Enhanced up-conversion luminescence of Er:LaOF oxyfluoride borosilicate glass ceramics

Er³⁺-doped transparent oxyfluoride borosilicate glass ceramics containing LaOF nanocrystals have been obtained by the high temperature melt-quenching and subsequent heat treatment method. The formation of LaOF nanocrystals in the glass matrix was confirmed by XRD and TEM results. In comparison with the precursor glass, Er³⁺-doped transparent oxyfluoride glass ceramics containing LaOF nanocrystals exhibited efficient up-conversion luminescence. Especially, the green emission intensity was greatly enhanced about nearly 200 times and its up-conversion mechanism can be ascribed to a two-photon absorption process.     

Enhanced upconverted luminescence and the optical thermometry behavior of Er3+-doped BaYbF5 transparent glass ceramics

Transparent SiO₂ - Al₂O₃ - Na₂O - CaO - BaF₂ - YbF₃ glass ceramics (GC) doped with Er³⁺ ions were successfully fabricated by a melt-quenching technique with subsequent heat treatment. The formation of BaYbF₅ nano-crystalline phase was confirmed by X-ray diffraction and transmission electron microscopy. Compared to the precursor glass (PG), the clearer Stark splitting and greatly enhanced up-conversion (UC) emission in GC indicate that Er³⁺ ions mainly enter into BaYbF₅ nanocrystals with low phonon energy after crystallization. The temperature dependent on purple UC emission ratio (which is due to the Er^{3+ 4}G_11/2→⁴I_15/2 and ²H_9/2→⁴I_15/2 transitions) and common green UC emission ratio with low-power excitation in BaYbF₅ GC have been studied respectively. In addition, the UC mechanisms in PG and GC are illustrated and analyzed. The outstanding properties of Er³⁺-doped BaYbF₅ transparent GC may present potential applications in all-solid-state UC lasers and optical fiber temperature sensors.     

Transparent Sr0.84Lu0.16F2.16: Yb3+, Er3+ glass ceramics: Elaboration,structure, up-conversion properties and applications

The development of optical temperature sensors is of fundamental and industrial importance for various applications. Despite the great advance in optical temperature-sensing techniques, challenges remain to search for novel sensing materials with low cost, easy fabrication and high sensitivity. Here, transparent glass ceramics (GC) embedded with cubic Sr_0.84Lu_0.16F_2.16:Yb³⁺/Er³⁺ nano-crystals were prepared via thermal annealing on the parent glass. The optical and structural properties were investigated. The enhanced emission intensity, obvious Stark splitting and prolonged lifetimes of Er³⁺ confirm the enrichment of Er³⁺ ions into formed Sr_0.84Lu_0.16F_2.16 nano-crystals. The temperature sensing performance of Yb³⁺/Er³⁺ ions in Sr_0.84Lu_0.16F_2.16GC were investigated based on up-conversion intensity ratio (FIR) from thermally coupled emitting states of Er³⁺. High energy difference ($\Delta E$?=?839?cm^?1) and high absolute sensitivity (27.4?×?10^?4?K^?1 at 606?K) are obtained. Our results reveal Sr_0.84Lu_0.16F_2.16GC are excellent host for rare earth ions doping and potential candidate for optical thermometry.     

Simultaneous high transmittance and large tunability of up-conversion photoluminescence in Er3+ doped KNN-based ceramics

0.98(0.94K_0.51Na_0.5NbO₃-0.06SrZrO₃)-0.02Li_0.5La_0.5TiO₃+x mol Er³⁺ ceramics were prepared using a conventional solid-state reaction method. The transmittance of the sample x = 0.5% sintered at 1210 °C reaches 56% in at the wave length of 780 nm and 73% at the wave length of 2000 nm (the thickness of the sample is 0.3 mm). Under 980 nm excitation, two typical emission bands are obtained, which are the green emission band at 510 nm–580 nm and the red emission band at 645–695 nm. Under the irradiation of visible light, the up-conversion luminescence intensity of the sample is significantly reduced, showing a luminescence quenching characteristic. The PL quenching degree (ΔR) of up-conversion emission is up to 78.2% for the sample x = 0.5% sintered at 1210 °C. Besides, a behavior of photosensitive resistance is achieved at room temperature and 350 °C, which suggests that this system has a great application prospect in optical information storage.     

