Er Phosphor Research Articles

Enhance optically stimulated luminescence sensitivity and improve fading of newly developed LiMgPO4:Er phosphor

To avoid fading, the readout time of the old LiMgPO4:Er in the previous study had to be taken to be at least 20 s. The readout time is up to 20 s, which not only contradicts the fast OSL readout, but also eliminates too many OSL signals per readout and is not favourable to the requirement that the OSL can be read multiple times. The primary objective of this study is to reduce readout time under conditions where the OSL signal of LiMgPO4:Er phosphor stabilizes after irradiation. The OSL properties were investigated. To achieve OSL fading of about 5% within 30 d after irradiation, the shortest integration time for new LiMgPO4:Er in this study was 1 s, whereas old LiMgPO4:Er required 20 s. When the integration time was 1 s, the OSL sensitivity of the new LiMgPO4:Er samples in this study was about 2.4 times that of the old LiMgPO4:Er samples. A new LiMgPO4:Er phosphor with an OSL signal loss of about 5% for the shortest integration time of 1 s within 30 days after irradiation, a sensitivity comparable to that of TLD-500k, and an MMD as low as 38 μGy was successfully prepared, which will meet the fast read out and the multiple readings requirements.

Novel multi-mode anti-counterfeiting encryption material of CaAl12O19:Eu, Er with multi-color down-conversion luminescence, up-conversion luminescence, dynamic luminescence, and photochromism

Multi-mode dynamic anti-counterfeiting materials can provide complex anti-counterfeiting performance and ensure the anti-counterfeiting strategy becomes more secure. Herein, a new type of multi-mode anti-counterfeiting encryption material of CaAl12O19:Eu, Er with different Er doping concentration was developed by sol–gel method. Interestingly, the CaAl12O19:Eu, Er phosphor and its composite have multi-mode anti-counterfeiting characteristics of multi-color down-conversion luminescence, up-conversion luminescence, dynamic luminescence, and photochromism. Effect of different Er doping concentration on the down-conversion luminescence, up-conversion luminescence, dynamic luminescence, and photochromism of CaAl12O19:Eu, Er was systematically investigated, and the relevant mechanisms were discussed. These anti-counterfeiting features can be simultaneously applied in both bright and dark fields, which can achieve high-level anti-counterfeiting in both spatial and temporal dimensions. The CaAl12O19:Eu, Er phosphors cannot be easily replaced by other materials with the same anti-counterfeiting properties. They display good application foreground in the field of anti-counterfeiting encryption.

Emission color tuning and enhancement of the upconversion emission in NaBiF4:Yb3+,Er3+ phosphors by controlling the Na/F ratio

NaBiF4:Yb3+(20 mol%),Er3+(2mol%) phosphors (NBF:Yb,Er) were synthesized by a simple precipitation method. Several NBF:Yb,Er samples were made with different Na/F ratios (from 2/16 to 6/16 and 6/24). XRD and SEM measurements indicated that all the NBF:Yb,Er phosphors presented an hexagonal phase and morphology of microbars with sizes of 1–2 μm, respectively. According to the photoluminescence measurements, these phosphors emitted red/green emission bands at 541/655 nm and their emission intensity increased ⁓10.5 and 21 times for the green and red bands, respectively, after increasing the Na/F ratio from 2/16 to 4/16. In addition, the emission color was tuned from deep-green to yellow. Moreover, the Na/F ratio was decreased from 6/16 to 6/24, this in turn, changed the color emission from deep-green to orange. This last change of color occurred because the red emission was mainly favored by the following two cross relaxation (CR) processes CR1: 4I11/2 (Er3+)+ 4F7/2 (Er3+)→4F9/2 (Er3+)+ 4F9/2 (Er3+) and CR2: 4S3/2 (Er3+)+ 2F7/2 (Yb3+)→4I13/2 (Er3+)+ 2F5/2 (Yb3+). The second CR2 process also promoted the NIR emission at 1527 nm. Additionally, the lifetimes for the green and red bands increased from 393 to 420 μs and from 428 to 518 μs with the Na/F ratio, respectively. Thus, we presented here a new strategy to enhance the photoluminescence intensity and to control the emission-color/lifetimes without using extra co-dopants (as previously reported in literature).

