Mn2+/Mn4+ co-doped LaM1-xAl11-yO19 (M = Mg, Zn) luminescent materials: electronic structure, energy transfer and optical thermometric properties

Cation Occupation Engineering Realizes Valence Modulation of Manganese-Activated ZnGa2O4

Herein, a series of Mn-activated ZnGa2O4 (ZGO) phosphors have been developed for multifunctional applications. The characteristic green and red emission at 503 and 668 nm of Mn-activated ZGO phosphors can be observed under excitation of 247 and 375 nm, respectively, attributed to the partial oxidation of Mn2+ ions resulting in the coexistence of Mn2+ and Mn4+ ions in the host lattice. The valence modulation of Mn content not only realizes the adjustment of red and green luminescence intensity but also achieves the management of persistent luminescence time and thermo-luminescence time. Further, the codoping of Mg2+ could transform the position occupancy preference of Mn and effectively facilitate the conversion of Mn2+ to Mn4+, leading to the regulation of the valence state of manganese ions. Surprisingly, the existence of Mg2+ ions broadens the emission band of Mn4+ and enhances the photoluminescence intensity to 3.8 times, which can be ascribed to the weakened crystal field leading to the downward shift of the 4T2 energy level and the increase of Mn4+ concentration. For this valence modulation behavior, two different hypotheses about the occupancy of Mg2+ have been proposed to explain the corresponding phenomenon. Finally, the potential applications of the synthesized phosphors have been explored in advanced anticounterfeiting strategies, information storage, and plant lighting field.

Ultralow pressure sensing and luminescence thermometry based on the emissions of Er3+/Yb3+ codoped Y2Mo4O15 phosphors

Pressure and temperature are fundamental physical parameters, so their monitoring is crucial for various industrial and scientific purposes. For this reason, we developed a new optical sensor material that allows monitoring of both the physical parameters. The synthesized material exhibits upconversion (UC) emission of Er3+ in the red and green spectral regions under NIR (975 nm) laser irradiation. These UC emissions are strongly temperature-dependent, allowing multimode temperature sensing, either based on the luminescence intensity ratio between thermal-coupled energy levels (TCLs) or non-thermal-coupled energy levels (NTCLs) of Er3+ ions. Meanwhile, the luminescence lifetime of the 4S3/2 state of Er3+ ions was used as the third temperature-dependent spectroscopic parameter, enabling multi-parameter thermal sensing. Moreover, the observed enhancement of laser-induced heating of the sample under vacuum conditions allows for the conversion of the luminescent thermometer into a remote vacuum sensor. The pressure variations in the system are correlated with changes in the band intensity ratio (525/550 nm) of Er3+ TCLs, which are further applied for optical, contactless vacuum sensing. This is because of the light-to-heat conversion effect, which is greatly enhanced under vacuum conditions and manifests as a change in the intensity ratio of Er3+ bands (525/550 nm). The obtained results indicate that an Y2Mo4O15:Er3+/Yb3+ (YMO) phosphor has great application potential for the development of multi-functional and non-invasive optical sensors of pressure and temperature.

