Oxide Host Research Articles

Symmetrical spirobi[xanthene] based locally asymmetrical phosphine oxide host for low-voltage-driven highly efficient white thermally activated delayed fluorescence diodes

• A spiro host with local asymmetry for blue and white TADF OLED. • Intermolecular interactions are optimized for optoelectronic improvement. • The full-TADF white OLED achieved the state-of-the-art performance. The balance between the electrical performance and quenching suppression is crucial to develop the efficient host materials for full-thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLEDs). In this work, through introducing one bulky diphenylphosphine oxide (DPPO) group at 4 position of each xanthene ring in a symmetrical and orthogonal spirobi[xanthene] (SX) skeleton, 9,9′-spirobi[xanthene]-4,4′-diylbis(diphenylphosphine oxide) ( SXDPO ) was constructed, giving rise to the optimized intermolecular interactions. Besides the high triplet (T 1 ) energy level of 2.94 eV, the highly rigid configuration of SXDPO simultaneously rendered the dramatically suppressed excited-state relaxation and the stable and uniform amorphous phase of its films before and after doping TADF dyes. It was interesting that SXDPO showed the complementary electrical properties to enhance the carrier transportation in the films. Therefore, SXDPO successfully achieved the balance between the electrical performance improvement and the collisional quenching suppression. As the result, SXDPO endowed its complementary TADF WOLEDs with the state-of-the-art performance, e.g. the turn-on voltage as low as 2.8 V and power efficiency beyond 60 lm W −1 , which was one of the best comprehensive results reported so far for full-TADF WOLEDs.

Fast anion intercalation into graphite cathode enabling high-rate rechargeable zinc batteries

Cheap, high-rate and long-life batteries are urgently needed for grid-scale storage of renewable energy. Rechargeable zinc (Zn) batteries are potential candidates due to the high volumetric energy density and low cost of Zn anode. However, conventional Zn batteries employing metal oxide cathodes usually suffer from poor rate capabilities caused by the high migration barrier of Zn2+ in the metal oxide host structure. Here, we circumvent this dilemma by integrating Zn electrochemistry with bis(trifluoromethanesulfonyl) imide (TFSI−) anion (de)intercalation into graphite cathode based on a Zn(TFSI)2/acetonitrile electrolyte. Owing to the fast intercalation of TFSI− along with the efficient Zn/Zn2+ redox kinetics, our Zn/graphite batteries enable an ultrafast charging rate up to 200C (to be fully charged in 18 s) and deliver a high power density of 16.3 kW kg−1, which is comparable to those of supercapacitors. Besides, the rational utilization of the acetonitrile-based electrolyte further endows the resultant battery with dendrite-free Zn deposition, high voltage output (>2.2 V) as well as wide-temperature adaptability from −40 to 80 °C, which is quite promising for grid-scale energy storage. Our work opens a new avenue for building high-rate low-cost batteries through coupling anion intercalation chemistry with multivalent metal anodes.

Impurity as a virtue

Understanding the activity and stability of oxygen-evolving anodes is crucial for developing better water splitting electrolysers. Researchers now show the importance of interactions between iron and hydr(oxy)oxide hosts in dynamically-stable electrocatalysts that balance dissolution and deposition of iron present in the electrolyte.

Zero-thermal-quenching of Mn4+ far-red-emitting in LaAlO3 perovskite phosphor via energy compensation of electrons’ traps

Nowadays, Mn4+-doped oxide phosphors have attracted more and more attentions owing to their widespread applications in white LEDs, optical data storage and agricultural production, but these phosphors have two most significant problems including thermal quenching (TQ) and low quantum efficiency. Here, we report a far-red-emitting LaAlO3:3%Ca2+,1%Bi3+,0.1%Mn4+ perovskite phosphor which exhibits zero-TQ even up to 150 °C and high internal quantum efficiency (IQE) of 89.3%. To our best knowledge, the zero-TQ phenomenon is first realized in Mn4+-activated perovskite phosphors caused by the synergistic action of Ca2+ and Bi3+ which is attributed to the efficient energy transfer, energy compensation and structural rigidity enhancement. Moreover, the gratifying luminous performance improvement is obtained due to charge compensation effect, optimized crystal field and excited electrons transfer. The main emission peak of this phosphor is monitored at ~730 nm which perfectly matches the absorption spectrum of phytochrome PFR which has a good application prospect for improving plant seed germination, flowering, fruiting and aging. These findings may provide a feasible way to simultaneously improve thermal stability and quantum efficiency of Mn4+ luminescence in oxide hosts.