Short-term fading studies on optically stimulated luminescence in LiMgPO4:Er

The main drawback of LiMgPO4 is high fading. In order to improve the time stability of the optically stimulated luminescence (OSL) signal of LiMgPO4 after irradiation, five preparation processes had been adopted to prepare five kinds of LiMgPO4:Er phosphor. The structure of the prepared samples was analyzed by X-ray diffraction. The OSL decay curves, thermoluminescence (TL) glow curves, OSL sensitivity, minimum detectable dose (MDD) and the fading properties after irradiation for the five kinds of LiMgPO4:Er phosphors were investigated. Considering minimizing fading 24 h after irradiation, the preparation process for samples heated at 900 °C for 10 h is optimal. The OSL fading of LiMgPO4 phosphor is improved significantly by changing the preparation processes. The less than 5% loss of the OSL signal was measured after 24 h of the irradiation for samples heated at 900 °C for 10 h when the integration time is more than 0.5 s, and the sensitivity by taking the total area under the OSL curve of this samples is about half that of TLD-500k. There is a loss of less than or equal to 5% of the OSL signal for samples heated at 900 °C for 10 h when the integration time is greater than or equal to 20 s within 30 days after irradiation. LiMgPO4:Er samples heated at 900 °C for 10 h is the LiMgPO4 phosphor with the lowest fading so far. It is possible to prepare a LiMgPO4 phosphor with a low fading after irradiation and a moderate sensitivity by further investigating the preparation processes.

Dependence of the temperature sensitivity on the shape of upconversion phosphors NaYF<sub>4</sub>:Yb,Er

Varying the synthesis parameters, NaYF4:Yb,Er phosphors were obtained, which have pronounced upconversion properties upon excitation according to the expression of 980 nm waves. Based on the data of luminescent spectroscopy, it was found that there are 240–350 particles.

Novel strategies to tune the color emission of Bi2Ti2-xZrxO7:Er3+,Yb+3 upconversion phosphors: Substituting Ti by Zr and annealing at high temperatures

Bi2Ti2-xZrxO7:Er3+,Yb3+ phosphors were synthesized with different content of Zr (X = 0–1.5) by combustion method at 550 °C, producing a mixture of Bi2Ti2O7/Bi4Ti3O12 phases. After increasing the synthesis temperature to 1000 °C, a pure Bi2Ti2O7 (BiTiO) phase was obtained as well as porous coalesced microparticles (2–10 µm) with pore sizes of 110–420 nm. Those samples produced green (548 nm)/red (655 nm) and NIR (1530 nm) emission bands after excitation with 980 nm and their color emission was tuned from green to yellow–red or viceversa using two strategies: i) by increasing the Zr content in the Bi2Ti2-xZrxO7:Er3+,Yb3+ host (from X = 0 to 1) or ii) by increasing the synthesis temperature from 550 to 1000 °C. Interestingly, the intensity of the NIR and red emission bands was enhanced with the content of OH groups on the surface of the BiTiO:Yb,Er phosphors.

Green Upconversion of a SrLaAlO4:Yb,Er Phosphor and Its Application for LED Illumination

Green Upconversion of a SrLaAlO4:Yb,Er Phosphor and Its Application for LED Illumination

Europium and erbium co-doped yttria-stabilized zirconia as a potential dual-sensor for simultaneous oxygen partial pressure and temperature measurements

In this study, the phosphorescence properties of Eu3+ and Er3+ co-doped yttria stabilized zirconia (YSZ: Eu3+, Er3+) as a function of oxygen partial pressure and temperature are investigated to explore the possibility of using this phosphor for pressure and temperature measurements at elevated temperature (up to 600 °C). The YSZ: Eu3+, Er3+ phosphors have a fixed Eu3+ concentration (1 mol%) and a varied Er3+ concentration (0.5–5 mol%). The phosphorescence intensity and lifetime of Eu3+ bands are sensitive to both oxygen partial pressure and temperature when temperature exceeds 400 °C. This oxygen/pressure sensitivity is related to the oxygen vacancy-induced non-radiative decay through charge transfer state (CTS), and is inversely correlated with Er3+ concentration. In contrast, the phosphorescence intensity and lifetime of Er3+ bands are temperature-sensitive but oxygen-insensitive, which is related to the dominant oxygen-independent 4S3/2 → 2H11/2 transition. Accordingly, two measurement strategies are proposed including an intensity ratio method and a lifetime method. The intensity ratio of the oxygen-sensitive Eu3+ bands and the oxygen-insensitive Er3+ reference bands is capable of 2D pressure measurement using a dual-camera system. But temperature-induced errors exist due to the temperature-sensitivity of intensity ratio. Simultaneous pressure and temperature measurements (point by point) can be achieved utilizing two PMTs that record the lifetimes of Eu3+ and Er3+, respectively. This method can resolve the issue of temperature sensitivity of Eu3+ and accurately correct the temperature-induced errors. The YSZ: Eu, Er phosphors show great potential for applications in high-temperature environment where the existing organic PSPs and TSPs cannot survive.

