Temperature-dependent Luminescence Research Articles

Sub-°C-precision temperature imaging using phase-shift luminescence thermometry

Abstract This work explores the potential of luminescence thermometry to provide temperature imaging with high temperature resolution using the phase-shift method. Phosphor thermometry has been widely used for temperature imaging, especially with the decay-time method. However, the phase-shift method was rarely used. In this approach, excitation is modulated in time, and due to the temperature-dependent luminescence dynamics of the painted luminescent probe, the emission waveform is phase-shifted with respect to the excitation waveform. Initially, a parametric study was performed on the effect of excitation waveform frequency and shape, based on a millisecond-decay time phosphor. The study found that the best precision is achieved with a square waveform at a frequency such that the phase shift is π÷4 at the target temperature. Then, this method was compared with the well-established decay-time method. Phase-shift method offered a three-fold improvement in temperature precision under identical peak excitation power. Finally, two-dimensional measurements were demonstrated on a temperature-controlled plate using a high speed CMOS camera, and an LED illumination. A temperature precision of 0.13 °C was obtained at a temporal resolution of 0.25 s and a spatial resolution of around 1 mm, due to a pre-processing binning of 7 X 7 pixels. This technique can be used as an alternative to infrared thermometry to probe the thermal processes with small temperature differences.

White emitting Sr3Ga2Ge4O14: Dy3+ phosphors with high purity and good thermal stability

A series of white emitting phosphors Sr3Ga2Ge4O14: xDy3+ (x = 1, 3, 5, 7, 9 and 11 %) were synthesized by a high-temperature solid-phase method. All samples exhibit two emission peaks at 478 nm and 571 nm, corresponding to the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+ ions, respectively. The optimal doping concentration of Sr3Ga2Ge4O14: xDy3+ phosphors was determined as 7 % mol, and the concentration quenching mechanism is confirmed as a dipole–dipole interaction. Finally, the temperature dependent luminescence spectra indicate that the synthesized Sr3Ga2Ge4O14: 7 % Dy3+ phosphors had good thermal stability.

Synthesis and photoluminescent spectroscopic analysis of lanthanum (III) coordinated with 1,10-Phenanthroline: A study of its thermally stable behavior

A blue-emitting phosphor designed by lanthanum (III) coordinated with two 1,10-Phenanthroline and three nitrate ligands, [La(Phen)2(NO3)3], was obtained by an effective and simple precipitation method. Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD) revealed the coordination modes in the compound and the chemical structure, crystallizing in a monoclinic system in the C2/c space group. The luminescence properties, absolute quantum yield (ϕ), and luminescence lifetime decay (τ) were determined by photoluminescence spectroscopy. Under a 350 nm excitation, the sample presents three emission bands corresponding to the π* → π transitions belonging to the organic ligand. The luminescence lifetime (τ) was determined through a monoexponentially fit, obtaining a value of 5616 ns. The [La(Phen)2(NO3)3] complex exhibits an absolute quantum yield of 3 % with the same excitation conditions. In addition, the photometric analysis shows that the luminescent response to a 350 nm excitation is that of a blue-emitting high-purity phosphor with 96 % and chromatic coordinates of 0.15, 0.05. The temperature-dependent luminescence properties revealed considerable thermal stability in the 20–150 °C range with a signal loss of 47 % and an activation energy of thermal quenching (ΔE) of 0.13 eV, the first value reported for a lanthanum complex based on 1,10-Phenanthroline.

New Insights in Luminescence and Quenching Mechanisms of Ag2S Nanocrystals through Temperature-Dependent Spectroscopy.

Bright near-infrared-emitting Ag2S nanocrystals (NCs) are used for in vivo temperature sensing relying on a reversible variation in intensity and photoluminescence lifetime within the physiological temperature range. Here, to gain insights into the luminescence and quenching mechanisms, we investigated the temperature-dependent luminescence of Ag2S NCs from 300 to 10 K. Interestingly, both emission and lifetime measurements reveal similar and strong thermal quenching from 200 to 300 K, indicating an intrinsic quenching process that limits the photoluminescence quantum yield at room temperature, even for perfectly passivated NCs. The low thermal quenching temperature, broadband emission, and multiexponential microsecond decay behavior suggest the optical transition involves strong lattice relaxation, which is consistent with the recombination of a Ag+-trapped hole with a delocalized conduction band electron. Our findings offer valuable insights for understanding the optical properties of Ag2S NCs and the thermal quenching mechanism underlying their temperature-sensing capabilities.

