Fluorescence Decay Curves Research Articles

Crystal growth and infrared-to-visible upconversion luminescence in Nd-Yb-Tm: CaYAlO4 single crystal

Yb3+/Tm3+: CaYAlO4 (CYA) and Nd3+/Yb3+/Tm3+: CYA bulk single crystals were grown using the Czochralski (Cz) method. The polarized absorption, upconversion luminescence (UCL) spectra under 980 nm and 808 nm pumping, and fluorescence decay curves were measured as well as Judd-Ofelt (J-O) theory calculations were performed to investigate the sensitization effect of Yb3+ and Nd3+/Yb3+co-doping in Tm3+: CYA single crystal. Obvious enhancement was observed in Tm3+-activated crystals for the blue upconversion emission (∼474 nm) when doped with Yb3+ or co-doped with Nd3+/Yb3+. The energy transfer efficiency is 72.6% (Yb3+→Tm3+) and 71.7% (Nd3+→Yb3+/Tm3+) in Yb3+/Tm3+: CYA and Nd3+/Yb3+/Tm3+: CYA single crystals respectively. The gain cross-sections were calculated, and it can stated that the blue laser output derived from upconversion is possible around 474 nm related to the transition of 1G4→ 3H6 in Yb3+/Tm3+: CYA and Nd3+/Yb3+/Tm3+: CYA crystals.

Time-resolved fluorescence spectroscopy for studying stepwise excited-state intramolecular double proton transfer

Nowadays, single excited-state intramolecular proton transfer (ESIPT) is well studied and widely reported. However, excited-state multiple intramolecular proton transfer has not been thoroughly researched until the past decade. And now there is an increasing scientific interest not only in single but also in multiple ESIPT processes occurred in various molecules, because it offers great opportunities to apply such compounds in chemical sensors, molecular switches, NIR emitting devices and liquid crystals with high fluorescence. A stepwise excited-state intramolecular double proton transfer (ESIDPT) is among such multiple ESIPT processes. Similar to the single ESIPT, stepwise ESIDPT also occurs via an intramolecular hydrogen bonding way. But in the stepwise ESIDPT, two proton transfers occur sequentially in a molecule, because there is only one proton transfer site in the initial molecular structure. Then, after the first ESIPT, an additional proton transfer site appears, and the second proton transfer will occur.In this work, an emission of stepwise ESIDPT-active molecules was studied from the point of view of a time-resolved fluorescence spectroscopy. The theoretical model for emission decay was discussed on the basis of a six states model. This model consists of three pairs of ground and excited states for normal molecular form and two tautomers. It leads to three-exponential equations for emission decay functions. It was shown that a thorough analysis of fluorescence decay curves allows to estimate the total decay rate constants for each excited molecular form. The proposed model has been validated for a numerically simulated case. The experimental data have also been discussed from the point of view of the proposed model.

Enhanced ∼2.85 μm mid-infrared emission of Na5Lu9F32: Pr3+/Ho3+ single crystal by introducing of non active Gd3+ ions

A series of novel Na5Lu9F32 fluoride single crystals by keeping the concentrations of Ho3+ (0.5 mol%) and Pr3+ (0.1 mol%) fixed and varying the concentrations of Gd3+ ions (i.e., 0, 0.5, 1.0, 1.2, 1.5 mol%) were prepared successfully by a reformative Bridgman technique for application of 2.85 μm mid-infrared. The impact of the non active Gd3+ ion on the crystallographic structure and optical properties of the single crystal were explored by the aid of the X-ray diffraction, Rietveld refinement, spectra of absorption and emission and decay curves of fluorescence. By leading Gd3+ (1.2 mol%) into Ho3+(0.5 mol%)/Pr3+(0.1 mol%) incorporated Na5Lu9F32 single crystal, the emission intensity at ∼ 2.85 μm was fulfilled significantly about two times enhancement. The destruction of [Ho3+-Ho3+] ion quench clusters and release more luminescent ions are in charge of the enhancement of the emission at 2.85 μm by leading Gd3+ into the fluoride single crystal. The maximum emission cross-section, ∼5.2 × 10−20 cm2, at ∼2.85 μm was estimated on the basis of the emission spectra. Thus, the grown Pr3+/Ho3+/Gd3+ incorporated Na5Lu9F32 fluoride single crystals could be an excellent candidate for source of ∼2.85 μm mid-infrared solid-state laser device.

