Efficient upconversion luminescence from Ba5Gd8Zn4O21:Yb(3+), Er(3+) based on a demonstrated cross-relaxation process

Color tunable luminescence in ThO2:Er3+,Yb3+ nanocrystals: a promising new platform for upconversion

Lanthanide-doped luminescent nanoparticles are an appealing system for many applications in the area of biomedical, solar cell, thermometry, anti-counterfeiting, etc. due to their sensitivity, reliability, high photochemical stability, and high optical transparency in the visible-NIR range. A color-tunable upconversion-luminescence (UCL) in a new low phonon energy ThO2 host based on modulating sensitizer concentration has been realized in this work and it may work as a potential candidate to replace corrosive and toxic fluoride based hosts in the future. Er3+-Yb3+ co-doped thoria nanoparticles were prepared using a gel combustion route and their structural and luminescence properties were determined as a function of the Yb3+ concentration. Phonon dispersion measurements have established the dynamic structural stability of the thoria nanoparticles. Density functional theory (DFT) was used to calculate the defect formation energy, highlighting the feasibility of dual ion (Er3+ and Yb3+) doping in thoria. The morphology and average size of the doped thoria was studied using high resolution transmission electron microscopy (HRTEM), and any defects evolving as a result of aliovalent doping were probed using positron annihilation lifetime spectroscopy (PALS). With 980 nm laser excitation, the nanothoria emits green and near-red light. A significant enhancement of the red-to-green intensity ratio of Er3+ ions in nanothoria was observed with an increase in Yb3+ concentration which resulted in beautiful color tunability from green to yellow light in going from lower (up to ∼5 mol%) to higher (10 and 15 mol%) Yb3+ concentration. The power dependence and the dynamics of the upconverted emission confirm the existence of two-photon upconversion processes for the green and red emissions.

Ultrapure single-band red upconversion luminescence in Er3+ doped sensitizer-rich ytterbium oxide transparent ceramics for solid-state lighting and temperature sensing

Achieving single-band upconversion (UC) is a challenging but rewarding approach to attain optimal performance in diverse applications. In this paper, we successfully achieved single-band red UC luminescence in Yb2O3: Er transparent ceramics (TCs) through the utilization of a sensitizer-rich design. The Yb2O3 host, which has a maximum host lattice occupancy by Yb3+ sensitizers, facilitates the utilization of excitation light and enhances energy transfer to activators, resulting in improved UC luminescence. Specifically, by shortening the ionic spacing between sensitizer and activator, the energy back transfer and the cross-relaxation process are promoted, resulting in weakening of green energy level 4S3/2 and 2H11/2 emission and enhancement of red energy level 4F9/2 emission. The prepared Yb2O3: Er TCs exhibited superior optical properties with in-line transmittance over 80% at 600 nm. Notably, in the 980nm-excited UC spectrum, green emission does not appear, thus Yb2O3: Er TCs exhibit ultra-pure single band red emission, with CIE coordinates of (0.72, 0.28) and color purity exceeding 99.9%. To the best of our knowledge, this is the first demonstration of pure red UC luminescence in TCs. Furthermore, the luminescent intensity ratio (LIR) technique was utilized to apply this pure red-emitting TCs for temperature sensing. The absolute sensitivity of Yb2O3: Er TCs was calculated to be 0.319% K-1 at 304 K, which is the highest level of optical thermometry based on 4F9/2 levels splitting of Er3+ known so far. The integration between pure red UC luminescence and temperature sensing performance opens up new possibilities for the development of multi-functional smart windows.

Phase Stability and Dual-Mode Photoluminescence Modulation in Er-Doped Lead Zirconate Titanate Antiferroelectrics

The electric-field-modulation (E-modulation) of photoluminescence (PL) properties in bulk ceramics has attracted tremendous interest due to its potential application in optical data storage and communication devices. One promising approach of reversibly and largely modulating the PL intensity has been proposed in rare-earth Er³⁺-doped Pb_0.96La_0.04Zr_0.9Ti_0.1O₃ (PLZT) antiferroelectrics (AFEs) based on the unique E-dependent antiferroelectric-ferroelectric (AFE-FE) phase transition. However, the AFE phase stability of PLZT doped with various Er contents and their E-modulated PL properties have not been systematically investigated. In this paper, the intrinsic AFE phase of PLZT-Er is found to be stabilized in the high-temperature and high-E regions with increasing Er³⁺ content. The enhanced AFE nature caused by increasing Er doping leads to a larger E-dependent PL tunability (∼35%). Moreover, the ceramics exhibit the characteristics of both upconversion and downconversion PL (UCPL and DCPL) effects. Based on the excellent E-dependent dual-mode PL tunability, an optoelectronic device named the optical latch is demonstrated, where an electric signal can be used to trigger a notable intensity change in both the UCPL and DCPL modes. This reversible E-dependent dual-mode capability in PLZT-Er sheds light on a feasible approach to optoelectronic applications.