Defect level induced negative thermal quenching of β-Ba3LuAl2O7.5: Yb3+, Er3+ phosphor

Temperature-dependent behavior of phosphors has recently attracted significant research attention. This is due to the widespread applications of phosphors. Unfortunately, the thermal quenching effect in many phosphors greatly limits their performance at high temperatures. Herein, negative thermal quenching phosphor β-Ba3LuAl2O7.5: 0.3Yb3+, 0.03Er3+ is synthesized using the high-temperature solid-state method. X-ray Rietveld refinement and EPR results indicate the defect state of oxygen vacancy. Temperature-dependent upconversion luminescence spectra demonstrate that the green and red emission intensities increase with temperature to reach maximums at 398 K and 348 K respectively. Diffuse reflectance spectrum and downshifting luminescence spectrum prove that the defect state is near the 4F7/2 state of Er3+ ions. The defect state traps electrons at room temperature and releases them to populate the 4F7/2 state of Er3+ ion at elevated temperatures to cause the observed thermal enhancement of upconversion luminescence. This material's negative thermal quenching effect makes it a suitable candidate for applications in displays and anti-counterfeiting.

Enhanced red luminescence from GdAl3(BO3)4: Pr3+ phosphors under NUV excitation.

The GdAl3(BO3)4:xPr3+ (0 ≤ x ≤ 5.0 mol%) phosphors were prepared through solid state reaction route and characterized for various lighting applications. Powder X-ray diffraction investigations revel rhombohedral structure matched to JCPDS card no. 83-1907. The morphological studies confirm the agglomeration of particles with different size and shape. The emission spectra show various emission transitions originating from Pr3+:(3P1,0, 1D2) emission states to their lower lying energy states upon 274 nm NUV excitation with a red shift for x > 0.5 mol%. The colour perception analysis results an intense red luminescence due to efficient energy transfer from Gd3+ to Pr3+ ions. The temperature-dependent luminescence investigations show good thermal stability even beyond 150°C with an activation energy of 0.24 eV. The observed experimental results show the potentiality of GdAl3(BO3)4:0.5 Pr3+ phosphor for red emitting devices and red component in phosphor converted white LEDs.

Highly efficient and water-resistant BaGa4S7:Eu2+ phosphor prepared by a self-reduction method

The development of eco-friendly luminescent materials is imperative for the advancement of phosphor-based technologies. This study corroborates the self-reduction of Eu3+ to Eu2+ through analyses utilizing photoluminescence (PL), excitation spectroscopy (PLE), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations demonstrate that Eu2+ ions can efficaciously substitute Ba2+ ions within the BaGa4S7 lattice, preserving its structural integrity. Upon blue light excitation, BaGa4S7:Eu2+ manifests a robust green emission attributed to Eu2+ ions, showcasing a peak wavelength near 526 nm. The quantum yield (QY) of BaGa4S7:Eu2+ is remarkably high, registering at 74.8 %. Moreover, the temperature-dependent luminescence properties of BaGa4S7:Eu2+ phosphor were subjected to thorough investigation. Water resistance assays indicate that the sample preserves 76 % of its initial luminous intensity following 40 days of aqueous immersion. Additionally, BaGa4S7:Eu2+ based phosphor-converted white light-emitting diodes (WLEDs) demonstrate emission of high-quality white light. This unique water-resistant green emission sulfide phosphor is expected to have potential applications in lighting fields.