Preparation and luminescence properties of Ba2P2O7:Dy3+, Ce3+ phosphors

In this paper, Ba_2-x-yP₂O₇:xDy³⁺,yCe³⁺ phosphors are synthesized by calcining the precursor via chemical co-precipitation. The phase structure, excitation and emission spectra, thermal stability, the chromatic performance of phosphors, and energy transfer from Ce³⁺ to Dy³⁺ are studied and discussed. The results indicate the samples keep a stable crystal structure as a high-temperature σ-Ba₂P₂O₇ phase with two different coordination of Ba²⁺ sites. Ba₂P₂O₇:Dy³⁺ phosphors can be effectively excited by 349 nm n-UV light and emit 485 nm blue light and a relatively stronger yellow light peaking at 575 nm, corresponding to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺, implying that Dy³⁺ mainly occupies the non-inversion symmetric sites. By contrast, Ba₂P₂O₇:Ce³⁺ phosphors exhibit a broadband of excitation peaking at 312 nm, and two symmetrical emission peaks at 336 nm and 359 nm from 5d¹→⁴F_5/2 and 5d¹→⁴F_7/2 transitions of Ce³⁺, showing Ce³⁺ should merely be presumed to occupy Ba1 site. After Dy³⁺ and Ce³⁺ are co-doped, Ba₂P₂O₇:Dy³⁺, Ce³⁺ phosphors exhibit the enhanced characteristic blue and yellow emission of Dy³⁺ with nearly equal intensity under excitation at 323 nm, meaning Ce³⁺ co-doping increases the symmetry of Dy³⁺ site as well as the sensitizer. Simultaneously, energy transfer from Dy³⁺ to Ce³⁺ is found and discussed. The thermal stability of co-doped phosphors was characterized and briefly analyzed. The color coordinates of Ba₂P₂O₇:Dy³⁺ phosphors fall in the yellow-green region near the white light, while the emission moves towards the blue-green region after the Ce³⁺ is co-doped.

X-ray triggered pea-shaped LuAG:Mn/Ca nano-scintillators and their applications for photodynamic therapy

Photodynamic therapy (PDT) is a new minimally invasive technology for disease diagnosis and treatment. However, the biological tissue attenuation of visible light renders the depth of its penetration in tissues quite modest, which significantly restricts its therapeutic applicability. Therefore, it is an essential but yet a difficult task to enhance the X-ray sensitization impact while concurrently limiting the tissue scattering by the rational design of novel biological vectors. Herein, a novel Lu3Al5O12:Mn/Ca-Ce6@SiO2 nanoparticle system (LAMCCS) based on a pea-shaped LuAG:Mn/Ca nano-scintillator (LAMC) activating photosensitizer agent (Ce6) was designed. Due to the high radiosensitization of LAMC nano-scintillators and efficient energy conversion efficiency between LAMC and Ce6, more singlet oxygen (1O2) could be generated to efficiently damage DNA fragments and reveal a good effect of inhibiting the long-term proliferation of tumor cells in vitro. Significantly, synergistic therapy with PDT/radiotherapy (RT) and from LAMCCS nanocomposites may still maintain a high tumor growth inhibition rate of 72% than single RT of 10% in vivo. Owing to their excellent ability for X-ray sensitization and energy conversion, LAMCCS nanocomposites may have significant tumor growth suppression rates under lower X-ray dose irradiation due to their outstanding X-ray sensitization and energy conversion capabilities, which may open up a new avenue for the advancement of cancer therapy.

Designing a Polyphosphate Polymorph of CsMg(PO3)3 as Host Lattice for Preparing Single Mn2+-Oxidation Doped Phosphor in the Open Environment

Within Mn-activated phosphors, the oxidation state of Mn dopant strongly depends on the structural features of the host lattice. This paper reported a new polymorph of CsMg(PO₃)₃ (CMP) with a complicated three-dimensional (3D) framework of [Mg(PO₃)₃]_∞ that is constructed by MgO₆ octahedra and 1D infinite [PO₃]_∞ chains. Then we prepared a series of red phosphors CsMg_1-x(PO₃)₃:xMn²⁺ (CMP:xMn²⁺) by high temperature solid state reactions in the open air. Powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) studies revealed the single Mn²⁺-oxidation. Under 404 nm light exciting, CMP:0.2Mn²⁺ can emit single-band emission at around 630 nm with full-width at half-maximum (fwhm) of 70 nm. Besides, CMP:0.2Mn²⁺ possesses excellent thermostability up to 450 K. These features indicate that CMP:0.2Mn²⁺ is suitable to be used for LED backlight display. Moreover, this work suggests that a host lattice with suitable structure feature can form single Mn²⁺-oxidation and is rigid enough to protect Mn²⁺ from being oxidized by O₂ at high temperature.