Original Na5(Lu1–x–yGdxYy)9F32: Pr3+/Ho3+ Hybrid Single Crystals for Efficient ∼2.9 μm Mid-Infrared Emission

A novel Ho3+/Pr3+/Y3+/Gd3+ multiply doped Na5Lu9F32 mixed single crystal was successfully grown via a modified Bridgman technique. The structure of the mixed crystal was characterized by means of X-ray diffraction and Raman spectra. The impacts of Y3+ and Gd3+ ions on the 2.9 μm emission of Na5Lu9F32 single crystals, which incorporated fixed Ho3+/Pr3+, were investigated systematically with the aid of the optical spectra and decay curves of fluorescence. The 2.9 μm emission intensity (Ho3+: 5I6 → 5I7) was further heightened upon gradually introducing both Y3+ and Gd3+ ions into Ho3+/Pr3+-incorporated single crystals pumped at 640 nm. The brokenness of ionic quenching clusters of [Ho3+–Ho3+] and the release of more luminescent ions are in charge of the augment of emission at 2.9 μm by introducing Gd3+ or Y3+ ions into the Ho3+/Pr3+ codoped single crystals. A value of ∼8.2 × 10–21 cm2 was estimated for the maximum emission cross section at 2.9 μm of the mixed crystal. The processing of energy transfer among Ho3+, Pr3+, Y3+, and Gd3+ ions was investigated, and the energy transfer efficiency for Ho3+: 5I7 → Pr3+: 3F2 was approximately 57.32%. The Na5Lu9F32-doped Ho3+/Pr3+/Y3+/Gd3+ mixed crystals may be a new laser gain medium for 2.9 μm generation because of their special spectral and physicochemical properties.

Growth and Characterization of All-Inorganic Halide Perovskite CsPbF3 Single Crystals

Lead-based halide perovskite semiconductors have demonstrated considerable potential in optoelectronic applications. However, the lack of high-quality crystals suitable for research has led to rare reports on CsPbF3 single crystals. Good quality CsPbF3 single crystals were successfully grown using the Bridgman method. The structure, luminescence, and electrical properties of crystals were investigated. At room temperature, the crystal structure was determined to be cubic perovskite, with a calculated bandgap of 3.68 eV. The measured emission spectrum showed one broad emission peak at approximately 400 nm. Three decay time constants were obtained from a sum of exponential functions fit to the fluorescence decay curve: 0.4 ns, 2.4 ns, and 15.0 ns for fast, middle, and slow decay times, respectively. The decay times excited by pulsed X-ray were measured to be 2.2 ns and 10.2 ns, indicating that CsPbF3 is an ultrafast scintillator. Furthermore, the electrical properties demonstrated that CsPbF3 exhibits high ion mobility, which is approximately 20 times that of electron mobility.

Photoluminescence investigation of Tb3+-activated barium lutetium oxide microphosphor for latent fingerprint visualization