Multi-mode up-conversion emission of Tm@Yb@Er phosphors for color modulation and thermometry

Rare earth doped up-conversion materials play an important role in information security, colorful display and temperature sensing. In this work, the up-conversion luminescence of NaYF4:0.2Tm/20Yb@NaYF4:20Yb@NaYF4:2Er/20Yb phosphors, synthesized by typical co-precipitation method, are investigated under different excitation condition. The emission color of sample can be tuned from yellow to blue-green through changing pump laser from 1550 to 980 nm because the Tm3+ ions in the core cannot be excited by 1550 nm laser. More interesting, the value of red-to-green (R/G) and blue-to-green (B/G) can be finely manipulated by tuning the excitation pulse width and frequency. This phenomenon can be interpreted by different rising processes of the green, red and blue up-conversion emission. In addition, the core-shell structured sample displays a temperature-dependent color change, ranging from blue-green to purple. The green emissions, radiated from thermal coupled levels (2H11/24S3/2), are used in thermometry and the max relatively sensing sensitivity reaches 0.01 K−1 at 303 K. The findings indicate that the core-shell Tm@Yb@Er phosphors, with excitation-dependent and temperature-dependent up-conversion luminescence, have potential applications in information security and temperature sensing.

Enhancement of Interlayer Exciton Emission in a TMDC Heterostructure via a Multi-Resonant Chirped Microresonator Upto Room Temperature.

We report on multi-resonance chirped distributed Bragg reflector (DBR) microcavities. These systems are employed to investigate the light-mater interaction with both intra- and inter-layer excitons of transition metal dichalcogenide (TMDC) bilayer heterostructures. The chirped DBRs consisting of SiO2 and Si3N4 layers of gradually varying thickness exhibit a broad stopband with a width exceeding 600nm. Importantly, the structures provide multiple resonances across a broad spectral range, which can be matched to resonances of the embedded TMDC heterostructures. Studying cavity-coupled emission of both intra- and inter-layer excitons from an integrated WSe2/MoSe2 heterostructure in a chirped microcavity system, an enhanced interlayer exciton emission with a Purcell factor of 6.67 ± 1.02 at 4 K is observed. The cavity-enhanced emission of the interlayer exciton is used to investigate its temperature-dependent luminescence lifetime of 60ps at room temperature. The cavity system modestly suppresses intralayer exciton emission by intentional detuning, thereby promoting a higher IX population and enhancing cavity-coupled interlayer exciton emission. This approach provides an intriguing platform for future studies of energetically distant and confined excitons in different semiconducting materials, which paves the way for various applications such as microlasers and single-photon sources by enabling precise emission control and utilizing multimode resonance light-matter interaction.

Synthesis, characterization, and temperature-dependent luminescence of Tb3+-activated and self-activated Sr10(PO4)6Cl2 phosphors

In this work, a series of new nanosized phosphors based on strontium chlorapatite (Sr10(PO4)6Cl2, abbreviated as SrClAp) with varying terbium concentration were synthesized using a modified microwave-hydrothermal method. This study meticulously investigated the impact of Tb3+ concentration and annealing temperature on factors such as crystal purity, particle morphology, photoluminescence, chromatic properties, and the mechanism of thermal quenching.The synthesized phosphors underwent characterization using X-Ray Diffraction (XRD) and scanning electron microscopy (SEM) to verify their crystal structure purity and examine their morphology. Upon near-ultraviolet (NUV) excitation at the 378 nm line, the obtained nanosized powders emitted green light arising from the characteristic 5D4→7FJ (J = 6, 5, 4, 3) transitions of Tb3+ ions. Notably, a broad host-related emission was discernible at 80 K, with its intensity diminishing as the temperature increased. The mechanism governing this host-related emission and the process of its thermal quenching have been proposed. Moreover, a comprehensive exploration of the influence of ambient temperature on the emission of Tb3+-doped SrClAp was undertaken.

Solvent-Assisted Structural Modifications of Sulfur Dots Followed by Time-Dependent Emergence of a New Emissive State and Long-Lived Afterglow.

Sulfur dots are a new class of recently developed nonmetallic luminescent nanomaterials with various potential applications. Herein, we synthesized sulfur dots using a mild chemical etching method and then modified the structural features of the as-synthesized sulfur dots using a slow and defined solvent-assisted aggregation process. This increases the particle size and overall crystallinity along with the modifications of the surface functional groups, which eventually show a new emission band at longer wavelengths. Detailed photophysical and temperature-dependent luminescence studies confirmed that the new emissive state evolves due to interparticle interactions in the excited state. Furthermore, the occurrence of a new emissive state in a longer-wavelength region helped reduce the energy gap between the lowest excited singlet state and the lowest excited triplet state in modified sulfur dots, resulting in an aqueous stable room-temperature phosphorescence/afterglow emission through efficient intersystem crossing. This typical efficacious afterglow emission directly shows the potential applicability of structurally modified sulfur dots in encryption devices and can also be potentially effective in light emitting diodes (LED) and sensing devices.

