Photoluminescence of Mn2+ in the Borosulfate Zn[B2 (SO4 )4 ] : Mn2+ -A Tool to Detect Weak Coordination Behavior of Ligands

The impact of the surrounding ligand field is successfully exploited in the case of Eu2+ to tune the emission characteristics of inorganic photoactive materials with potential application in, e.g., phosphor-converted white light-emitting diodes (pc-wLEDs). However, the photoluminescence of Mn2+ related to intraconfigurational 3d5 -3d5 transitions is also strongly dependent on local ligand field effects and has been underestimated in this regard so far. In this work, we want to revive the idea how to electronically tune the emission color of a transition metal ion in inorganic hosts by unusual electronic effects in the metal-ligand bond. The concept is explicitly demonstrated for the weakly coordinating layer-like borosulfate ligand in the Mn2+ -containing solid solutions Zn1-x Mnx [B2 (SO4 )4 ] (x = 0, 0.03, 0.04, 0.05, 0.10). Zn[B2 (SO4 )4 ]:Mn2+ shows orange narrow-band luminescence at 590 nm, which is an unusually short wavelength for octahedrally coordinated Mn2+ and indicates an uncommonly weak ligand field. On the other hand, the analysis of the interelectronic Racah repulsion parameters reveals ionic Mn-O bonds with values close to the Racah parameters of the free Mn2+ ion. Overall, this strategy demonstrates that electronic control of the metal-ligand bond can be a tool to make Mn2+ a potent alternative emitter to Eu2+ for inorganic phosphors.

Thermoluminescent characteristics of UV-irradiated Aluminum nitride (AlN)

This paper presents results of studying the thermoluminescence (TL) properties of aluminum nitride (AlN) synthesized by chemical vapor deposition (CVD) method. Previously to study the TL properties, the phosphor was characterized by means of X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FT-IR), photoluminescence (PL), and electron microscopy (EDS-SEM). TL studies were performed after ultraviolet (UV) irradiation using the whole spectrum of the xenon (Xe) lamp. XRD results show that AlN has a hexagonal crystalline structure. EDS-SEM analysis revealed the presence of oxygen (O) and Carbon (C) impurities in the powders. FT-IR spectroscopy lets us discuss the distribution of these impurities in the crystalline structure. The sample with 9.54% of C and 7.36% of O exhibits a TL glow curve with a predominant peak around 450 K, and according to the deconvolution method was found that the glow curve is composed by six peaks each one centered at 383, 446, 478, 540, 587 and 637 K. The TL response as a function of dose fits a logarithmic increasing function along the dose range studied: These results suggest that AlN is a promising material for application as a TL dosimeter for UV radiation.

Investigation of dosimetric properties of CaSO4:Mn phosphor prepared using slow evaporation route

The objective of this work was to investigate the luminescent properties of CaSO₄:Mn synthesized by slow evaporation route. The crystalline structure, morphology, thermal and optical properties of the phosphors were characterized by X-ray diffraction analysis (XRD), Scanning electron microscopy (SEM), photoluminescence (PL) and thermogravimetric analysis (TGA). Moreover, using thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques, the dosimetric properties of the phosphors, such as emission spectra, glow curve reproducibility, dose-response linearity, fading of the luminescent signal, variation of the TL intensity with the heating rate, OSL decay curves, correlation between TL and OSL emissions and minimum detectable dose (MDD) were comprehensively investigated. For dosimetric analyses, the samples were irradiated with doses from 169 mGy to 10 Gy. The emission band fits with the characteristic line of the Mn²⁺ emission features, ascribed to ⁶A₁→⁴T₁ transition. CaSO₄:Mn pellets present a TL glow curve with a single typical peak centered around 494 nm, an OSL decay curve with predominance of a fast decay component, and a MDD on the order of mGy. The luminescent signals showed to be linear and reproducible in the studied dose range. The trapping centers located between 0.83 eV and 1.07 eV were revealed for different heating rates in the TL study. The high TL sensitivity of CaSO₄:Mn was proven when comparing with commercially available dosimeters. The luminescent signals exhibit a smaller fading than described in the literature for CaSO₄:Mn produced by other methods.

