Upconversion Emission Intensity Research Articles

Green upconversion luminescence of ZnO:Yb3+/Ho3+ nanophosphors prepared by various synthesis methods: Sol-gel and co-precipitation

ZnO: Yb3+/Ho3+ nanophosphors were synthesized using sol-gel and co-precipitation methods. The effects of co-doping and synthesis methods were investigated on the nanopowder's crystal structure, morphology, and optical properties. X-ray diffraction (XRD) confirmed the hexagonal wurtzite structure of the ZnO powder. The calculated crystallite sizes of the nanopowders are 30.4 nm and 21.3 nm for sol-gel and co-precipitation methods, respectively. Scanning electron microscopy (SEM) revealed that different synthesis methods and doping influence the morphology of the prepared nanophosphors. Energy dispersive X-ray spectrometer (EDS) confirmed the elemental composition and phase purity. Diffuse reflectance spectra (DRS) exhibited several absorption bands at 448 and 541 nm from sol-gel synthesized nanopowders and 453, 483, 536, and 641 nm from co-precipitation synthesized nanopowders. The energy band gap (Eg) was affected by the various methods and doping. DRS with the aid of Kubelka-Munk demonstrated that Eg ranges from 3.23 to 3.27 eV and 3.28–3.33 eV for samples prepared with sol-gel and co-precipitation method, respectively. The upconversion (UC) photoluminescence (PL) emission spectra upon excitation wavelength of 980 nm revealed two emission peaks located at 545 and 661 nm from ZnO:Yb3+/Ho3+ nanophosphors prepared by sol-gel method. These emission peaks can be attributed to 5S2/5F4 → 4I8 and 5F5 → 5I8 transitions of Ho3+ ions. The power dependence of the UC emission intensity of ZnO:Yb3+/Ho3+ was also examined. Power dependence revealed that a two-photon process was involved in the UC emissions and the possible UC mechanisms were discussed in detail. To investigate possible degradation, the stability of the UC was examined. In fact, there was no indication of phosphor UC degradation. Green emission, on the other hand, increased by about 10 % during the first 8 h of the experiment before stabilizing.

Multi-shell structured nanomaterials with strong red upconversion emission for trimodal biomedical imaging

Upconversion nanomaterials show promising applications in multimodal imaging due to their advantages such as sharp emission bands and non-autofluorescence in tissue. Obtaining intense red upconversion emission is crucial for fluorescence imaging. Herein, we designed a multi-shell structured NaErF4:0.5%Tm3+@NaYF4:20%Yb3+ @NaLuF4 upconversion nanomaterial exhibiting strong red emission and high red-to-green ratio under 980 nm irradiation. The main mechanism of the strong emission is attributed to the inert NaLuF4 shell which serves to block the energy transfer from Yb3+ to surface defects. In addition, a NaGdF4 shell is further cladded considering the property of Gd3+ of facilitating longitudinal relaxation rate of water. The properties of X-ray attenuation, longitudinal relaxation rate, and the upconversion emission of the measured sample suggest that our designed nanomaterial possesses potential for X-ray computed tomography (CT), magnetic resonance imaging (MRI), and fluorescence trimodal imaging.

Understanding and Effective Tuning of Red‐to‐Green Upconversion Emission in Ho‐Based Halide Double Perovskite Microcrystals