Design,simulation, elaboration and luminescence of Tb3+-doped Ba0.84Gd0.16F2.16 fluoroaluminosilicate scintillating glass ceramics

Extensive researches on scintillators have been executed to satisfy the excellent radiation detection materials in broad applications. However, practical application of conventional scintillators is limited due to the limitations of high cost, time-consuming fabrication process and insufficient radioluminescence. Herein, high density precursor glass doped with Tb³⁺ was designed to absorb X-ray efficiently and produce green emission. Molecular dynamics simulation was used to simulate the phase separation process in melting process. Then, Tb³⁺-doped Ba_0.84Gd_0.16F_2.16 glass ceramics (GCs) with excellent structural and optical properties were elaborated by melt quenching technic and further heat treating. Their structural properties, photoluminescence (PL) and X-ray excited luminescence (XEL) were explored detailedly. The internal quantum efficiency of PL is 64 % in GCs. The XEL intensity is 192 % of that of Bi₄Ge₃O₁₂ (BGO) commercial scintillator. Our results suggest that Ba_0.84Gd_0.16F_2.16:Tb³⁺ GCs might have potential application in X-ray detection.     

Tuning size and up-conversion luminescence of CeO2:Yb3+/Er3+ nanoparticles through lanthanide doping

Particle size is a critical parameter in up-conversion luminescence tuning and application research. In this study, CeO₂:Yb³⁺/Er³⁺ nanospheres were synthesized via coprecipitation. The average size of these nanospheres gradually decreased as the Yb³⁺ doping concentration increased, which might be attributed to the influence of Yb³⁺ doping on the growth rate of nanospheres by surface charge repulsion. Upon exciting these nanospheres using a 980-nm laser, the corresponding up-conversion red-green emission intensity ratio gradually increased as the Yb³⁺ doping concentration increased, which might be ascribed to two reasons: the strengthened ⁴S_3/2 → ⁴F_9/2 nonradiative relaxation process and the enhanced Er³⁺ → Yb³⁺ energy back-transfer process. To assess the influence of the nonradiative relaxation process on the up-conversion emission red-green ratios, the down-conversion emission spectra and decay curves of CeO₂:x%Yb³⁺/2%Er³⁺ nanospheres that were excited by a 520 nm laser were investigated. To validate how the particle size affects the up-conversion emission, CeO₂:x%Lu³⁺/2%Yb³⁺/2%Er³⁺ nanospheres of various sizes were synthesized by substituting optically active Yb³⁺ using optically inert Lu³⁺. The corresponding up-conversion emission spectra and decay curves were investigated. The experimental results enhanced our understanding of how lanthanide doping affects the up-conversion luminescence tuning of Er³⁺, offering great potential to regulate the morphology and optical properties of the up-conversion luminescence nanoparticles.     

Effect of glass-ceramics network intermediate Al2O3 content on up-conversion luminescence in Er3+/Yb3+ co-doped NaYF4 oxy-fluoride glass-ceramics

Effect of alumina as a glass network intermediate on the up-conversion luminescence (UCL) in NaYF₄:Er³⁺/Yb³⁺ co-doped oxy-fluoride glass-ceramics (GCs) was investigated. Combinations of smaller NaYF₄ nanocrystals (10 and 13 nm) and lower Al₂O₃ contents (5% and 10%), as well as larger NaYF₄ nanocrystals (26 and 40 nm) and higher lower Al₂O₃ contents (15% and 20%) were prepared after heat-treatment, respectively. The glass network of intermediate partial replacement of SiO₂ with Al₂O₃ was investigated, and the consequence on the response to the up-conversion of the lanthanide ions was also studied. The UCL properties of Er³⁺ ions were changed in accordance with the addition of Al₂O₃, the red UCL intensity decreased with an increased Al₂O₃ concentration, while the green emission intensity showed opposite tendency. Our results showed that adding Al₂O₃ to 20 mol% is an effective strategy to simultaneous control of the magnitude and luminescence properties of lanthanide ion doped GCs.     

