Cross-relaxation Process Research Articles

Steady state effects introduced by local relaxation modes on J-driven DNP-enhanced NMR

One of solution-state Nuclear Magnetic Resonance (NMR)’s main weaknesses, is its relative insensitivity. J-driven Dynamic Nuclear Polarization (JDNP) was recently proposed for enhancing solution-state NMR’s sensitivity, by bypassing the limitations faced by conventional Overhauser DNP (ODNP), at the high magnetic fields where most analytical research is performed. By relying on biradicals with inter-electron exchange couplings Jex on the order of the electron Larmor frequency ωE, JDNP was predicted to introduce a transient enhancement in NMR’s nuclear polarization at high magnetic fields, and for a wide range of rotational correlation times of medium-sized molecules in conventional solvents. This communication revisits the JDNP proposal, including additional effects and conditions that were not considered in the original treatment. These include relaxation mechanisms arising from local vibrational modes that often dominate electron relaxation in organic radicals, as well as the possibility of using biradicals with Jex of the order of the nuclear Larmor frequency ωN as potential polarizing agents. The presence of these new relaxation effects lead to variations in the JDNP polarization mechanism originally proposed, and indicate that triplet-to-singlet cross-relaxation processes may lead to a nuclear polarization enhancement that persists even at steady states. The physics and potential limitations of the ensuing theoretical derivations, are briefly discussed.

Ultrapure single-band red upconversion luminescence in Er3+ doped sensitizer-rich ytterbium oxide transparent ceramics for solid-state lighting and temperature sensing.

Achieving single-band upconversion (UC) is a challenging but rewarding approach to attain optimal performance in diverse applications. In this paper, we successfully achieved single-band red UC luminescence in Yb2O3: Er transparent ceramics (TCs) through the utilization of a sensitizer-rich design. The Yb2O3 host, which has a maximum host lattice occupancy by Yb3+ sensitizers, facilitates the utilization of excitation light and enhances energy transfer to activators, resulting in improved UC luminescence. Specifically, by shortening the ionic spacing between sensitizer and activator, the energy back transfer and the cross-relaxation process are promoted, resulting in weakening of green energy level 4S3/2 and 2H11/2 emission and enhancement of red energy level 4F9/2 emission. The prepared Yb2O3: Er TCs exhibited superior optical properties with in-line transmittance over 80% at 600 nm. Notably, in the 980nm-excited UC spectrum, green emission does not appear, thus Yb2O3: Er TCs exhibit ultra-pure single band red emission, with CIE coordinates of (0.72, 0.28) and color purity exceeding 99.9%. To the best of our knowledge, this is the first demonstration of pure red UC luminescence in TCs. Furthermore, the luminescent intensity ratio (LIR) technique was utilized to apply this pure red-emitting TCs for temperature sensing. The absolute sensitivity of Yb2O3: Er TCs was calculated to be 0.319% K-1 at 304 K, which is the highest level of optical thermometry based on 4F9/2 levels splitting of Er3+ known so far. The integration between pure red UC luminescence and temperature sensing performance opens up new possibilities for the development of multi-functional smart windows.

Realization of broadband ∼1.8 μm luminescence by level population inversion in Tm3+ doped tellurite glass for laser applications

This study aims to investigate the characteristics of Tm3+ doped TeO2–B2O3–Al2O3Na2O glass. The structures that exist in host glass were obtained from the Raman spectrum. Due to the introduction of sodium and aluminum, the TeOTe bond is broken, and the amount of bridge oxygen is reduced, causing the transformation of [TeO4] structural units to [TeO3+1] and [TeO3] structural units. The spectrum characteristics of Tm3+ in the samples were predicted by theoretical calculations. Prepared Tm3+ doped glass has large Ω2 and small Ω6, which is connected to the ligand field's asymmetry and the stiffness of the network. Furthermore, under the excitation of 808 nm laser diode, broadband ∼1.8 μm fluorescence was observed and the effective fluorescent bandwidth Δλeff of 1830 nm emission in the glass is about 234 nm. For the sample with 0.5 mol% Tm2O3, the large values of emission cross-section product (9.08 × 10−21 cm2) and σemi × Δλeff product (21.25 × 10−26 cm3) indicate a good gain property as well as a good gain bandwidth. Eventually, the energy migration process and cross-relaxation process between thulium ions were analyzed. The micro-parameter of the CR process is 4.049 × 10−40 cm6/s. Hence, the results indicate that the prepared Tm3+ doped glass could be a potential candidate for ∼2 μm mid-infrared laser devices.