Evolution of Highly Biocompatible and Thermally Stable YVO4:Er3+/Yb3+ Upconversion Mesoporous Hollow Nanospheriods as Drug Carriers for Therapeutic Applications

In recent times, upconversion nanomaterials with mesoporous hollow structures have gained significant interest as a prospective nano-platform for cancer imaging and therapeutic applications. In this study, we report a highly biocompatible YVO₄:1Er³⁺/10Yb³⁺ upconversion mesoporous hollow nanospheriods (YVO₄:Er³⁺/Yb³⁺ UC-MHNSPs) by a facile and rapid self-sacrificing template method. The Rietveld analysis confirmed their pure phase of tetragonal zircon structure. Nitrogen adsorption–desorption isotherms revealed the mesoporous nature of these UC-MHNSPs and the surface area is found to be ~87.46 m²/g. Under near-infrared excitation (980 nm), YVO₄:Er³⁺/Yb³⁺ UC-MHNSPs showed interesting color tunability from red to green emission. Initially (at 0.4 W), energy back transfer from Er³⁺ to Yb³⁺ ions leads to the strong red emission. Whereas at high pump powers (1 W), a fine green emission is observed due to the dominant three-photon excitation process and traditional energy transfer route from Er³⁺ to Yb³⁺ ions. The bright red light from the membrane of HeLa cells confirmed the effective cellular uptake of YVO₄:Er³⁺/Yb³⁺ UC-MHNSPs. The resonant decrease in cell viability on increasing the concentration of curcumin conjugated YVO₄:Er³⁺/Yb³⁺ UC-MHNSPs established their excellent antitumor activity. Therefore, the acquired results indicate that these YVO₄:Er³⁺/Yb³⁺ UC-MHNSPs are promising drug carriers for bioimaging and various therapeutic applications.

Influence of the synthesis route on the spectroscopic, cytotoxic, and temperature-sensing properties of oleate-capped and ligand-free core/shell nanoparticles

The right choice of synthesis route for upconverting nanoparticles (UCNPs) is crucial for obtaining a well-defined product with a specific application capability. Thus we decided to compare the physicochemical, cytotoxic, and temperature-sensing properties of UCNPs obtained from different rare earth (RE) ions, which has been made for the first time in a single study. The core/shell NaYF₄:Yb³⁺,Er³⁺/NaYF₄ UCNPs were obtained by reaction in a mixture of oleic acid and octadecene, and their highly stable water colloids were prepared using the ligand-free modification method. Both oleate-capped and ligand-free UCNPs exhibited a bright upconversion emission upon 975 nm excitation. Moreover, slope values, emission quantum yields, and luminescence lifetimes confirmed an effective energy transfer between the Yb³⁺ and Er³⁺ ions. Additionally, the water colloids of the UCNPs showed temperature-sensing properties with a good thermal sensitivity level, higher than 1 % K^-1 at 358 K. Evaluation of the cytotoxicity profiles of the obtained products indicated that cell viability was decreased in a dose-dependent manner in the analyzed concentration range.

Insight into the mechanism of intense NIR-to-red upconversion luminescence in Er3+ doped and Er3+–Yb3+ co-doped SrF2 nanoparticles

SrF₂:Yb³⁺,Er³⁺ NPs were synthesized by the hydrothermal method and their luminescence mechanism was discussed in detail, which provided a theoretical basis for further understanding the properties of the materials.

Ba5Zn4Gd8O21:Tb3+-structural characterization and the Judd-Ofelt parameterization from emission spectra

Ba₅Zn₄Gd₈O₂₁:Tb³⁺ nanorods; synthesized via solution combustion route; were found to crystallize in the tetragonal (I4/m, 87) crystal system. The UV excitation at 290 nm of all Ba₅Zn₄Gd₈O₂₁:Tb³⁺ samples yielded the characteristics emission corresponding to ⁵D₄ → ⁷F_6,5,4,3 transitions in Tb³⁺ activator (used for Judd-Ofelt analysis). A detailed investigation of photoluminescence decay curves and emission spectra of Ba₅Zn₄Gd₈O₂₁:Tb³⁺ nanorods provided the radiative lifetime (1.0889 ms) and total radiative transition rates from ⁵D₄ state in Tb³⁺ ion. The electric-dipole radiative transition probabilities (extracted from total radiative rates i.e. electric-dipole + magnetic-dipole) were used to calculate the Judd-Ofelt intensity parameters (Ω₂ = 4.76 × 10^-20, Ω₄ = 2.11 × 10^-20 and Ω₆ = 2.00 × 10^-20 cm²). The very high quantum efficiency of ⁵D₄ state (81%) suggests their potential use in lighting and display devices. Finally, a large magnitude of peak stimulated emission cross section of ⁵D₄ → ⁷F₅ (16.5838 × 10^-20 cm²) transition also claims their promising candidature as a good laser material.