Orbital reconstruction mediated giant vertical magnetization shift and insulator-to-metal transition in superlattices based on antiferromagnetic manganites

Heterostructures made of strongly correlated oxides host various fundamentally interesting and potentially useful emergent phenomena. ${(\mathrm{LaMn}{\mathrm{O}}_{3})}_{n}/{{(\mathrm{SrMn}{\mathrm{O}}_{3})}_{n}}_{\ensuremath{-}1}$ superlattices that consist of an $A$-type antiferromagnetic insulator $\mathrm{LaMn}{\mathrm{O}}_{3}$ and a $G$-type antiferromagnetic insulator $\mathrm{SrMn}{\mathrm{O}}_{3}$ were investigated in this work. Several very intriguing effects were observed in such superlattices that include (1) the coexistence of a strong exchange bias effect and a giant vertical magnetization shift in superlattices with intermediate periods, (2) an insulator-to-metal transition associated with a change in the superlattice thickness, and (3) a large nontrivial negative magnetoresistance around the insulator-to-metal transition. To understand these phenomena, microscopic preferential orbital occupancy in different superlattices was studied through measurements of x-ray linear dichroism at Mn $L$ edges. This study facilitated the construction of a spin configuration model that takes into account the competition between interfacial ferromagnetism and underlying canted antiferromagnetism in the superlattices and can successfully explain the observed novel magnetic and transport properties. The phase transition and giant vertical magnetization shift phenomena observed in this work offer additional degrees of freedom for applications of antiferromagnetic insulator manganite-based superlattices, enabling novel device concepts.

Cost effective way of tuning physical properties of MgAl2O4 spinel nanomaterials by Sr+2/ Mn2+ cations doped at the T-Sites

The oxide host systems in use to date have very complicated crystalline phases and obtaining the pure phase requires specific synthesis procedures and high temperatures. Secondly, the expensive and bigger rare earth ions add up to the additional costs and their accommodation in the lattice becomes a difficult task. This leads to the deterioration of the properties of host material due to the formation of secondary phases. The current project aims at the synthesis and study of the physical properties of dielectric spinel magnesium aluminate host doped at tetrahedral sites with Sr2+/Mn2+ as an alternative simple and cost-effective oxide host. Mg1-xSrxAl2O4 (x = 0.0–1.0) and Sr2+/Mn2+ co-doped derivatives having general formula Mg1-x-ySrxMnyAl2O4 (x = 0.1–0.7, y = 0.1) were prepared and studied. X-ray diffraction analysis shows a random distribution of Sr2+ at both the T- and O-sites of spinel lattice. Subsequent oxygen vacancies, empty lattice sites and antisite defects make these materials very promising luminescent materials having variety of optical centres to play with. UV–Vis spectra showed maximum absorption at 220 nm, whereas a broad emission band ranged between 350-550 nm with high intensity peak at 436 nm and two shoulders at 417 and 465 nm is observed when excited at 320 nm. The coordination environment of the optical centres is also affected by the Mn2+/Sr2+ doping resulting in blueshift in the absorbance band. Transition of color from greenish-blue to blue is observed on account of Mn2+ doping in Mg1-xSrxAl2O4 materials.

Mixed-Valence Lanthanide-Activated Phosphors: Invariance of the Intervalence Charge Transfer (IVCT) Absorption Onset across the Series

Recently, direct evidence was given for the existence of intervalence charge transfer (IVCT) states of Eu2+/Eu3+ pairs in Eu-doped fluorite hosts and their signature in absorption spectra was characterized [J. Phys. Chem. Lett. 2019, 10, 1851]. Here we show, by means of multiconfigurational ab initio calculations, that the IVCT absorptions of all 2+/3+ mixed valence lanthanides doped in CaF2 start basically at the same energy. This is rationalized with a simplified model of IVCT absorptions. Emissions above that energy are expected to be partly or totally quenched when 2+/3+ pairs are formed. On the basis of this finding and existing calculations, we report expected IVCT absorptions of mixed valence lanthanides doped in several fluoride, oxide, and sulfide hosts.

Development of Magnesium Oxide-Silver Hybrid Nanocatalysts for Synergistic Carbon Dioxide Activation to Afford Esters and Heterocycles at Ambient Pressure.