Unveiling highly sensitive Dy3+ doped BaMgAl10O17 phosphor’s thermoluminescence trap features and temperature dependent luminescence for solid state lighting applications

This article explores the structural, morphological, thermoluminescence, and temperature-dependent emission properties of novel Dy3+ doped BaMgAl10O17(BAM-Dy) phosphors. Structural studies reveal that the phosphor has a similar structure to β-alumina. Rod-shaped interlinked surface morphology is a notable characteristic of the BAM-Dy samples. Incorporation of Dy3+ ions lead to the formation of distinct emission peaks (485 nm, 577 nm, and 635 nm) in the PL emission spectra. The effect of dopant concentration on the light output is crucial, and the highest PL intensity is observed for 1.5 mol% of Dy3+ concentration. The potential use of BAM-Dy phosphors for Gamma radiation detection and measurement is tested through thermoluminescence studies, which reveal high sensitivity, low threshold dose values, and exceptional response to low gamma doses, making them suitable for dosimetry applications. The investigation of trap parameters provides useful information about the number of traps, trapping mechanism, and trap energies, which is essential for in-depth study of synthesized phosphors for γ dosimetry application. The study of the effect of temperature on the luminescence behaviour is crucial for the application of phosphors in the light-emitting field. The BAM-Dy samples exhibit excellent thermal stability even at 210 °C, making them suitable for use in the field of White LEDs.

Effect of Ca co-doping on gamma-stimulated luminescence of Lu2SiO5:Ce

In order to estimate the stability of the light output of the scintillation detector, the Lu2SiO5:Ce scintillation crystals, additionally doped with Ca2+ ions at concentrations of 0 ÷ 0.4 at%, were studied. The spectra of optical absorption, gamma-luminescence, thermal luminescence, dose and temperature dependences of luminescence were measured. Gamma-luminescence in the dose range 10 - 5·107 Gy was recorded using 60Co gamma-source at the temperature range of 310–460 K. In contrast to the initial sample (non-doped with Ca), in the sample doped with 0.1 at% of Ca, an increase in the luminescence intensity was observed in the range of 390–425 nm, but further with an increase in the concentration of Ca (0.3–0.4 at%), the intensity of this band decreased to the initial level (undoped). At Ca concentrations of 0.3 and 0.4 at%, the intensity of the Ce1 center band remains practically unchanged up to a dose of 5·107 Gy. LSO crystals doped with Ce 0.1 at% and co-doped with Ca 0.1 at% can be recommended as a scintillation detector up to a gamma-dose of 105 Gy at room temperature.

Mn4+-activated NaSr10Y5W4O30 far-red emitting luminescent material for plant growth lighting

A series of Mn4+-doped NaSr10Y5W4O30 (NSYWO) phosphors have been successfully synthesized and further characterized to estimate their potentials for application as a far-red emitting component of pc-LED. An XRD analysis and crystal structure refinement have been carried out to characterize its quality. The doping concentration and temperature (80–500 K) dependent luminescence properties as well as decay kinetics have been studied and analyzed. It has been found that Mn4+ substitutes for W6+ sites resulting in far-red emission at 688 nm. The temperature quenching is attributed to thermal activation of an electron from Mn4+ 2Eg to 4A2g state via crossover, yielding an activation energy of 0.35 eV. Furthermore, to assess practical application of the novel phosphor, a blue-emitting LED chip combined with NSYWO: 0.8 mol% Mn4+has been packaged. The light from both the blue-emitting LED chip and NSYWO: Mn4+ phosphor was shown to be effectively utilized, revealing a good promise for application of the phosphor in the field of plant growth lighting.

