Green Upconversion Emission Research Articles

High-sensitive nonthermally coupled upconversion for ultralow temperature sensing

Upconversion based nanothermometry has received much attention due to its merits of stability, narrow band emission and rich emission peaks. However, the previous works are mainly focused on the emissions from thermally coupled energy levels which is theoretically limited by Boltzmann distribution theory with resultant low temperature sensitivity in particular at ultralow temperatures. Here we report a LiYF4:Yb/Ho@LiYF4 core-shell nanostructure to improve the sensitivity at low temperatures by taking advantage of non-thermally coupled energy levels of Ho3+. In detail, the green upconversion emission of Ho3+ shows an increase with reducing temperature while its red upconversion emission presents a decline during the same process. This is primarily due to the suppression of the non-radiative multi-phonon relaxation occurred at the green emitting levels (5F4,5S2) and the intermediate level (5I6) at low temperatures. Such a feature contributes to a high relative sensitivity of 7.17%/K at 11 K, much higher than reported values. Our results provide a promising candidate for the development of nanothermometer with high-sensitive low-temperature sensing performance.

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.

Up-conversion phosphor Na2MoO4:Er3+/Yb3+ for the optical temperature sensing and anti-counterfeiting

Lanthanide-based upconversion (UC) materials exhibit remarkable temperature-sensing properties as excited by near-infrared light. This article aims to investigate the UC emission and its temperature-sensing behavior of Na2MoO4:Er3+/Yb3+. The molybdate powder Na2MoO4:Er3+, Yb3+ shows bright green UC emission under a 980 nm laser. By monitoring the temperature-dependent green emission, the optical thermometric properties of Na2MoO4:xEr3+/0.01 Yb3+ are investigated. 1.38% K−1 is the maximum absolute sensitivity (SA) and the relative sensitivity (SR) is 1.21% K−1 with a 0.09–0.22 K temperature resolution (ΔT) at 0.001Er3+. The material was successfully combined with acrylic to prepare invisible anti-counterfeit patterns. These significant findings provide a theoretical foundation for temperature-sensing capabilities and potential applications in anti-counterfeiting measures.

Crystallization in the TeO2 - Ta2O5 - Bi2O3 system: From glass to anti-glass to transparent ceramic

Glass samples belonging the TeO2 - Ta2O5 - Bi2O3 (TTB) system are prepared by conventional melt-quenching technique and the corresponding vitreous domain is identified. A crystallization study of the 80 TeO2 - 10 Ta2O5 - 10 Bi2O3 glass composition versus temperature shows structural transitions from glass to the stabilization of an unreported translucent anti-glass phase and eventually to a fully transparent crystalline ceramic in both the visible and infrared ranges. The structure and microstructure of the anti-glass and ceramic phases are characterized by Powder X-Ray Diffraction, Electron Back-Scatter Diffraction, Transmission Electron Microscopy and Raman spectroscopy. The optical properties of undoped and Er3+-doped transparent samples are also discussed. Up-conversion green emission band shows that the glass intensity is about 2 and 4 times more intense than that of the anti-glass and the ceramic, respectively. Furthermore, a large spectral bandwidth of 105 nm is found in the anti-glass sample. The advantageous spectroscopic characteristics found here, together with the good thermal stability of these samples, suggest that the anti-glass phase has potential applications as amplification medium for the generation of ultrashort (femtoseconds) pulses.

Hydrothermal synthesis and upconversion luminescence of cubic-shaped LiNbO3:Yb3+/Er3+ nanocrystals

We exploited a simple hydrothermal route without adding organic additives or hard templates to synthesize cubic-shaped LiNbO3:Yb3+/Er3+ with the size of 400–500 nm. Based on the time-dependent investigation on the crystal structure and morphology, Yb(NO3)3 and Er(NO3)3 not only could emit green and red upconversion (UC) emission but also could be used as an etchant to increase dissolution rate of the Nb2O5 raw material in the hydrothermal synthesis route. Without addition of Yb3+/Er3+ ions, LiNbO3 phase could not be formed at even hydrothermal time of 48 h. The time-dependent Raman spectra showed the Raman peaks of LiNbO3 were occurred at the reaction time of 48 h, and the impurity Nb2O5 phase was disappeared with lengthening hydrothermal time. After calcining at 1050 °C for 2 h, the new Raman peaks at 440/487/531/552 cm−1 and the disappeared OH– absorption peaks at 3429 and 1628 cm−1 favored to produce the bright UC emissions in LiNbO3:Yb3+/Er3+ nanocrystals. The pump power dependence and UC mechanism were studied under 980 nm excitation.