AbstractHo‐based lead‐free double perovskite microcrystals (MCs), Cs2NaHo1‐xYbxCl6, are synthesized and demonstrated to be promising optical temperature sensing materials by understanding the concentration‐dependent upconversion (UC) luminescence mechanisms. By optimizing the dopant concentration, a dominant emission shifting from red to green is successfully achieved in an activator‐rich system. During this process, the red to green emission intensity ratio (R/G) can be changed from 12.5 (pure red light) to 0.14 (pure green light). It is clarified that the cross‐relaxation (CR) process between activator and the energy transfer process between Yb3+ and Ho3+ are the key mechanisms of UC luminescence intensity and R/G ratio variation. Moreover, the intensity of red and green UC emission shows strong dependence on temperature, resulting from the competition between CR and energy transfer in the emission levels. The high‐sensitivity Ho‐based thermometer can be obtained by Cs2NaHo0.99Yb0.01Cl6 MCs with bright red UC luminescence, whose fluorescence intensity ratio thermometer gains maximum relative sensitivities reaching 0.68% K−1 at 400 K. The multicolor UC luminescence quantitative modeling mentioned here is crucial for understanding the concentration‐dependence UC luminescence characteristics and to optimize the design of the Ho‐based thermometer. This study can be an extension of the application range for perovskite UC materials.

Impact of varying Li+ concentration on the upconversion emission and temperature sensing characteristics of YVO4: Tm3+/Yb3+ phosphor

A series of Li+ codoped YVO4: Tm3+/Yb3+ phosphors were prepared by Pechini sol–gel reaction technique. Structural study of the material confirms the crystal structure of the prepared samples and also gives information about the crystallite size and phase purity with the variation of Li+ ion concentrations. Emission peaks around ∼ 476, and ∼ 799 nm corresponds to the 1G4→3H6, and 3H4→3H6 transitions, which could be seen under irradiation of NIR (980 nm) laser light. Li+ (10 mol%) codoped sample shows maximum upconversion. Li+ doping significantly increases the up-conversion emission intensities by more than 5 times for emission peaks around 476 nm and 799 nm.The possible explanation for the increase in UC (Upconversion) emission intensity is attributed to both improved crystallinity and crystal field modification around Tm3+ ions. The variation of UC emission spectra with respect to pump power was observed to investigate the underlying UC luminescent mechanism in YVO4: Tm3+/Yb3+ codoped with Li+ (10 mol%). The multiphoton involvement is observed in the power-dependent study of upconverted blue and NIR emission bands. Widely used fluorescence intensity ratio (FIR) technique was used to evaluate the temperature sensing capability of the optimized Li+ codoped phosphor. The FIR study of Stark components 3F2, and 3H4 levels indicates that this material is an efficient material for temperature sensing. The optimized sample, doped with Li+, exhibits relative sensitivity of 0.78% K−1 at a temperature of 548 K. This material have utility in both light-emitting diodes and as a temperature-sensing probe.

Effect of Mg2+ and Zn2+ addition on photoluminescent and photoacoustic spectroscopy of La2O3:Er3+/Yb3+ phosphors

Photoluminescence (PL) and photoacoustic spectroscopy (PAS) are important techniques for materials characterization. The La2O3: Er3+/Yb3+ phosphors samples were synthesized by combustion method and annealed at 800–1200 °C for 2 h for improved photoluminescence properties. XRD data confirmed that all samples have pure hexagonal phase and FE-SEM shows irregular granular-like morphological structures and particle size that improved with annealed temperature. Then the photoacoustic (PA) amplitude and upconversion (UC) emission intensity were successively measured by a homemade PA cell under 980 nm laser excitation. A comparative relationship was made between PA and UC varying excitation power. Then, the authors showed the effect of codoped Mg2+ and Zn2+ ions on the radiative and non-radiative properties. It is observed that UC emission intensity for Zn2+ codoped La2O3: Er3+/Yb3+ phosphor has maximum, and also observed prominent absorption peaks at 521, 658, and 955 nm. These results indicate its high potential for application in photo-thermal therapy and upconversion imaging.

Absorption bandwidth broadening of photon upconversion solid-solution organic crystals by co-dissolution of multiple sensitizers

Photon upconversion (UC) enhances the utilization efficiency of solar energy. However, UC materials generally exhibit a narrow optical absorption bandwidth of the sensitizing molecules that create excited triplet states, including the case of solid-state UC materials. Here, we demonstrate the concept of simultaneous dissolution of multiple sensitizers into crystals of fluorescent molecules to broaden the absorption bandwidth, by using an example of combining two sensitizing porphyrins. Consequently, we appreciably enhanced the UC emission intensity under simulated sunlight. In the air, the developed solid-solution crystals exhibited excellent photostability over 50 h and a low excitation threshold of <1-Sun intensity.

