High-temperature Luminescence Research Articles

Unlocking structural and photoelectric properties of lead-free double perovskites at high temperature

The lead-free double perovskite, increasingly sought for optoelectronic pursuits, is distinguished by its notable stability, optical properties, and non-toxic characteristic. An extensive inquiry into the structural and photoelectric properties of Cs2NaBiCl6 at heightened temperatures was undertaken using experimental evaluations and theoretical computations. The compound Cs2NaBiCl6, synthesized using a hydrothermal technique, was confirmed via various analytical methods. Advanced techniques such as high-temperature X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, and selected area electron diffraction were employed for the investigation of its crystal structure. Further investigation of microstructure was undertaken using electron microscopes. High-temperature luminescence stability disclosed a high exciton binding energy of 326 meV. The Huang-Rhys factor (6.4) denotes a robust electron-phonon coupling effect and facile formation of self-trapped excitons (700 nm). Applied first principles render valuable insight into structural and photoelectric nuances, notably at escalated temperatures. Cs2NaBiCl6 as an indirect bandgap semiconductor and details the experimental and theoretical bandgap, which exhibits an increasing trend before subsequently declining at elevated temperatures. These results strongly support the material's high-temperature stability, emphasizing its applicability in applications such as rare-earth-doped phosphors. The dynamic stability of the material, evidenced by its mechanical performance, further underscores its potential for application in photoelectric devices.

Frenkel Defect-modulated Anti-thermal Quenching Luminescence in Lanthanide-doped Sc2 (WO4 )3.

Although large amount of effort has been invested in combating thermal quenching that severely degrades the performance of luminescent materials particularly at high temperatures, not much affirmative progress has been realized. Herein, we demonstrate that the Frenkel defect formed via controlled annealing of Sc2 (WO4 )3 :Ln (Ln=Yb, Er, Eu, Tb, Sm), can work as energy reservoir and back-transfer the stored excitation energy to Ln3+ upon heating. Therefore, except routine anti-thermal quenching, thermally enhanced 415-fold downshifting and 405-fold upconversion luminescence are even obtained in Sc2 (WO4 )3 :Yb/Er, which has set a record of both the Yb3+ -Er3+ energy transfer efficiency (>85 %) and the working temperature at 500 and 1073 K, respectively. Moreover, this design strategy is extendable to other hosts possessing Frenkel defect, and modulation of which directly determines whether enhanced or decreased luminescence can be obtained. This discovery has paved new avenues to reliable generation of high-temperature luminescence.

Glowing performance for a luminescence thermometry technique

Doubling the thermalizations in the emission measurement doubles sensitivity for high temperature luminescence thermometry applications.

Understanding and Hindering Ion Migration in Er,Yb:LiLuF4 Core–Shell Nanoparticles for Nanothermometers with Enhanced Photoluminescence

Developing core–shell nanoparticles is a common approach to improve the luminescence performance of nanomaterials, as an inert shell shields the core, which is doped with luminescent ions, from the quenching influence of the environment. Core-only nanoparticles are susceptible to solvent overtones, which can couple with the emissive dopants on the surface and quench their intensity. This is undeniably highly undesired for any luminescence application. It was recently shown by some of us that previously unreported ion migration takes place in 2%Er,18%Yb:LiLuF4@LiLuF4 core–shell nanoparticles, which was proven both with energy-dispersive X-ray (EDX) maps and high-temperature luminescence measurements. These findings lead us to the investigation presented here, which explores in detail how to hinder the migration of Er3+ and Yb3+ ions in LiLuF4 and LiYF4 hosts by implementing an interface region. First, different synthesis routes were explored to see if the chosen approach had any effect on the ion migration process from the doped core into the inert shell in a homogeneous core–shell system. Next, a LiYF4 inert shell was grown around a 2%Er,18%Yb:LiLuF4 core forming a heterogeneous core–shell system. We observed that the heterogeneous 2%Er,18%Yb:LiLuF4@LiYF4 and LiLuF4@2%Er,18%Yb:LiYF4 core–shell combinations showed significantly less ion migration based on EDX maps and high-temperature luminescence measurements exhibiting a behavior similar to the well-studied 2%Er,18%Yb:NaYF4@NaYF4 core–shell structures that, according to previous studies, show no or very little ion migration.