Dual role of oxygen-related defects in the luminescence kinetics of AlN:Mn2

This study presents the impact of temperature and pressure on AlN:Mn²⁺ luminescence kinetics. Unusual behavior of Mn²⁺ optical properties during UV excitation is observed, where a strong afterglow luminescence of Mn²⁺ occurs even at low temperatures. When the temperature increases, the contribution of the afterglow luminescence is further enhanced, causing a significant increase in the luminescence intensity. The observed phenomena may be explained by an energy diagram in which the O_N-V_Al complex in AlN:Mn²⁺ plays a key role. Hence the O_N-V_Al complex defect in AlN:Mn²⁺ plays a double role. When the O_N-V_Al defect is located close to Mn²⁺ ions, it is responsible for transferring excitation energy directly to Mn²⁺ ions. However, when the O_N-V_Al defect complex is located far from Mn²⁺ ions, its excited state level acts as an electron trap responsible for afterglow luminescence. Additionally, three models have been tested to explain the structure of the emission spectrum and the strong asymmetry between the excitation and emission spectra. From the most straightforward configuration coordinate diagram through the configuration coordinate diagram model assuming different elastic constants in the excited and ground-states ending by a model based on the Jahn-Teller effect. We proved that only the Jahn-Teller effect in the excited ⁴T₁ electronic state with spin-orbit coupling could fully explain the observed phenomena. Finally, high-pressure spectroscopic results complemented by the calculations of Racah parameters and the Tanabe-Sugano diagram are presented.

Angular Jahn-Teller Effect and Photoluminescence of the Tetrahedral Coordinated Mn2+ Activators in Solids-A First-Principles Study

First-principles calculations based on density functional theory have been performed to investigate the electronic structure, excited-state Jahn-Teller distortion, and photoluminescence of the multielectron d⁵ system of the strongly covalent tetrahedral coordinated Mn²⁺ activator in solids. The electronic structure of the ⁴T₁ and ⁴A₁/⁴E excited states is analyzed, and Slater's transition-state method and occupation matrix control methodology are applied to deal with the spin contamination in the lower-spin excited states, which is due to the mixing of the ground state of the same spin projection number. In a series of covalent tetrahedral coordinations, the ⁶A₁ → ⁴T₁ and ⁴A₁/⁴E excitations and the ⁴T₁ → ⁶A₁ emission energies are obtained and compared to the reported experimental results. The nephelauxetic effect follows O^2- < S^2- ≈ Se^2- < N^3-, and the larger nephelauxetic effect and crystal field strength lead to the red-shifted emission of nitride phosphors. The Jahn-Teller distortion of the ⁴T₁ states is dominated by the e-type angular distortion of the [MnL₄] moiety (L being the ligand), which accounts for the small Stokes shift of tetrahedral coordinated Mn²⁺. The results show that the ground- and excited-state electronic and geometric structures and the luminescent property of tetrahedral coordinated Mn²⁺ can be reliably predicted. The method can be further explored to interpret and discriminate the luminescent properties of materials containing a variety of different Mn²⁺ sites and complexes and even other transition metals.

Novel organic-inorganic hybrid powder SrGa12O19:Mn2+-ethyl cellulose for efficient latent fingerprint recognition via time-gated fluorescence

Latent fingerprints (LFPs) are important evidence in crime scenes and forensic investigations, but they are invisible to the naked eye. In this work, a novel fluorescent probe was developed by integrating a narrow-band-emitting green afterglow phosphor, SrGa₁₂O₁₉:Mn²⁺ (SGO:Mn), and ethyl cellulose (EC) for the efficient visualization of LFPs. The hydrophobic interactions between the powder and lipid-rich LFPs made the ridge structures more defined and easily identifiable. The background fluorescence of the substrates was completely avoided because of the time-gated fluorescence of the afterglow phosphor. All the three levels of LFP degrees were clearly imaged due to the high sensitivity. Moreover, the SGO:Mn-EC powder was highly stable in neutral, acidic, and alkaline environments. In addition, 60 day-aged LFPs were successfully visualized by the powder. All performances showed that this strategy for LFP recognition has merits such as low cost, non-destructive nature, reliability, superior universality, and legible details. Together, these results show the great application prospects of this powder in forensic identification and criminal investigation.