In situ growth of lanthanides-doped nanoparticles inside zeolites with enhanced upconversion emission for gallic acid detection

The combination of upconversion nanoparticles (UCNPs) with porous zeolites could enable the development of multifunctional composites and extend their optical applications in sensing, detection and biomedical monitoring. Herein, a series of high luminescent UCNPs@Zeolites nano-micro composites were constructed via the in situ growth strategy, by taking the low phonon-energy fluoride nanoparticles of NaLnF4 (Ln = Y, Gd) as doping hosts for Er3+/Yb3+, desilicated FAUY and ZSM-5 as the target zeolites. Benefiting from the formation of tightly combined interfaces between the UCNPs and the target zeolites that effectively passive the surface defects of UCNPs, three orders of magnitude of improved upconversion emission in maximum was obtained under 980 nm excitation through afterward heat treatment at 400 ℃. Moreover, the pre-exchange of Yb3+ into target zeolites before the in situ growth of UCNPs is another feasible approach to drastically improve the upconversion emission intensity of the UCNPs@Zeolites nano-micro composites. By taking NaGdF4:Yb,Er@DSZSM-5/HT as an example probe, the detection of GA was demonstrated and the detection ability of which is super than that of the corresponding bare NaGdF4:Yb,Er UCNPs. This research provided a universal approach to construct the UCNPs@Zeolites nano-micro composites with varied upconversion emission colors simply by choosing activator ions, which therefore indicates wide potential applications.

Constructing 3D flower-like Ho3+/Yb3+-codoped BiOCl upconverting microspheres with splendid visible-light driven photocatalytic activities towards ultrafast tetracycline removal

Exploring effective strategy to improve visible and near-infrared (NIR) light response of semiconductor photocatalysts is an urgent challenge. Herein, series of 3D flower-like BiOCl and Ho3+/Yb3+-codoped BiOCl microspheres were designed to fulfill the aforementioned issues. Via controlling the reaction time, both the morphology details and photocatalytic behaviors of 3D flower-like BiOCl microspheres are simultaneously manipulated. Moreover, excited by 980 nm light, intense upconversion emissions arising from Ho3+ are observed in 3D flower-like BiOCl microspheres, reaching up to their states when Yb3+ content is 5 mol%. On the other hand, the photocatalytic features of resultant microspheres are systematically investigated by detecting the tetracycline (TC) removal ability under visible-NIR light irradiation. Compared with 3D flower-like BiOCl microspheres, these products doped with Ho3+ and Yb3+ exhibit much better photocatalytic activities, in which the 3D flower-like BiOCl:Ho3+/0.03Yb3+ microspheres can remove 85% of TC within 2 min upon visible light irradiation. Furthermore, the 3D flower-like Ho3+/Yb3+-codoped BiOCl microspheres can also harvest the NIR light to degrade TC. It is found that h+,·O2- and·OH active species are generated during the photocatalytic process. Additionally, the toxic TC can decompose into non-biotoxicity producst by using the designed microspheres to realize wastewater purification. Our currently finding may propose prospective guidance for the preparation of highly efficient photocatalysts via using rare-earth ions doping, morphology control and upconversion emission strategy.

Morphology and luminescent properties of NaYF4 microcrystalline upconversion materials doped with ytterbium(III) and holmium(III) ions

Microcrystalline upconversion materials NaY0.8- x Yb0.2Ho x F4 ( x = 0-0.1) were synthesized by hydrothermal synthesis for the first time. All the synthesized compounds have hexagonal β-NaYF4 crystalline phase. Holmium(III) ions isomorphically replace yttrium ions. The maximum upconversion emission intensity is observed for NaY0.78Yb0.2Ho0.02F4 in the visible region of the spectrum upon excitation at a wavelength of 973 nm.