Er3+/Yb3+ co-doped bioactive glasses with up-conversion luminescence prepared by containerless processing

Er³⁺/Yb³⁺ co-doped bioactive glasses were prepared via containerless processing in an aerodynamic levitation furnace. The as-prepared glasses were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) equipped with energy dispersive X-Ray spectroscopy (EDX). The up-conversion luminescence of as-prepared glasses was measured using an Omni- 3007 spectrometer. Furthermore, the in vitro bioactivity was evaluated by soaking the materials in simulated body fluid, and the biocompatibility was evaluated in MC3T3-E1 cell culture.The results show that containerless processing is a unique method to prepare homogeneous rare earth doped bioactive glasses. The obtained Er³⁺/Yb³⁺ co-doped glasses show green and red up-conversion luminescence at the excitation of 980 nm laser. The XRD analysis confirmed that calcium silicate powders, as starting materials, were completely transformed from the original multi-crystalline phase (CS-P) into the amorphous-glassy phase (CS-G, EYS, LCS) via containerless processing. The SEM observation combined with EDX and FTIR analyses showed that the as-prepared glasses were bioactive. The cell proliferation assay also revealed that the as-prepared glasses were biocompatible and nontoxic to MC3T3-E1 cells. This study suggests that the luminescent bioactive glasses prepared by containerless processing could be used for studying biodegradation of bone implantation materials.     

High-accuracy dual-mode optical thermometry based on up-conversion luminescence in Er3+/Ho3+-Yb3+ doped LaNbO4 phosphors

Due to the non-contact and high sensitivity, optical thermometry based on rare earth doped phosphors has been paid much attention to. Herein, dual-mode optical thermometers are designed using up-conversion luminescence of Er³⁺/Ho³⁺-Yb³⁺ doped LaNbO₄ phosphors, which were synthesized for the first time by high-temperature solid-state reaction method. The LaNbO₄:1Er³⁺:10Yb³⁺ and LaNbO₄:1Ho³⁺:10Yb³⁺ phosphors exhibit reliable and excellent thermometric performance by combining fluorescence intensity ratio and decay lifetime for self-calibration. Specifically, the maximal relative sensitivities based on fluorescence lifetime were 0.27 %K⁻¹ and 0.33 %K⁻¹ for LaNbO₄:1Er³⁺:10Yb³⁺ and LaNbO₄:1Ho³⁺:10Yb³⁺ phosphors, respectively. The maximal relative sensitivity is 1.12 %K⁻¹ when using intensity ratio between thermal coupling energy levels in LaNbO₄:1Er³⁺:10Yb³⁺ as a detecting signal. Furthermore, the maximal relative sensitivity reaches as high as 0.98 %K⁻¹ when taking advantage of special non-thermal coupling energy levels in LaNbO₄:1Ho³⁺:10Yb³⁺. These results indicate that Er³⁺/Ho³⁺-Yb³⁺ doped LaNbO₄ phosphors possess great potential in self-calibrated optical thermometric techniques.     

Bioactivity and up-conversion luminescence characteristics of Yb3+/Tb3+ co-doped bioglass system

The present study elaborates the bioactive and optical features of Yb³⁺/Tb³⁺ co-doped bio-active glass. Three different combinations with assorted elemental concentrations were investigated. The amorphous nature of bioglass devoid of crystalline phases until 700 °C has been confirmed through XRD analysis. The results from Raman and FT-IR accomplished the presence of Si–O–Si broad vibrational modes typical of amorphous glass and further the characteristic PO₄ vibrations were also confirmed. The up-conversion luminescence studies revealed the typical Tb³⁺ emission excited at 976 nm. The mechanism that involved in the up-conversion and energy transfer emission phenomena were discussed. Morphological features of SBF immersed specimen affirm the formation of apatite layer by the spherical spongy agglomerates observed over the surface.     

