Temperature-dependent Emission Spectra Research Articles

Luminescence and spectroscopic studies on Dy3+-Eu3+ doped SiO2-B2O3-ZnO-La2O3-BaO glass for WLED

A series of SiO2-B2O3-ZnO-La2O3-BaO (SBZLBa) glasses doped with Dy3+ and Eu3+ were synthesized using the melt-quenching technique. Their optical characteristics and potential applications in W-LED devices were investigated. The structural effects resulting from doping the glass with Dy3+ and Eu3+ ions were elucidated through infrared spectroscopy and an examination of the physical properties. The variations in emission intensity within the fluorescence spectrum validated the sensitizing effect of Dy3+ on Eu3+ within the glass matrix. By manipulating the transitions of both Dy3+ and Eu3+, the excitation wavelength was altered, enabling the realization of cool white, neutral white, and warm white luminescence, thus accommodating the diverse requirements for white light emission in lighting applications. After incorporating 1.0 mol% of Dy2O3 and 0.8 mol% of Eu2O3, respectively, the glass exhibited CIE coordinates of (0.3332, 0.3535), positioning it within the white light spectrum and in close proximity to the ideal white light coordinates of (0.33, 0.33). The SBZLBa-Dy2O3–0.8Eu2O3 glass exhibited a quantum yield of 5.98 %. It has been demonstrated through acid and alkali resistance tests that this glass possesses excellent chemical stability. Additionally, temperature-dependent emission spectra have revealed that the luminous intensity of the glass maintains over 85 % of its room temperature value at 185 °C, with Eα determined to be 0.2387 eV.

Crystal-Rigidifying Strategy in Hybrid Manganese Halide to Achieve Narrow Green Emission and High Structural Stability.

Although organic-inorganic hybrid Mn2+ halides have advanced significantly, achieving high stability and narrow-band emission remains enormously challenging owing to the weak ionic nature and soft crystal lattice of the halide structure. To address these issues, we proposed a cationic engineering strategy of long-range cation π···π stacking and C-H···π interactions to simultaneously improve the crystal structural stability and rigidity. Herein, two organic zero-dimensional (0D) manganese halide hybrids of (BACQ)2MnX4 [BACQ = 4-(butylamino)-7-chloroquinolin-1-ium; X = Cl and Br] were synthesized. (BACQ)2MnX4 display strong green-light emissions with the narrowest full width at half-maximum (fwhm) of 39 nm, which is significantly smaller than those of commercial green phosphor β-SiAlON:Eu2+ and most of reported manganese halides. Detailed Hirshfeld surface analyses demonstrate the rigid environment around the [MnX4]2- units originating from the interactions between [BACQ]+. The rigid crystal structure weakens the electron-phonon coupling and renders narrow fwhm of these manganese halides, which is further confirmed by temperature-dependent emission spectra. Remarkably, (BACQ)2MnX4 realizes outstanding structural and luminescence stabilities in various extreme environments. Benefiting from the excellent performance, these Mn2+ halides are used to assemble light-emitting diodes with a wide color gamut of 105% of the National Television System Committee 1931 standard, showcasing the advanced applications in liquid-crystal-display backlighting.

Double perovskite quantum dots Cs2AgInCl6: Tb3+/Sm3+/Bi3+ for dual-mode fluorescence temperature sensing

In this research, double perovskite quantum dots Cs2AgInCl6: Tb3+/Sm3+/Bi3+ are synthesized employing a high-temperature thermal injection method. The temperature-dependent emission spectra and the fluorescence decay curves of samples show the quantum dots can be applied to dual-mode temperature sensing employing fluorescence intensity ratio technique (between 656 nm (Sm3+) and 549 nm (Tb3+)) and fluorescence lifetime thermometry (549 nm (Tb3+)), achieving maximal relative sensitivities of 3.24%/K (351 K) and 0.68%/K (373 K), respectively. This study offers valuable insights into the temperature sensing capabilities of these quantum dots, which shows that these quantum dots are promising high-sensitivity dual-mode temperature sensing materials.