Variable ratio blue/red upconversion in Yb3+-Tm3+ codoped fluorosilicate glasses.

Simultaneous blue-red emission in a fiber pumped by a single wavelength source is perceived as a great challenge because of the large energy difference of the emitted photons. This Letter reports the dependence of the blue-to-red upconversion (UC) emission ratio in Yb3+-Tm3+ codoped fluorosilicate glasses (FSGs) under the excitation of a 980-nm laser on the host glass silica content. Photoluminescence spectra and SEM-EDS are used to clarify the UC mechanism, indicating that the probability of the cross-relaxation (CR) process 1G4 + 3F2→3H6 + 3F4 is key to the dominance of the blue or red emissions. This research can provide a new platform for variable UC luminescence.

Spectral study and energy transfer analysis of Er:YAlO3 crystals

Er:YAP crystals have been proved promising mid-infrared gain materials but there is few systematic study focused on the relationship between the doping concentration and spectral properties. In this work, Er:YAP crystals with a series of doping concentrations(0.1 at.%, 1 at.%, 5 at.%, 10 at.%, 15 at.%, 30 at.%) were fast grown successfully by a modified laser-heated pedestal growth (LHPG) method. Through investigating doping concentration dependent spectral characteristics in detail, we found that the cross relaxation process (Er3+: 4S3/2+4I15/2 → 4I9/2+4I13/2) gets significantly enhanced with the doping concentration when it is below 5 at.%, and eventually tends to saturate. And the cooperative up-conversion process (Er3+: 4I13/2+4I13/2 → 4I15/2+4I9/2) conducive to high-efficiency ∼3 μm laser starts to dominate when the doping concentration is 5 at.% or even less. This result demonstrates the potential of Er:YAP crystals to achieve high-power and high-efficiency laser output under relatively low Er-doping concentration, and offers a valuable guidance for doping optimization of Er:YAP systems.

Impacts of Ce3+ doping on temperature sensing characteristics of LuAG: Yb3+/Ho3+ up-conversion fluorescent materials

A series of LuAG: 5 mol%Yb3+/0.5 mol%Ho3+/x mol%Ce3+ (x = 0, 0.2, 0.5, 1.0, 2.0) up-conversion (UC) fluorescent materials were prepared using CO2 laser heating zone melting method. The X-ray diffraction (XRD) patterns confirm that the prepared samples have a pure LuAG crystal phase. Under excitation of a 980 nm laser, the up-conversion luminescence (UCL) spectra of the prepared samples were obtained. Two UCL emission bands of Ho3+ ions were observed, including green emission band of the 5F4/5S2→5I8 transition, and red emission band of the 5F5→5I8 transition. Due to the cross-relaxation (CR) processes between Ce3+ ions and Ho3+ ions, the doping of Ce3+ ions can effectively improve the UCL efficiency of Ho3+ ions, and the emission intensity reaches maximum when doped with 1 mol% Ce3+. The temperature sensing characteristics of LuAG: Yb3+/Ho3+ and LuAG: Yb3+/Ho3+/Ce3+ from 303 K to 723 K were studied by fluorescence intensity ratio (FIR) method. By doping 1 mol% Ce3+ ions, the absolute sensitivity of the sample has been significantly improved, with the maximal absolute sensitivity of 0.0951 K−1 (303 K), and the maximal relative sensitivity of 0.0103 K−1 (343 K). The high sensitivity and wide measurement range make LuAG: Yb3+/Ho3+/Ce3+ UCL material ideal for temperature sensing.