Enhanced near-infrared emission in Yb3+-Cr3+ codoped KZnF3 glass ceramics excited by a solar simulator

Cr³⁺-Yb³⁺ codoped bulk glass-ceramics containing KZnF₃ nanocrystals are fabricated by thermal treatment of cast glass samples and characterized by X-ray diffraction and transmission electron microscopy. The luminescent properties of the glass and glass ceramic are investigated from the measured photoluminescence spectra and fluorescent lifetime. The measurement results demonstrate that Cr³⁺ and Yb³⁺ ions are both predominantly hosted in the KZnF₃ nanocrystals, and the energy absorbed by Cr³⁺ ions is efficiently transferred to Yb³⁺ ions when excited at 450?nm. Compared to the glass, the near-infrared emission in the Cr³⁺-Yb³⁺ codoped glass ceramics is significantly enhanced when the excitation wavelength lies in the range λ~400–800?nm of a solar simulator. Results indicate that the Cr³⁺-Yb³⁺ codoped KZnF₃ glass ceramic provides a promising material for spectral conversion from visible sunlight to near-infrared emission and a novel gain material for solar pumped fiber laser.     

Temperature sensing properties of self-crystalized Ba2LaF7: Tb3+ glass ceramics

Fluorescence intensity ratio (FIR) techniques for temperature sensing based on the thermally-coupled energy levels (TCELs) of two excited states of rare earth ions are widely investigated. However, their performance in lower temperature detection are poor because of thermal decoupling between two emitting levels with relatively large energy gap. On the other hand, most of luminescent thermometer materials so far reported are in powder form, which suffer from severe light scattering and high hygroscopicity. Fortunately, transparent glass ceramics offer an alternative to improve optical property as well as stability of luminescent materials. Hence, herein self-crystallized 20% Tb³⁺ doped transparent Ba₂LaF₇ glass ceramics were synthesized by traditional high-temperature melting method to examine its temperature sensing ability by employing the two low-lying states ⁷F₅ and ⁷F₆ of Tb³⁺, which are thermally coupled even at lower temperature. Under the resonance excitation of ⁷F₅ → ⁵D₄ transition at 543 nm, the emission intensity of ⁵D₄ → ⁷F₆ enhances with the temperature rising from 300 K to 630 K. The maximum relative sensitivity reaches 2.88% K^?1 at 300 K, which is better than the previous results reported. Moreover, the repeatability of the integrated intensity of ⁵D₄ emission of Tb³⁺ under eight consecutive heating-cooling cycles indicates that the sample has a good reliability and reusability. All results suggest that the 20% Tb³⁺ doped transparent Ba₂LaF₇ glass ceramics are one of the excellent candidate materials for optical thermometers.     

Gd3+ doping induced enhanced upconversion luminescence in Er3+/Yb3+ co-doped transparent oxyfluoride glass ceramics containing NaYF4 nanocrystals

In this article, transparent oxyfluoride glass ceramics containing $\mathrm{\beta }$-NaYF₄ nanocrystals were successfully prepared via Gd³⁺ doping. Compared to conventional non-doped glasses, the thermal treatment temperature required for the precipitation of $\mathrm{\beta }$-NaYF₄ nanocrystals can be lowered with the doping of Gd³⁺. Furthermore, under the same thermal treatment condition, more $\mathrm{\beta }$-NaYF₄ nanocrystals were precipitated in Gd³⁺ doped ones, which greatly improves the luminescence efficiency of rare earth doped glass ceramics. Possible mechanism for the Gd³⁺ doping induced enhanced upconversion luminescence phenomenon was proposed, based on thorough structural and optical characterizations. The results revealed that the doping of Gd³⁺ ions could decrease the crystallization activation energy and promote the formation of Y-F-Na bonding, which helps the precipitation of $\mathrm{\beta }$-NaYF₄ nanocrystals. Consequently, a large enhancement in upconversion luminescence was achieved. Moreover, the strategy can be successfully applied to the development of other glass ceramic systems for various optoelectronic applications.     