Light Enhancement of Green Up-Conversion Emission from Er-Doped Silica Microspheres by Carbon Quantum Dot Coatings.

Combination of high quality cavity such as glass microsphere and emitting nano-particle coating layers can create novel strongly emitting devices. Herein, we demonstrate an erbium-doped silica microsphere coated by dual-emission carbon quantum dots, which have the sizes of 3-5nm, emitting green up-conversion with narrow line-width green light at wavelength of 537nm. The dual-emission carbon quantum dots fabricated by hydrothermal process and have luminescent emission wavelengths in the range of 410-550nm. The carbon quantum dot coated erbium silica microsphere is pumped at wavelength of 976nm through the optical fibre on which microsphere attached on the tip. The dual-emission carbon quantum dot layers attributed to the strong green up-conversion light enhancement similar coated noble metallic thin films, however the light enhancement from dual-emission carbon quantum dot coated erbium silica microsphere depended on the thickness of coating layers. This result is useful for making visible emitting micro-devices and photonic integrated circuits.

NIR activated Er3+/Yb3+ doped LiYF4 upconverting nanocrystals for photothermal treatment, optical thermometry, latent fingerprint detection and security ink applications

This work reports the upconversion (UC) emission studies on Er3+/Yb3+ doped LiYF4 nanoparticles for radiation-to-heat conversion, optical thermometry using thermally coupled and uncoupled levels, latent fingerprint detection and security ink applications. LiYF4:Er3+/Yb3+ nanoparticles have been synthesized using the thermal decomposition reaction method using oleic acid and 1-octadecane as reaction medium. Crystal phase, crystallinity and size have been investigated using XRD and TEM techniques. UC emission ability of the prepared phosphor was tested using a CW laser source having 980 nm excitation. Under 980 nm excitation, synthesized nanoparticles have shown emission bands around 522 nm, 550 nm and 668 nm corresponding to transitions from 2H11/2, 4S3/2, and 4F9/2 levels to 4I15/2 level of Er3+ ions, respectively. Further, the number of photons involved in the UC process has been calculated using a pump power UC study. Decay time analysis of the most intense green (550 nm) and red (668 nm) emission bands is performed to study the emission dynamics. A study on the radiation-to-heat conversion phenomenon has revealed photothermal conversion efficiency of 29.5% which is important for photothermal therapy. The green and red UC emissions from the sample under stimulation at very low pump power (35 mW) are used to study the optical temperature sensing characteristics. The findings of this study suggest that the Er3+/Yb3+ co-doped LiYF4 phosphor may be particularly useful for creating NIR to visible upconversion and temperature sensing. Moreover, latent fingerprint detection and security ink for anti-counterfeiting applications are also demonstrated.

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.

Upconversion luminescence and temperature sensing performance of Er3+ ions doped self-activated KYb(MoO4)2 phosphors

In this work, a series of self-activated KYb(MoO4)2 phosphors with various x at% Er3+ doping concentrations (x = 0.5, 1, 3, 5, 8, 10, 15) was synthesized by the solid-state reaction method. The phase structure of the as-prepared samples was analyzed by X-ray diffraction (XRD), XRD Rietveld refinement and Fourier transform infrared (FT-IR) spectroscopy. The as-prepared samples retain the orthorhombic structure with space group of Pbcn even Er3+ doping concentration up to 15 at%. High-purity upconversion (UC) green emission with green to red intensity ratio of 55 is observed from the as-prepared samples upon the excitation of 980 nm semiconductor laser and the optimum doping concentration of Er3+ ions in the self-activated KYb(MoO4)2 host is revealed as 3 at%. The strong green UC emission is confirmed as a two-photon process based on the power-dependent UC spectra. In addition, the fluorescence intensity ratios (FIRs) of the two thermally-coupled energy levels, namely 2H11/2 and 4S3/2, of Er3+ ions were investigated in the temperature region 300–570 K to evaluate the optical temperature sensor behavior of the sample. The maximum relative sensitivity (SR) is determined to be 0.0069 K−1 at 300 K and the absolute sensitivity (SA) is determined to be 0.0126 K−1 at 300 K. The SA of self-activated KYb(MoO4)2:Er3+ is almost twice that of traditional KY(MoO4)2:Er3+/Yb3+ codoping phosphor. The results demonstrate that Er3+ ions doped self-activated KYb(MoO4)2 phosphor has promising application in visible display, trademark security and optical temperature sensors.

