Luminescence Intensity Research Articles

Near-infrared luminescence shift in Ni2+-doped double perovskite phosphors

For applications such as near-infrared (NIR) spectroscopy requiring energy-efficient and compact broadband NIR light sources, a variety of Ni2+-doped phosphors emitting in the 1100–2000 nm range has been developed. However, the commercialization of Ni2+-doped NIR phosphors has not yet been achieved, and material exploration is ongoing. To gain insight into the luminescence properties of Ni2+, including emission wavelength and efficiency influenced by compositional and structural variations, Ni2+-doped double-perovskite AELaMgTaO6:Ni2+ (AE = Ba, Sr, or Ca) ceramic samples were synthesized, and their optical properties were examined. Because the energy of the Ni2+ 3d-3d transition is sensitive to structural variations in the local environment around the Ni2+ ions, we investigated the variation in optical properties by indirect ligand field engineering of NiO6 octahedra following the substitution of alkaline earth ions AE2+. The prepared AELaMgTaO6:Ni2+ samples were Ba-Sr or Ba-Ca complete solid solution systems with cubic-to-monoclinic phase transitions. The broad NIR luminescence band at ∼1350–1700 nm was blue-shifted by ∼100 nm, accompanied by Sr2+ or Ca2+ substitution. The local symmetry of the NiO6 octahedra was reduced from Oh to Ci owing to the phase transition, resulting in an enhancement of the NIR luminescence intensity and an increase in the quenching temperature. This study demonstrated that Ni2+ phosphors with the desired optical properties for NIR spectroscopy applications can be designed by controlling the composition ratio of the host compounds and the resultant variation in the local environment of the solid solution compounds.

Enhancement of upconversion luminescence in NaBiF4: Er3+/Yb3+/Lu3+ for temperature detection

Optical thermometer has got lots of attention by virtue of non-contact, fast response speed, high sensitivity, anti-interference ability, which is less affected by the environment. However, most fluorescent thermometers still suffer from low sensitivity. Here, an optical thermometer based on NaBiF4: Er3+/Yb3+/Lu3+ with enhanced upconversion luminescence is reported. The sample emits strong green light of Er3+ under 980 nm laser excitation and with the increase of Lu3+, the whole luminescence intensity of NaBiF4: 2 % Er3+/20 % Yb3+/ 2.5 % Lu3+ is enhanced by about 3 times, which due to local crystal field distortion. Meanwhile, the lifetime of Er3+ is prolonged and the temperature detection performance is also improved with the substitution of Lu3+. The relative sensitivity reaches a maximum of 0.841 % K−1 at 301 K. The results suggest that it is an optical nanothermometer with great potential.

Synthesis and photoluminescence properties of Ce3+/Tb3+ and Eu3+ ions doped GdB3O6/Ca10(PO4)6(OH)2 Core/Shell particles as well as its cytotoxicity against colon cancer cells

In this study, Ce3+/Tb3+ co-doped, Eu3+ doped GdB3O6 phosphor particles were synthesized by sol-gel method, coated with hydroxyapatite (HAP) and loaded with doxorubicin. Different chelating agents and surfactants (Cetyltrimethylammonium bromide (CTAB), citric acid, glycine, ethylenediaminetetraacetic acid (EDTA) and tartaric acid) were used in the synthesis in order to see their effect on the structure. While single phase Gadolinium triborate, GdB3O6 was obtained by using CTAB in precursor solution in the synthesis and Gadolinium orthoborate, GdBO3 produced when EDTA was used in precursor solution. Other organic molecules added to precursor solution produced mixtures of both phases. The highest photoluminescence intensity was obtained in the Gd0.95Ce0.025Tb0.025B3O6 and Gd0.825Eu0.175B3O6. In order to increase the drug loading efficiency, The Gd0.825Eu0.175B3O6 core was coated with Calcium hydroxyapatite, HAP. The core had an average size of 458.65 nm which increased to 616.85 nm after coating as seen with dynamic light scattering (DLS). Gd0.825Eu0.175B3O6@HAP particles were loaded with 7.82 % ± 0.80 wt doxorubicin and the release was studied at 37 °C in pH 7.4 phosphate-buffered saline (PBS) and pH 5.5 acetate buffer solutions. The total number of moles of drug released versus luminescence intensity was measured during the release studies and real-time imaging studies were carried out. Finally, cytotoxicity experiments were performed on HCT-116 colon cancer cells.

