Frequency Upconversion Emission Research Articles

BaMoO4:Nd3+-Yb3+ upconverting phosphors for NIR to NIR contactless temperature reading out

BaMoO4:Nd3+–Yb3+ phosphors have been synthesized by using conventional solid state reaction synthesis technique. Frequency up-conversion (UC) emission studies have been performed under 980 nm excitation. The developed UC phosphors show multicolor upconverted emission bands in the 400–900 nm wavelength range and assigned via the radiative transitions of Nd3+ ion. FIR technique based on frequency upconversion has been applied for the 4F7/2→4I9/2 and 4F5/2→4I9/2 transitions of Nd3+ ion in the NIR (750–804 nm) region arising from the two thermally coupled energy states. The energy gap (ΔE) between the upper and lower excited levels (4F7/2 and 4F5/2) was found to be ∼ 800 cm−1. The maximum sensor sensitivity ∼ 23.2 × 10−4 K−1 at 306 K (operating temperature range 306–483 K) under 980 nm NIR laser irradiation for BaMoO4:Nd3+-Yb3+ phosphors is reported. The prepared phosphors have proven their utility as a novel upconverting material for NIR to NIR contactless temperature reading out.

Photocatalytic activity of Ho3+-Yb3+ activated BiVO4 upconverting phosphors

The BiVO4:Ho3+-Yb3+ upconverting phosphors have been synthesized by using the chemical co-precipitation method and optimized with 0.7 % Ho3+ + 6 % Yb3+ combination through frequency upconversion emission study. The synthesized phosphors have been characterized through XRD (X-Ray diffraction), FESEM (Field emission scanning electron microscopy), HR-TEM (High resolution- Transmission electron microscopy), UV–vis diffuse reflectance spectroscopy (DRS), Raman, and FT-IR (Fourier transform infrared spectroscopy). The XPS (X-ray photoelectron spectroscopy) analysis has been performed to study the elemental composition, chemical, and electronic states of the atoms present in the optimized sample. The specific surface area of the pure and optimized phosphors has been determined through BET (Brunauer-Emmett-Teller) analysis. From the XRD analysis, it is clear that on doping, the crystal structure of BiVO4 changes from monoclinic to tetragonal structure. The values of rate constants for the photocatalytic performance of the upconverting codoped and pure BiVO4 phosphors under the illumination with an artificial solar lamp for degradation of MB dye are found to be 0.00498 min−1 and 0.00269 min−1, respectively. To verify these results, the same experiment has also been performed under the visible LED (Light-emitting diode) light illumination. This enhancement of ∼ 85 % in the rate constant of the photocatalytic performance ensured the utilization of the NIR portion of the light by the codoped BiVO4 phosphors through the frequency upconversion process. The material’s recycling photocatalysis experiment for three cycles has been performed to check its reusability. The upconversion emission and XRD analysis of the materials after photocatalysis have been performed. From this study, it is confirmed that the stability of the sample is better even after three cycles of photocatalytic dye degradation experiment.

Blue frequency upconversion emission and optical thermometry of Ca3(PO4)2: Tm3+/Yb3+

Rhombohedral phase Ca3(PO4)2: Tm3+/Yb3+ phosphor is synthesized via hydrothermal route, and then frequency upconversion emission is studied upon 980 nm excitation. The samples have resulted strong blue emission around 472 nm and two weak emission bands at 650 and 700 nm wavelengths. The blue emission was optimized by changing the Yb3+ ion concentration, and optimum emission is observed for the sample having 0.5 mol% Tm3+ and 5 mol% Yb3+. The temperature-dependent upconversion luminescence studies were done under 980 nm excitation. The Judd–Ofelt intensity parameters were calculated using the absorption spectra and found in Ω2 > Ω4 > Ω6 order. Further temperature sensitivity of sample is explored by considering 1G4 and 3F2,3 levels as non-thermally coupled. Maximum absolute sensor sensitivity is found to be 3.63 × 10−3 K−1 at 623 K. The results indicate that Ca3(PO4)2 host is suitable for achieving intense blue upconversion emission and may be helpful for biological imaging considering the biocompatibility nature of Ca3(PO4)2.