Synthesis and optical properties of highly efficient Na7Mg13La(PO4)12:Eu3+ powders with excellent thermal stability

In the pursuit of efficient red-emitting phosphors, a series of red-emitting Na7Mg13La(PO4)12:Eu3+ phosphors was prepared using a high-temperature solid-state synthesis method. The phase purity was monitored using powder X-ray diffraction (XRD). The morphological features of the synthesized samples were evaluated by taking scanning electron microscopy (SEM) images. The optical properties of the synthesized polycrystalline samples were investigated by recording room-temperature and temperature-dependent (77–500 K interval) excitation and emission spectra, and photoluminescence (PL) decay curves. The calculated TQ1/2 values were above 420 K, regardless of the Eu3+ concentration, indicating the high thermal stability of the phosphors. The optimal Eu3+ concentration was 100 %, which indicated the absence of concentration quenching in the given host. Furthermore, the quantum efficiency of fully Eu3+-substituted compound reached 100 %, which is an excellent feature for practical phosphor applications.

LaBaMg(Ti0.5W0.5)O6:Mn4+ for plant growth lighting: Luminescence properties and synthesis

With the need of food safety and high yield, new luminescent materials with promoting plant photosynthesis have attracted more and more attention. In this research, we synthesize the far-red-emitting LaBaMg(Ti0.5W0.5)O6:Mn4+ phosphor in air. We investigate the crystal structure and phase, particle morphology and size, and the luminescence properties. The samples show a broad excitation spectrum under monitored 704 nm due to the Mn4+ - O2− charge transfer (CT) and the transitions 4A2g → 4T1g, 2T2g, and 4T2g of Mn4+ in the range of 300 – 600 nm. The far-red emission of sample is observed with the emission spectrum (650 – 790 nm) is attributed to the Eg → 4A2g transitions. The chromaticity coordinates are (0.7329, 0.2671). The crystal field strength (Dq), the Racah parameters (B and C), and Dq/B values are ∼ 1972 cm−1, 596 cm−1, 3219 cm−1, and 3.31, respectively. 0.2 mol% is the optimal Mn4+ concentration. Emission spectra under excitation wavelength from 320 nm to 560 nm and time-resolved emission spectra confirm the only luminous center (Mn4+) in LaBaMg(Ti0.5W0.5)O6:Mn4+. Lifetime reduces with added Mn4+ concentration. The temperature-dependence emission spectra confirm that sample has a good thermo-stability. The thermal quenching phenomenon and luminous mechanism are analyzed. The luminescence properties of sample infer its application prospect in plant growth light-emitting diode (LED).

Confinement of Sustainable Carbon Dots Results in Long Afterglow Emitters and Photocatalyst for Radical Photopolymerization.

Sustainable carbon dots based on cellulose, particularly carboxymethyl cellulose carbon dots (CMCCDs), were confined in an inorganic network resulting in CMCCDs@SiO2. This resulted in a material exhibiting long afterglow covering a time frame of several seconds also under air. Temperature-dependent emission spectra gave information on thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) while photocurrent experiments provided a deeper understanding of charge availability in the dark period, and therefore, its availability on the photocatalyst surface. The photo-ATRP initiator, ethyl α-bromophenylacetate (EBPA), quenched the emission from the millisecond to the nanosecond time frame indicating participation of the triplet state in photoinduced electron transfer (PET). Both free radical and controlled radical polymerization based on photo-ATRP protocol worked successfully. Metal-free photo-ATRP resulted in chain extendable macroinitiators based on a reductive mechanism with either MMA or in combination with styrene. Addition of 9 ppm Cu2+ resulted in Mw/Mn of 1.4 while an increase to 72 ppm improved uniformity of the polymers; that is Mw/Mn=1.03. Complementary experiments with kerria laca carbon dots confined materials, namely KCDs@SiO2, provided similar results. Deposition of Cu2+ (9 ppm) on the photocatalyst surface explains better uniformity of the polymers formed in the ATRP protocol.

Ultrastable Copper Iodide Hybrid with Intrinsic Greenish White-Light Emission by Incorporating an Anionic Inorganic Functional Unit into an Extended Structure.