Effect of Structural Perfection of Crystalline β-NaYF4:Yb,Er Phosphor Powders on the Efficiency of Their Upconversion Luminescence

Effect of Structural Perfection of Crystalline β-NaYF4:Yb,Er Phosphor Powders on the Efficiency of Their Upconversion Luminescence

Tuning the structural and luminescence properties of LiYF4:Yb, Er upconversion phosphor: Understanding the role of K ion concentration

Influence of K+ ion concentrations on the upconversion emissions of LiYF4: Yb, Er phosphor has been investigated. Li1−xKxY0.77F4:Yb0.2, Er0.03 phosphors are synthesized by solid-state reaction method under reduced atmosphere. X-ray diffraction analysis revealed a major phase transition from tetragonal LiYF4 to hexagonal KYF4 as the concentration of K+ ion increases. Blue, green and red upconversion emissions are observed when the samples are excited at 980 nm. Green and red luminescence intensities are affected by the inclusion of K+ ion concentrations in the host lattice. Downshifting photoluminescence and the corresponding decay analysis are carried out for the Li1−xKxY0.77F4:Yb0.2, Er0.03 phosphors under the excitation wavelength of 378 nm. Significant changes in the emission intensity of the green to red ratio suggest the tuning of the emission color with the modification of the K+ ion concentrations in Li1−xKxY0.77F4:Yb0.2, Er0.03 host and such successful tuning in the color of emission can find potential applications in the field of display devices.

Quintuple-mode dynamic anti-counterfeiting using multi-mode persistent phosphors

Multi-level, dynamic optical anti-counterfeiting has been achieved using multi-mode phosphors as luminescent inks. The ZGGO:Cr,Yb,Er phosphors exhibit quintuple luminescence modes, while the ZLGO:Mn phosphors possess quadruple luminescence modes.

Synthesis and luminescence of Gd2-x-yYbxEr(Ho)yGeMoO8 germanate-molibdates with scheelite structure

A series of Gd2-x-yYbxEr(Ho)yGeMoO8 sheelites comprising Gd2GeMoO8 matrix doped by Yb3+-Er3+ and Yb3+-Ho3+in various concentrations (GGMO:Yb,Er and GGMO:Yb,Ho) have been prepared by solid state and sol-gel (Pechini) methods. Besides the confirmation of monophasic state (powder XRD) of the samples prepared at different temperatures, their morphology (scanning electron microscopy, SEM) as well as luminescence under infrared (IR) laser excitation (974 ​nm) with 1.0 and 2.5 ​W/cm2 pumping power density of GGMOs have been systematically investigated. All synthesized samples possess Scheelite structure (tetragonal syngony, sp. gr. I41/a). Under 974 ​nm excitation, GGMO:Yb,Er phosphors exhibit upconversion (UC) emission peaks at 525, 545 and 655 ​nm originating from 2H11/2, 4S3/2 - 4I15/2 and 4F9/2 - 4I15/2 Er3+ transitions with a significant predominance of green band. Virtually monochromatic bright green emission was observed for GGMO:Yb,Er with Yb:Er 8:3 ratio, synthesized by solid-state method at 1250 ​°C. In the UC luminescence spectra of GGMO: Yb, Ho the intensity of the Ho3+ red band (5F5 → 5I8 transition, λ ​= ​665 ​nm) exceeds that of green band (5S2, 5F4 → 5I8, λ ​= ​545 ​nm), but visually, the color of the luminescence was perceived as yellow.Among GGMO:Yb,Er and GGMO:Yb,Ho samples, those with Yb:Er and Yb:Ho ratios of 9:4 were revealed as more promising. The application of Pechini method affords nanosized GGMO:Yb,Er and GGMO:Yb,Ho UC phosphors already after annealing at 1000 ​°C, but phosphors annealed at 1200 ​°C were more efficient. Their morphology is irregularly shaped and strongly aggregated roughly-spherical grains with average size of 150–200 ​nm. Due to high thermal and chemical stability, these phosphors may be applied in various fields requiring IR detection.