Polymorphism and up-conversion photoluminescence properties of Y2WO6 doped with Yb3+/Er3+ under excitation at 975 nm

This article reports the synthesis and luminescent properties (up-conversion and down-shifting) of the tetragonal and orthorhombic polymorphs of Y2WO6 doped with Erbium (Er3+) and Ytterbium (Yb3+) cations. The syntheses were carried out by a high temperature solid state reaction. The orthorhombic phase was prepared by pressing the parent compounds into pellets of 13 mm diameter. The samples were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Luminescence up-conversion measurements were analyzed using a tunable continuous wave (CW) Ti:sapphire laser system tuned at 975 nm. The results show that the green up-conversion emission is more intense than the red one in both polymorphs. To gain further clarity on this matter, we have also conducted a study on down-shifting emission spectra measured at 378 nm, where only the strong green emission is observed. The pump power dependence and the decay curves of the (4S3/2 → 4I15/2) transition were also evaluated.

Enhanced upconversion luminescence and single-band red emission in β-Ba2ScAlO5: Yb3+/Er3+ phosphor through doping Cu2+

This study reports on a single-band red upconversion emission of Er3+ in a pure-phase β-Ba2ScAlO5: Yb3+/Er3+ fluorescent powder by doping Cu2+. The optimum concentration of Cu2+ ions in β-Ba2ScAlO5: Yb3+/Er3+ powder was 0.20. The red and green emission intensity of β-Ba2ScAlO5: Yb3+/Er3+ sample with optimum concentration of Cu2+ ions increased by 19.1 and 3.6 times, respectively, relative to the β-Ba2ScAlO5:Yb3+/Er3+ material lacking Cu2+ ions. The red-green integral intensity ratio of the β-Ba2ScAlO5:Yb3+/Er3+/Cu2+ phosphor reached 141.9. The potential upconversion luminescence (UCL) mechanism was explored by analyzing the down-shift luminescence (DS) spectra, upconversion luminescence spectra, and upconversion fluorescence lifetime decay curves of Yb3+/Er3+/Cu2+ triple-doped β-Ba2ScAlO5. Enhanced red emission and green upconversion emission are achieved by energy transfer between defect band by the oxygen vacancy and Er3+ energy levels. This study's findings establish the foundation for developing novel phosphors with single UC red light emission, which has potential applications in illumination displays, optical thermometry, and biomedicine.

Color Tuning and Optical Temperature Sensing Properties of Upconversion Emission in Yb3+/Er3+/Tm3+Doped Boro-Zinctellurite Glasses

Zinc borotellurite (B2O3/BaO/ZnO/TeO2) glasses co-doped with Tm3+/Yb3+, Er3+/Yb3+ and tri-doped Tm3+/Er3+/Yb3+ were prepared using the traditional melt quenching method. Optical absorption spectra were measured in the wavelength range of 350 nm-1100 nm at room temperature. The optical bandgap (Eg) and Urbach energy were calculated from Tauc’s plot. Blue and green emissions that can be seen by the naked eye were generated under 975 nm laser light excitation in doped Tm3+/Yb3+ and Er3+/Yb3+ doped glasses. Shifts in both blue and green color coordinates were seen as the excitation power density increased from 0.5 to 15.1 W cm−2. A white light generation was generated in glass doped with Tm3+/Er3+/Yb3+ ions, although a noticeable shift was not observed in both blue and green color coordinates for the same excitation power density range. Temperature sensing properties were investigated using the fluorescence intensity ratio of upconversion green emissions from the two thermally coupled 2H11/2 and 4S3/2 levels of Er3+ ions between 304 K and 443 K. The maximum sensitivity of the glasses doped with Er3+ and Er3+/Yb3+ were found to be 7.2 × 10−3 K−1 and 1.2 × 10−2 K−1 at 429 K, respectively.