Multi-metallic hybrid nancatalysts consisting of a porous metal oxide host and metal satellite guests serve as a scaffold for multi-step transformations of divergent and energy-challenging substrates. Here we have developed a 3D porous MgO framework (Lewis basic host) with Ag0 nanoparticles (noble metal guest) for ambient pressure activation and insertion of CO2 into unsaturated alkyne substrates. The hybrid MgO@Ag-x (x = 2, 5, 7, 8 at % Ag) catalysts are synthesized by impregnating Ag+ ions in porous MgO cubes followed by reduction using NaBH4. Morphological (SEM, TEM, EDX mapping) and structural (PXRD, XPS) characterization reveal that the micron-sized hybrid cubes derive from self-assembly of ~100 nm (edge length) MgO cubes decorated with ~ 5 to 25 nm Ag0 NPs. Detailed XPS analysis illustrates Ag0 is present in two forms, <10 nm NPs and ~25 nm aggregates. The MgO@Ag-7 catalyst is effective for inserting CO2 into aryl alkynes followed by SN2 coupling with allylic chlorides to afford a wide range of ester and lactone heterocycles in excellent yields (61-93%) and with low E-factor (2.8). The proposed mechanism suggests a CO2 capture and substrate assembly role for 3D porous MgO while Ag0 performs the key activation of alkyne and CO2 insertion steps. The catalyst is recyclable (5x) with no significant loss of product yield. Overall, these results demonstrate viable approaches to hybrid catalyst development for challenging conversions such as CO2 utilization in a green and sustainable manner.

Crystal-field and Racah parameters of Mn4+ ion in red and deep red-emitting phosphors: Fluoride versus oxide phosphor

A variety of rare earth-free phosphors enabling light emission in the red spectral region have drawn much interest for use in creating a warm white-LED device with a high color rendering index and a high luminous efficacy. The Mn4+-activated phosphor properties are discussed in detail from an aspect of spectroscopic point of view. First, we classify the various host materials used in red or deep red-emitting phosphors from a different kind of host materials and from a view point of the photoluminescence (PL) and PL excitation (PLE) properties. The ever-reported Mn4+-activated phosphors can be divided into five groups, namely, fluorides, oxides, oxyfluorides, and two fluorine-based compounds. They are then classified into totally eleven subgroups from an aspect of the spectroscopic properties, e.g., whether the zero-phonon emission peak can be clearly observed or not. Next, the PL and PLE properties of the Mn4+-activated “fluoride” and “oxide” phosphors as representatives of those phosphor groups are discussed in more detail. Finally, a method is proposed for determining reliable crystal-field (Dq) and Racah parameters (B and C) with drawing an attention to difficulty in the exact estimation of such parameters using a ligand field theory. The intra-d-shell electronic states, such as 2Eg, 4T2g, and 4T1g, of Mn4+ ions activated in the fluoride and oxide hosts are obtained and plotted against Dq in the Tanabe−Sugano diagram.

Anti-oxidant activity reinforced reduced graphene oxide/alginate microgels: Mesenchymal stem cell encapsulation and regeneration of infarcted hearts

Mesenchymal stem cell (MSC) transplantation is promising for repairing heart tissues post myocardial infarction (MI). In particular, paracrine effects of the transplanted MSCs have been highlighted to play major roles in heart regeneration by secreting multiple growth factors and immune-modulatory cytokines. Nevertheless, its therapeutic efficacy still remains low, which is strongly associated with low viability and activity of the transplanted stem cells, because the transplanted MSCs are exposed to high shear stress during injection and harsh environments (e.g., high oxidative stress and host immune reactions) post injection. In this study, we aimed to develop novel injectable MSC-delivery microgel systems possessing high anti-oxidant activities. Specifically, we encapsulated MSCs in graphene oxide (GO)/alginate composite microgels by electrospraying. To further enhance the anti-oxidizing activities of the gels, we developed reduced MSC-embedded GO/alginate microgels (i.e., r(GO/alginate)), which have the potential to protect MSCs from the abovementioned harsh environments within MI tissues. Our in vitro studies demonstrated that the MSCs encapsulated in the r(GO/alginate) microgels showed increased viability under oxidative stress conditions with H2O2. Furthermore, cardiomyocytes (CMs), co-cultured with the encapsulated MSCs in transwells with H2O2 treatment, showed higher cell viability and cardiac maturation compared to monolayer cultured CMs, likely due to ROS scavenging by the gels and positive paracrine signals from the encapsulated MSCs. In vivo experiments with acute MI models demonstrated improved therapeutic efficacy of MSC delivery in r(GO/alginate) microgels, exhibiting significant decreases in the infarction area and the improvement of cardiac function. We believe that our novel MSC encapsulation system with GO, alginate, and mild reduction, which exhibits high cell protection capacity (e.g., anti-oxidant activity), will serve as an effective platform for the delivery of stem cells and other therapeutic cell types to treat various injuries and diseases, including MI.