Crystal structure and temperature sensing performance of the novel Sr2Y8(1-x-y)(SiO4)6O2:xCe3+,yTb3+ thermometric phosphors

For the research of the thermometric performance, a series of Sr2Y8(1-x-y) (SiO4)6O2:xCe3+,yTb3+ phosphors were synthesized with the solid-state reaction method at N2/H2 atmosphere. The crystal structure, room and high temperature photoluminescence spectra, luminescence decay, CIE variation, energy transfer and thermometric performance have been investigated. With the ultraviolet light excitation, both the Ce3+ broadband spectrum and Tb3+ line spectra have been observed. With the increase of the Tb3+ concentration, the emission color chromaticity varies from dark blue to bright green for the series of Sr2Y8(1–0.07-y)(SiO4)6O2:0.07Ce3+,yTb3+ phosphors. Under high temperature, the Ce3+ emission intensity quenches faster than that of Tb3+. Based on the different temperature quenching speeds of Ce3+ and Tb3+, the fluorescence intensity ratio technique was used to evaluate the thermometric performance of the series of Sr2Y8(1–0.07-y) (SiO4)6O2:0.07Ce3+,yTb3+ phosphors. During the temperature range of 298–498 K, the maximum relative sensitivity values of the phosphors of yTb = 0.05, 0.08, 0.1, 0.15, 0.2, 0.25 were calculated as 0.65, 0.69, 0.74, 0.71, 0.66, 0.6% K−1, which are much better than the recommended value of 0.30% K−1 for the practical application. The physical mechanisms for the Ce3+/Tb3+ excitation and emission, energy transfer and temperature quenching have been discussed. Sr2Y8(1-x-y) (SiO4)6O2:xCe3+,yTb3+ phosphors are the candidate thermometric probes for the non-contact temperature sensing applications.

Stability enhancement of InP quantum dot/poly(methyl methacrylate) nanocomposites for light-emitting diode applications by grafting thermoresponsive poly(N-isopropylacrylamide)

Nanocomposites containing thermoresponsive poly(N-isopropylacrylamide)-grafted InP QDs exhibit enhanced stability against high temperature and humidity and luminescence properties.

Quenching in Mn4+-Complex Fluoride Phosphors: Initial Relationships Based upon NaKSiF6:Mn4+

Mn4+-doped complex fluoride compositions are an important class of phosphors that provide narrow-band 2E→4A2 red emission for liquid crystal display (LCD) backlighting and illumination light emitting diodes (LEDs). In this report, we discuss the high temperature quenching in these phosphors, focusing on the NaKSiF6:Mn4+ phase that has a lower quenching temperature by >75K versus the two end-member compositions, K2SiF6:Mn4+ and Na2SiF6:Mn4+. Measurements of the 2E electron-phonon coupling through line shift versus temperature measurements do not give significant differences between NaKSiF6:Mn4+ and other Mn4+-doped complex fluoride phosphors with higher quenching temperatures. We tentatively attribute the stronger quenching in NaKSiF6:Mn4+ to additional distortion in the excited 4T2 state that is thermally populated from the 2E level at high temperatures. In addition, we discuss potential trade-offs between high temperature luminescence quenching and faster 2E→4A2 emission lifetimes.