Microwave hydrothermal synthesis and upconversion properties of BiVO4 nanoparticles

Nanomaterials are the subject of extensive investigations due to their applications in medicine, multimodal imaging, volumetric displays, and photonics. Here, lanthanide-doped bismuth vanadate (BiVO₄) upconverting nanoparticles (UCNPs) have been reported. The nanoparticles have been synthesized by a microwave hydrothermal method. As-synthesized nanoparticles are highly crystalline in the tetragonal zircon phase with particles about 200 nm in size. Under 980 nm excitation, intense multicolor visible and near-infrared upconversion emissions are observed. Moreover, broadband infrared downshifting emissions are also observed. Time-resolved emission measurements have been carried out to investigate the involved upconversion and energy transfer mechanism. The BiVO₄-based UCNPs may provide a new class of nanomaterials for multifunctional applications.

Enhancing the upconversion luminescence properties of Er3+–Yb3+ doped yttrium molybdate through Mg2+ incorporation: effect of laser excitation power on temperature sensing and heat generation

Upconversion luminescence was enhanced by incorporating Mg²⁺ into Er³⁺–Yb³⁺-doped yttrium molybdate and the effect of laser excitation power on temperature sensing and nanoheating was investigated.

SC, Chidangil S, George SD. Post annealing induced manipulation of phase and upconversion luminescence of Cr3+ doped NaYF4:Yb,Er crystals

The role of post synthesis annealing at different temperatures (200–600 °C) on the structural as well as luminescence properties of NaY_80%F₄:Yb_17%,Er_3% prepared via a coprecipitation method was found to change the structure from a cubic to hexagonal phase with a concomitant increase in upconversion luminescence by 12 times for the green region and 17 times for the red region. Addition of the Cr³⁺ ions (5–20 mol%) into the host followed by post annealing at 200–600 °C causes that the samples to exhibit phase dependent and upconversion luminescence behavior that depend upon the doping concentration as well as the annealing temperature. The inductively coupled optical emission spectroscopy reveals that only 1/600 times of the desired volume of the co-dopant goes to the lattice and it can manifest visible spectral changes in the diffuse reflectance spectra of the samples. The samples co-doped with Cr³⁺ ion concentrations of 10–15% and post-annealed at 600 °C were found to have maximum emission with an enhancement factor of 24 for the green region and 33 for the red region. In addition, the laser power dependent studies reveal that even for the power density levels 3.69 W cm⁻² to 32.14 W cm⁻², the samples are in the saturation regime and most of the samples investigated here follow a single photon process, and a few samples show a slope value less than 1 for laser power dependent intensity plots. The results show the remarkable promise of controlled tailoring of the properties of upconversion crystals via post annealing and co-doping.

Co-dopant (Cr³⁺ ion) concentration as well as post annealing found to change the structural as well as luminescence properties of Cr³⁺ ion doped NaY_80%F₄:Yb_17%,Er_3% prepared via a co-precipitation method.

Concentration and pump power-mediated color tunability, optical heating and temperature sensing via TCLs of red emission in an Er3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor

The Er³⁺/Yb³⁺/Li⁺ co-doped ZnGa₂O₄ phosphor gives intense red upconversion photoluminescence, color tunability with Er³⁺ ion concentration and incident pump power, R/G ratio, induced optical heating and temperature sensing characteristics.