Incorporating a functional unit into the multidimensional coordination polymer skeleton is an efficient way to improve the stability of materials and expand their application. In this paper, anionic copper iodide inorganic functional modules are incorporated into one-dimensional extended chains by using a unique bidentate cationic organic ligand. Benefiting from the ionic extended structure, the resulting hybrid possesses a remarkable stability with a decomposition temperature as high as 300 °C. Meanwhile, the hybrid material exhibits intrinsic greenish white-light emission with a high photoluminescent quantum yield of 70%. The emission was investigated by temperature-dependent emission spectra, which proved to be the result of the synergistic effect of two energy states. The novel synthetic strategy provides an efficient route for the development of functional organic metal halides.

Optical and photoluminescence properties of trivalent rare earth ions doped LiMgPO4

Trivalent rare-earth-activated luminescent materials have attracted a lot of attention due to their fascinating optical properties and broad range of applications. In this study, polycrystalline Sm and Eu-doped LiMgPO4 luminescent materials were synthesized using a solid-state reaction technique. The crystalline structures, morphological features, and optical characteristics of the synthesized materials were thoroughly investigated using x-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field-Emission Scanning Electron Microscopy (FE-SEM) and UV–vis spectroscopy. The Rietveld refinement analysis confirmed the phase purity of synthesized phosphors. In addition, the strain induced owing to the incorporation of trivalent rare-earth ions and crystallite sizes of each synthesized material was estimated using the Williamsons-Hall (W-H) and modified Debye-Sherrer equations. The estimated results of the microstrain were reported to be 0.0010, 0.0023 and 0.0020. Subsequently, as a consequence of distinct peak profile options, the projected average crystallite size by both approaches was distinct. The UV–vis spectroscopy analysis reveals that Sm and Eu doped materials exhibit absorption bands around 402 nm and 396 nm and depicts the declining band gap values. The Photoluminescence (PL) spectra at 402 nm and 395 nm excitation wavelengths exhibited the distinctive emissions of both Sm3+ (4G5/2 → 6H7/2) and Eu3+ (5D0 → 7F2) ions emanating due to the intra-configurational f - f and 4 f − 4 f transitions. Finally, the CIE diagram explicitly demonstrates that the Sm and Eu-modified materials reveal their exceptional color purity. McCamy’s approach was used to determine various parameters of trivalent rare-earth doped materials. The correlated color temperature ( TCCT ) and their coordinates TCCT (ζ, β) was found to be 2287 K, 1900 K, 0.281, 0.632, and 0.302, 0.681 respectively. Temperature-dependent emission spectra exhibit excellent color and thermal stability at high temperatures. The obtained results in this study indicate that the synthesized luminescent materials can potentially be used in white light-emitting diode applications.

Temperature sensing of novel Tb3+/Ho3+/Bi3+ co-doped lead-free double perovskite Cs2AgInCl6 nanocrystals

Up to now, the research field of application of lanthanide ions doped lead-free double perovskite Cs2AgInCl6 nanocrystals (NCs) was relatively limited, even less in temperature sensing. Here, Tb3+/Ho3+/Bi3+ ions were successfully doped into Cs2AgInCl6 NCs by hot-injection. The temperature sensing performance of co-doped NCs by using the fluorescence intensity ratio (FIR) was studied through the temperature-dependent emission spectra. By analyzing the influence of ions' doping concentration on temperature sensing performance, the optimal doping concentration of co-doped Cs2AgInCl6 NCs was determined to be 7 % Tb3+, 20 % Ho3+ and 1 % Bi3+. The highest absolute and relative sensitivities reach 1.48 K−1 and 2.48 %/K, respectively. We provide a new doping scheme of lead-free double perovskite NCs which have good temperature sensing performance. This co-doped NCs have great potential application value in non-contact temperature sensing in nanoscale.