Silica encapsulated LuAG:Pr3+ nanocrystals by surfactant assisted co-precipitation and microwave calcination: Structural, growth mechanism, photoluminescence and thermoluminescence properties

Surface encapsulation of nanophosphors by nanoscale silica (SiO2) coating is an effective strategy to enhance the luminescence property for opto-electronic application. The present work investigates about the synthesis of silica encapsulated LuAG:Pr3+ nanocrystals by surfactant assisted co-precipitation and rapid microwave calcination. The ultrafast microwave heating of silica encapsulated LuAG:Pr at 1050 °C for 10 min resulted in the formation of well-crystallized nanocrystals in cubic phase that evidenced by XRD Rietveld analysis. FE-SEM and HR-TEM examinations revealed the formation of ∼6 nm nanoscale silica film encapsulation on LuAG:Pr nanocrystals. EDS elemental and XPS investigations confirmed the presence of SiO2 layer encapsulation on the surface of nanoparticle. The nanoscale silica encapsulated LuAG:Pr nanocrystals displayed two-fold enhancement in luminescence red emission than uncoated counterpart nanocrystals. The continuous nanoscale silica coating served as an integrating sphere that confides incident photons by means of multiple reflections and improved the light extraction. Temperature dependent photoluminescence analysis of the silica coated LuAG:Pr3+ nanocrystal was also studied. It revealed the original emission intensity was stable up to 425 K and start decreasing to 55% at 520 K, which promoted stable high temperature luminescence behavior. Thermoluminescence investigation was also performed for uncoated and silica-coated LuAG:Pr nanocrystals by irradiated them with high energy γ-ray (60Co) source at 200 Gy for 2 min. The trap-depth in terms of activation energy (E) and frequency factor (s) of the gamma ray irradiated nanoparticles was estimated by computerized GCD operation.

Optical pressure nano-sensor based on lanthanide doped SrB2O4:Sm2+ luminescence – Novel high-pressure nanomanometer

A new, non-contact optical sensor of pressure based on the SrB2O4:Sm2+ nanoparticles has been successfully synthesized via a simple and low-cost Pechini method. The obtained nanomaterial was thoroughly characterized using powder X-ray diffraction, transmission electron microscopy, and Raman and luminescence spectroscopies, including high-pressure and high-temperature extreme conditions measurements. Compression of the material leads to a significant red-shift of the intraconfigurational 5D0→7FJ (J = 0−3) emission bands, and to an increase of the Raman mode energies, whose shift rates as a function of pressure were determined. The shift of the extremely sharp and the most intense 5D0→7F0 emission band (Δλ ≈0.24 nm/GPa; Γ (FHWM) ≈0.15 nm) has been used for the determination of the pressure calibration curve. The high-temperature luminescence measurements revealed a desirably weak temperature dependence of the peak spectral position, which was included in the determined pressure calibration curve. The SrB2O4:Sm2+ nanomaterial studied exhibits a negligible temperature-induced emission lines broadening, and relative low thermal quenching of luminescence. The use of such Sm2+-based contactless pressure nano-sensor allows a very accurate pressure sensing ( ± 0.01 GPa), in the sub-micro sized regions, both at low and high temperature conditions.

Nanosecond time‐resolved Raman spectroscopy for solving some Raman problems such as luminescence or thermal emission

AbstractRaman spectroscopy is experimentally widely available and relatively simple to perform at room temperature. Some difficulties nevertheless remain, as for instance separating some various contributions from the Raman spectrum, such as thermal emission for high temperature measurements or luminescence. Here, an optimized time‐resolved Raman spectroscopy system based on a gated detection and a nanosecond pulsed laser excitation (30 ns width, 532 nm wavelength) is described. The system allows contactless Raman measurements, at high temperatures, of some materials such as zirconia and yttria. An example of Raman spectra collected on yttria at very high temperature up to 2100 °C is provided. This optimized system may also be used to discriminate between Raman scattering and luminescence as demonstrated in zirconia material.

Enhancement of Exciton Emission from Multilayer MoS2 at High Temperatures: Intervalley Transfer versus Interlayer Decoupling.

