Down-conversion Luminescence Research Articles

Controllable Synthesis, Formation Process, and Luminescence Performances of Diverse Yttrium Compounds with Hollow Structures.

Hollow spherical Y2O3 and YBO3 have been prepared by a facile template-directed strategy using phenol-formaldehyde (PF) resin spheres as templates. The PF@Y(OH)CO3 precursor can be fabricated by a simple precipitation route. The Y2O3 hollow spheres are obtained via a direct annealing process, and the hollow spherical YBO3 are fabricated via a hydrothermal route followed by an annealing process at the expense of the same PF@Y(OH)CO3 precursor. The whole synthesis procedure is performed in aqueous solution without any surfactant or catalyst. Moreover, YVO4 quasi-octahedral microcrystals with spherical holes are obtained. The formation mechanisms of the yttrium compounds with different morphologies have been discussed. By incorporating proper rare earth activator ions into the Y2O3, YBO3, and YVO4 hosts, the as-synthesized luminescent materials can exhibit eminent performances with both down-conversion and up-conversion luminescence. Furthermore, the as-fabricated light-emitting diode (LED) devices can emit dazzling characteristic emission light, which reveals that the phosphors have application potential in lighting and displays. This simple synthesis strategy may provide a new idea for the fabrication of inorganic compounds with perfect hollow structures and excellent properties.

Designing X-ray-Excited UVC Persistent Luminescent Material via Band Gap Engineering and Its Application to Anti-Counterfeiting and Information Encryption.

Persistent luminescent materials (PLMs) are promising candidates for the anti-counterfeiting and information encryption field. However, ultraviolet (UV) excitation and visible emission are partially responsible for enabling information that has been encrypted to combat counterfeiting to be accessed by trial and error, resulting in imitation and information leakage. Here, we propose the possibility of controlling the persistent luminescent (PersL) emission spectra and its excitation light source with the use of band gap engineering, while obtaining X-ray exciting, not UV exciting UV PLM for advanced anti-counterfeiting and encryption application. Cationic substitution was used to adjust the width of the band gap of Lu(X)O4 (X = V, Nb, Ta, and P) from ∼4 to 9 eV. In addition, Bi3+ was introduced into the host as an emitter, which enabled the PersL emission spectra to be modulated from ∼550 to 230 nm. Among these PLMs, LuPO4:Bi3+ has unique optical properties. Under UV excitation, LuPO4:Bi3+ exhibits weak, inconspicuous visible down-conversion luminescence (DCL), without PersL ceasing once excitation is discontinued. Interestingly, LuPO4:Bi3+ displays UV PersL after X-ray excitation, and human eyes are insensitive to UV PersL, which requires specialized optical equipment to detect. A proof-of-concept assessment of LuPO4:Bi3+ for anti-counterfeiting and information encryption applications demonstrated its suitability in this regard.

Boltzmann- and Non-Boltzmann-Based Thermometers in the First, Second and Third Biological Windows for the SrF2:Yb3+, Ho3+ Nanocrystals Under 980, 940 and 915 nm Excitations

Spectrally determination of temperature based on the lanthanide-doped nanocrystals (NCs) is a vital strategy to noninvasively measure the temperature in practical applications. Here, we synthesized a series of SrF2:Yb3+/Ho3+ NCs and simultaneously observed the efficient visible upconversion luminescence (UCL) and near-infrared (NIR) downconversion luminescence (DCL) under 980, 940 and 915 nm excitations. Subsequently, these NCs were further utilized for thermometers based on the Boltzmann (thermally coupled levels, TCLs) and non-Boltzmann (non-thermally coupled levels, NTCLs) of Ho3+ ions in the first (~ 650 nm), second (~ 1012 nm) and third (~ 2020 nm) biological windows (BW-I, BW-II and BW-III) under tri-wavelength excitations. The thermometric parameters including the relative sensitivity (S_{{text{r}}}) and temperature uncertainty (delta T) are quantitatively determined on the I648/I541 (BW-I), I1186/I1012 (BW-II), and I1950/I2020 (BW-III) transitions of Ho3+ ions in the temperature range of 303–573 K. Comparative experimental results demonstrated that the thermometer has superior performances.

DNA Stabilizes Eight-Electron Superatom Silver Nanoclusters with Broadband Downconversion and Microsecond-Lived Luminescence.

DNA oligomers are known to serve as stabilizing ligands for silver nanoclusters (AgN-DNAs) with rod-like nanocluster geometries and nanosecond-lived fluorescence. Here, we report two AgN-DNAs that possess distinctly different structural properties and are the first to exhibit only microsecond-lived luminescence. These emitters are characterized by significant broadband downconversion from the ultraviolet/visible to the near-infrared region. Circular dichroism spectroscopy shows that the structures of these two AgN-DNAs differ significantly from previously reported AgN-DNAs. We find that these nanoclusters contain eight valence electrons, making them the first reported DNA-stabilized luminescent quasi-spherical superatoms. This work demonstrates the important role that nanocluster composition and geometry play in dictating luminescence properties of AgN-DNAs and significantly expands the space of structure–property relations that can be achieved for AgN-DNAs.

