%Mn⁴⁺ still maintained 79% of the initial emission intensity at room temperature at 150 °C. This was due to the fact that with the substitution of Sr for Ba, the W-O bond length gradually decreases, which gradually enhanced the crystal field strength of Mn⁴⁺.

A high sensitivity dual-mode optical thermometry based on charge compensation in ZnTiO3:M (M = Eu3+, Mn4+) hexagonal prisms

Optical thermometer based on dual-mode fluorescence intensity ratiometric thermometry has been attracted more attention due to its higher sensitivity. In order to obtain optical thermal probe with high sensitivity, ZnTiO₃ hexagonal prisms with hexagonal perovskite structure were fabricated by using self-assembly method, and Al³⁺ ions were introduced into the crystal lattices of ZnTiO₃ doped with Eu³⁺/Mn⁴⁺ to improve the optical properties. The emission intensity assigned to Eu³⁺ was enhanced about twice with the charge compensation of Al³⁺ between Eu³⁺ and Ti³⁺. While the luminescence ratio between the thermal coupled level of Eu³⁺ revealed poor temperature dependence property. The emission assigned to ²E_g→⁴A_2g (713 nm) transition of Mn⁴⁺ revealed an huge thermal quenching. Using the luminescence ratio between ⁵D₀→⁷F₂ (⁵D₀→⁷F₁) transition of Eu³⁺ to ²E_g→⁴A_2g of Mn⁴⁺, the higher relative sensitivity of 2.7 %K^-1was obtained. The charge compensation of Al³⁺ improved the coordination and reduced the relative sensitivity, Sr =1.85 %K^-1. The results suggested the potential application in optical temperature probes for ZnTiO₃: Mn⁴⁺,Eu³⁺ phosphor.

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

A bifunctional luminescent material is one of the most intriguing topics in recent years with significant growth in the number of investigations. Herein, we report the potential of Ba₂MgWO₆ doped with Er³⁺ as a candidate for white-light emitting phosphor and noncontact luminescent thermometry. The synthesis of the samples was carried out by the co-precipitation method. The influence of the dopant concentration on the emission intensity, as well as the capability of temperature readout, was investigated for the first time. The highest emission intensity exhibits a sample comprising 4% Er³⁺; above it, the concentration quenching process by the dipole-dipole interaction occurs. However, high quality white light generates Ba₂MgWO₆ with 0.5% of Er³⁺ due to the coexistence of the host and erbium ion emission with a CIE of (0.30, 0.35). To construct a non-contact luminescent thermometer based on Er³⁺, the ratio of the emission from ⁴I_11/2 → ⁴I_15/2 to the host emission was examined. The highest sensitivity S_r of the obtained luminescent thermometers was 2.78% K^-1 at 198 K. The repeatability of the calculated results and the uncertainty δT of the temperature readout were investigated.

Enhanced self-activated far-red photoluminescence from Sr3LiSbO6 phosphors by Gd3+ doping for plant growth

Sr₃LiSbO₆ phosphors were prepared by high temperature solid state reaction method. The crystal phase, morphology and optical properties were characterized by X-ray powder diffraction spectroscopy, scanning electronic microscope, absorption and photoluminescence (PL) spectra. The XRD Rietveld refinement was performed to obtain the detailed crystal structure of Sr₃LiSbO₆. The electronic structure was analyzed by density functional theory (DFT) calculation. Sr₃LiSbO₆ possessed indirect band structure and the band-gap were determined to be 3.17 eV. Self-activated far-red emissions at 630-800 nm were detected under the excitation at 340 nm, which was proposed to originate from the transition between interstitial oxygen defective state to six hybrid 4d¹⁰5s⁰ states of Sb⁵⁺ according to the results of PL spectra of samples annealed at different atmospheres. The PL intensity can be significantly enhanced by 2.9 times after doping 2 mol% Gd³⁺ ions in Sr₃LiSbO₆. The internal quantum efficiency of Sr₃LiSbO₆:2 mol%Gd³⁺ was determined to be 25.2%. The influence of the Gd³⁺ doping on the self-activated PL lifetimes of Sr₃LiSbO₆ and the thermal quenching property of Sr₃LiSbO₆:2 mol%Gd³⁺ was studied.