Comparative study of upconversion and photoacoustic measurements of Er3+/Yb3+ doped La2O3 phosphor under 980 nm

The Er3+/Yb3+doped La2O3 phosphor samples were synthesized by the combustion method and then photoluminescence and photoacoustic spectroscopic studies were done. Prepared samples were annealed at 800 °C, 1000 °C and 1300 °C and all samples were found in pure hexagonal phase as confirmed by XRD analysis. From FE-SEM images it is found that particle size increases with increase in annealing temperature. The frequency upconversion emission spectra of samples were recorded by exciting the sample with 980 nm diode laser and maximum emission intensity is obtained for the sample annealed at 1000 °C for 2 h. A photoacoustic cell was designed and wavelength dependent photoacoustic spectra were measured. The effect of sample storage time on radiative and non-radiative emission properties of sample was checked by measuring upconversion emission and photoacoustic spectra, simultaneously. It is observed that the emission intensity and photoacoustic signal both decreases with time. The maximum photoacoustic signal is obtained around 974 nm wavelength and it indicates its potential for photo-thermal therapy using infrared excitation.

Spiking dynamics of frequency upconverted field generated in continuous-wave excited rubidium vapors

We report on spiking dynamics of frequency upconverted emission at 420 nm generated on the 6 P 3 / 2 − 5 S 1 / 2 transition in Rb vapor two-photon excited to the 5 D 5 / 2 level with laser light at 780 and 776 nm. The spike duration is shorter than the natural lifetime of any excited level involved in the interaction with both continuous and pulsed pump radiation. The spikes at 420 nm are attributed to temporal properties of the directional emission at 5.23 µm generated on the population-inverted 5 D 5 / 2 − 6 P 3 / 2 transition. A link between the spiking regime and cooperative effects is discussed. We suggest that the observed stochastic behavior is due to the quantum-mechanical nature of the cooperative effects rather than random fluctuation of the applied laser fields.

Er3+-Yb3+-Na+:ZnWO4 phosphors for enhanced visible upconversion and temperature sensing applications

The crystal structure and surface morphology of the Er3+/Yb3+/Na+:ZnWO4 phosphors synthesized by solid state reaction method were analyzed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) analysis. The frequency upconversion (UC) emission study in the developed phosphors was investigated by using 980 nm laser diode excitation. The effect of codoping in the Er3+:ZnWO4 phosphors on the UC emission intensity was studied. The UC emission bands that are exhibited in the blue (490 nm), green (530, 552 nm), red (668 nm) and NIR (800 nm) region correspond to the 4F7/2→4I15/2, 2H11/2, 4S3/2→4I15/2, 4F9/2→4I15/2 and 4I9/2→4I15/2 transitions, respectively. The temperature sensing performance of the Er3+-Yb3+-Na+:ZnWO4 phosphors was investigated based on the 2H11/2→4I15/2 and 4S3/2→4I15/2 thermally coupled transitions of the Er3+ ions. The photometric study was also carried out for the developed phosphors.

Thermally stable red emitting xenotime phosphate nanophosphors for displays

The synthesis, structural and optical properties of the Ho3+/Tm3+/Yb3+ codoped xenotime YPO4 nanophosphors have been reported. The developed phosphors have been structurally characterized through XRD, FESEM, HRTEM, EDAX and FTIR analysis. The diffuse reflectance and frequency upconversion (UC) emission study have been performed. In the developed nanophosphors, the red UC emission intensity remains always five times stronger than the green emission of Ho3+ ion irrespective of the concentration of Ho3+ ion. The pump power dependence UC luminescence intensity and the photon numbers involved have been also studied. The energy transfer efficiency has been calculated from the decay curve analysis. The developed nanophosphors emit intense red colour having (0.60, 0.32) CIE co-ordinate with 78.4% colour purity. The nanophosphors exhibit good thermal stability having 0.22 eV activation energy.

Nd3+ -Yb3+ /Nd3+ -Yb3+ -Li+ co-doped Gd2 O3 phosphors for up and down conversion luminescence.

Frequency up-conversion (UC) emission from the Nd3+ -Yb3+ /Nd3+ -Yb3+ -Li+ co-doped gadolinium oxide (Gd2 O3 ) phosphors prepared by the solution combustion technique in the visible range have been studied by using 980nm near infrared (NIR) laser diode excitation. The crystalline structure and formation of the cubic phase has been confirmed with the help of X-ray diffraction (XRD) studies. XRD peak shifts have been found towards the lower diffraction angle side in the case of the Nd3+ -Yb3+ -Li+ co-doped phosphors. Surface morphology and particle size information have been observed by using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis. Down-conversion emission study under 351nm excitation in the visible region for the Nd3+ -Yb3+ /Nd3+ -Yb3+ -Li+ co-doped phosphors has been performed. The UC emission bands lying in the green and red region arising from the Nd3+ ions have been enhanced by ~260 times, ~113 times due to incorporation of Li+ ions in the Nd3+ -Yb3+ co-doped phosphors. Photometric characterization has been done for the Nd3+ -Yb3+ /Nd3+ -Yb3+ -Li+ co-doped phosphors. The present study suggests the capability of the synthesized phosphors in near-infrared (NIR) to visible upconverter and luminescent device applications.