Aggregation-Induced Enhanced Electrochemiluminescence Resonance Energy Transfer Biosensor for Ultrasensitive Detection of Carcinoembryonic Antigen Based on Donor-Acceptor Organic Nanoparticles.

Aggregation-induced electrochemiluminescence (AIECL) combines the merits of aggregation-induced emission (AIE) and electrochemiluminescence (ECL), which has become a research hot spot in recent years. Therefore, we synthesized a novel AIE compound (Z)-3-(4-(2-butyl-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)phenyl)-2-(4-(1,2,2-triphenylvinyl)phenyl)acrylonitrile (TPENI) with a donor-acceptor (D-A) structure, that is, a simple peripheral modification of 4-(2-butyl-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl) benzaldehyde (NI-CHO) with AIE-active tetraphenylethylene (TPE) to achieve the transition of NI-CHO from aggregation-caused quenching (ACQ) to an AIE molecule. When TPENI was in the aggregated state, the luminescence intensity was significantly enhanced due to the TPE structural unit restricting the free rotation of the intramolecular benzene ring, as well as the π-π stacking interactions of the molecules, which was conducive to the preparation of TPENI NPs as ECL materials. Satisfactorily, we found that the ECL intensity of TPENI NPs was increased by about 4.8-fold compared with that of the molecules dispersed in organic solution, and the stability reached about 1000 s. Based on the excellent ECL properties of TPENI NPs, an "on-off-on" ECL biosensor with a wider detection range (1 fg/mL to 100 ng/mL) and a lower detection limit of 0.20 fg/mL (S/N = 3) was proposed for sensitive analysis of a carcinoembryonic antigen (CEA). Overall, this work provided a new approach to the realization of AIECL and laid the foundation for the application of naphthalimide derivatives in ECL.

Study on Synergistic Radiation Yellow Light of Strontium Nitrate/Barium Nitrate-Based Illuminant

ABSTRACT In order to change the problem of a single yellow light color emitted by sodium salt illuminant. Based on the principle of color-light mixing and the mechanism of synergistic radiation of double-dyeing flame agents, four groups of strontium nitrate/barium nitrate-based yellow light illuminant formulations with different ratios were designed, which were calculated and comparatively analyzed by REAL and MATLAB software through experiments. From the experimental results, it can be seen that the virtual main wavelength of strontium nitrate/barium nitrate-based yellow light illuminant was adjusted in the range of 579 nm-591 nm, and the color ranged from light yellow to golden yellow, among which the best formulation was strontium nitrate/barium nitrate/magnesium/worm gum/polyvinyl chloride with the ratio of 50.25/16.25/13.5/2.5/17.5. The oxygen balance of this formulation was −0.130 g-g-1, and the combustion temperature was 2790.88 K. The color light emitters were Sr, SrO, SrOH, SrCl, Ba, BaO, BaOH, BaCl, the color coordinates were (0.5256, 0.3988), the virtual dominant wavelength was 591 nm, the color purity was 0.79, and the luminescence intensity was 247,893.18 cd, and the combustion time was 6.8s.

Effective Enrichment of Free Radicals through Nanoconfinement Boosts Electrochemiluminescence of Carbon Dots Derived from Luminol.

Local enrichment of free radicals at the electrode interface may open new opportunities for the development of electrochemiluminescence (ECL) applications. The sensing platform was constructed by assembling ECL-emitting luminol derived carbon dots (Lu CDs) onto the heterojunction Tungsten disulfide/Covalent organic frameworks (WS2@COF) for the first time, establishing a nanoconfinement-reactor with significantly heightened ECL intensity and stability compared to the Lu CDs-H2O2 system. This enhanced performance is credited to the COF domain's restricted pore environment, where WS2@COF exhibits a more negative adsorption energy for H2O2, effectively enriching H2O2 in the catalytic edge sites of WS2. Furthermore, the internal electric field at the WS2 and COF interface accelerates electron flow, boosting WS2's catalytic activity and achieving domain-limited catalytic enhancement of ECL. Self-designed DNA nanomachines combined with cascading molecular keypad locking mechanisms are integrated into the biosensors, effectively guaranteeing the accuracy of the sensing process while providing crucial safeguards for molecular diagnostics and information security applications. In essence, this innovative approach represents the first system to enhance local free radical concentrations by enriching co-reactants on the electrode surface through nanoconfinement catalysis, yielding heightened ECL luminescence intensity. The potential impact of this novel strategy and sensing mechanism on real-bioanalysis applications is promising.