Phase evolution and photoluminescence in Er3+ doped glass ceramics containing lutetium oxyfluoride nanocrystals

Crystalline phase evolution through merely adjusting composition was achieved in silicate glass ceramics containing Lu_nO_n-1F_n+2 (n = 5–10) nanocrystals. Orthorhombic or cubic phase nanocrystals were precipitated in the aluminosilicate glass matrix after thermal treatment together with varying the Na₂O/NaF ratio. Oxyfluoride nanocrystals with quasi-spherical shape show homogenous and dense distribution in glass matrix by transmission electron microscopy measurement. Intense upconversion and mid-infrared emissions were realized in these glass ceramics compared to the precursor glass, and the emission spectral shapes, relative emission intensity and fluorescence decay curves of Er³⁺ in cubic LuOF embedded samples exhibit remarkable differences due to the crystal phase dependent effect in glass ceramics. These results indicate that the crystallization and luminescence properties of oxyfluoride glass ceramics could be modified through the alteration of glass composition, which could be used for the development of novel glass ceramics and design of luminescent properties.     

Transparent glass ceramics containing Lu6O5F8:Tb3+ nano‐crystals: Enhanced photoluminescence and X‐ray excited luminescence

The development of scintillators is of fundamental and industrial meaning for their diverse applications. Despite the great advance in scintillating mono‐crystals, challenge remains to search for novel scintillating materials with low cost, large volume, and high efficiency. Here, Tb³⁺‐doped glass ceramics (GC) with crystallized Lu₆O₅F₈ nano‐crystals were prepared and characterized as potential X‐ray scintillators. Their structural, optical, and luminescent properties were explored systematically. After thermal treatment, X‐ray excited luminescence (XEL) intensity from Lu₆O₅F₈:Tb³⁺ GC is greatly increased and the relative intensity is about 64% of commercial BGO scintillator, benefiting from preferential enrichment of Tb³⁺ ions into Lu₆O₅F₈ nano‐crystals with low phonon energy. Moreover, unusual decay behaviors of Tb³⁺ emissions in GC sample are observed and discussed. Our results indicate that rare earth doped GC may offer a novel platform for designing and fabricating new scintillating materials in the future.     

Enhancement of up-conversion emission and emerging cool white light emission in co-doped Yb3+/ Er3+: Li2O-LiF-B2O3-ZnO glasses for photonic applications

A series of co-doped (Yb³⁺/Er³⁺): Li₂O-LiF-B₂O₃-ZnO glasses were prepared by standard melt quenching technique. Structural and morphological studies were carried out by XRD and FESEM. Phonon energy dynamics have been clearly elucidated by Laser Raman analysis. The pertinent absorption bands were observed in optical absorption spectra of singly doped and co-doped Yb³⁺/Er³⁺: LBZ glasses. We have been observed a strong up-conversion red emission pertaining to Er³⁺ ions at 1.0 mol% under the excitation of 980 nm. However, the up-conversion and down conversion (1.53 µm) emission intensities were remarkably enhanced with the addition of Yb³⁺ ions to Er³⁺: LBZ glasses due to energy transfer from Yb³⁺ to Er³⁺. Up-conversion emission spectra of co-doped (Yb³⁺/Er³⁺): LBZ glasses exhibits three strong emissions at 480 nm, 541 nm and 610 nm which are assigned with corresponding electronic transitions of ²H_9/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 respectively. Consequently, the green to red ratio values (G/R) also supports the strong up-conversion emission. The Commission International de E′clairage coordinates and correlated color temperatures (CCT) were calculated from their up-conversion emission spectra of co-doped (Yb³⁺/Er³⁺): LBZ glasses. The obtained chromaticity coordinates for optimized glass (0.332, 0.337) with CCT value at 5520 K are very close to the standard white colorimetric point in cool white region. These results could be suggested that the obtained co-doped (Yb³⁺/Er³⁺): LBZ glasses are promising candidates for w-LEDs applications.     