Luminescence properties and thermal stability of Dy2O3/Sm2O3 doped glass ceramics containing NaBi(WO4)2

Dy2O3–Sm2O3 co-doped transparent glass ceramics (GCs) containing NaBi(WO4)2 crystalline phase were prepared by melt-curing-crystallization method. The optimal heat treatment condition is 580 °C/2 h. The optimum incorporation concentration of Dy2O3 is 0.4%, exceeding which a quenching phenomenon dominated by quadrupole-quadrupole interactions emerges. Meanwhile, when the concentration of Dy2O3 was fixed, the chromaticity coordinate of the sample moved the cool white light region to the warm white light region as the concentration of Sm2O3 increased. The temperature-dependent emission spectra of the 0.4% Dy2O3-0.7% Sm2O3 co-doped GC samples show that emission intensity at 575 nm at 185 °C still reaches 80% of the room temperature. The thermal quenching activation energy was 0.1537 eV and the activation energy after the addition of Mo6+ was 0.1957 eV. This study indicates that Dy2O3–Sm2O3 co-doped GCs containing NaBi(WO4)2 crystalline phase can achieve light-color tunable emission, which is potentially valuable for solid-state color rendering and illumination applications.

Optical properties and Judd-Ofelt analysis of a novel Red-Emitting monoclinic Li3Ba2Gd3(WO4)8: Eu3+ phosphor

Red-emitting Li3Ba2Gd3(WO4)8: x at.% Eu3+ (0.5 ≤ x ≤ 10) phosphors were effectively produced using a conventional solid-state reaction method at high temperature in air atmosphere. The phosphors exhibited monoclinic crystalline structure with the C2/c space group and 2/m point group. The unit cell parameters determined from the Rietveld refinement for 3 at.% doped sample are a = 5.2149(4) Å, b = 12.7447(1) Å, c = 19.2058(3) Å, α = γ = 90°, β = a^c = 91.9315(1)° and Vcalc = 1275.748(2) Å3. Photoluminescence spectra, lifetimes, colour coordinates and purity, and temperature-dependent emission spectra have been systematically studied. Upon excitation at 395 nm, the phosphors displayed red emission with a peak centered at 614 nm, which was associated with the 5D0→7F2 electrical dipolar transition of Eu3+. At the same time, the influence of different Eu3+ ion concentration on the photoluminescence intensity is also discussed. The optimal concentration of Eu3+ ions in Li3Ba2Gd3(WO4)8 was found to be 3 at.%. The mechanism behind concentration quenching was ascribed to dipole–dipole interactions, and the critical distance for energy transfer among Eu3+ ions was determined to be 7.409 Å. The Judd–Ofelt theory was utilized to assess the intensity parameters and radiative properties. The fluorescence decay times were also determined for the different concentration levels of Eu3+ cations. The chromatic coordinates of Li3Ba2Gd3(WO4)8: Eu3+ were found to be (0.653, 0.345), closely resembling the standard red light (0.670, 0.330) and demonstrated high colour purity (98.42 %) under excitation at 395 nm. Moreover, the phosphors Li3Ba2Gd3(WO4)8: Eu3+ exhibited favorable thermal stability, characterized by an activation energy of 0.219 eV. The aforementioned findings indicate that the phosphors Li3Ba2Gd3(WO4)8 doped with Eu3+ have the potential to function as a red-emitting phosphor in near-ultraviolet-driven white light-emitting diodes.

Optical transition tuning of Er3+ in continuous tungsto-molybdate solid solution NaY(MoxW1-xO4)2 phosphors

Nowadays, the application scenarios of rare earth doped luminescent materials tend to be refined and complicated. The optical properties of rare earth doped materials are difficult to precisely control via the traditional design and synthesis methods, namely, changing doping concentration or preparative conditions. The aim of this study is to tune the optical transition properties of Er3+ in tungsto-molybdate NaY(MoxW1-xO4)2 (x = 0, 0.01, 0.1, 0.3, 0.5, 0.7, 0.9, 0.99 and 1.0) phosphors by changing the host matrix. The Er3+ doped continuous tungsto-molybdate solid solution NaY(MoxW1-xO4)2 phosphors were prepared via a solid state reaction technique at optimized calcination temperatures. The refractive indexes of the obtained solid solution samples were confirmed according to different models and compared. Subsequently, the optical transition intensity parameters, radiative transition rates and intrinsic radiative lifetimes of Er3+ in these solid solution phosphors were calculated in the framework of Judd-Ofelt theory. It was confirmed that the optical transition properties of Er3+ can be greatly tuned by the solid solution composition, and the tuning effects for different transitions are different. To validate the reliability of the Judd-Ofelt calculations, the temperature-dependent emission spectra of two green emissions of Er3+ for different solid solution samples were studied. It was found that the radiative transition rate ratios between two green emissions derived from theoretical calculations and experimental measurements are in reasonable agreement, thus proving that the optical transition calculations are reliable and the optical transition properties of Er3+ in the tungsto-molybdates can be tuned in a large range. This work reminds us of a new route for developing novel luminescence materials based on practical demands.