Rational growth of highly luminescent CsPbBr3 nanoparticles via alkali metal doping-enabled modification of glass networks

Embedding halide perovskite nanoparticles (NPs) into glasses can be regarded as a feasible approach to improve their long-term stability when they are exposed to air or moisture. However, it remains elusive to rationally grow highly luminescent halide perovskite NPs owing to poor understanding of the relationship between glass network topology and NP precipitation. Here, by introducing alkali metal ions as “B-phase structural scissors”, the precipitation and aggregation of NPs are optimized based on glass network topology modulation, which boosts their photoluminescence performance. After Li doping, the photoluminescence quantum yield of CsPbBr3 perovskite NPs embedded in glass increases by 39% with respect to that of the undoped counterpart. The alkali metal ions are utilized to reduce thermal activation energy from 130.04 KJ mol-1 to 125.35 KJ mol-1 according to thermodynamics analysis, which corresponds to an increase in the size of the NPs. Benefiting from excellent chemical inertness, the luminescence intensity of as-made CsPbBr3 NP embedded glass retains near unity after soaking them in water for 180 days. The utilization of alkali metals as a facile strategy to modify the glass network enables improved performance of target NPs, thereby providing deeper insights into the design of host-dependent NP-functionalized glass.

Effective Enrichment of Free Radicals through Nanoconfinement Boosts Electrochemiluminescence of Carbon Dots Derived from Luminol

Local enrichment of free radicals at the electrode interface may open new opportunities for the development of electrochemiluminescence (ECL) applications. The sensing platform was constructed by assembling ECL‐emitting luminol derived carbon dots (Lu CDs) onto the heterojunction Tungsten disulfide/Covalent organic frameworks (WS2@COF) for the first time, establishing a nanoconfinement‐reactor with significantly heightened ECL intensity and stability compared to the Lu CDs‐H2O2 system. This enhanced performance is credited to the COF domain's restricted pore environment, where WS2@COF exhibits a more negative adsorption energy for H2O2, effectively enriching H2O2 in the catalytic edge sites of WS2. Furthermore, the internal electric field at the WS2 and COF interface accelerates electron flow, boosting WS2's catalytic activity and achieving domain‐limited catalytic enhancement of ECL. Self‐designed DNA nanomachines combined with cascading molecular keypad locking mechanisms are integrated into the biosensors, effectively guaranteeing the accuracy of the sensing process while providing crucial safeguards for molecular diagnostics and information security applications. In essence, this innovative approach represents the first system to enhance local free radical concentrations by enriching co‐reactants on the electrode surface through nanoconfinement catalysis, yielding heightened ECL luminescence intensity. The potential impact of this novel strategy and sensing mechanism on real‐bioanalysis applications is promising.

Effect of inorganic compound size on the relative gain of polymer-based optical waveguide amplifiers

Polymer based waveguide amplifiers are the key devices to improve the performance of integrated communication systems. However, due to their comparatively low relative gain, their widespread practical application has been limited. In polymer based optical waveguide amplifiers, the size of inorganic compounds in the composite gain media has a significant impact on the gain performance of the amplifier. Up to now, there has been limited research on the size influence of inorganic compound on the gain variation in organic polymer based optical waveguide amplifiers. In this study, a series of NaLu0.8-xYxF4: Yb, Er-PMMA composite polymer were used as gain media to prepare organic waveguide amplifiers working in the C-band (1530–1565 nm). The size of NaLu0.8-xYxF4: Yb, Er compounds varies between 20 nm and 150 nm. In the polymer based optical waveguide amplifiers, variations in the size of the inorganic NaLu0.8-xYxF4:Yb,Er compound affects not only the C-band emission intensity but also the relative gain. When the size of the inorganic compound is 65 nm, the composite gain media exhibits the maximum emission peak intensity at 1550 nm and the corresponding device achieves a maximum relative gain of 19.3 dB/cm. Our results show that the size of inorganic compounds affects the variation of luminescence intensity and ultimately the gain of waveguide amplifiers. The gain of future polymer optical waveguide amplifiers can be improved by this method.