Delineating Dy3+ and Sm3+ in thermally stable strontium silicate apatites for multifunctional applications

The structural, optical and temperature dependent luminescence properties of a series of Sr2Y8-xREx(SiO4)6O2 (RE=Dy and Sm) silicate phosphors are investigated for their multifunctional applications. The phosphors were synthesized using the solid-state reaction route with varying doping levels and characterized for phase purity. X-ray Diffraction analysis revealed the hexagonal crystal structure of (Sr2RE2)(RE6)(SiO4)6O2, indicating the incorporation of rare earth (RE) ions into two distinct crystallographic sites, thereby augmenting the luminescence properties. Dy3+ doped compounds exhibit intense yellow emission, promising white light generation when paired with InGaN blue LED chips. Sm3+ doped samples show orange-red emission around 601 nm, attributed to multipole-multipole interactions, with rapid decay curves suitable for high-speed response LEDs. Correlated Color Temperature (CCT) values were computed to assess the commercial viability of these phosphors in luminescence applications and the role of lighting in the growth of indoor plants and office spaces is discussed. The Sr2Y7.8Dy0.2(SiO4)6O2 phosphor with remarkable quantum yield of 63.56% demonstrated a thermal stability of 0.27 eV with enhanced sensitivity of about 0.39% K−1 and Sr2Y7.8Sm0.2(SiO4)6O2 with stability around 0.31eV with sensitivity of 1.11% K⁻¹ at 100K reveals them as potential candidates for optical temperature sensing. These results declare the competence of synthesized novel silicate apatites in solid-state lighting and optical thermometry.

Investigation of the luminescence properties and temperature dependent luminescence properties of Sm3+ doped NaPbBi2(PO4)3 orthophosphate phosphor: A promising candidate for light and light sensing applications

The red phosphor for light application is in high demand. In this regard, a series of orange-red phosphors, NaPbBi2(PO4)3: Sm3+, with a single phase were obtained by the conventional solid state reaction method. The X-ray diffraction (XRD) confirms that the phosphor belongs to the cubic structure with a space group I-43d (220). The optical property of the phosphor was studied through the diffuse reflectance spectroscopy measurements and the characteristic peaks of the Sm3+ ions were identified. Exciting the phosphors at 404 nm, produced a strong orange-red emission at 601 nm. The optimum concentration of the phosphor was found to be 0.03 mol. In all emission transitions of the Sm3+ ions within the host lattice, the energy transfer (ET) occurs among the nearest neighbour ions. The lifetime values were in the order of milliseconds. The photometric parameters revealed that the emission lies in the orange-red region with color coordinates (0.5863, 0.4129) and a color purity of 99.4 %. The temperature dependent luminescence properties of the phosphor were also investigated and all these results showed that the phosphor could serve as a good candidate for light/light sensing applications.

Construction of a Zn(II)-Eu(III) Nanoring with Temperature-Dependent Luminescence for the Qualitative and Quantitative Detection of Neopterin as an Inflammatory Marker.

A nine-metal Zn(II)-Eu(III) nanoring 1 with a diameter of about 2.3 nm was constructed by the use of a long-chain Schiff base ligand. It shows a luminescence response to neopterin (Neo) through the enhancement of lanthanide emission with high selectivity and sensitivity, which can be used to quantitatively analyze the concentrations of Neo in fetal calf serum and urine. The luminescence sensing of 1 to Neo is temperature-dependent, and it displays more obvious response behavior at lower temperatures. Filter paper strips bearing 1 can be used to qualitatively detect Neo by the color change from chartreuse to red under a UV lamp. The limit of detection is as low as 3.77 × 10-2 nM.