An effective way to enhance upconversion emission and temperature sensing via Zn2+ incorporation in Er3+-Yb3+:YMoO4 nanophosphors

Frequency upconversion (UC) emission in the Er3+/Yb3+/Zn2+:YMoO4 nanophosphors synthesized via chemical coprecipitation method has been reported under 980nm diode laser excitation. The intensity ratio of two closely spaced green UC emission transitions peaking at ∼531nm and ∼552nm at different temperatures has been monitored. UC emission intensity and temperature sensing capability of Er3+-Yb3+:YMoO4 nanophosphors have been greatly enhanced via Zn2+ ions incorporation and explained in terms of electronegativity, breakdown in crystal field symmetry and increase in transition probability. The sensitivity, energy transfer efficiency and population redistribution ability have also been determined.

Intense Frequency Upconversion Emission of Rare Earth Codoped Lead Bismuth Gallium Borate Glasses

Intense Frequency Upconversion Emission of Rare Earth Codoped Lead Bismuth Gallium Borate Glasses

Asymmetric Nanocrescent Antenna on Upconversion Nanocrystal.

Frequency upconversion activated with lanthanide has attracted attention in various real-world applications, because it is far simpler and more efficient than traditional nonlinear susceptibility-based frequency upconversion, such as second harmonic generation. However, the quantum yield of frequency upconversion of lanthanide-based upconversion nanocrystals remains inefficient for practical applications, and spatial control of upconverted emission is not yet developed. Here, we developed an asymmetric nanocrescent antenna on upconversion nanocrystal (ANAU) to deliver excitation light effectively to the core of upconversion nanocrystal by nanofocusing light and generating asymmetric frequency upconverted emission concentrated toward the tip region. ANAUs were fabricated by high-angle deposition (60°) of gold (Au) on the isolated upconversion nanoparticles supported by nanopillars then moved to refractive-index matched substrate for orientation-dependent upconversion luminescence analysis in the single-nanoparticle scale. We studied shape-dependent nanofocusing efficiency of nanocrescent antennae as a function of the tip-to-tip distance by modulating the deposition angle. The generation of asymmetric frequency upconverted emission toward the tip region was simulated by the asymmetric far-field radiation pattern of dipoles in the nanocrescent antenna and experimentally demonstrated by the orientation-dependent photon intensity of frequency upconverted emission of an ANAU. This finding provides a new way to improve frequency upconversion using an antenna, which locally increases the excitation light and generates the radiation power to certain directions for various applications.

Frequency upconversion and fluorescence intensity ratio method in Yb3+-ion-sensitized Gd2O3:Er3+-Eu3+ phosphors for display and temperature sensing

Near infrared (NIR) to visible frequency upconversion emission studies in Er3+-Eu3+/Er3+-Eu3+-Yb3+ co-doped/tri-doped Gd2O3 phosphors prepared by the co-precipitation technique have been explored under 980 nm laser diode radiation. The developed phosphors were characterized with the help of XRD, FE-SEM and FTIR analysis. No upconversion (UC) emission was found in the Eu3+-doped Gd2O3 phosphor. UC emission from Eu3+ ions along with Er3+ ions was observed in Er3+-Eu3+ and Er3+-Eu3+-Yb3+ co-doped/tri-doped phosphors. The UC emission arising from the Er3+ and Eu3+ ions was enhanced several times due to the incorporation of Yb3+ ions. The processes involved in the UC emission were obtained on the basis of the effect of energy transfer/sensitization through the Yb3+ → Er3+ → Eu3+ process. The red/green intensity ratio was improved from 0.16 to 1.50 and 1.01 to 1.50 for Er3+-Eu3+-Yb3+ tri-doped phosphors as compared to the Er3+-doped and Er3+-Yb3+ co-doped phosphors, respectively, at a fixed pump power density. A UC fluorescence intensity ratio (FIR)-based temperature sensing study was performed in the prepared Er3+-Eu3+-Yb3+ tri-doped Gd2O3 phosphors for green upconversion emission bands in the 300 K–443 K temperature range. A maximum sensor sensitivity of about ∼0.0043 K−1 at 300 K was achieved for the synthesized tri-doped phosphors upon excitation with a 980 nm laser diode. The colour coordinates lying in the green–yellow region are invariant, with variation in pump power density and temperature. The observed results support the utility of the prepared tri-doped phosphors in optical temperature sensing, display devices and NIR to visible upconverters.