PEG-coated NaYF4:Tm3+/Yb3+ upconversion nanoparticles for OCT image contrast enhancer, optical thermometry, and security applications

Polyethylene glycol (PEG) coated NaYF4:Tm3+/Yb3+ upconversion nanoparticles (UCNPs) were synthesized, and their usefulness in improving image contrast in Swept source optical coherence tomography (SS-OCT) and photo-thermal (PT-OCT) imaging was assessed. Synthesized UCNPs have shown biocompatibility with a cell survival rate of more than 90% after 24 h of incubation of HeLa cells. Prepared particles have shown intense blue upconversion emission along with a photo-thermal conversion efficiency of 30.4%. Leveraging these UCNPs, enhancements in image quality were achieved in both SS-OCT and PT-OCT imaging modalities, manifesting improved scattering coefficients and contrast-to-noise ratios. Temperature-dependent upconversion emission spectra were used to assess temperature sensing and thermal sensitivity of 107×10-3 K-1 at 300 K is obtained for the synthesized nanoparticles. Additionally, these UCNPs have demonstrated utility in latent finger-marks detection and anti-counterfeiting applications.

The development of a dual-mode optical temperature sensor based on fluorescence intensity ratio and lifetime

The utilization of optical parameters is crucial for achieving accurate temperature detection, which in turn facilitates the development of new phosphors used for non-contact optical thermometers. In this study, a series of phosphors of KSrGdTeO6 (KSGT) co-doping Mn4+ and Sm3+ luminescent centers, were synthesized through high temperature solid-state reactions. Notably, the temperature-dependent emission spectra and attenuation curves of KSGT:Mn4+/Sm3+ were measured across a wide temperature range of 298–573 K. In the absence of energy transfer between Mn4+ and Sm3+, Mn4+ and Sm3+ activators can emit their characterized emissions by 405 nm excitation. With increasing temperature, the fluorescence intensity of Mn4+ ions decreases at a faster rate compared to that of Sm3+ ions as the temperature increases. Consequently, by utilizing the fluorescence intensity ratio (FIR) between the two activators Mn4+ and Sm3+, the optimal temperature sensing relative sensitivity (Sr) and absolute sensitivities of (Sa) of KSGT:Mn4+/Sm3+ were found to be 2.591 % K−1 at 298 K and 0.0246 K−1 at 573 K. Moreover, the luminescent lifetime of Mn4+ emission decreases rapidly with increasing temperature, which makes it also possible to be a lifetime-based thermometry with Sa and Sa of 2.3233 %K−1 at 448 K and 0.1444 K−1 at 398 K. The dual-mode sensing properties of KSGT:Mn4+/Sm3+ make it a highly sensitive temperature thermometer, which provides design ideas for future researchers in this field.

Origin of the Cr3+ concentration-dependent broadband near-infrared emission in Sc2Si2O7.

The challenge of developing phosphors with tailored near-infrared (NIR) emission ranges to meet the diverse demands of various applications is a paramount concern in the contemporary realm of NIR phosphor research. A strong dependence of NIR emission on Cr3+ concentration has been demonstrated in Sc2-xSi2O7:xCr3+, which exhibits an NIR emission band at 840 nm for low Cr3+ doping concentrations (x = 0.001-0.01) and an anomalous NIR emission band at 1300 nm for high Cr3+ doping concentrations (x = 0.01-0.10). Careful investigation of the crystal structure, excitation and emission spectra, and luminescence decay curves indicates that the two NIR emissions can be attributed to the isolated Cr3+ ions and the Cr3+-Cr3+ pairs, respectively. The strong interaction of exchange-coupled Cr3+-Cr3+ pairs is supported by temperature-dependent emission spectra, luminescence decay curves and electron paramagnetic resonance (EPR) measurements. This work provides a new insight into the study of Cr3+-Cr3+ pairs for broadband NIR emission.