Effect of radiative loss mechanisms on FIR thermometric parameters of Nd3+-doped lithium tellurite glasses

Nd3+-doped tellurite glasses are promising materials for thermometers based on the fluorescence intensity ratio (FIR) technique. Nevertheless, at high Nd3+ concentrations, energy transfer (ET) processes such as optical reabsorption and cross-relaxation can affect the Nd3+ emission, which has been little explored in the literature. Therefore, the present work investigated the use of Nd3+-doped tellurite glass (samples doped with Nd3+ at 0.2 mol%, 0.5 mol%, 2.0 mol%, and 4.0 mol%) in fluorescence thermometers, in the temperature range from 299 to 371 K. The results indicate a strong dependence of the FIR parameters on the Nd3+ concentration, due to changes in the emission band profiles caused by optical reabsorption of the Nd3+ emissions and cross-relaxation processes. A decrease of the relative sensitivity of the ratio 4F5/2 → 4I9/2/4F3/2 → 4I9/2 is observed for samples doped with higher amounts of Nd3+. The maximum relative sensitivity at 299 K is 3.00%/K, which is the highest value among the reported Nd3+ ions.

Effects of Eu3+ concentration on the thermoluminescence properties of narrow-band red-emitting Eu3+: SrLaGaO4 phosphor

A series of Eu3+ doped SrLaGaO4 ceramic phosphors were successfully synthesized by the solid-state reaction method. The optical properties of (x at%) Eu: SrLaGaO4 samples with x = (0.1, 1, 3, 5, 10, 15, 20, 30) were investigated and analyzed. The room temperature emission spectra of xEu: SrLaGaO4 ceramic samples, under blue and UV excitation wavelengths, showed a maximum relative emission intensity at 620 nm, corresponding to the hypersensitive 5D0→7F2 transition, with a full width at half maximum (FWHM) of ∼7 nm, for a doping concentration with Eu3+ ions of 10 at% (x = 10). The asymmetry parameter (the ratio between the 5D0→7F2 and 5D0→7F1 transitions) and the critical distance between Eu3+ ions allowed to obtain a very good color purity of the red emission (88 %) for the 10Eu: SrLaGaO4 phosphor. The cross-relaxation and energy migration processes between Eu3+ ions in the 10Eu: SrLaGaO4 sample are negligible and do not contribute to the quenching of the 5D0 emitting level. From the investigation of the temperature-dependent luminescence intensity ratio (LIR) of the 5D0→7F2 and 5D0→7F1 transitions of the 10Eu: SrLaGaO4 sample in the range of 10–575 K, the relative sensitivity parameter (Sr) was found to be 0.4 % K−1 at 10 K and 0.45 % K−1 at 450 K. These results suggest that 10Eu: SLO phosphor is a versatile material that could be operated as a temperature sensor over a wide range of temperatures, as well as a narrow-band red-emitting phosphor for phosphor-converted white light-emitting diodes (pc-WLEDs).

Spectroscopy evaluation of Nd3+-activated novel CdO–V2O5–ZnO–B2O3 inverted glasses for near infrared laser applications