Simple express precursor synthesis of erbium-doped yttrium oxide luminescent material for optical thermometry

A new, simple and inexpensive method for the preparation of nanosized (Y1-xErx)2O3 oxides, including the stages of synthesis and thermolysis of Y1-xErx(HCOO)3 precursors, has been developed. The precursors were obtained by the interaction of mixtures of yttrium and erbium nitrates with formic acid. The effect of erbium concentration on the structure, morphology, and optical properties of (Y1-xErx)2O3 oxides was studied using X-ray diffraction, scanning electron microscopy, and optical absorption methods. Under UV excitation (Y1-xErx)2O3 oxides with 0.005≤x ≤ 0.25 exhibit strong green luminescence related to the 2H11/2/4S3/2 → 4I15/2 transitions and weak red luminescence associated with the 4F9/2 → 4I15/2 transition. According to the CIE chromaticity coordinates, the oxides demonstrate a yellowish-green color emission. A noticeable decrease in the luminescence intensity was recorded for oxides with erbium concentrations above 2.5 mol.% (x = 0.025). Yellowish-green and yellow green upconversion emission resulting from the 4S3/2 → 4I15/2 and the 4F9/2 → 4I15/2 transitions of Er3+ ions were observed upon continuous 980 nm diode laser excitation. When the concentration of erbium in (Y1-xErx)2O3 oxides increases, the luminescence color changes and the intensity of upconversion emission rises. The maximum intensity of upconversion emission was observed for the (Y0.9Er0.1)2O3 oxide. A two-photon upconversion mechanism was established based on the pumping power dependence of UC luminescence intensity. The thermoluminescence characteristics of (Y0.9Er0.1)2O3 oxides based on the ratio of the intensities of the lines corresponding to thermal-coupled 2H11/2 and 4S3/2 levels were determined, the absolute and relative sensitivity values was calculated, and the prospects for using this oxide in non-contact optical thermometers were estimated.

Near-infrared photo-responsive Er3+-K+ co-doped Y2O3 phosphors with enhanced UC luminescence

Y2O3: x% Er3+ (x=5, 7, 10, 12, 15) and Y2O3: 10% Er3+，x% K+ (x=0, 1, 3, 5, 7, 10, 15) phosphors were successfully prepared by a low-temperature combustion method. The structure as well as the absorption/emission spectra of phosphors were investigated. The effect of doping concentration of K+ ions on the upconversion (UC) luminescence of Y2O3: 10% Er3+ phosphor was examined and the possible optical transitions were discussed. The results showed that K+ ion doping not only changed the microstructure and crystallinity of the phosphors, but also enhanced its UC luminescence intensity. The Y2O3: 10% Er3+, 7% K+ phosphor exhibit the strongest UC emission intensity. Compared with the Y2O3: 10% Er3+ phosphor, the UC luminescence intensity at 563 nm and 661 nm was enhanced by 67.8 and 27.3 times for the K-codoped samples, respectively. The phosphor with the optimal doping concentration was mixed with a polymer to form a composite film, which was employed for the fabrication of near-infrared (NIR) photo-responsive detection devices. The device exhibited strong photo-current response to NIR light at 980 nm, implying that our work could inspire new design strategy for the development of NIR photo-detection devices.