A green light emissive LaSr2AlO5:Er3+ nanocrystalline material for solid state lighting: crystal phase refinement and down-conversion photoluminescence with high thermal stability.

The present study reveals the structural and optoelectronic characteristics of a down-converted (DC) green luminous Er3+ doped LaSr2AlO5 phosphor that was produced by employing an efficient and reliable gel-combustion process assisted with urea as a fuel. Using Rietveld refinement of diffraction data, the crystal structure and phase formation were examined. The surface morphology and elemental configuration of the phosphor were analyzed via TEM and EDX spectroscopy, respectively. The band gap of LaSr2AlO5 (5.97 eV) and optimized La0.96Sr2AlO5:4 mol% Er3+ (5.51 eV) classify the optimized sample as a direct band-gap material. The PL peaks located in the visible range corresponding to transitions 2H9/2 → 4I15/2 (406 nm), 2H11/2 → 4I15/2 (520 nm), 4S3/2 → 4I15/2 (550 nm), and 4F9/ 2 → 4I15/2 (665 nm) were revealed by photoluminescence spectroscopy under 377 nm excitation. Above 4 mol% Er3+ doping, concentration quenching was observed, which was controlled by the quadrupole-quadrupole interaction. Based on the findings of the double exponential fitting of lifetime curves acquired from the emission spectra at λex = 377 nm and λem = 550 nm, the average lifetime of the excited levels of considered nanomaterials was estimated. The temperature-dependent emission spectra of the La0.96Sr2AlO5:4 mol% Er3+ sample were collected in the range 298-498 K. The considered phosphor was found to have a high thermal stability as evidenced by the luminous intensity being sustained at 74.29% at 498 K compared to the intensity at ambient temperature (298 K) with an activation energy of 0.1453 eV. The calculated color purity and superb chromaticity coordinates indicates that the phosphors have a high degree of color purity, which further supports its applicability as a green component in solid-state lighting.

Intense green up/down conversion emission and high-sensitivity optical thermometry of NaYb(WO4)2:Er3+ stoichiometric phosphors

Optical thermometry based on fluorescence intensity ratio (FIR) has garnered significant interest among researchers due to its rapid, non-contact, and high sensitivity characteristics. In this study, stoichiometric NaYb(WO4)2 phosphors, doped with varying concentrations of Er3+, were successfully synthesized using the high-temperature solid-state method. Under both 980 nm and 266 nm excitation, the samples exhibited strong green and very weak red upconversion (UC) and downconversion (DC) luminescence. The structural and morphological properties of the prepared samples were thoroughly characterized using techniques such as X-ray diffraction (XRD), XRD Rietveld refinement, scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectroscopy. The phosphors demonstrated high-purity UC and DC emission, with maximum green-to-red ratios of 60.9 and 77.0, respectively. This discovery opens up vast possibilities for their application as pure green color converters. The UC emission of Er3+ ions in the stoichiometric NaYb(WO4)2 phosphor was identified as a two-photon UC process, as evidenced by the relationship between the luminescence intensity and the excitation power of the sample. Moreover, the temperature-dependent emission spectra of UC and DC were monitored, and investigated the fluorescence intensity ratios (FIRs) of 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+ ions to assess the optical temperature sensing behavior of NaYb(WO4)2:Er3+. The experimental results revealed that the maximum absolute sensitivities (SA) of NaYb(WO4)2 phosphors were 0.0120 K-1 (UC) and 0.0077 K-1 (DC), and the maximum relative sensitivities (SR) were 0.0089 K-1 (UC) and 0.0092 K-1 (DC), respectively. These findings highlight the promising of Er3+-doped Yb3+ stoichiometric NaYb(WO4)2 phosphors in optical temperature sensors.

Pressure-Induced Remarkable Spectral Red-Shift in Mn2+ -Activated NaY9 (SiO4 )6 O2 Red-Emitting Phosphors for High-Sensitive Optical Manometry.