A novel germanate based red-emitting phosphor with high efficiency, high color purity and thermal stability for white light-emitting diodes and field emission displays

A series of Eu³⁺-activated K₂SrGe₈O₁₈ phosphors for white light emitting diodes and field emission displays were developed and explored.

A novel blue-emitting Eu2+-doped chlorine silicate phosphor with a narrow band for illumination and displays: structure and luminescence properties

A novel silicate-based phosphor Ba₅SiO₄Cl₆:Eu²⁺ (BSOC:Eu²⁺) was successfully designed and investigated through the solid-state method.

Co-doping effect of Mn2+ on fluorescence thermostability of Ca-α-sialon:Eu2+ phosphors

To reveal Mn²⁺ influence on emission of Ca-α-sialon:Eu²⁺, the Mn²⁺ and Eu²⁺ co-doped phosphors were synthesized by a solid state reaction method. The produced powders show an enhanced fluorescence thermostability and the roles of Mn²⁺ addition have been investigated.

Multi-modal imaging of HeLa cells using a luminescent ZnS:Mn/NaGdF4:Yb:Er nanocomposite with enhanced upconversion red emission

ZnS:Mn/NaGdF₄:Yb:Er nanocomposite was synthesized using a single-step hot injection method and then applied in the downconversion and upconversion optical imaging of living HeLa cells.

Versatile properties of CaGd₂ZnO₅:Eu³⁺ nanophosphor: its compatibility for lighting and optical display applications

Red color-emitting CaGd2ZnO5:Eu(3+) (CGZO:Eu(3+)) nanophosphors were synthesized by a facile sol-gel process. The structural and luminescent properties of these phosphors were investigated as a function of annealing temperature and Eu(3+) ion concentration. The orthorhombic phase was confirmed at different annealing temperatures, showing an irregular morphology within the nanoscale range. Photoluminescence (PL) excitation spectra of CGZO:Eu(3+) showed host absorption band (HAB), charge transfer band (CTB), and intense f-f transitions of Eu(3+) in the violet and blue wavelength regions. The CTB intensity increased and the HAB intensity decreased with increasing annealing temperature or Eu(3+) ion concentration. The CGZO:Eu(3+) exhibited a strong absorption in the blue region as compared to the CTB and had a superior property compared to available commercial phosphors. This feature facilitates the fabrication of high color rendering index white light-emitting diodes for display systems. In PL spectra, an intense red emission was observed due to the hypersensitive (5)D0→(7)F2 transition with good asymmetry ratio and chromaticity coordinates. Optimized annealing temperature and concentration of Eu(3+) ions were observed for CGZO host lattice based on the 466 nm excitation wavelength. The cathodoluminescent properties were also similar to the PL results.

Photoluminescence and cathodoluminescence properties of Na2MgGeO4:Mn2+ green phosphors

The cathodoluminescence properties of green phosphor Na₂MgGeO₄:0.03Mn²⁺.

Bifunctional AlN:Tb semiconductor with luminescence and photocatalytic properties

AlN doped with Tb semiconductors exhibit strong green emission and excellent photocatalytic property.

Rare-earth free narrow-band green-emitting KAlSi2O6:Mn2+ phosphor excited by blue light for LED-phosphor material

A novel rare-earth free narrow-band green-emitting KAlSi₂O₆:Mn²⁺ phosphor excited by blue light for LED is synthesized by solid-state reaction.