Trivalent dysprosium activated LaSr2AlO5 nanophosphors for NUV-excited wLEDs: Insights into structural, optical, Judd-Ofelt parameters and temperature dependent photoluminescence

Gel-combustion (GC) methodology was implemented in the present research to produce a series of single phase Dy3+ doped LaSr2AlO5 nanophosphors for the usage in wLEDs. X-ray powder diffraction patterns verified the phase purity and crystal structure of the produced materials. The XRD inspection supported the successful fabrication of tetragonal structured (I4/mcm space group) phosphors and revealed good accordance with card number 70–2197 on the JCPDS database. We collected diffuse reflectance spectra (DRS) to examine how doping affects the band gap. Furthermore, energy-dispersive X-ray (EDX) spectroscopy and transmission electron microscopy (TEM) have been employed for assessing elemental composition and surface morphology. On 349 nm excitation, LaSr2AlO5:Dy3+ phosphors produce the distinctive yellow PL emissions causedby 4F9/2→6H13/2 transition. Using excitation spectra, the Judd-Ofelt (J-O) characteristic (Ω = 2, 4, 6) have been determined. The Dy3+ transition's features show that the J-O parameters followed the trend which suggested an asymmetric environment around the ligand. The electric dipole transition predominated in the luminescence spectrum, causing the LaSr2AlO5:Dy3+ phosphor to emit a yellowish whitecolor. The fundamental mechanism for the energy transfer and concentration quenching instances among activator ions was discovered to be dipole-quadrupole interactions. Temperature dependent luminescence showed that the synthesized phosphors had thermal stability up to 523 K with activation energy of 0.1312 eV. The future prospects of the synthesized phosphor as an effective choice for near-ultraviolet-activated wLEDs are substantially supported by current comprehensive research.

Spectroscopic studies of TeO2-based glasses doped with Sm3+ and its use as an optical temperature sensor

This study reports the synthesis and characterization of glasses in the (100-x)65TeO2-15Li2O-20ZnO + xSm2O3 system doped with Sm2O3, denoted as Sm3+: TLZ glasses, with varying doping concentrations from 0.1, 0.15, 0.2, 0.35, 0.5, and 1 mol%. The structural and optical properties, as well as the temperature dependence of luminescence, were investigated. Excitation at 405nm resulted in strong orange-red luminescence at 566, 600, and 646 nm. The local environment surrounding Sm3+ ions was explored using the intensity ratio of electric and magnetic dipole transitions. The non-radiative energy transfer between neighboring Sm3+ ions was evaluated using the Inokuti-Hirayama model, allowing for the determination of the critical transfer distance. The temperature dependence of luminescence, displayed by Commission Internationale de L’Eclairage (CIE) chromaticity coordinates, exhibited a monotonic change from (0.611, 0.387) at 295 K to (0.605, 0.393) at 479 K. The Sm3+:TLZ glasses doped with 0.15 mol% showed the highest relative thermal sensitivity of 0.10%K-1 at 479 K, suggesting their potential as luminescent thermometers.

Interrupting the long-range energy migration among Eu3+ by the introduction of unequivalent [NaO8] units to achieve both high quenching concentration and quantum yield in NaY2Ga2InGe2O12

In the pursuit of optimizing white light-emitting diodes (WLEDs), Eu3+-doped phosphors have emerged as a key component in strategies that combine ultraviolet (UV) LED chips with red, green, and blue (RGB) tricolor phosphors. However, their application has been notably constrained by concentration quenching and thermal quenching. To address this challenge, we have developed a series of novel red phosphors, NaY2-xGa2InGe2O12:xEu3+. The powder X-ray diffraction (XRD) indicates that the NaY2Ga2InGe2O12(NYGIG) belongs to the garnet family. The [NaO8] unit replaces one-third of the eight-coordinated sites of garnet and leaves the other two-thirds for the [YO8], which helps to prevent long-range energy migration among Eu3+ especially when the eight-coordinated sites were highly substituted. Such a structure feature allowed the NaY2-xGa2InGe2O12:xEu3+ phosphor to achieve an optimal quantum yield of 95.6% at an extremely high Eu3+ doping x value up to 1.2. Moreover, further studies on the temperature-dependent luminescence spectra confirm that an anomalous thermal quenching phenomenon will occur when the NaY2-xGa2InGe2O12:1.2Eu3+ phosphor is properly excited. In application, the combination of the red-emitting NaY2-xGa2InGe2O12:1.2Eu3+, blue-emitting BaMgAl10O17:Eu2+, and green-emitting Zn2SiO4:Mn2+ phosphors can realize high color rendering (CRI∼93) white light with the with CIE coordinates of (0.353,0.350), indicating that the NYGIG:Eu3+ phosphor own a promising potential for WLEDs.