Efficient and Near-Zero Thermal Quenching Cr3+-Doped Garnet-Type Phosphor for High-Performance Near-Infrared Light-Emitting Diode Applications.

In recent years, near-infrared (NIR) phosphors have attracted great research interest due to their unique physical properties and broad application prospects. However, obtaining NIR phosphors with both high quantum efficiency and excellent thermal stability remains a great challenge. In this study, novel NIR Ca3Mg2ZrGe3O12:Cr3+ phosphors were successfully prepared using a high-temperature solid-phase method, and the structure and luminescent properties of the material were systematically investigated. Ca3Mg2ZrGe3O12:0.01Cr3+ emits NIR light in the range of 600 to 900 nm with a peak at 758 nm and a half-height width of 89 nm under the excitation of 457 nm blue light. NIR luminescence shows considerable quantum efficiency, and the internal quantum efficiency of the optimized sample is up to 68.7%. Remarkably, the Ca3Mg2ZrGe3O12:0.01Cr3+ phosphor exhibits a near-zero thermal quenching behavior, and the luminescence intensity of the sample at 250 °C maintains 92% of its intensity at room temperature. The mechanism of high thermal stability has been elucidated by calculating the Huang Kun factor and activation energy. Finally, NIR pc-LED devices prepared from Ca3Mg2ZrGe3O12:0.01Cr3+ phosphor with commercial blue LED chips have good performance, proving that this Ca3Mg2ZrGe3O12:0.01Cr3+ NIR phosphor has potential applications in night vision and biomedical imaging.

NIR‐induced upconversion‐assisted photopolymerization: Key factors, challenges, and future directions

AbstractNIR‐induced upconversion‐assisted photopolymerization has gained growing attention in the past two decades because of its numerous advantages over conventional UV/visible photopolymerization and two‐photon polymerization processes. However, research in this area is still in its early stages. To extend the practical application of NIR‐induced radiation curing, it is essential to optimize the factors affecting the photopolymerization reactions. Researchers have been constantly trying to improve these factors to tune the photo‐physical characteristics (luminescence intensity and color) of upconversion particles (UCPs), enhance curing depths and degree of double bond conversion (DC), and investigate the application of UCPs in emerging fields. In this review, first, a brief discussion of the upconversion mechanisms and upconversion efficiency is provided. Then, a detailed discussion of the factors influencing the upconversion‐assisted photopolymerization comprising UCP nature and characteristics, UCP content, presence of fillers/pigments/additives, laser intensity, photoinitiator content, and maximum absorption wavelength of photoinitiator is provided, and recent progress in improving these factors is presented. Finally, the advantages and drawbacks of the UC‐initiated polymerization are discussed, and perspectives for future directions are suggested.Highlights NIR‐induced upconversion‐assisted photopolymerization garners growing interest. Influential factors in upconversion‐assisted photopolymerization are thoroughly discussed. The recent progress on improving these factors and the future directions are provided.

Fluoride Hafnium/Zirconium-Softened Nanoprobes for Near-Infrared-IIb and CT Dual-Mode Bioimaging.

Fluoride-based lanthanide-doped nanoparticles (LDNPs) featuring second near-infrared (NIR-II, 1000-1700 nm) downconversion emission for bioimaging have attracted extensive attention. However, conventional LDNPs cannot be degraded and eliminated from organisms because of an inert lattice, which obstructs bioimaging applications. Herein, the core-shell LDNPs of Na3HfF7:Yb,Er@CaF2:Ce,Zr(Hf) [labeled as Zr(Hf)Ce-HC] with pH-selective and tunable degradability were synthesized for dual-modal bioimaging. Notably, the "softening" lattice of the Na3HfF7 matrix and different Zr4+(Hf4+) doping amounts in the shell enable Zr(Hf)Ce-HC with acidity-dependent and tunable degradability. After coating of an optimized Ce3+-doped CaF2:Zr shell, the near-infrared-IIb (NIR-IIb, 1500-1700 nm) luminescence intensity of ZrCe-HC is enhanced by 5.2 times compared with that of Na3HfF7:Yb,Er. The Hf element with high X-ray attenuation allows ZrCe-HC as the contrast agent for computed tomography (CT) bioimaging. The modification of oxidized sodium alginate endows ZrCe-HC with satisfying biocompatibility for NIR-IIb/CT dual-modal bioimaging. These findings would benefit the bioimaging applications of degradable fluoride-based LDNPs.