To settle the low sensitivity of luminescent manometers, the Mn2+ -activated NaY9 (SiO4 )6 O2 red-emitting phosphors with splendid pressure sensing performances are developed. Excited by 408nm, the resulting products emit bright red emission originating from 4 T1 (4 G) → 6 A1 transition of Mn2+ , in which the optimal concentration of the activator ion is ≈1 mol%. Moreover, the admirable thermal stability of the developed phosphors is studied and confirmed by the temperature-dependent emission spectra, based on which the activation energy is derived to be 0.275eV. By analyzing the pressure-dependent Raman spectra, the structural stability of the synthesized compounds at extreme conditions is verified. Furthermore, the designed phosphors exhibit remarkable spectral red-shift at elevated pressure. Especially, as pressure increases from 0.75 to 7.16GPa, the emission band centroid shifts from 617.2 to 663.4nm, resulting in a high sensitivity (dλ/dP) of 7.00nm GPa-1 , whereas the full width at half maximum (FWHM) increases from 83.0 to 110.6nm, leading to the ultra-high sensitivity (dFWHM/dP) of 10.13nm GPa-1 . These achievements manifest that the designed red-emitting phosphors are appropriate for ultrasensitive optical manometry. More importantly, the developed manometer is a current global leader in sensitivity, when operating in the band-width mode, that is, FWHM.

Concentration- and temperature- dependent luminescence quenching and optical transition of Sr2GdTaO6: Eu3+ phosphor for potential applications in white LEDs

A series of Eu3+ doped Sr2GdTaO6 (SGT) phosphors with double perovskite structure were synthesized via a high-temperature solid-state reaction approach. The crystal structure, morphology and luminescence properties were characterized by means of X-ray diffraction, transmission electron microscope, luminescence spectroscopy and fluorescence decay lifetimes, respectively. Under the excitation of 394 nm, intense red emission in the visible region was observed in Eu3+ doped SGT phosphors, and the critical quenching concentration of Eu3+ in SGT phosphors was derived to be 15 mol%. The chromaticity coordinates and color purity of SGT: 15 mol% Eu3+ were calculated to be (0.61, 0.36) an 93.82 %, respectively. Meanwhile, it was also confirmed that the electric quadrupole–quadrupole interaction is responsible for the luminescence concentration quenching of Eu3+. The internal quantum efficiency of SGT: Eu3+ phosphors with different Eu3+ concentrations were calculated. Furthermore, the crossover process was confirmed to be the main mechanism for luminescence thermal quenching based on the temperature-dependent emission spectra and temperature-dependent fluorescence lifetimes. In addition, the Judd-Ofelt parameters, radiative transition rates and branch ratios from the 5D0 emitting states to various lower energy states were evaluated with the aid of the Judd-Ofelt theory, respectively. All results indicate that SGT: Eu3+ samples are a promising red-emitting phosphor.

On the optical properties of gallium based garnet phosphors according to Ca2Ln1-xCexZr2Ga3O12 (with Ln = Y, La, Gd, Lu)

Several samples of a gallium based garnet phosphor activated by cerium were investigated and reported upon in this work. Firstly, a solid solution corresponding to Ca2Lu1-xCexZr2Ga3O12 (x = 0.001–0.1), in which a doping level of 1 atom-% was revealed as the optimal activator concentration for high efficiency. Secondly, a range of samples according to the general composition Ca2(Y,La,Gd,Lu)0.99Ce0.01Zr2Ga3O12 was investigated to study the effect of different non emitting lanthanide ions on the optical properties. For this work various polycrystalline samples were synthesized and investigated by X-ray powder diffraction to determine the phase purity of the prepared samples. Fluorescence properties were examined employing excitation, emission, and diffuse reflectance spectroscopy. Temperature dependent emission spectra and fluorescent lifetimes were investigated to gain insight into the thermal quenching behaviour. From the spectroscopic investigation it was confirmed that the crystal field splitting of the cerium 5di components is strongly influenced by the size of the non-emitting lanthanide ion and the molar concentration of cerium. The change in crystal field splitting consequently shaped the excitation and emission wavelengths. Additionally, T1/2 values were determined from temperature dependent emission spectra and found to be between 230 and 250 K. Furthermore, luminescent lifetimes were calculated from pulsed laser excited decay curves. On the basis of the spectroscopy results potential applications of these phosphors are discussed.