Bright Green Frequency Upconversion in Catechin Based Yb3+/Er3+ Codoped LaVO4 Nanorods upon 980 nm Excitation

A series of Yb3+–Er3+ codoped LaVO4 phosphors using catechin as a chelating agent and phase director have been prepared by the low temperature hydrothermal synthesis technique. The sample exists in two different crystalline phases, i.e., monoclinic and tetragonal, depending on the concentration of dopants. Structural, optical, and thermal characterizations have been done by using X-ray diffraction, EDX, FE-SEM, UV–vis diffuse reflectance, FTIR, and TGA analysis. Upconversion emission (UC) based imaging and drug delivery systems have been proposed to overcome some significant drawbacks of existing systems. Though fluorides are better hosts for UC, their harmful character has forced researchers to look at alternatives including oxides. The frequency upconversion emission (UC) study upon excitation at 980 nm has been performed in this particular host (m-LaVO4) which is not an ideal upconverting host. The sample emits bright green color upconversion emission, along with relatively weak emissions in the blue, ...

Ho3+-Yb3+ codoped tellurite based glasses in visible lasers and optical devices: Judd-Ofelt analysis and frequency upconversion

The optical absorption and frequency upconversion emission in the Ho3+/Yb3+ codoped TeO2-ZnO (TZ), TeO2-ZnO-WO3 (TZW) and TeO2-ZnO-WO3-TiO2 (TZWTi) glasses prepared by melting and quenching method has been studied. Judd-Ofelt theory has been used to calculate the Judd-Ofelt intensity parameters (Ω2, Ω4 and Ω6), transition probabilities, radiative lifetimes, absorption cross sections and the branching ratios. Upconversion (UC) emission bands centered at ∼ 549 nm, ∼658 nm and ∼754 nm are observed upon 980 nm excitation. On codoping with the Yb3+ ions at 3.0 mol% the upconversion emission intensity enhancement of about ∼57 times, ∼342 times and ∼480 times for the green band whereas for the red band arising from the Ho3+ ions it is about ∼71 times, ∼438 times and ∼707 times respectively have been observed. The enhancement observed in the UC emission intensity is explained on the basis of efficient energy transfer from Yb3+ to Ho3+, larger absorption cross section, larger oscillator strengths and increase in the local field corrections factor. The spectroscopic quality factor Ω4/Ω6 has been calculated to get the information about the developed materials for laser applications. The upconversion emission cross section determined on the basis of Judd-Ofelt analysis is found to be maximum for Ho-Yb-TZWTi glass. The nephelauxetic ratio, bonding and covalency parameters have been calculated to know the nature of bonding between the rare earth ions and neighbouring oxygen atoms. The high color purity 83.8% has been reported in the codoped glasses at ∼81.2 W/cm2 pump power density.

Near infrared to blue upconverting Tm3+/Yb3+/Li+:Gd2(MoO4)3 phosphors for light emitting display devices

Tm3+-Yb3+/Tm3+-Yb3+_Li+ codoped/tridoped Gd2(MoO4)3 phosphors using chemical co-precipitation method have been synthesized and characterised by XRD, FTIR, diffuse reflectance spectra and FE-SEM analysis. The downconversion emission spectra recorded by using 390nm radiation shows blue colour emission band due to the 1G4→3H6 transition of Tm3+ ion. Frequency upconversion emission study show overall intense blue, red and NIR upconversion emission bands due to the 1G4→3H6, 1G4→3F4 and 3H4→3H6 transitions of Tm3+ ion under 980nm laser diode excitation. The effect of incorporation of Li+ ions in the codoped phosphors produces small shifting in the XRD peaks towards the higher diffraction angle side and also intensity of the blue upconversion emission bands is enhanced around ∼510 times in the Tm3+-Yb3+_Li+:Gd2(MoO4)3 phosphors as compared to the Tm3+ doped phosphors. The confirmation of overall blue colour emission has been identified by colour co-ordinate analysis. The result shows that the developed tri-doped phosphors show improved blue colour emission and hence could be a proper material for near infrared to blue upconverter and blue colour emitting device fabrications.