It is very important to obtain a deeper understand of the carrier dynamics for indirect-bandgap multilayer MoS2 and to make further improvements to the luminescence efficiency. Herein, an anomalous luminescence behavior of multilayer MoS2 is reported, and its exciton emission is significantly enhanced at high temperatures. Temperature-dependent Raman studies and electronic structure calculations reveal that this experimental observation cannot be fully explained by a common mechanism of thermal-expansion-induced interlayer decoupling. Instead, a new model involving the intervalley transfer of thermally activated carriers from Λ/Γ point to K point is proposed to understand the high-temperature luminescence enhancement of multilayer MoS2 . Steady-state and transient-state fluorescence measurements show that both the lifetime and intensity of the exciton emission increase relatively to increasing temperature. These two experimental evidences, as well as a calculation of carrier population, provide strong support for the proposed model.

MnBr₂/18-crown-6 coordination complexes showing high room temperature luminescence and quantum yield.

The reaction of manganese(ii) bromide and the crown ether 18-crown-6 in the ionic liquid [(n-Bu)3MeN][N(Tf)2] under mild conditions (80-130 °C) resulted in the formation of three different coordination compounds: MnBr2(18-crown-6) (), Mn3Br6(18-crown-6)2 () and Mn3Br6(18-crown-6) (). In general, the local coordination and the crystal structure of all compounds are driven by the mismatch between the small radius of the Mn(2+) cation (83 pm) and the ring opening of 18-crown-6 as a chelating ligand (about 300 pm). This improper situation leads to different types of coordination and bonding. MnBr2(18-crown-6) represents a molecular compound with Mn(2+) coordinated by two bromine atoms and only five oxygen atoms of 18-crown-6. Mn3Br6(18-crown-6)2 falls into a [MnBr(18-crown-6)](+) cation - with Mn(2+) coordinated by six oxygen atoms and Br - and a [MnBr(18-crown-6)MnBr4](-) anion. In this anion, Mn(2+) is coordinated by five oxygen atoms of the crown ether as well as by two bromine atoms, one of them bridging to an isolated (MnBr4) tetrahedron. Mn3Br6(18-crown-6), finally, forms an infinite, non-charged [Mn2(18-crown-6)(MnBr6)] chain. Herein, 18-crown-6 is exocyclically coordinated by two Mn(2+) cations. All compounds show intense luminescence in the yellow to red spectral range and exhibit remarkable quantum yields of 70% (Mn3Br6(18-crown-6)) and 98% (Mn3Br6(18-crown-6)2). The excellent quantum yield of Mn3Br6(18-crown-6)2 and its differentiation from MnBr2(18-crown-6) and Mn3Br6(18-crown-6) can be directly correlated to the local coordination.

Abnormal high-temperature luminescence enhancement observed in monolayer MoS2 flakes: thermo-driven transition from negatively charged trions to neutral excitons

Abnormal high-temperature luminescence enhancement is observed in monolayer MoS2, owing to the joint effect of trion self-dissociation and p-type doping.

Robust luminescence of the silicon-vacancy center in diamond at high temperatures

We performed high-temperature luminescence studies of silicon-vacancy color centers obtained by ion implantation in single crystal diamond. We observed reduction of the integrated fluorescence upon increasing temperature, ascribable to a transition channel with an activation energy of 180 meV that populates a shelving state. Nonetheless, the signal decreased only 50% and 75% with respect to room temperature at 500 K and 700 K, respectively. In addition, the color center is found highly photostable at temperatures exceeding 800 K. The luminescence of this color center is thus extremely robust even at large temperatures and it holds promise for novel diamond-based light-emitting devices.

High power and temperature luminescence of Y3Al5O12:Ce3+ bulky and pulverized single crystal phosphors by a floating-zone method

Yellow Y3Al5O12:Ce3+ single crystal phosphor was grown through a floating zone method. It showed a broader blue excitation and yellow emission spectra with lower quantum efficiency due to large internal reflections but higher thermal stability due to high thermal conductivity than the conventional powder. With pulverizing the as-grown single crystal down to micron powder, its quantum efficiency was enhanced, while its lumen maintenance at high temperature (200°C) was reduced due to a generation of more phonons, confirmed by temperature-dependent Raman spectra. The as-grown and pulverized single crystal samples were applied to a high-power blue laser diode, and thus they gave an excellent luminescence feasibility to a high-power lighting source.