(Invited) In Situ Grown Metal Nanoparticle Catalysts from Perovskites: Properties and Control

The ability to produce supported metal nanoparticle catalysts via exsolution from a perovskite type oxide support under reducing conditions has been known for some time and is used in solid oxide electrochemical cells. The ability to re-dissolve and exsolve the metal via redox cycling has led to these systems being referred to as smart or regenerable catalysts. While this phenomenon is well known, the mechanism by which the transition metal is exsolved from the oxide host is still poorly understood. The relationships between the exsolution process and the resulting structure of the metal nanoparticles are also not well understood. In this talk I will discuss our recent mechanistic studies of the exsolution process. Using well-defined model systems and detailed structural analysis by electron microscopy and atomic force microscopy, the nucleation and exsolution of Ni particles from Ni-doped strontium titanate was monitored. These studies show how exsolution produces unique surface structures consisting of metal particles partially submerged in pits on the oxide surface. I will show that this particle-in-a-pit morphology imparts unusually high thermal stability as well as significantly decreased carbon filament formation. Metal exsolution control will be discussed for host oxide lattices in thin film form.

In situ exsolution of PdO nanoparticles from non-stoichiometric LaFePd0.05O3+δ electrode for impedancemetric NO2 sensor

Second phase enhanced sensing electrodes have attracted special attention with respect to the effectively improved sensing performance for the solid electrolyte type gas sensors. Herein, we present a facile exsolution process conjunction with non-stoichiometry of oxide host (LaFePd0.05O3+δ) to prepare PdO nanoparticles (NPs) decorated sensing electrode for impedancemetric NO2 sensor. The as-prepared composite electrode was evaluated using various characterization methods and used to detect NO2 with phase angle (Θ) as response signal. The B site excess of the perovskite effectively promoted the NPs exsolution. Well-dispersed PdO NPs were exsolved after treatment in 10% H2/Ar at 700 °C for 30 min and then re-oxidization by switching the Ar to Air atmosphere during the cooling process. The sensor with PdO NPs decorated LaFeO3 sensing electrode exhibited excellent Θ sensing performances toward NO2 at 450–550 °C. Compared with the pristine LaFeO3 and LaFePd0.05O3+δ sensing electrodes, the decoration of PdO NPs further enhanced the response signal (ΔΘ) of the sensor accompanied by the improved sensitivity and detection limit due to the improved electro-catalytic activity of the materials. The concept exemplified here may serve in the design and development of more sensing materials with advanced functionality for gas sensors.

Unraveling the association of fecal microbiota and oxidative stress with stillbirth rate of sows

Previous studies have shown that the composition and function of gut microbiota possibly contribute to the oxidative stress and host metabolism of sows. However, a functional link between gut bacteria with oxidative stress and stillbirth rate of sows remain unclear. To address this issue, the reproductive performance, oxidative stress and gut microbiota of sows with high (H) and low (L) stillbirth rate were analyzed. Results showed that, compared with the H group, the L group had a shorter farrowing duration as well as higher concentration of serum total antioxidant capacity and hydroxyl radical scavenging capacity. For the gut microbiota composition of the tested sows, 6 genera differed between the two groups, 7 genera were correlative with stillbirth rate, and 2 genera were correlated with farrowing duration. The relative abundance of Lachnospiraceae_UCG-001, Marvinbryantia and Ruminococcaceae_UCG-004 were negatively correlated with antioxidant capacity, but positively correlated with the stillbirth rate of sows. Furthermore, the microbiota functions in the polyketide sugar unit biosynthesis and nitrotoluene degradation were found to be different between the two groups through the phylotypic investigation of communities by reconstruction of unobserved states. Collectively, gut microbiota and their functions vary between sows with high or low stillbirth rate, while stillbirth rate and farrowing duration are significantly correlated with the gut microbiota composition and oxidative stress status of sows.