Structural, morphological, optical and down-conversion studies of NaLaMgTeO6:Dy3+ single phase phosphor for white light emitting applications and solar spectral converter for photovoltaic applications

Researches on rare earth activated phosphors in solid state lighting and enhancement in efficiency of solar cells pave attention to develop efficient phosphor materials. In the present work, Dy3+ doped NaLaMgTeO6 phosphors are synthesized using solid state reaction method. The structural studies using XRD analysis confirmed the successful formation of the compound. SEM analysis reveals that the particles are closely packed, which in turn exhibit intense luminescence intensity due to low scattering and high packing density. Elemental configuration were analyzed using EDS analysis. FTIR analysis revealed the vibrational bands of the host matrix. Optical energy bandgap was calculated using DRS spectra. The luminescence characteristics of the samples were investigated using excitation and emission spectra. Upon most intense 351 and 388 nm excitation, sharp yellow emission peak at 572 nm dominates blue emission at 478 nm, further reveals that Dy3+ ions occupy low symmetry site in the host lattice. The optimum concentration of Dy3+ in the present host is x = 0.04 mol and concentration quenching is due to dipole-quadrupole interaction of adjacent Dy3+ ions. The thermal quenching phenomenon is studied using temperature dependent photoluminescence analysis. The CIE chromaticity coordinates and CCT values conclude NaLaMgTeO6:Dy3+ phosphors are good candidate for cool near-white light emitting materials for outdoor illumination. The study on solar spectral response and down-conversion property of the synthesized phosphor demonstrate its applicability as solar spectral converters in solar cell applications.

Wavelet optical flow velocimetry of a scramjet combustor using high-speed frame-straddling focusing schlieren images

Scramjet combustors feature ultra-high-speed turbulent reacting flows with high temperatures and intense luminescence. Measurement of velocity fields under such extreme conditions presents great challenges. The present work demonstrated a seedless velocimetry approach using focusing schlieren images (FSIs) of high spatiotemporal resolution in a scramjet engine. Two fuel mass flow rates (Case1 and Case2) were investigated with corresponding global equivalence ratios of 0.27 and 0.13, respectively. The FSIs enabled by the employment of a high-speed pulsed LED light source are characterized by an effective exposure of 100 ns, and a 500-ns frame-straddling time interval with full resolution of 1280 × 800 pixels recorded at 76 kHz. The 100-ns exposure allows for capturing of transient high-speed flow motion without blurring, and the 500-ns time interval ensures an appropriate spatiotemporal correlation between subsequent schlieren images for high-speed reacting flows. A wavelet-based optical flow velocimetry (wOFV) algorithm was developed and applied to the FSIs. In contrast to the correlation-based algorithms widely employed in PIV for distinct particles, the wOFV algorithm suits better FSIs with continuous variation in brightness. The maximal velocities in the main duct of the scramjet combustor were measured to be approximately 550 m s-1 and 1100 m s-1 for Case 1 and Case2, suggestively corresponding to subsonic and supersonic combustion modes, respectively. The measured velocity inside the cavity is generally below 200 m s-1 for both cases. Recirculation regions and their dynamic motions inside the cavity were well resolved. In summary, the development of the novel velocimetry approach holds great potential for applications in extreme flow conditions. Novelty and Significance Statement: Present work demonstrates a seedless velocimetry approach based on high-speed frame-straddling focusing schlieren imaging coupled with the novel wavelet optical flow velocimetry (wOFV) algorithm. Velocity field measurement realized in a scramjet combustor with high spatiotemporal resolution (1280 × 800 pixels at 38 kHz) for the first time, showing great abilities to accommodate wide velocity range and to resolve dynamic flow characteristics with potentials for broader future applications.

Maximizing Upconversion Luminescence of Co-Doped CaF₂:Yb, Er Nanoparticles at Low Laser Power for Efficient Cellular Imaging.