Winning wide-temperature-range and high-sensitive thermometry by a multichannel strategy of dual-lanthanides in the new tungstate phosphors

Abstract Both high sensitivity and wide temperature range are vital guides for up-conversion (UC) thermometers. However, high sensitivities were limited to a very narrow temperature range in existing optical thermometers. Also, the highest sensitivity usually occurred at elevated temperatures, while the sensitivity at room temperature or below it is very low or scarce. To overcome such a state, a novel optical thermometer with high sensitivities over a wide temperature range was designed. Lanthanide-doped UC phosphors with LiCaYb(WO4)3 (LCYW) as a novel host, were synthesized by a solid-state reaction process. Temperature sensing properties were carried out by a fluorescence intensity ratio (FIR) technique. High sensitivities of 0.01–0.0191 K-1 over the temperature range of 288–663 K were obtained in LCYW:0.03Er phosphor, which originated from the energy levels of Er3+ (2H11/2/4S3/2). Then, the thermal coupling levels (TCLs) and non-thermal coupling levels (NTCLs) were used to study the temperature sensing properties by co-doping Tm3+ ion. Excellent temperature sensing sensitivities were achieved, which are the higher sensitivities of 0.01–0.0216 K-1 over the range of 253–663 K based on the same TCLs of 2H11/2/4S3/2 and the highest sensitivity of 0.0563 K−1 at 663 K based on the NTCLs of 4S3/2 (Er3+)/3F2,3 (Tm3+). Besides, a multichannel strategy that mentions both sensitivity and temperature range was provided. Thus, the resulting new sensor can be operated in the wide temperature sensing range of 163–663 K with sensitivities of 0.011–0.0563 K-1. All of the results suggest that the LCYW:Er/Tm UC phosphor could be a good candidate with its high sensitivities for optical thermometry and as a safety sign in low and high temperatures.

Luminescence decay-based Y2O3:Er phosphor thermometry: Temperature sensitivity governed by multiphonon emission with an effective phonon energy transition

To shift the onset of thermal quenching by multiphonon emission to higher temperatures, thermographic phosphors for high-temperature applications are usually selected with a large energy gap between the radiatively emitting energy level and the next lowest energy level. An alternate approach is presented where Y2O3:Er, with a relatively small energy gap of 2795 cm−1 between the 4S3/2 emitting level and the 4F9/2 level below it, provides effective temperature measurements from room temperature to 1200 °C. The smaller energy gap results in an expanded temperature measurement range because (1) it results in a lower temperature onset of thermal quenching by multiphonon emission and (2) the smaller number of phonons required to bridge the energy gap produces a weaker temperature-dependent increase in multiphonon emission rates with temperature. Utilizing the intense hypersensitive 4I15/2 → 2H11/2 Er3+excitation at 522 nm offsets the temperature precision reduction due to the decreased decay time temperature sensitivity. Two distinct temperature sensitivity ranges are observed due to a crossover in multiphonon emission relaxation from high to low effective phonon energies at about 950 °C. The implications of this transition from high to low effective phonon energies for selection of dopant hosts for high-temperature thermographic phosphor applications are discussed.

Investigations of the effect of trivalent erbium concentration on orthophosphate powder for green and yellow-orange light emitting phosphor

Lately, interesting features of lighting Rare Earths doped phosphorus have gained much attention and became favorite research matter among various groups of scientists. In this context, polycrystalline powders of Na3La(PO4)2: Er (0%, 2,5%) have been prepared by the solid state method. Powder X-ray diffraction, infrared spectroscopy have been used to identify these materials. The spectroscopic properties of Na3La(PO4)2: Er (2,5%) have been investigated through absorption, excitation, emission spectra and decay curves of Er3+ at room temperature. The decay time reveal that Na3La(PO4)2: Er (2,5%) possesses a radiative transition and the lifetime value for the transition 4F9/2 → 4I15/2 is found equal to 144.92 μs. All obtained results have been presented, compared and discussed with last reported works. The CIE chromaticity coordinates have been highlighted. They reveal that Na3La(PO4)2: Er (2,5%, 10%, 20% and 50%) phosphor can be a promising green and yellow-orange luminophore for application in LED.

Synthesis, structure and optical properties of erbium-doped lithium barium phosphate

Li2BaP2O7 activated with Er3+ ions was prepared by the classic ceramic method and characterized by X-ray diffraction technique, IR, Raman and photoluminescence (PL) spectroscopies. The Li2BaP2O7: Er phosphors exhibited a monoclinic single phase structure with C2/c space group. A green and red emission lines dominate the spectrum upon excitation at 400 nm. The CIE-coordinate (x = 0.308, y = 0.512) were found in green light. Free ion parameters of the Er3+ ions in Li2BaP2O7 and the Judd–Ofelt parameters were calculated and they were used to explore the radiative parameters such as transition probability (AT), and branching ratios (β) related to the Er3+ emission transitions. The calculated 4S3/2 radiative life time around 0.198 ms is compared with the experimental value. The calculated quantum efficiency is about 42%. Li2BaP2O7: Er can be considered as a novel green phosphor.