Designing multi-mode optical thermometers via Sb3+/Er3+ co-doped Cs2NaInCl6 lead-free double perovskite microcrystals

Contactless optical thermometers are widely studied in scientific research and technology because of their apparent advantages. The combination of multi-mode thermometric techniques can realize self-referenced temperature sensing, making temperature monitoring signals more accurate. Herein, a series of Cs2NaInCl6: Sb3+, Er3+ microcrystals (MCs) were prepared via the ligand-assisted reprecipitation method. Under 320 nm excitation, the energy transfer from the self-trapped excitons (STEs) to Er3+ is established, which leads to the blue emission of STEs and intrinsic emissions of Er3+. Additionally, the MCs can also produce up-conversion green emissions under the excitation of NIR laser. Based on this, a multi-mode thermometer is developed, including the luminescence intensity ratio of two thermally coupled levels of Er3+ (2H11/2/4S3/2), the luminescence intensity ratio of a non-thermally coupled system of STEs and Er3+(4S3/2), and fluorescence lifetime of Er3+(4S3/2). Moreover, the MCs exhibit thermochromic properties, the luminescent color changes from blue to green as the temperature increases. To monitor the temperature more objectively by color variation, a novel sensing mode is constructed via the relationship between chromatic coordinates and temperature. The favorable thermometry performances for four-mode temperature sensing reveal that Cs2NaInCl6: Sb3+/Er3+ MCs are good candidates for thermometric materials for the novel multi-mode design.

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.

Activating ultralow upconversion nanothermometry in neodymium sublattice for heart tissue imaging rapid-responsive

The fields of biosensitivity and biological imaging have received a lot of attention from rare earth-doped upconversion nanoparticles (UCNPs). However, owing to the relatively large energy difference of rare earth ions, biological sensitivity based on UCNPs is restricted to detect at low temperature. Here, we design core-shell-shell NaErF4:Yb@Nd2O3@SiO2 UCNPs as a dual-mode bioprobe that produces blue, green, and red multi-color upconversion emissions at extremely low temperatures between 100 K and 280 K. Based on the thermally coupled energy levels (TCELs) of Er3+ (2H11/2 and 4S3/2) and Nd3+ (4F5/2 and 4F3/2) at 100 K, the greatest relative sensitivity (SR) approaches 12.7% K−1. NaErF4:Yb@Nd2O3@SiO2 injection is used to achieve blue upconversion emission imaging of frozen heart tissue, showing that this UCNP can serve as a low-temperature sensitive biological fluorescence.

Structure, morphology, photonconversion and energy transfer characteristics of Er3+/Yb3+:BaYF5 nanocrystals synthesized by hydrothermal method for photovoltaics

Lanthanide doped nanocrystalline fluoride optical materials have been explored for diverse applications in the solar energy harvesting, industry, medical, forensic and biological fields because of high photoluminescence quantum yield and low phonon energy. In this manuscript, Er3+/Yb3+:BaYF5 nanocrystals were synthesized by hydrothermal process. These nanocrystals were investigated through X-ray diffraction (XRD), SEM/TEM, Raman, quantum yield, photoluminescence upconversion (UC) and downconversion (DC) studies. XRD patterns exhibited the cubic phase and no phase deviation with the addition of Er3+ and Yb3+ ions. The TEM images illustrate the cubic-like morphologies of the obtained nanocrystals. Raman spectrum unveils the characteristic vibrational bands with an intense band at 498 cm−1, which is considered the phonon energy of the BaYF5 matrix. Under 488 nm excitation, the near infrared (NIR) emission of Er3+ increases up to 5 mol% and then decreases for a 10 mol% doped sample. Photoluminescence DC quantum yield of Er3+/Yb3+:BaYF5 sample is measured by using integrating sphere in the visible region under 488 nm (Xe flash lamp) excitation, is 4.25%. Under 900 nm laser excitation, intense NIR emissions at 978 and 1550 nm corresponding to Yb3+ (2F5/2 → 2F7/2) and Er3+ (4I13/2 → 4I15/2) ions, respectively, were observed. With the increase of Yb3+ concentration, the NIR emissions of both Er3+ and Yb3+ increase to 5 mol% and then decrease to 10 mol%. The strength of green UC emission of Er3+ decreases with increase of Er3+ concentration, whereas it enhances with the rise of Yb3+ concentration under 980 nm laser excitation. Two-photon UC process is confirmed as the slopes of the green, and red intensities are 2 and 2. These nanocrystals exhibit intense UC and DC emissions under 980 nm and 480 nm, respectively, which can be suitable for improving the efficiency of solar cells.