Upconversion nanoparticles (UCNPs) are well-reported for bioimaging. However, their applications are limited by low luminescence intensity. To enhance the intensity, often the UCNPs are coated with macromolecules or excited with high laser power, which is detrimental to their long-term biological applications. Herein, we report a novel approach to prepare co-doped CaF2:Yb3+ (20%), Er3+ with varying concentrations of Er (2%, 2.5%, 3%, and 5%) at ambient temperature with minimal surfactant and high-pressure homogenization. Strong luminescence and effective red emission of the UCNPs were seen even at low power and without functionalization. X-ray diffraction (XRD) of UCNPs revealed the formation of highly crystalline, single-phase cubic fluorite-type nanostructures, and transmission electron microscopy (TEM) showed co-doped UCNPs are of ~12 nm. The successful doping of Yb and Er was evident from TEM-energy dispersive X-ray analysis (TEM-EDAX) and X-ray photoelectron spectroscopy (XPS) studies. Photoluminescence studies of UCNPs revealed the effect of phonon coupling between host lattice (CaF2), sensitizer (Yb3+), and activator (Er3+). They exhibited tunable upconversion luminescence (UCL) under irradiation of near-infrared (NIR) light (980 nm) at low laser powers (0.28-0.7 W). The UCL properties increased until 3% doping of Er3+ ions, after which quenching of UCL was observed with higher Er3+ ion concentration, probably due to non-radiative energy transfer and cross-relaxation between Yb3+-Er3+ and Er3+-Er3+ ions. The decay studies aligned with the above observation and showed the dependence of UCL on Er3+ concentration. Further, the UCNPs exhibited strong red emission under irradiation of 980 nm light and retained their red luminescence upon internalization into cancer cell lines, as evident from confocal microscopic imaging. The present study demonstrated an effective approach to designing UCNPs with tunable luminescence properties and their capability for cellular imaging under low laser power.

Robust Luminescent Pyrene-Based Metal-Organic Framework Hydrogel as a pH-Responsive Fluorescence Emitter for Sensitive Immunoassay of Cardiac Troponin I.

Despite many luminescent advantages including outstanding absorption coefficient and high quantum yield, pyrene and its derivatives have been suffering from a dramatic aggregation-caused quenching (ACQ) effect. Although the dramatic ACQ effect of pyrene-based fluorophores has been restrained in pyrene-doped metal-organic frameworks (MOFs), the low loading of fluorescent (FL) units substantially impedes the improved luminescent behaviors. Herein, pyrene-based MOFs hydrogel was synthesized with a high loading of pyrene as the unique organic linker blocks instead of a dopant in MOFs. The gel matrix contributed to rigidifying the location of the FL emitters and achieving intensive FL emission and high luminescent stability and therefore efficiently overcoming the ACQ effect. Furthermore, the protonation of pyrene in the MOFs hydrogel remarkably decreased the luminescent intensity, which endowed the FL hydrogel with highly pH-responsive activity in the broad range (pH 4-10). Interestingly, glucose oxidase was immobilized into ZIF-8 as a highly efficient luminescent quencher, which contributed to catalyzing the form of gluconic acid and thus drastically quenching the FL signal of the MOFs hydrogel. Furthermore, the emitter-quencher pair of pyrene-based MOFs hydrogel and glucose oxidase was successfully employed to develop an ultrasensitive FL immunoassay platform for cardiac troponin I (as a model analyte). The limit of detection for cardiac troponin I was 5.2 pg/mL (3σ). The proof-of-principle study demonstrated the thrilling auxiliary effect of tailorable MOFs hydrogel on boosting the feasibility of aqueous insoluble FL chromophores for trace analysis.

Single-Band Ratiometric Thermometry Strategy Based on the Completely Reversed Thermal Excitation of O2- → Eu3+ CTB Edge and Eu3+ 4f → 4f Transition.

Single-band ratiometric (SBR) strategies present huge potential in the field of luminescence intensity ratio thermometry owing to their excellent signal discrepancy and appealing simplicity. Herein, we employ the approach of Na replacing Li in the LiYGeO4:Eu3+ phosphor to regulate the thermal stability of the O2- → Eu3+ charge-transfer band (CTB) and obtain significant thermal enhancement of luminescence under CTB edge excitation. Combined with the obvious thermal quenching of luminescence under ground-state absorption excitation, the ratio of the single emission band increases by 18 times when the temperature increases from 300 to 570 K. Therefore, such excitation-wavelength-dependent diametrically opposite thermal luminescence behaviors enabled SBR thermometry, whose maximum relative sensitivity can reach up to 3.6% K-1. We demonstrate that the O2- → Eu3+ CTB thermal red-shifts and enhancements are particularly attractive for SBR thermometry with high sensitivity by utilizing the diametrically reversed thermal excitation between the O2- → Eu3+ CTB edge and the 4f → 4f transition of Eu3+. These advances have opened up a novel horizon for the development of high relative sensitivity and performance of the SBR thermometry strategy.