The feasibility of utilizing the microphosphor Ba3Lu4O9:Tb3+ in latent fingerprint visualization was explored in this work. The micromorphology and elemental composition of the phosphor particles were examined by X-ray photoelectron spectroscopy and transmission electron microscopy. The photoluminescence performance of Ba3Lu4O9:Tb3+ was characterized by the photoluminescence emission and excitation spectra together with the fluorescence decay curves. All the as-synthesized phosphors could be pumped by the ultraviolet, and the photoluminescence spectra consisted of line peaks from the typical 4 f→4 f transitions of Tb3+. The Ba3Lu3.98O9:0.02Tb3+ gave off intense green emission with CIE coordinate of (0.2904, 0.5430). The emission of this phosphor was well matched with the photopic luminosity curve. The photoluminescence intensity of the phosphor recorded at 425 K retained 77.8% of that at room temperature. Furthermore, in the fingerprint visualization experiment, based on this phosphor, the multilevel characteristics of LFP attached with the as-studied phosphor could be clearly identified. All the results signified that Ba3Lu4O9:Tb3+ microphosphor was a promising candidate for latent fingerprint visualization.

Evaluation of Steady-State and Time-Resolved Fluorescence Spectroscopy as a Method for Assessing the Impact of Photo-Oxidation on Refined Soybean Oils.

The type of material used in packaging, lighting, and storage time can impact food quality during storage. This study aimed to investigate the progress of photosensitized oxidation in refined soybean oil using steady-state and time-resolved fluorescence spectroscopy. The experiment was conducted through accelerated photo-oxidation with Light-Emitting Diode (LED) in samples stored for ten days at room temperature (26.0 ± 2.0 °C) in clear polyethylene terephthalate (PET) packaging of different colors and different transmission spectra in the UV and visible range. Emission spectra were obtained with excitation at 373, 405, and 500 nm, resulting in two main emission peaks: the first with maximum emission between 430 and 555 nm and the second at around 660 nm. Fluorescence decay curves were obtained with excitation at 340 and 405 nm. The results indicated that transparent PET bottles are not effective in protecting soybean oil from photosensitized oxidation under the studied conditions. Strong correlations were observed between fluorescence parameters and peroxide and conjugated diene values, indicators of lipid oxidation progress. Fluorescence spectroscopy has several advantages over traditional methods as it is a simple, fast, low-cost, and low-waste technique.

Spectral Broadening in Cr3+-Doped Sr0.92Mg0.91Al10.1O17 NIR Phosphor Realized by Multi-crystallographic Site Occupation

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) play an important role in nondestructive testing, medical imaging, food analysis, and so on. Broadband NIR phosphors are needed in order to cover the characteristic wavelengths of various matters. In this paper, a NIR phosphor, Sr0.92Mg0.91Al10.1O17 (SMAO):Cr3+, with a full width at half maximum (FWHM) of 12–102 nm is achieved as a function of Cr3+ concentration. Two Cr3+ sites are observed by means of excitation spectra and fluorescence decay curves. The spectral broadening with the increase of Cr3+ concentration is attributed to the increase of occupation ratio on the weak crystal field site by Cr3+. In addition, the difference in thermal stability between 2E and 4T2 is employed to conduct the temperature measurement with a relative sensitivity of 0.43% K–1 at 270 K. A NIR pc-LED is fabricated using SMAO:0.03Cr3+ phosphor combined with a 395 nm LED chip with radiation flux of 2.2 mW@10 mA and 15 mW@100 mA.

Structure and spectral properties of Dy3+ doped CaYAlO4 single crystal

A 2 at.% Dy3+: CaYAlO4 single crystal was grown successfully. The electronic structures of Ca2+/Y3+ mixed sites in CaYAlO4 were investigated using first-principles based on density functional theory. The effects of Dy3+ doping on the structural parameters of host crystal were studied using XRD pattern. The optical properties including absorption spectrum, excitation spectrum, emission spectra and fluorescence decay curves were thoroughly investigated. The results show that the Dy3+: CaYAlO4 crystal could be pumped by the blue InGaN and AlGaAs or 1281 nm laser diodes. Furthermore, an intense 578 nm yellow emission was obtained directly under excitation at 453 nm, meanwhile, evident mid-infrared light emitting was observed by 808 or 1281 nm laser excitation. The fitted fluorescence lifetimes of 4F9/2 and 6H13/2 levels were about 0.316 ms and 0.038 ms, respectively. It can be concluded that this Dy3+: CaYAlO4 crystal could simultaneously act as a promising medium for both solid-state yellow and mid-infrared laser outputs.