Pr3+ doped Li2SrSiO4: an efficient visible-ultraviolet C up-conversion phosphor

Up-conversion (UC) phosphor converting visible light into ultraviolet C light (UVC) has potential application in many fields. However, the lower energy conversion efficiency limits its practical application. Here, we proven that the synthesized Li₂SrSiO₄:Pr³⁺ phosphor is an efficient UV phosphor with the emission power of 0.25 mW/cm² (0.1 mW/cm² for UVC band), which can effectively inactivate bacteria within 10 min. Based on the different propagation properties of visible light and UVC in ordinary glass, we proposed a scheme to coat this phosphor inside the slide and cover glass of a confocal microscope to realize the real-time observation of the response of microorganisms under UVC irradiation, thereby providing a new effective method for microbial research.     

Distribution of Nd3+ ions in oxyfluoride glass ceramics

It has been an open question whether Nd³⁺ ions are incorporated into the crystalline phase in oxyfluoride glass ceramics or not. Moreover, relative research has indicated that spectra characters display minor differences between before and after heat treatment in oxyfluoride glass compared to similar Er³⁺-, Yb³⁺-, Tm³⁺-, Eu³⁺-, etc.-doped materials. Here, we have studied the distribution of Nd³⁺ ions in oxyfluoride glass ceramics by X-ray diffraction quantitative analysis and found that almost none of the Nd³⁺ ions can be incorporated into the crystalline phase. In order to confirm the rationality of the process, the conventional mathematical calculation and energy-dispersive spectrometry line scanning are employed, which show good consistency. The distribution of Nd³⁺ ions in oxyfluoride glass ceramics reported here is significant for further optical investigations and applications of rare-earth doped oxyfluoride glass ceramics.     

Structure and luminescence of Eu doped glass ceramics embedding ZnO quantum dots

Eu³⁺ doped glass ceramics embedding ZnO quantum dots (QDs) were successfully prepared by a sol–gel method. High-resolution transmission electron microscopy (HRTEM) observations revealed that ZnO QDs with size of 3–6 nm precipitated homogeneously among the SiO₂ glassy matrix after thermal treatment of the precursor sample. Such glass ceramics show a high transparency in the visible-infrared range due to the much smaller size of the ZnO QDs than the wavelength of the visible light. The emission and excitation spectra of the samples with various ZnO contents were studied. Based on Judd–Ofelt theory, the intensity parameter Ω₂ was evaluated to investigate the change of the environment around Eu³⁺ in samples with and without QDs.     

Spectroscopic analysis of up conversion luminescence in doped halogeno-antimonite glass

The up-conversion emission of Nd³⁺, Sm³⁺ and Er³⁺ has been studied in a new halogeno-antimonite glass with the chemical composition 80 Sb₂O₃ – 10 ZnBr₂ – 10 KCl. Doping concentration was 0.2?mol% of lanthanide (Ln) ions. Rare earths were introduced as fluorides LnF₃ that were further converted into oxides. Main physical properties of base glass were measured, including density, thermal expansion, characteristic temperatures, refractive index and optical transmission. The amount of residual hydroxyls was calculated from the OH absorption band around 3000?nm. The recorded up-conversion emission lines are λ_em =?536?nm for Nd³⁺ pumped at 805?nm; λ_em =?563?nm, 600?nm, 631?nm and 645?nm for Sm³⁺ pumped at 945?nm; λ_em =?531?nm for Er³⁺ pumped at 798?nm. Co-doped glass (0.1 Yb³⁺ + 0.1 Er³⁺) pumped at 980?nm has three emission lines at 524?nm, 545?nm and 650?nm. Corresponding transitions have been identified and the mechanisms ruling the up-conversion process is discussed. They include excited state absorption (ESA), energy transfer (ET) cooperative energy transfer (CET), emission assisted by phonon (EAP), multiphonon relaxation (MR) and cross- relaxation (CR).