Nd3+-activated CdO–V2O5–ZnO–B2O3 (CVZB) inverted glasses with chemical composition of 80–5.0-2.5–12.5 mol%, respectively, were prepared by melt-quenching to analyze their optical spectroscopy features by applying the Judd-Ofelt (JO) theory. The Nd3+ content was changed from 0.4 up to 4.0 mol%. The structural characterization carried out by X-ray diffraction patterns and Raman spectroscopy, confirmed the amorphous nature for doping contents up to 4.0 mol% of Nd3+. The direct (Egdir) and indirect (Egind) band gap obtained from the absorption spectra, showed values of 2.76 ± 0.12 and 2.50 ± 0.10 eV, respectively, without significative changes by the Nd3+ doping variations. Such band gap energy values are suitable to allow the Nd3+ emissions centered at 878, 1060 and 1332 nm, corresponding to the 4F3/2 → 4I9/2,11/2,13/2 transitions, respectively. The Nd3+ emission intensity reached the optimum at 2.8 mol% of Nd3+. At larger Nd3+ concentrations, the emission is gradually quenched due to cross-relaxation processes. These processes were dominated by electric dipole-dipole interactions within Nd3+-Nd3+ clusters, as suggested by the Inokuti-Hirayama model and critical interaction distance. The experimental branching ratios (βexp) were stables up to 1130 mW of 808 nm laser excitation, with values of (4F3/2 → 4I9/2) βexp = 0.28, (4F3/2 → 4I11/2) βexp = 0.56, and (4F3/2 → 4I13/2) βexp = 0.16. The JO parameters for the optimal emitting glass (2.8 mol% of Nd3+) obtained from least-square fitting between theoretical (fcal) and experimental (fexp) oscillator strengths, were Ω2 = 5.31 × 10−20, Ω4 = 2.81 × 10−20 and Ω6 = 3.34 × 10−20 cm2. The stimulated cross-section peak (σp), obtained from the JO parameters, resulted to be σp = 1.21 × 10−20 and 3.50 × 10−20 cm2 for the 4F3/2 → 4I9/2 and 4F3/2 → 4I11/2 transitions, respectively. The radiative (τR) and experimental (τexp) lifetimes led to quantum yield value of 0.49. Finally, laser parameters for the 4F3/2 → 4I11/2 emission, such as bandwidth (σPEMI × Δλem) and optical gain (σPEMI × τR) were calculated from the emission cross-section peak (σPEMI, 1061 nm), resulting values of 165 × 10−27 cm3 and 37 × 10−25 cm2s, respectively.

Upconversion luminescence enhancement and color modulation in Yb3+/Er3+/Ln3+ (Ln = Tm, Ho) tri-doped YF3 microrods

Intelligent regulation of energy transfer process among different rare earth ions doped in the matrix is an effective strategy to realize high-performance upconversion (UC) luminescence. Based on this, wheat ears like Yb3+/Er3+/(Tm3+, Ho3+) triple doped YF3 microrods were fabricated via hydrothermal method, and the morphology, crystal structure, UC luminescence performance dependent on Tm3+/Ho3+ doping concentrations were studied. By comparing with the Yb3+, Er3+ co-doped YF3 microrods, the UC luminescence intensity is enhanced in Yb3+/Er3+/(Tm3+, Ho3+) triple doped YF3 samples due to the cross relaxation processes between Er3+ and Tm3+/Ho3+. Moreover, red emission is enhanced more significantly than green emission in YF3: Yb3+, Er3+, Tm3+, which is contrary to that in YF3: Yb3+, Er3+, Ho3+. The possible energy transfer upconversion mechanism involved is discussed in detail. Meanwhile, an adjustable emission color is easy to achieve via altering the doped Er3+/Tm3+/Ho3+ ion concentration. These studies on the UC luminescence enhancement mechanism of Yb3+/Er3+/(Tm3+, Ho3+) triple doped YF3 microrods are expected to provide a reference for the development of high-efficiency luminescent materials.