A novel reddish-orange-emitting phosphor Ca3Gd7(PO4)(SiO4)5O2: Sm3+ for white light-emitting diodes

Phosphor is the decisive material in white light-emitting diodes (WLED), affecting light quality. Silica phosphate has good stability, low cost and environmentally friendly features, so it has great application potential. In this paper, a self-activated reddish-orange phosphor Ca3Gd7(PO4)(SiO4)5O2: xSm3+ was prepared by the high-temperature solid-phase method. The phase purity of the sample was verified by X-ray diffraction (XRD). The Rietveld refinement method was used to resolve further the sample structure and the location of the substitution of rare earth ions. The photoluminescence properties were studied in detail using fluorescence spectra, temperature-dependent emission spectra and other characterization methods. The electron transition and energy transfer processes of Gd3+ in Ca3Gd7(PO4)(SiO4)5O2 were analyzed. The fluorescence decay curve of the sample was obtained, which belongs to the double exponential curve, and the decay lifetime depending on the Sm3+ doping concentration was calculated. Furthermore, a WLED device was assembled, and warm white light was obtained, with a spectrum showing characteristic red emission, proving to complement the missing red component of commercial WLEDs. These results indicate that Ca3Gd7(PO4)(SiO4)5O2: xSm3+ phosphor has great potential for application.

Luminescent ionic lattice occupation and wide tunable emission spectra of La2MgZrO6:Bi3+,Eu3+ double perovskite phosphors for white light LED

La 2 Mg 1– x /2 Zr 1– x /2 O 6 : x Bi 3+ ( x = 0.01–0.035, abbreviated as LMZ:Bi 3+ ) and La 2– y Mg 0.99 Zr 0.99 O 6 :0.02Bi 3+ , y Eu 3+ ( y = 0.1–0.11, abbreviated as LMZ:Bi 3+ ,Eu 3+ ) double-perovskite phosphors were prepared through high-temperature solid-phase method. The emission spectrum of LMZ: x Bi 3+ ( x = 0.01–0.035) phosphors excited at 353 nm is asymmetric in the range between 375 and 650 nm, showing strong green light. There are two luminescent centers of [Mg1/Zr2–O 6 ] and [Mg2/Zr1–O 6 ] for Bi 3+ occupation, which were analyzed through different excitation wavelengths, Gaussian fitting peaks, fluorescence decay curves and Rietveld refinement of powder X-ray diffraction data. Through deep study of the luminescent lattices in the LMZ matrix, the green to blue tunning-emission is observed by different excitation wavelengths. In addition, red emission is obtained by co-doping Bi 3+ /Eu 3+ , and adjustable emission was investigated by changing the content of Eu 3+ in the co-doped phosphor formulation, so it is converted from green emission to red emission. The above results demonstrate how to tune emission color by co-doping rare earth ions in the double perovskite phosphor, which is attractive for future applications. The Gaussian deconvolution of the emission spectrum of LMZ:Bi phosphors was performed to obtain two sub-Gaussian components, and the selective site occupancy of Bi 3+ was analyzed. By co-doping Bi 3+ and Eu 3+ , the luminescence intensity of Eu 3+ can be effectively improved.