(INVITED) Ultraviolet and visible luminescence from bismuth doped materials

Bismuth is a non-toxic posttransition metal with a large number of possible valence states which, together with to its tendency to form clusters, make it a versatile but complex dopant for possible luminescence applications. The outer orbitals responsible for luminescence are unshielded and strongly influenced by the surrounding environment, so that their energies are host dependent. In this review article we surveyed models that have been developed to understand the optical properties of bismuth based materials and compiled a few case studies on the luminescence of bismuth doped materials, with some emphasis on trivalent Bi3+ and simple oxide hosts (e.g. CaO:Bi; Y2O3:Bi; ZnO:Bi; La2O3:Bi; SrO:Bi; YPO4:Bi and LaPO4:Bi). Special emphasis was given to the compilation of simplified energy diagrams under different conditions. For the most stable trivalent Bi3+ state it has been experimentally found by many researchers that the absorption spectra consist of medium, weak and strong bands in order of increasing energy (designated the A, B and C bands, respectively), which were interpreted in terms of transitions to the states associated with the 3P1, 3P2 and 1P1 levels of the excited 6s1p1 configuration. Traditionally above the C band energy, but before the host absorption, a further D band is generally encountered, which is attributed to a metal-to-metal charge transfer (MMCT) transition corresponding to the transfer of an electron from the Bi3+ ion to the bottom of the conduction band. Recent modelling of this MMCT band in different materials has clarified that it may occur at energies below the C band and be an important influence on excitation spectra at lower energies. The challenge of unambiguously identifying the nature of emissions is still an ongoing challenge, as illustrated by some of the case studies.

Bipolar Poly(arylene phosphine oxide) Hosts with Widely Tunable Triplet Energy Levels for High-Efficiency Blue, Green, and Red Thermally Activated Delayed Fluorescence Polymer Light-Emitting Diodes

Polymer light-emitting diodes (PLEDs) based on thermally activated delayed fluorescence (TADF) emitters show great potential in developing high-efficiency solution-processed light-emitting devices ...

Segregation of Nickel/Iron Bimetallic Particles from Lanthanum Doped Strontium Titanates to Improve Sulfur Stability of Solid Oxide Fuel Cell Anodes

Perovskite derived Ni catalysts offer the remarkable benefit of regeneration after catalyst poisoning or Ni particle growth through the reversible segregation of Ni from the perovskite-type oxide host. Although this property allows for repeated catalyst regeneration, improving Ni catalyst stability towards sulfur poisoning by H2S is highly critical in solid oxide fuel cells. In this work Mn, Mo, Cr and Fe were combined with Ni at the B-site of La0.3Sr0.55TiO3±δ to explore possible benefits of segregation of two transition metals towards sulfur tolerance. Catalytic activity tests towards the water gas shift reaction were carried out to evaluate the effect of the additional metal on the catalytic activity and sulfur stability of the Ni catalyst. The addition of Fe to the Ni perovskite catalyst was found to increase sulfur tolerance. The simultaneous segregation of Fe and Ni from La0.3Sr0.55Ti0.95-xNi0.05FexO3±δ (x ≤ 0.05) was investigated by temperature programmed reduction, X-ray diffraction and X-ray absorption spectroscopy and catalytic tests after multiple redox cycles. It is shown that catalytic properties of the active phase were affected likely by the segregation of Ni/Fe alloy particles and that the reversible segregation of Ni persisted, while it was limited in the case of Fe under the same conditions.