Optical Temperature Sensors Based on Down-Conversion Nd3+,Yb3+:LiYF4 Microparticles

Nd3+ (0.3 mol.%), Yb3+ (0, 1, 2, 3 and 5 mol.%): LiYF4 phosphors were grown by the Bridgman–Stockbarger technique. The luminescence intensity ratio (LIR) of Nd3+ (4F3/2–4I9/2, ~866 nm) and Yb3+ emission (2F5/2–2F7/2, ~980 nm) was taken as a parameter. The energy exchange between 4F3/2 (Nd3+) and 2F5/2 (Yb3+) occurs via phonons, which elucidates the LIR temperature dependence. The influence of the cross-relaxation process on the temperature sensitivity was estimated as negligible. The LIR function depends on the Yb3+ concentration at a fixed 0.3 mol.% Nd3+. The maximum Sa and Sr value were reached for Nd3+ (0.3%), Yb3+ (1.0%): LiYF4 (Sa = 0.007 K−1 at 320 K) and Nd3+ (0.3%), Yb3+ (5.0%): LiYF4 (Sr = 1, 1.03%*K−1 at 260 K), respectively.

Composition dependence visible fluorescence from praseodymium ions doped Al2O3–CaO-M(M=B2O3, GeO2, Ga2O3) glasses

Pr3+ doped Al2O3–CaO based glasses were excellent candidate optical gain mediums for visible solid-state lasers due to its wide transmittance region and excellent mechanical properties. However, poor glass-forming ability limited its further application in visible fiber laser. In this work, B2O3, GeO2, Ga2O3 were employed for modifying the glass-forming ability and lowing the melting temperature of the Al2O3–CaO based glasses. By introducing 15 mol% GeO2 and Ga2O3, the thermal stability ΔT were enlarged to be 199 and 264 °C, respectively. The influence of glass composition on the fluorescence characteristic of Pr3+ were systematically investigated. For lower doping concentration, different multiphonon relaxation rare of 3P0 and 1D2 energy levels accounting for the different fluorescence spectra of Pr3+ doped Al–Ga, Al–Ge and Al–B glasses, while for the higher doping concentration, cross relaxation processes lead to the fluorescence was gradually dominated by the transition of 3P0 with increasing Pr3+ concentration.

Structural and temperature dependence luminescence characteristics of RE (RE=Eu3+, Dy3+, Sm3+ and Tb3+) in the new gadolinium aluminate borate phosphor

GdAl3(BO3)4:Dy3+, Sm3+, Eu3+, and Tb3+ samples were successfully achieved via a sol-gel combustion method. The observed XRD analysis confirms the formation of the desired GAB host, indicating rhombohedral structures that agree well with JPCD card number 72–1985. The FTIR analyses show the detection of B − O stretching and B − O − B bending modes as well as Al − O and Gd − O bonds in the phosphor samples. Energy dispersive spectroscopy (EDS) analysis reveals that Sm, Eu, Dy, and Tb have been successfully doped into GdAl3(BO3)4. The observed broad intrinsic luminescence band can be caused by oxygen-induced luminescence defects in the GAB host with hydrous precursors. The luminescence properties of rare earth ion-doped GdAl3(BO3)4 samples are analysed by photoluminescence spectra, showing their optimal doping concentrations and critical distances of Dy3+, Eu3+, Sm3+ and Tb3+ are 2 wt% − 25.8 Å, 7 wt% − 17 Å, 1 wt% − 32.59 Å, and 7 wt% − 17.03 Å. Additionally, the energy transfer mechanism for luminescence quenching was determined as dipole-dipole (for Dy3+, Eu3+, and Tb3+) or dipole-quadrupole (for Sm3+) and the cross-relaxation process. GdAl3(BO3)4 samples obtained by doping with different RE3+ ions exhibit intense light emissions with different colors originating from different RE3+ ions under 349 nm excitation. When doped with different concentrations of RE3+ ions, the luminescence properties of the samples changed. The synthesized luminescence materials have potential applications in lighting and display technologies.

The Theoretical and Experimental Study on High Power Quasi Single Mode Tm-Doped All-Fiber Laser at 1908 Nm

Thulium-doped all-fiber lasers at wavelength of 1908 nm have developed rapidly because of more applications. In this paper, a quasi single mode thulium-doped quasi single mode all-fiber laser is reported, which can generate laser powers of 30.8 W in oscillator and 83.5 W in amplifier at wavelength of 1908 nm. The slope efficiencies are 43.93% and 55.65%, respectively. Besides, the effect of active fiber length on the conversion efficiency are studied theoretically and experimentally. The results show that optimal fiber length could improve the cross-relaxation process and pump utilization. Based on the thermal conduction equations, experiments theoretically study the cooling temperature and the coefficient of convective heat transfer impacted on thermal management to obtain high laser power output.