Intense UV and visible up-conversion emissions from RE-doped SiO2-BaGdF5 nano-glass-ceramics

RE-doped (Yb3+, Er3+ and Tm3+) nano-glass-ceramics (nGCs) comprising BaGdF5 nanocrystals have been developed under thermal treatment of precursor sol-gel glasses. Structural analysis by means of X-ray diffraction patterns, high-resolution transmission electron microscopy images, and energy dispersive X-ray spectroscopy measurements, confirmed the precipitation and distribution of cubic BaGdF5 nanocrystals (around 10 nm in size) in the silica glass matrix. Under near-IR excitation at 980 nm, up-conversion (UC) emissions have been studied as a function of selected dopants, the doping level and the pump power. In addition to the characteristic NIR, vis and UV UC emissions of Er3+ and Tm3+ dopant ions, the studied nGCs present intense UV UC emissions of the host fluoride nanocrystal, Gd3+. It was also observed that the relative Yb3+ content tended to improve the UC emission intensities. Corresponding UC mechanisms and energy transfer processes were analysed in terms of their energy level diagrams and confirmed by transient emission and pump power measurements. Moreover, power dependence analysis revealed that these emissions present saturation effects with the increase of Yb3+ content, even at low pump power. Results suggest that these high-efficiency UC nGCs have potential applications in UV solid state laser materials, solid state lighting and photovoltaics.

Ultrafast Single-Band Upconversion Luminescence in a Liquid-Quenched Amorphous Matrix

Achieving single-band upconversion is a challenging but rewarding approach to attain optimal performance in diverse applications, such as multiplexed molecular imaging, security coding, and nonlinear photonic devices. Here, highly efficient single-band upconversion luminescence in the green spectral regime (16.4 times increase in emission at 525 nm) accomplished by realizing minimal energy loss from two-photon upconversion in a newly synthesized liquid-quenched amorphous matrix is reported. In contrast to previously reported single-band upconversion, this phenomenon originates from the elevated transition probability of the host sensitive transition via changes in the host matrix's microstructure. The elevated transition probability facilitates ultrafast decay of upconversion luminescence with decay times as short as 0.2 µs, the fastest decay ever reported. The material in this study therefore has strong potential for use in photonic devices demanding high upconversion efficiency with a fast response time, which to date has been inaccessible using upconversion materials.

A review and outlook in the treatment of osteosarcoma and other deep tumors with photodynamic therapy: from basic to deep

Photodynamic therapy, one of the most promising minimally invasive treatments, has received increasing focus in tumor therapy research, which has been widely applied in treating superficial tumors. Three basic factors - photosensitizer, the light source, and oxidative stress - are responsible for tumor cell cytotoxicity. However, due to insufficient luminous flux and peripheral tissue damage, the utilization of photodynamic therapy is facing a huge limitation in deep tumor therapy. Osteosarcoma is the typical deep tumor, which is the most commonly occurring malignancy in children and adolescents. Despite developments in surgery, high risks of the amputation still threatens the health of osteosarcoma patients. In this review, we summarize recent developments in the field of photodynamic therapy and specifically PDT research in OS treatment modalities. In addition, we also provide some novel suggestions, which could potentially be a breakthrough in PDT-induced OS therapies. PDT has the potential to become an effective therapy while the its limitations still present when applied on the treatment of OS or other types of deep tumors. Thus, more researches and studies in the field are required.

Microwave hydrothermal synthesis and upconversion properties of Yb3+/Er3+ doped YVO4 nanoparticles

Yb³⁺ and Er³⁺ doped YVO₄ (Yb³⁺/Er³⁺:YVO₄) nanoparticles with highly efficient near-infrared to visible upconversion properties have been synthesized by microwave hydrothermal process. Uniform-sized Yb³⁺/Er³⁺:YVO₄ nanoparticles were synthesized within 1 h at 140 °C which is relatively faster than the conventional hydrothermal process. Under 980 nm laser excitation, strong green and less strong red emissions are observed which are attributed to ²H_11/2, ⁴S_3/2 to ⁴I_15/2 and ⁴F_9/2 to ⁴I_15/2 transitions of Er³⁺ respectively. The emission intensity is found to depend strongly on the concentration of Yb³⁺. The quadratic dependence of upconversion intensity on the excitation power indicates that the upconversion process is governed by two-photon absorption process.

The role of Yb3+ concentrations on Er3+ doped SrLaMgTaO6 double perovskite phosphors

The upconversion photoluminescence (UCPL) spectra of SrLaMgTaO₆:Er³⁺/Yb³⁺ phosphor with different concentration of Yb³⁺ ion under a 975 nm excitation and the insert shows the downconversion photoluminescence (DCPL) spectra under a 355 nm excitation.

Simultaneous spectra and dynamics processes tuning of a single upconversion microtube through Yb3+ doping concentration and excitation power

Doping and varying pump laser parameters are the widely applied technological processes for tuning spectra to yield desirable luminescence properties and functions.

Up/down-converted green luminescence of Er3+–Yb3+ doped paramagnetic gadolinium molybdate: a highly sensitive thermographic phosphor for multifunctional applications

Optical temperature sensing and nano-heating behavior of Er³⁺–Yb³⁺ doped multifunctional gadolinium molybdate phosphor.