Up-conversion luminescence and defect structures in Sc: Dy: LiNbO3 crystals affected by Sc3+ concentration

Up-conversion luminescent material LiNbO3 crystal has been studied intensively due to its applications in solar cells, medical applications, color displays and so on. LiNbO3 crystal with poor ability of photodamage resistance limits its application in practice. Up-conversion luminescence properties of Dy: LiNbO3 crystals doped with anti-optical damage dopants have a promising future. Four Sc: Dy: LiNbO3 crystal samples were prepared by the Czochralski technique with Sc3+ concentrations of 0, 1, 2, and 3 mol%. Effective concentrations of Sc3+ and Dy3+ in the crystals were measured by ICP-AES. The occupancy rate of the dopant and crystal structure were investigated by XRD and IR transmission spectra. The properties of up-conversion emission were studied in view of up-conversion emission intensity and fluorescence lifetime. Blue (474 nm), yellow (583 nm), and red (655 nm) up-conversion luminescence were achieved under 800 nm excitation. Remarkably, the luminescence intensity increases significantly by several times when the Sc3+ doping concentration was 3 mol%. This indicates that Sc: Dy: LiNbO3 crystals have potential as optical devices.

Benefit of Pr3+ ions to the spectral properties of Er3+/Pr3+:SrLaAlO4 crystal for use in 2.7 μm mid-infrared laser

High optical quality Er3+ single doped and Er3+/Pr3+ co-doped SrLaAlO4 crystals were grown by the Czochralski method. Detailed spectroscopic analyses of Er3+:SrLaAlO4 and Er3+/Pr3+:SrLaAlO4 crystals were carried out. With the presence of Pr3+, the intensities of the red up-conversion and near-infrared emissions reduce to 1/4 and 1/10, while the intensity of mid-infrared emission increases to 1.6 times of those for Er3+:SrLaAlO4. Furthermore, the lifetimes of 4I11/2 upper and 4I13/2 lower laser levels for 2.7 μm emission fall from 1.06 ms to 4.42 ms–0.73 ms and 0.93 ms. It means that the self-termination bottleneck in Er3+ 2.7 μm laser was inhibited in a great degree. Deactivation effect of Pr3+ ions as well as the energy transfer mechanism in Er3+/Pr3+:SrLaAlO4 crystal are discussed in detail. The results indicate that the introduce of deactivation ion Pr3+ can be beneficial for achieving an enhanced 2.7 μm emission in Er3+/Pr3+:SrLaAlO4.

High-efficiency upconversion process in cobalt and neodymium doped graphene QDs for biomedical applications

Multiphoton absorbing upconversion nanoparticles are emerging as bioimaging materials but are limited by the low quantum yield of their visible fluorescence. This article contains colloids of graphene quantum dots (GQDs), Neodymium, and Cobalt doped Graphene Quantum dots (Co-GQDs and Nd-GQDs) surrounded by carboxylic acids are synthesized which especially are suitable for bio applications; in this way, carboxylic acid groups exchanged by Amoxicillin as an antibiotic with bactericidal activity. The XRD diffraction method, TEM microscope, UV–Vis, and photoluminescence spectroscopies characterize the synthesized materials. The synthesized Quantum dots (QDs) exhibit upconversion properties and their emission is centered at 480 nm, but a red shift was observed with the increase of the excitation wavelength. In the emission spectra of synthesized QDs that can be related to the defect levels introduced by passivation of the QDs in the structure, the results show that with the interaction of the surface QDs with more carboxylic groups, the redshift is not observed. As the results indicate an increase in the intensity of upconversion emission is recorded for Co-GQDs and Nd-GQDs. The absolute quantum efficiency (QY) for Co-GQDs and Nd-GQDs were determined to be 41% and 100% more than GQDs respectively. DFT calculations indicate a strong bond between graphene and cobalt and Neodymium atoms. In doped materials, there are trap levels between the band gap of the GQDs which are responsible for increasing the intensity of the upconversion phenomenon.