Effect of the Er3+ Co-dopant on the Green Upconversion Emission of LaSr2AlO5:Yb3+ Phosphors

This work presents the structural, morphological and optical properties of LaSr2AlO5:Yb3+,Er3+ phosphors (LSA:Yb,Er) synthesized by a combustion method. The Yb3+ concentration was kept constant at 2 mol.%, while the Er3+ concentration changed from 0.2 mol.% to 6 mol.%. X-ray diffraction measurements revealed that all the LSA:Yb,Er phosphors presented a pure tetragonal phase. Scanning electron microscopy images show that LSA:Yb,Er phosphors increased their size as the Er3+ concentration increases (from 1.95 μm for Er3+ concentrations 1 mol.%, the LSA:Yb,Er phosphors present a notorious increase of conglomeration, and the particles had irregular morphologies. According to luminescence measurements, the LSA:Yb,Er phosphors present a green luminescence centered at 549 nm (λexc = 968 nm). The strongest green emission was observed for an Er3+ concentration of 1 mol.%, above this concentration, the green emission intensity decreases due to an excess of OH and carbonate groups on the surface of LSA:Yb,Er phosphors, as confirmed by the FTIR spectra. Moreover, the CIE coordinates for the green emission were tuned with the Er3+ concentration. These results suggest that LSA host could be a good candidate to produce upconversion emission when doped with rare earths, which could be attractive for the development of lighting sources.

Upconversion/Downconversion luminescence and preparation of NIR-to-UV-excited Gd2O2S:Er phosphor

Efficient conversion of ultraviolet (UV) and near-infrared (NIR) radiations to visible emissions were carried out through Gd2O2S:Er phosphor synthesized by solid-state reaction method in vacuum. The spectra study of Gd2O2S:Er phosphor was performed as a function of firing temperature under the excitation wavelengths of 379 and 980 nm, respectively. The emission bands in visible light region corresponding to the transitions between 2H9/2 → 4I15/2 (412 nm), 4F7/2 → 4I15/2 (488 nm), 2H11/2 → 4I15/2 (531 nm), 4S3/2 → 4I15/2 (554 nm) and 4F9/2 → 4I15/2 (670 nm) were demonstrated. Color emission can be tuned from red to green due to Er3+ ions doping by varying the firing temperature under 379 nm UV light excitation. First principles calculation results indicated that crystallographic plane of (101) has higher absorption efficiency than the crystallographic plane of (100) thus to result in higher luminescent intensity.

Mechanisms and absolute quantum yield of upconversion luminescence of fluoride phosphors

Mechanisms of upconversion luminescence (UCL) of SrF2:Er phosphors corresponding to the G411/2→I415/2, H29/2→I415/2, F45/2→I415/2, F47/2→I415/2, H211/2→I415/2, S43/2→I415/2, F49/2→I415/2, and I49/2→I415/2 transitions upon excitation of the I411/2 level of Er3+ ions were investigated. Energy transfer upconversion processes are responsible for the populating of the H29/2, H211/2, S43/2, and F49/2 levels. Cooperative process is the dominant mechanism of luminescence from S43/2 and F49/2 levels for SrF2:Er with high concentrations of Er3+ ions. The UCL from G411/2 and F45/2 is explained by excited-state absorption. Cross-relaxation processes take part in the population of F49/2 and I49/2 levels. For quantifying material performance, the Er3+-concentration dependence of UCL and the absolute quantum yields of SrF2:Er were studied. The most intensive visible luminescence was obtained for SrF2:Er (14.2%) with 0.28% maximum quantum yield.

Cooperative upconversion luminescence of Er3 + in Gd2O3 − xSx phosphor

Gd2O3−xSx:Er crystals were prepared through high-temperature solid-state reaction method in vacuum, with the vacuum synthesis mechanism determined by thermal analysis. The crystal structure and upconversion luminescence properties were investigated respectively by XRD, TEM and spectrophotometer. Well crystallized Gd2O2S:Er phosphors were prepared under 1000°C in vacuum with a certain excessive amount of sulfur content than stoichiometric. It is confirmed that with the increasing sulfur content the green emission was enhanced and red emission was weakened. The cooperative upconversion luminescence of Er3+ in non-stoichiometric Gd2O3−xSx crystals was interpreted as a result of two photon absorption and the photon avalanche process.