Effect of Mn doping on structural, optical and photocatalytic properties of SnO2 nanoparticles

The bare and Mn-doped SnO2 products were prepared using a simple chemical precipitation process, which was discussed in the preparation aspect. XRD, SEM with EDS, TEM, and HRTEM studies were used to analyse the obtained Mn-doped SnO2. According to the UV-DRS data, SnO2 from Mn doping significantly reduced its band gap. The photoluminescence emissions of doped SnO2 exhibit an intensity reduction caused by the cross-relaxation process when compared to pure SnO2. The photocatalytic degradation of brilliant green (BG) using a bare SnO2 and Mn doped sample was investigated under visible light illumination. The Mn-doped SnO2 sample demonstrated a greater level of degradation (92.84%) due to its increased surface area (32.70 m2/g) and lower band gap (3.57 eV), which prevent the recombination of photogenerated charge carriers.

Cross-relaxation induced efficient 1.55 μm emission in La1.95Er0.05Ti2O7 towards an application as an amplifier for silica-fibers

The La2-xErxTi2O7 samples (with x = 0 and 0.05) were synthesized using the conventional solid-state reaction method. The spectroscopic properties of the La2-xErxTi2O7 sample (x = 0.05) were investigated. The temperature-dependence emission spectra of La1.95Er0.05Ti2O7 display several lines in the visible and infrared regions. Under the excitation of a 488 nm laser, the La1.95Er0.05Ti2O7 exhibits efficient infrared emission at 1.55 μm. The intensity of emission bands arising from the transitions 4S3/2 → 4I15/2, 4I13/2 → 4I15/2 increase with increasing temperature. To explain the efficient emission at 1.55 μm, multiphonon-relaxation and energy transfer mechanism that contains cross-relaxation processes were proposed. Under a pump of 488 nm; La1.95Er0.05Ti2O7 could serve as an amplifier for silica fibers and can be used to fabricate green light-emitting displays.

Synthesis and up-conversion luminescence of Er3+ and Yb3+ co-doped La14W8O45 phosphors

Pure phase orthorhombic Er3+ and Yb3+ co-doped La14W8O45 up-conversion luminescent materials were successfully prepared by the hydrothermal method combined with calcination treatment. The structures, morphology, and optical properties of the samples were analyzed by X-ray powder diffractometer (XRD), scanning electron microscope (SEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), and up-conversion photoluminescence spectroscopy (UPL) with a 980 nm laser. XRD results indicated that the obtained samples are single-phase orthorhombic Er3+ and Yb3+ co-doped La14W8O45 crystals. SEM results showed that the prepared sample exhibits an irregular and melted polyhedral-like morphology with agglomeration in submicron size of particles approximately 50–200 nm. UV–vis DRS results revealed that the La14W8O45 crystal is a direct semiconductor with an optical band gap of 3.84 eV. The prepared Er3+ and Yb3+ co-doped La14W8O45 crystals exhibit strong up-conversion emission peaks at about 526 nm, 548 nm, and 660 nm under 980 nm laser excitation. The intensity of up-conversion luminescence is affected by the Er3+ doping concentration, and concentration quenching will be observed due to the cross-relaxation (CR) process when the Er3+ doping content is above 1%. The pumping power dependence of the luminescence indicated that the up-conversion emissions of samples are excited by a two-photon absorption process. The color coordinates of the samples are located in the green light region.