An Integrated Temperature-Feedback Photothermal Therapy Platform Based on Dual-Functional Rare Earth-Doped NaSrGd(MoO4)3 Phosphors

Nd3+ doped and Er3+/Yb3+ codoped NaSrGd(MoO4)3 (NSGM) phosphors were synthesized and used to build an integrated temperature-feedback photothermal therapy platform. Intense green upconversion emissions were observed in Er3+/Yb3+-codoped NSGM phosphors and used to construct an all-fiber temperature sensing probe. The temperature dependent fluorescence intensity ratio (FIR) calibration curve was established and the absolute temperature sensitivity Sa reached the maximum value of 0.013 K–1 at 423 K. The photothermal conversion performance of NSGM:Nd3+ phosphors could be easily modified by altering Nd3+ doping concentration and 808 nm laser irradiation power. An integrated all-fiber photothermal temperature measurement platform was built and the temperature measurement error was smaller than ±1 K, which could simultaneously achieve photothermal conversion and temperature measurement in narrow spaces and was expected to be used in local photothermal therapy applications.

Highly hydrostable and flexible opal photonic crystal film for enhanced up-conversion fluorescence sensor of COVID-19 antibody

Efficient detection of related markers is significant for the early screening of COVID-19. Near infrared (NIR) light excited up-conversion fluorescence probes are ideal for biosensing but limited by the low luminescence efficiency. In this work, a novel highly stable opal photonic crystal (OPC) structure was designed to provide an OPC effect for up-conversion fluorescence enhancement, and sensitive Novel Coronavirus IgG up-conversion FRET-based sensor was further constructed. For the problems of water stability and mechanical stability of polymer OPC which cannot be solved for a long time, polymer spray combined with a flipped OPC film strategy is presented. Fragmented size OPC film was firmly fixed by polymer modification layer, which gave large size OPC film great water stability, mechanical stability and bending performance without affecting the fluorescence enhancement property. On this basis, the up-conversion emission intensity was enhanced significantly, and fluorescence resonant energy transfer (FRET) based Novel Coronavirus IgG antibody sensor was constructed. Monolayer up-conversion nanoparticles (UCNPs) on the surface of the polydopamine (PDA)/OPC film can make the fluorescent signal more sensitive, and effectively reduce the detection limit. The test device integrating NIR excitation and mobile phone realized the visual fast detection, showing remarkable sensing performance for COVID-19 antibodies with the limit of detection (LOD) of 0.1 ng mL−1. This detection platform will provide a more effective tool for early detection of the novel coronavirus.

Effect of Li+/K+/Zn2+ doping on the optical and temperature sensing properties of Tm3+ and Yb3+ doped YVO4 phosphor

The Pechini sol-gel reaction technique has been used to produce Tm3+, Yb3+ co-doped YVO4 and Li+/K+/Zn2+ codoped YVO4: Tm3+,Yb3+ phosphors. Post-heat treatment (at 800 °C) was given to all the samples to strengthen the material's structural and optical characteristics. Prepared phosphors exhibit blue and near-infrared (NIR) light. The crystalline structure and morphology of the prepared phosphors were studied by using powder X-ray diffraction (PXRD), Fourier transform Infrared spectroscopy (FTIR) and scanning electron microscope (SEM). All prepared phosphors crystallise in the tetragonal crystal structure having space group I41/amd. Prepared phosphors, when pumped with the laser at 980 nm, give strong upconversion emission in blue and NIR regions that correspond to Tm3+ transitions 1G4→3H6 and 3H4→3H6, respectively. Li+/K+/Zn2+ co-doping enhances the luminescence intensity significantly. Among Li+/K+/Zn2+ ions, Zn2+ co-doping increases the upconversion emission intensity mostly compared to others, the blue emission intensity get increased by ∼7 times and the NIR by ∼6 times. The main cause of enhancement in the emission intensity may be primarily due to the charge imbalance and asymmetry in the crystal field.Further, optical temperature sensing was also investigated by using the fluorescence intensity ratio (FIR) of the transitions (3F2,3→3H6) and (3H4→3H6). Co-doping of Li+/K+/Zn2+ ions also affects the temperature sensitivity. The relative sensitivity and absolute sensitivity of the samples were also calculated. This study indicates that this phosphor is a suitable candidate as a blue phosphor for display devices, WLEDs and optical temperature-sensing probes.