High temperature luminescence of Dy^3+ in crystalline silicon in the optical communication and eye-safe spectral regions

We report on photoluminescence in the 1.3 and 1.7 μm spectral ranges in silicon doped with dysprosium. This is attributed to the Dy3+ internal transitions between the second Dy3+ excited state and the ground state, and between the third Dy3+ excited state and the ground state. Luminescence is achieved by Dy implantation into Si substrates codoped with boron, to form dislocation loops, and show a strong dependence on fabrication process. The spectra consist of several sharp lines with the strongest emission at 1736 nm, observed up to 200 K. No Dy3+ luminescence is observed in samples without B codoping, showing the paramount importance of dislocation loops to enable the Dy emission.

Thermally activated luminescence in InN nanowires

The photoluminescence from InN nanowires is known to decrease in magnitude with increasing temperature up to 300K. Here it is shown that the luminescence reappears at higher temperatures, and continues to increase in intensity with increasing temperature up to 600K. The high temperature luminescence has similar features as the low temperature spectrum, however the magnitude of the high temperature peaks show activated temperature dependence not observed at low temperatures. This suggests that the high temperature luminescence is due to the thermal excitation of charge from long-lived trap states into the conduction band where it then relaxes radiatively.

Barium rare earth fluoride nanocrystals: high temperature solution synthesis, characterization and luminescence

A high temperature solution system with BaCO3/RECl3·xH2O in oleic acid/1-octadecene has been developed to prepare barium rare earth fluoride nanocrystals: tetragonal phase of BaREF5 (RE = Pr, Nd, Eu, Tb, Dy, Tm, Lu, Y), pure cubic phase Ba2REF7 (RE = La, Sm, Ho, Er, Yb), and BaREF5 (RE = Ce, Gd) colloidal nanocrystals. In addition, it is proved that the functionalization of these nanocrystals by means of doping with Eu, Tb, and Yb, Er/Tm ion pair can obtain red, green, and visible-to-the-naked-eye green/blue upconversion emissions.

Blue emissions in Dy^3+ doped Y_4Al_2O_9 crystals for temperature sensing

Temperature dependent emission spectra and decay times of trivalent dysprosium (Dy3) activated Y4Al2O9 (YAM) crystals have been studied for the first time (to our knowledge). The ratio of emission lines intensity can be used in temperature measurements, as it is not dependent on the variability of absolute intensity. The Boltzmann model was applied for modeling the temperature variation of the 4I15/2 and 4F9/2 states emissions relative intensities 455 and 481 nm, respectively. The calculated approximation gives highest sensor sensitivity of about 3×10(-3)°C-1 for the 600°C-800°C range, which allows for an expectation of usefulness of Dy3+:YAM in high-temperature luminescence thermometry. Also, the measured decay times are suitable for temperature sensing.

High-Temperature Luminescence Quenching of Colloidal Quantum Dots

Thermal quenching of quantum dot (QD) luminescence is important for application in luminescent devices. Systematic studies of the quenching behavior above 300 K are, however, lacking. Here, high-temperature (300-500 K) luminescence studies are reported for highly efficient CdSe core-shell quantum dots (QDs), aimed at obtaining insight into temperature quenching of QD emission. Through thermal cycling (yoyo) experiments for QDs in polymer matrices, reversible and irreversible luminescence quenching processes can be distinguished. For a variety of core-shell systems, reversible quenching is observed in a similar temperature range, between 100 and 180 °C. The irreversible quenching behavior varies between different systems. Mechanisms for thermal quenching are discussed.