Upconversion white-light emission luminescence characteristics based on single-particle NaYF<sub>4 </sub>microrod

White upconversion (UC) luminescent materials have shown incomparable advantages over other light sources in the fields of solid-state lighting, liquid crystal display, and bioimaging, and received extensive attention from researchers. In this work, a series of microcrystals doped with different ion concentrations is synthesized by hydrothermal method, such as NaYF<sub>4</sub>: Yb<sup>3+</sup>/Ho<sup>3+</sup>/Tm<sup>3+</sup> and NaYF<sub>4</sub>: Yb<sup>3+</sup>/Ho<sup>3+</sup>/Tm<sup>3+</sup>, and their corresponding micron core-shell (CS) structures are constructed based on epitaxial growth technology. The structure and morphology of the prepared microcrystals are characterised by X-ray diffractometer (XRD) and scanning electron microscope (SEM), showing that the microcrystal has a pure hexagonal-phase crystal structure with a rod-like shape. Under the excitation of 980 nm near-infrared laser, the white UC luminescence characteristics of Ho<sup>3+</sup>/Tm<sup>3+</sup> and Er<sup>3+</sup>/Tm<sup>3+</sup> co-doped single-particle NaYF<sub>4</sub> microcrystals are systematically studied by modulating the concentration of the doping ions. The study shows that in Ho<sup>3+</sup>/Tm<sup>3+</sup> co-doped NaYF<sub>4</sub> microcrystals, white UC luminescence can be easily achieved by modulating the concentration of Yb<sup>3+</sup> ions, while in the Er<sup>3+</sup>/Tm<sup>3+</sup> co-doped NaYF<sub>4</sub> microcrystal, the white UC luminescence can be effectively achieved by modulating the concentration of Er<sup>3+</sup> ions. According to the luminescence characteristics of the microncrystals in different doping systems, the physical mechanism of white light emission regulation is revealed, which is mainly due to the interaction between the doped ions, including cross relaxation (CR) process and energy back transfer (EBT) process. Meanwhile, an effective enhancement of the white UC luminescence on CS microrod is achieved by coating the NaYF<sub>4</sub> inert shell. Therefore, ion doping technique and the construction of CS structure can not only realize the white UC luminescence of microrods, but also provide important experimental reference for further enhancing the luminescence characteristics of microrods, and expand the applications of microcrystals in the fields of display, optoelectronics and anti-counterfeiting.

Alkaline earth metal ion doping to enhance the light emission from Er3+:SnO2 nanocrystal Co-doped silica films.

Alkaline earth metal ions (Mg2+, Ca2+, Sr2+) have been introduced into Er3+:SnO2 nanocrystal co-doped silica thin films fabricated by a sol-gel method combined with a spin-coating technique. It is found that the incorporation of alkaline earth metal ions can enhance the light emission from Er3+ at the wavelength around 1540 nm and the strongest enhancement is observed in samples doped with 5 mol% Sr2+ ions. Based on X-ray diffraction, X-ray photoelectron spectroscopy and other spectroscopic measurements, the improved light emission can be attributed to more oxygen vacancies, better crystallinity and a stronger cross-relaxation process with the introduction of alkaline earth metal ions.

Enhanced red emission of doped lanthanide ions in Gd2O3: In the perspective of phase transformation

Exploring the relationship between luminescence and the structure and morphology of rare-earth-doped host materials is essential for their expanded use in various fields. The present work investigates the luminescent properties of rare-earth ions within two structural frameworks: cubic and monoclinic Gd2O3 systems. The phase transformation of the Gd2O3 systems was determined via X-ray powder diffraction with increasing sintering temperatures. The results indicated that doping the monoclinic system with rare-earth ions resulted in significantly enhanced red emissions; in contrast, this outcome was not observed for the cubic framework. The specific crystal structure of monoclinic phase also played a key role in determining the tunable emissions as it enhanced the energy-back-transfer and cross-relaxation processes within energy transfer in ladder-like sequence. The distinguished spectral profile of rare-earth ions doped into monoclinic Gd2O3 systems leads to good potential candidates for plant growth LED applications.