Concentration- and temperature-dependent luminescence mechanisms and fluorescence dynamic temperature sensing of NaY(MoO4)2:Tb3+ phosphors

High-temperature solid-state reaction technique was used to prepare NaY(MoO4)2:Tb3+ phosphors with different Tb3+ concentrations. XRD patterns showed that the prepared samples contained only single-phased compound NaY(MoO4)2. The concentration-dependent green luminescent intensity of Tb3+ was studied, and it was found that the concentration quenching process is in charge of Ozawa's model. The concentration-effect of luminescence decay of 5D4 level was explained by the Auzel's self-generated quenching theory. Starting from the Reisfeld's theory, the analysis on the luminescence decays also indicated exchange interaction was responsible for the concentration quenching. Temperature dependences of the green emission intensity and decay were comprehended based on the crossover mechanism. A novel temperature sensing technique rooting in the fluorescence dynamics of 5D4 level of Tb3+ in NaY(MoO4)2 was proposed, and the absolute and relative sensitivities were deduced and assessed.

Polarized luminescence of bound excitons in Cu2O single crystal

Photoluminescence was studied for Cu2O (100) single crystal in the 1.2–1.9 eV spectral range under polarized laser excitation 532 nm at low temperature. Polarized luminescence and negative thermal quenching were detected for the emission bands at 1.34, 1.53 and 1.7 eV, assigned to the bound excitons localized at copper vacancies VCu and oxygen vacancies VO+, VO2+, correspondingly. The complex structure of the most intense emission bands 1.34 and 1.7 eV containing spectrally shifted orthogonally polarized subbands was identified. Luminescence polarization degree, intensity and spectral position of the subbands depend on temperature as well as on the excitation light density and vary from point to point. The origin of the polarized luminescence and negative thermal quenching of the bound excitons in Cu2O crystal is discussed.

Thermal-dependent luminescence in Er³⁺-doped BaHfO₃ and SrHfO₃ perovskites: Improve temperature sensing via Ba-Sr exchange

The luminescence process behavior stimulated by temperature changes is examined by using the theory of thermally coupled energy levels of erbium ion (Er3+) 2H11/2 and 4S3/2. The different mechanisms and environments are compared and elucidated in crystalline structures of BaHfO3 and SrHfO3 as a product of the atomic exchange of Ba2+ for Sr2+ respectively. The undoped and erbium-doped materials were synthesized by hydrothermal route, the erbium-doped materials were impurified with different Er3+ concentrations; 0.25, 0.5, 1, 3, and 5 at.%. X-ray diffraction (XRD) patterns of both materials present a cubic perovskite-type phase, with space group Pm-3m. High-resolution transmission electron microscopy (HRTEM) micrographs show for both materials the presence of nanocrystals with straight profiles and with an approximate size of 36 nm for BaHfO3 and 32 nm for SrHfO3. The room temperature photoluminescent emission spectra shows the highest luminescent intensity at 1 % Er3+ for both materials, showing different spectral characteristic shapes for each material, due to the different electrostatic forces produced by either Ba2+ or Sr2+ ions surrounding Er3+. Using the “Fluoresce Intensity Ratio” (FIR) technique, the temperature sensing properties of these materials were analyzed and compared from 290 to 330 K covering the well-known physiological range (298.15 K–318.15 K). Both materials, BaHfO3:1%Er3+ and SrHfO3:1%Er3+, show dependence to temperature changes, and the experimental energy gap (ΔE) was used to improve (or decrease) the temperature sensing properties. The theoretical ΔE, maximum relative sensitivity (SRMAX), and the resolution in temperature (δT) were obtained, for BaHfO3: 1 % Er3+ these values were: ΔE = 505.73 cm−1, SRMAX = 0.87 % K−1 at 288.5 K and δT = 0.02 K, while for SrHfO3: 1 % Er3+ the values were: ΔE = 649.21 cm−1, SRMAX = 1.12 % K−1 at 288.5 K and δT = 0.01 K.