Near-zero thermal quenching of upconversion green emission implemented with the polymorphic phase transition

Thermally stable upconversion luminescence is highly expected for applications in high-temperature environments. Herein, the mechanism of the phase transition inducing near-zero thermal quenching in upconversion green light is reported. The phosphor Ba3Gd0.78Yb0.2Er0·02Al2O7.5 is synthesized by the conventional high-temperature solid-state method and quenched in air during cooling. In-situ XRD and DSC curves demonstrate the polymorphic phase transition in the subsequent heating. The temperature-dependent upconversion luminescence exhibits stable green emission instead of thermal quenching when the material is excited by a 980 nm near-infrared laser. The more intense green emission resulting from the low symmetry of the low-temperature phase and its increase in the phase content with temperature are responsible for the thermal stability in the luminescence of the material. This research provides an approach to utilizing phase transformation to obtain stable emissions in upconversion phosphors.

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.

Optical properties of Er3+ doped NaLuF4 transparent glass-ceramics produced by spark plasma sintering

Transparent oxyfluoride glass-ceramics (GCs) containing NaLuF4 nanocrystals doped with Er3+ have been prepared by combination of glass melt-quenching and spark plasma sintering (SPS) of glass powders. The parameters, such as temperature, pressure, particle size and holding times were optimized to obtain the densification of the powdered samples together with the desired transparency. The major advantage of this technique is the shorter times (few minutes) compared with those used for the preparation of these GCs by conventional heat treatments (more than 10 h). SPS presents an important inconvenient, which is the carbon contamination coming from graphite punch, this has been improved using Pt foils.The structural study indicates the presence of nanocrystals corresponding to the crystalline phase α-NaLuF4, with a crystal size between 26 and 31 nm. The optical characterization, which includes near infrared emission and infrared-to-visible up-conversion, confirms the incorporation of Er3+ ions in the nanocrystals. The longer lifetimes of the 4I11/2 and 4I13/2 levels together with the enhancement of the upconverted green and red emissions (as well as the weak blue emission) in the SPS-GCs samples, if compared with the precursor glass, indicates the presence of Er3+ ions in a crystalline environment. Possible energy conversion mechanisms for the green and red emissions based on the temporal behavior of the upconverted luminescence are discussed.

Emission colour tuning in KLnF4:Yb3+,Er3+/Ho3+ phosphor

KLnF4:Yb3+,Er3+/Ho3+ (Ln = Y, Yb, Gd) phosphors were prepared by solid-state reaction technique. For each of the Yb3+/Er3+ and Yb3+/Ho3+ co-doped phosphors independently, phase confirmation and morphological examination were accomplished using the X-ray diffraction technique and scanning electron microscope analysis. X-ray photoelectron spectroscopy analysis shows the charge state and existence of lanthanides and dopants. Upconversion luminescence emissions of green and red colour were detected for the synthesized phosphors. The changes in the upconverted emission intensities and colour output pertaining to the change of the lanthanide host matrix along with dopants were investigated for the prepared phosphors. In the upconversion luminescence, erbium-doped samples exhibit a predominance of red emission while holmium-doped samples display a prevalence of green emission. The rare-earth Er/Ho doped KYbF4 shows strong red emission compared to other hosts. KYF4:Yb,Er/Ho exhibits relatively significant green upconversion emissions, while Yb,Er-doped KGdF4 host displays a 10-fold increase in green/red emission ratio with an increase in the input power of 20–780 mW. Downshifting photoluminescence studies and decay curve analysis were carried out using UV light excitation for the developed phosphors. A higher lifetime of 2.2 ms was measured for the downshifting red emission in the Ho doped KYbF4 sample. This study suggests a potential for colour tunability in the upconversion and downshifting emissions through host modifications to the fluoride phosphor.