Yb3+ sensitized Na2Y2B2O7:Er3+ phosphors in enhanced frequency upconversion, temperature sensing and field emission display

Na2Y2B2O7:Er3+/Yb3+ crystalline phosphors with single monoclinic phase have been synthesized by urea assisted solution combustion method and characterized through X-ray diffraction and Field emission scanning electron microscopy analysis. Frequency upconversion (UC) emission study has been carried out upon 980nm laser diode excitation and maximum enhancement of about ∼1433 times for the UC emission intensity of the green band in the codoped phosphor compared to that of the singly Er3+ doped phosphor has been reported. Optical temperature sensing study performed in the developed codoped phosphor reveals that the material can be used temperature sensing application within 300–613K temperature range with maximum sensitivity ∼7.9×10−3K−1 at 300K. The low-voltage cathodoluminescence measurements have been performed for Na2Y2B2O7:Er3+-Yb3+ phosphors as a function of accelerating voltage and filament current. The developed phosphors exhibit highly intense green emission with some weak emission bands in violet, blue and red regions upon electron beam excitation.

Enhanced green upconversion emission in Ho3+:Gd2O3 phosphor by codoping of Yb3+ ions

The present study explores the enhanced visible frequency upconversion emissions in the Ho3+-Yb3+ codoped Gd2O3 phosphors prepared by combustion technique. The green colour emission capability with relatively low red and NIR emissions has been confirmed under 980 nm continuous wave (CW) laser diode excitation. Three upconversion emission transitions (5F4, 5S2 →5I8, 5F5→ 5I8 and 5F4, 5S2 →5I7) has been confirmed due to presence of Ho3+ ions in Gd2O3 phosphors. By further codoping of Yb3+ ions in Ho3+:Gd2O3 phosphor, an improved upconversion emission has been reported due to the energy transfer between Yb3+ to Ho3+ ions. The observed results support that the prepared codoped phosphor can produce overall green colour emission and may be used in making green display devices and upconverters.

Up-Conversion Luminescence Properties of Ho<sup>3+</sup> Doped and Yb<sup>3+</sup>/Ho<sup>3+</sup> Co-Doped Y<sub>2</sub>WO<sub>6</sub> Phosphors

In this article, Ho3+ doped and Yb3+/ Ho3+ co-doped Y2WO6 phosphors were successfully prepared via high temperature solid method. Their structures were investigated with X-ray diffraction, the up-conversion (UC) excitation from a 980 nm diode laser, and the developed phosphor shown two UC emission bands in the visible region 540 and 643 nm. Based on the result, the intensity of the frequency up-conversion emission was enhanced significantly through co-doping with Yb3+ ions in the Y2WO6: Ho3+ phosphor. The dependence of emission intensity on the pump power indicated that the up-conversion emission was a two-photon process. At last, the energy level diagrams was discussed. The results show that Y2WO6 is a promising host material for UC phosphors.

Er3+-Tm3+-Yb3+:Gd2O3 upconverting phosphors for sensing and laser induced heating applications

This paper explores the near infrared (NIR) to visible frequency upconversion emissions in the Er3+−Tm3+−Yb3+ tri-doped Gd2O3 phosphors prepared by the combustion technique. The cubic phase formation and crystalline structure of the prepared materials has been examined with the help of X-ray diffraction study. The multicolour upconversion emission capability of the prepared materials has been confirmed under the excitation with 980-nm NIR laser source. The relative intensity variation corresponding to the transitions from the thermally coupled energy levels ( $^{2}\text{H}_{11/2}$ , $^{4}\text{S}_{3/2}$ ) to the ground level ( $^{4}\text{I}_{15/2}$ ) of Er3+ ions with pump power and temperature has been studied to investigate the optical temperature sensing ability of the prepared material. The maximum sensor sensitivity of the synthesized material reaches the value 0.0073 $\text{K}^{-1}$ at 443 K. The laser-induced heating capacity of the prepared material caused by laser excitation at different pump powers has been analyzed. The observed results support the utility of the prepared materials in optical temperature sensing and laser-induced heating along with additional capability for being used in making NIR to visible upconverter.

1.319 μm excited intense 800 nm frequency upconversion emission in Tm3+-doped fluorogermanate glass

Generation of near-infrared light within the first biological optical window via frequency upconversion in Tm3+-doped PbGeO3-PbF2-CdF2 glass excited within the second biological window at 1.319 μm is reported. The upconversion emission at 800 nm is the sole light signal observed in the entire ultraviolet-visible-near-infrared spectral region making it possible obtaining high contrast imaging. The dependence of the 800 nm signal upon the sample temperature was investigated and results showed an increase by a factor of ×2.5 in the 30–280 °C range. Generation of detectable 690 nm for temperatures above 100 °C in addition to the intense 800 nm main signal was also observed. The proposed excitation mechanism for the 800 nm thulium emitting level is assigned to a multiphonon-assisted excitation from the ground-state 3H6 to the 3H5 excited-state level, a rapid relaxation to the 3F4 level and followed by an excited-state absorption of the pump photons mediated by multiphonons connecting the 3F4 level to the 3H4 emitting level.