A multi-mode optical thermometer based on the up-conversion Ca3Y2Ge3O12: Er3+, Yb3+ phosphor

In order to develop a new up-conversion luminescent temperature measurement material with a garnet structure, Ca3Y2Ge3O12: Er3+, Yb3+ phosphors were prepared by a simple high temperature solid phase method. The structural phase and luminescence characteristics of the samples were characterized by X-ray powder diffraction, field emission scanning electron microscopy and photoluminescence spectra. It can be observed that the characteristic emission of Er3+ ion appears in the sample under 980 nm excitation, and it's up-conversion emission intensity increases with the increase of Yb3+ ion concentration. The maximum relative sensitivity is 1.29 %K−1, 1.09 %K−1 and 1.03 %K−1 based on the different temperature dependence of the thermal coupled energy levels (TCELs), non-thermal coupled energy levels (NTCELs) and the fluorescence lifetime (FL) of 4S3/2 state, respectively. The results show that Ca3Y2Ge3O12: Er3+, Yb3+ phosphor is excellent a material for optical temperature measurement.

Intense up-conversion luminescence from Dy3+-doped multi-component telluroborate glass matrix: Role of CuO nanoparticles embedment

This paper reports an intense up-conversion luminescence from Dy3+-doped strontium-telluro-alumino-magnesium-borate glasses for the first time. The samples were made via the melt-quenching method and characterized to determine the influence of various CuO nanoparticles contents change on their up-conversion emission traits. Absorption spectral data were used to calculate the Judd-Ofelt intensity parameters. The sample without CuO nanoparticles revealed two intense photoluminescence up-conversion emission peaks at 478 and 570 nm. In addition, CuO nanoparticles-activated sample displayed about 1.4-fold up-conversion emission intensity improvement due to strong light absorption in the visible to the infrared region at 799 nm excitation. The stimulated emission cross-section of the CuO nanoparticles-activated glasses was increased from 102.4 × 10−23 to 1301.1 × 10−23 cm2 (nearly 10-fold amplification) while the branching ratio was reduced to 66.9%. Thus, CuO nanoparticles as an additive in the current glass matrix enhanced the up-conversion emission and strengthened the associated nonlinear optical properties. CIE 1931 color matching revealed the influence of CuO in modifying the up-conversion color coordinates, thereby improving the white color purity. The achieved up-conversion emission coupled with the color tunability of the proposed glasses may be advantageous for the up-conversion UV tunable laser making.

Enhanced green up/down-conversion emissions through phase transformation in Ho3+/Yb3+ co-doped Y2O3:ZrO2 phosphors in presence of Na+ ions

This study reports the intense green upconversion and downconversion emissions from Ho3+/Yb3+/Na+ co-doped Y2O3:ZrO2 phosphor prepared by traditional solid-state reaction technique for fixed concentration of Ho3+/Yb3+ ions and different concentrations of Na+ ion. The phosphor samples exhibit a multiphase crystalline structure in the absence of Na+ ions. However, with co-doping of Na+ ions (at 20 mol%), it almost turns into Y4Zr3O12 with single rhombohedral phase. When Na + ions are present in the sample, the SEM image reveals a growth in particle size. The UV–Vis–NIR measurements show an enhancement in the absorbance of doped REs ions (Ho3+/Yb3+) on Na+ co-doping. The Ho3+/Yb3+ co-doped Y2O3:ZrO2 phosphor shows an intense green upconversion (UC) emission at 549 nm due to Ho3+ ions on the excitation with 980 nm radiation. In the presence of Na + ions, a modification of the crystallinity, growth in crystallite size (particle size) and an increase in the asymmetry of the crystalline structure around the REs ions led to an enhancement in the intensity of the UC emission almost about ∼8.5 times. The Log-Log plot demonstrates the involvement of two photons in the UC process. The lifetime of the 5F4/5S2 level decreases with increasing the concentration of Na + ion. Thus, the prepared phosphor could be an excellent candidate for source of green light, finger printing, optoelectronic devices etc.