The Luminescence Properties of the Interstitial Eu2+ in SrB2O4 for UV Light‐Emitting Diode

SrB2O4:Eu2+ is prepared by the high‐temperature solid‐phase method. The structure is characterized by X‐ray diffraction, and the luminescence properties are analyzed using fluorescence spectroscopy and decay curves. SrB2O4:Eu2+ has strong absorption in the UV region and two broadband emissions in the 350–550 nm, located at 374 and 458 nm. The broadband emission around 374 nm belongs to Eu2+ emission at the Sr lattice position, and the emission around 458 nm belongs to interstitial Eu2+ ions. At low concentrations, Eu2+ replaces the position of Sr2+ first, and the emission peak of 374 nm is stronger than that of 458 nm in the emission spectrum. The luminescence at 458 nm enhances significantly as the concentration of Eu2+ ions increases. The fluorescence lifetime confirms the presence of two luminescent centers, the EuSr and the interstitial Eu2+ ions. The temperature dependence luminescence of SrB2O4:Eu2+ is explored, and the activation energy is calculated to be ΔEa = 0.3622 eV. The Commission Internationale de l'Éclairage (CIE) chromaticity coordinates of SrB2O4:Eu2+ are in the blue area. The results indicate that the interstitial Eu2+ benefits the color‐rendering index when SrB2O4:Eu2+ is used as a blue phosphor in UV light‐emitting diode (LED).

Luminescent Properties and Charge Compensator Effects of SrMo0.5W0.5O4:Eu3+ for White Light LEDs

The high-temperature solid-phase approach was used to synthesize Eu3+-doped SrMo0.5W0.5O4 phosphors, whose morphological structure and luminescence properties were then characterized by XRD, SEM, FT-IR, excitation spectra, emission spectra, and fluorescence decay curves. The results reveal that the best phosphor synthesis temperature was 900 °C and that the doping of Eu3+ and charge compensators (K+, Li+, Na+, NH4+) had no effect on the crystal phase change. SrMo0.5W0.5O4:Eu3+ has major excitation peaks at 273 nm, 397 nm, and 464 nm, and a main emission peak at 615 nm, making it a potential red fluorescent material to be used as a down converter in UV LEDs (273 nm and 397 nm) and blue light LEDs (464 nm) to achieve Red emission. The emission spectra of Sr1-yMo0.5W0.5O4:yEu3+(y = 0.005, 0.01, 0.02, 0.05, 0.07) excited at 273 were depicted, with the Eu3+ concentration increasing the luminescence intensity first increases and then decreases, the emission peak intensity of SrMo0.5W0.5O4:Eu3+ achieves its maximum when the doping concentration of Eu3+ is 1%, and the critical transfer distance is calculated as 25.57 Å. When various charge compensators such as K+, Li+, Na+, and NH4+ are added to SrMo0.5W0.5O4:Eu3+, the NH4+ shows the best effect with the optimal doping concentration of 3wt%. The SrMo0.5W0.5O4:Eu3+,NH4+ color coordinate is (0.656,0.343), which is close to that of the ideal red light (0.670,0.333).

Visible and mid-infrared spectral features of Dy3+: SrF2 and Dy3+/Y3+: SrF2 crystals

In this work, Dy3+: SrF2 and Dy3+/Y3+: SrF2 crystals have been grown successfully by the Bridgman-Stockbarger method, and their absorption spectra, visible and mid-infrared (MIR) emission spectra, as well as fluorescence decay curves were analyzed. The advantages of co-doping Y3+ ions on the yellow and MIR emissions of Dy3+ ions were investigated. The intensity of yellow emission in the doubly-doped crystal is ∼ 4 times stronger than that of the singly-doped crystal. The absorption cross-section (0.782 × 10−21 cm2) at 452 nm and emission cross-section (1.156 × 10−21cm2) at 573 nm of Dy3+/Y3+: SrF2 crystal is higher than that of Dy3+: SrF2 crystal related values. Also, compared to Dy3+: SrF2 crystal, the emission cross-section (3.55 × 10−21 cm2) at 2880 nm and fluorescence decay time (1.062 ms) of Dy3+/Y3+: SrF2 crystal are found to be higher. When co-doped Y3+ ions, the distance between Dy3+ ions increased leading to the reduction of cross-relaxation and resonant energy transfer probabilities while enhancing the intensities of yellow and MIR emissions. From all the optical results, it can be inferred that Dy3+: SrF2 and Dy3+/Y3+: SrF2 crystals are potential materials to simultaneously realize yellow and MIR lasing action.