Chronic Alcohol Administration Induces Inflammasome Activation in Mouse Lungs

ObjectiveExcessive alcohol misusers are 2–4 times more likely to develop respiratory infections and acute respiratory distress syndrome as compared to non‐alcoholics. Alcohol misuse enhances oxidative stress in the lung, leading to impaired lung immunity. The molecular mechanisms by which this lung immune dysfunction occurs remain poorly defined. Inflammasome activation occurs in alcoholic steatohepatitis and functions in oxidative stress and host defense. Autophagy is critical for the engulfment and degradation of intracellular pathogens and regulates inflammasome activation. Thus, we hypothesized that autophagy prevents oxidative stress and inflammasome activation in the lung induced by alcohol.MethodsLungs were collected from littermate Atg5F/F control or LysM‐Cre‐Atg5F/F mice with a macrophage‐specific knockout of the autophagy gene Atg5 that were fed either a control or ethanol‐containing (5% vol/vol) Lieber‐DeCarli diet for 5 weeks. Markers of oxidative stress and inflammation were measured in the lungs from these mice. mRNA levels of NADPH oxidase 4 (Nox4) and transforming growth factor beta (TGFβ) were assessed by qRT‐PCR. Protein expression of NLRP3, caspase‐1 and ASC were measured by western blotting and interleukin (IL)‐1β was quantitated by ELISA.ResultsIn vivo studies demonstrated that alcohol: 1) increased the mRNA levels of Nox4 and TGFβ; 2) increased components of the inflammasome complex, namely NLRP3, ASC and caspase‐1; and 3) elevated IL‐1β expression, indicative of inflammasome activation. Knockdown of Atg5 enhanced inflammasome activation and exacerbated the oxidative stress and inflammatory effects of alcohol.ConclusionsMacrophage autophagy likely plays a critical role in regulating lung oxidative stress and inflammasome activation during chronic alcohol ingestion. Inactivation of the autophagic pathway exacerbates the deleterious effects of alcohol. Therapeutic targeting of autophagy or inflammasome activation pathways could mitigate alcohol's detrimental effects on the lung and improve lung host immune defense.Support or Funding InformationResearch Funding Source: Department of Veterans Affairs 2I01BX001786 (RTS), and National Institute of Alcohol Abuse and Alcoholism 4R00AA021803 (SMY) and 5R01AA022601 (MJC).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Promoting polythionate intermediates formation by oxygen-deficient manganese oxide hollow nanospheres for high performance lithium-sulfur batteries

Mediating polysulfides redox by forming surface-bound insoluble intermediates on metal oxides is an efficient strategy to curtail polysulfides shuttling. Herein, the formation of surface-bound insoluble intermediates is further promoted by surface engineering of manganese oxide host via introducing oxygen vacancies. Hollow MnO2 nanospheres are first synthesized via a facial hard-template method, which provide a huge void for sulfur immobilization and volumetric expansion. Surface oxygen vacancies are then introduced by heating the products in a reduction atmosphere. These oxygen vacancies are proposed to accelerate the formation of polythionate intermediates, and which can adsorb polysulfides species more strongly than normal oxide sites and assist in their dissociation to lithium sulfide. The cathode based on oxygen-deficient manganese oxide hollow nanospheres achieves high initial discharge capacity of 1053 mAh g−1 at 0.5 C and high reversible capacity of 551 mAh g−1 at 2 C over 400 cycles, while only initial discharge capacity of 918 mAh g−1 and reversible capacity of 410 mAh g−1 are obtained for pristine MnO2. This work provides a novel strategy to establish cathode with engineered surface chemistry of metal oxides for high performance Li-S batteries.

Mass Transfer of Divalent Ions in an Oxide Host: Comparison of Mg2+ and Zn2+ Diffusion in Hexagonal KxW3O9 Bronze

Pure and isovalent cation-substituted potassium hexagonal tungsten bronze (KHTB) have been synthesized and used as a model oxide host to study the electrochemically driven bulk diffusion of divalen...

Up-Conversion Photoluminescence of Sol–Gel Derived CaY2O4 Powders Under 980 nm Excitation

Up-conversion is an anti-stokes process that can convert near-infrared light into visible light. Besides the requirement of high optical conversion efficiency, the thermochemical stability of the host materials is critical for in practical applications, and a stable oxide host material is optimal. CaY₂O₄ follows the same ordered structure of CaFe₂O₄, which is composed of an (R₂O₄)2- (R = rare earth metal) framework of double octahedral moieties with rare earth ions residing within the framework. CaY₂O₄ is a promising host material due to its favorable characteristics such as high chemical and thermal stability, low-phonon energy, and environment friendliness. Rare earth ion (Er3+ and Yb3+)-doped nano-crystalline phosphors were prepared by a sol-gel process. The synthesized sample was characterized by X-ray diffraction analysis and the crystallite size was confirmed by Scherrer's formula and transmission electron microscopy. The surface morphology of the powders was determined by scanning electron microscopy. X-ray diffraction patterns confirmed their pure orthorhombic structure after annealing at 1,200 °C and the morphology of particles was found to be a nearly spherical shape with a diameter of the order of ~100 nm. Photoluminescence properties of the powders were measured by exciting the samples with a 980 nm diode laser at room temperature. Under the 980-nm laser excitation, the green and red up-conversion emissions were observed at around 520- 540 nm, 540-570 nm and 640-680 nm, which, are attributed to the transitions of ²H11/2 →⁴I15/2, ⁴S3/2 →⁴I15/2 and ⁴F9/2 →⁴I15/2 of Er3+ ions, respectively. The up-conversion intensity as a function of laser power shows that the up-conversion mechanism corresponding to green and red emissions occurs via a two-photon process.