Spectroscopic characterization of Tm:CaYAlO4 shaped crystal fibers grown by the micro-pulling-down method

Tm3+-doped CaYAlO4 (Tm:CALYO) shaped crystals fibers with various doping concentration of 2 at.%, 3 at.%, 5 at.% and 7 at.% have been successfully grown by the micro-pulling-down (μ-PD) method. The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curves were analyzed at room temperature. The absorption bands of 3H6→3H4 transition centered at around 800 nm match well with commercial AlGaAs laser diode pumping sources. For 7 at.% Tm:CALYO crystal fiber, the full width at half maximum (FWHM) of the emission band for π polarization at 1806 nm was 225.4 nm. The fluorescence of 3F4 level decreased strongly as the thulium concentration increased. All the results indicate that Tm:CALYO crystal fibers are promising for ultrashort and tunable laser operation.

Auto-combustion synthesis of Sm3+-doped NaYF4 phosphors: Concentration quenching, optical transition and luminescent properties

A series of NaYF4:Sm3+ phosphors with various Sm3+ concentrations were prepared via an auto-combustion-assisted fluorination method. By the use of X-ray diffraction (XRD), we investigated the phosphors' crystal structure, and pure phase NaYF4:Sm3+ were confirmed. Irregular and agglomerated hexagonal-like particles were observed in FE-SEM images of the phosphors. Moreover, higher magnification TEM images have been collected. Based on fluorescence spectra, the concentration quenching and luminescence thermal stability of NaYF4:Sm3+ phosphors were studied. On the basis of Van Uitert's model, the electric dipole-dipole interaction was proven to be the mechanism for energy transfer between Sm3+ ions. Furthermore, the temperature-dependent fluorescence was investigated in depth, and it was shown that the Arrhenius model-based crossover process can adequately describe the temperature-dependent thermal quenching behavior of 4G5/2 level for Sm3+ in NaYF4 powders. Finally, based on the diffuse-diffraction spectrum and the fluorescence decay curve, the optical transition properties of Sm3+ in the examined NaYF4 phosphors were analyzed in the framework of Judd-Ofelt theory.

Discovery of a novel yellow-orange-emitting low oxygen nitride phosphor Lu6.254Si11N20.762O0.238:Ce3+ for white LED

A novel broadband orange emitting phosphor Lu6.254Si11N20.762O0.238:Ce3+ was prepared via solid state reaction from the series of compounds R6+x/3Si11N20+xO1-x (R = Y and Gd→Lu, x = 1 or 0.762). The results of TEM, XRD and refinements verified the phase purity and crystal structure and also indicated that Ce3+ was successfully integrated into the main lattice to replace the Lu3+ ions. The phosphor Lu6.254Si11N20.762O0.238:Ce3+ presents a broadband bright orange emission peaking at 556 nm with a full width at half-maximum (FWHM) of 110 nm. The unique photoluminescence properties arise from the fact that Ce3+ occupies three different crystallographic sites, which is verified by spectral Gaussian fitting and three-exponential fluorescence decay curves. The PL emission intensity at 150 °C maintained 54.2% of that at room temperature (25 °C), the relatively poor thermal stability of this phosphor may be determined to the octahedrals [LuO6]1, [Lu(O/N)6]2 and [Lu(O/N)7]3 are connected each other so closing, which enhances the nonradiation transition. A w-LED device with CCT (5100 K) and high CRI (96.5) was fabricated by combining commercial blue phosphor SPOCl:Eu2+, green phosphor BSSO:Eu2+, red phosphor SCASN:Eu2+ and LSNO:0.24Ce3+ phosphor with 410 nm n-UV LED. Thus, this work provide an low oxygen nitride phosphor for application in high color rendering and full-spectrum warm white lighting.

Design of Eu2+‐activated broadband orange‐emitting phosphors with excellent luminescent performance for warm WLEDs

AbstractWe report orange‐emitting Sr8La0.5Na0.5Mg1.5(PO4)7:Eu2+ (SLNMPO‐0.5:Eu2+) and Sr7LaNaMg1.5(PO4)7:Eu2+ (SLNMPO‐1:Eu2+) phosphors with broad emission bands covering from 450 to 800 nm. The phosphors can be excited by n‐ultraviolet and blue light efficiently. Their crystal structure, diffuse reflection spectra, photoluminescence (PL) spectra, fluorescence decay curves and thermal stability were investigated systematically. Under the excitation of 365 and 400 nm, SLNMPO‐0.5:Eu2+ and SLNMPO‐1:Eu2+ both exhibit better PL properties and contain more red emissions than SMPO:Eu2+. CIE coordinates of SLNMPO‐0.5:Eu2+ and SLNMPO‐1:Eu2+ under 365 nm excitation are (0.460, 0.497) and (0.457, 0.494), respectively. Furthermore, high‐quality warm white light can be generated by fabricating warm white light‐emitting diode (WLED) devices with 370 nm LED chips, BaMgAl10O17:Eu2+ commercial blue phosphor and orange‐emitting SLNMPO‐0.5:Eu2+ (or SLNMPO‐1:Eu2+) phosphor. The correlated color temperature, Ra and color coordinates are 3880 K, 94.05, (0.3895, 0.3922) and 3736 K, 91.73, (0.4005, 0.4078) for the fabricated WLED devices with SLNMPO‐0.5:Eu2+ and SLNMPO‐1:Eu2+, respectively. The excellent performances indicate that SLNMPO‐0.5:Eu2+ and SLNMPO‐1:Eu2+ have great potential to be attractive candidates in the application of warm WLEDs.

Novel Mn4+-activated NaLiTi3O7 far-red emitting phosphors

Novel and efficient broadband excited far-red emitting NaLiTi3O7:Mn4+ phosphors were synthesized by solid state reaction. Phase purity of NaLiTi3O7 was analyzed using X-ray powder diffraction technique. The luminescence properties and fluorescence decay curves were explored to characterize the phosphors. Under UV/VIS excitation, Mn4+ doped NaLiTi3O7 shows intense emission around 681 nm. To analyze the nephelauxetic impact of Mn4+ in the NaLiTi3O7 host lattice, the crystal field strength (Dq) and the Racah parameters (B and C) are determined. The estimated findings are in good agreement with the linear dependency of 2E on the β1 parameter, which may provide an indicative of the position of the Mn4+ emission based on β1. A Tanabe-Sugano energy level diagram was also used to evaluate the luminescence process. Fluorescence decay measurement was used to discuss the concentration quenching phenomenon.

Probing Red Blood Cell Membrane Microviscosity Using Fluorescence Anisotropy Decay Curves of the Lipophilic Dye PKH26.

Red blood cell (RBC) aggregation and deformation are governed by the molecular processes occurring on the membrane. Since several social important diseases are accompanied by alterations in RBC aggregation and deformability, it is important to develop a diagnostic parameter of RBC membrane structural integrity and stability. In this work, we propose membrane microviscosity assessed by time-resolved fluorescence anisotropy of the lipophilic PKH26 fluorescent probe as a diagnostic parameter. We measured the fluorescence decay curves of the PKH26 probe in the RBC membrane to establish the optimal parameters of the developed fluorescence assay. We observed a complex biphasic profile of the fluorescence anisotropy decay characterized by two correlation times corresponding to the rotational diffusion of free PKH26, and membrane-bounded molecules of the probe. The developed assay allowed us to estimate membrane microviscosity ηm in the range of 100-500 cP depending on the temperature, which paves the way for assessing RBC membrane properties in clinical applications as predictors of blood microrheological abnormalities.