Electromechanical properties and photoluminescence of Er3+-doped PMN-33PT single crystal

Based on the successful growth of large-sized Er3+-doped PMN-PT single crystal, the phase composition, electromechanical properties and photoluminescence of [001]C-oriented Er3+-doped PMN-33PT crystal were investigated in detail. The results show that the crystal coexists in rhombohedral and monoclinic phases at room temperature. The crystal possesses excellent piezoelectric (d33 ∼ 2103 pC/N), dielectric (ε33T ∼ 7589), and electromechanical coupling properties (k33 ∼ 0.91), accompanied by a higher phase transition temperature and larger coercive field compared with that of PMN-33PT single crystal. This indicates an improved electromechanical performance induced by Er3+ doping. Additionally, the crystal achieves upconversion and downconversion luminescence, and a strong dependence of the upconversion emission on temperature is demonstrated. Furthermore, a comparable optical temperature sensing performance based on the fluorescence intensity ratio of the upconversion luminescence is verified. These results demonstrate a promising multifunctional material. The electro-optical coupling performance of the Er3+-doped PMN-33PT crystal is under evaluation.

External-field-dependent tunable emissions of Er3+-In3+ Co-doped Cs2AgBiCl6 for applications in anti-counterfeiting

Anti-counterfeiting materials play an irreplaceable role in information security and reducing national and enterprise losses, while the fluorescent anti-counterfeiting materials are widely used because of their feasible and flexible designs, visibility, easy identification and difficulty in cracking. For enhancing the security of fluorescent anti-counterfeiting materials, it is a popular choice to increase the modulus throung combining the up-conversion (UC) and down-conversion (DC) together with dynamic luminescence in one. Herein, Er3+ and In3+ co-doped Cs2AgBiCl6 phosphors with UC and DC emissions were successfully developed, in which Er3+ ions are responsible for the green UC emission under the excitation of 980 or 1550 nm laser while In3+ take the responsibility of enhancing yellow DC emission with 365 nm near ultraviolet light excitation. Furthermore, the DC luminescence color gradually changes to white from yellow as the ambient temperature increases from room temperature to 490 K. The potential application of the present samples in the field of anti-counterfeiting was evaluated by designing different patterns with the help of screen printing technology, which implied that the present sample provided a feasible and facilitated way to address the counterfeit issues.

Multimode Anticounterfeiting Labels Based on a Flexible and Water-Resistant NaGdF4Yb3+,Er3+@Carbon Dots Chiral Fluorescent Cellulose Film.

Advanced fluorescent anticounterfeiting technology has attracted a great deal of attention and inspired researchers to develop reliable fluorescent materials with multimodal luminescence. Herein, hydrophobic NaGdF4:Yb3+,Er3+ nanoparticles with dual-mode luminescence were prepared through a one-step solvothermal method using oleic acid as a chelating agent and octadecene as a solvent. The as-synthesized sample was found to provide both green upconversion luminescence and blue downconversion luminescence at excitation wavelengths of 365 and 980 nm. The structure and composition analysis showed that the as-obtained samples were spherical NaGdF4:Yb3+,Er3+@carbon dots (CDs) with a 14.5 ± 0.2 nm particle size and good dispersity in nonpolar solvents. Subsequently, NaGdF4:Yb3+,Er3+@CDs were coated on a cholesteric nanocellulose film with structural color to prepare multimode circularly polarized fluorescent materials. The prepared composite film is flexible and water-resistant, meaning that it is very suitable for anticounterfeiting labels, not only providing a simple and rapid synthesis method with which to prepare multimode fluorescent materials but also presenting a novel anticounterfeiting technology.

Simultaneous Observation of Visible Upconversion and Near-Infrared Downconversion in SrF2:Nd3+/Yb3+/Er3+ Nanocrystals and Their Application for Detecting Metal Ions under Dual-Wavelength Excitation.

In this work, a sequence of Nd3+, Yb3+, and Er3+ tridoped SrF2 nanocrystals (NCs) is synthesized by a hydrothermal method. Both the efficient near-infrared downconversion luminescence (DCL) and visible upconversion luminescence (UCL) of the Er3+ and Nd3+ ions are simultaneously observed and systematically demonstrated under dual-wavelength excitation (808 and 980 nm continuous-wave lasers). Subsequently, the SrF2:Nd3+/Yb3+/Er3+ (15/4/0.2 mol %) NCs with the strongest luminescence were utilized for detecting the metal ion concentrations under 808 nm excitation. The results reveal that both the UCL and DCL gradually decrease as the metal ion concentrations increase, and high sensitivity is obtained for Cu2+ ions with a detection limit of 0.22 nM (∼650 nm) and 0.63 nM (∼976 nm). In addition, these SrF2:Nd3+/Yb3+/Er3+ NCs are further demonstrated to achieve a solid-state display under 980 nm excitation, exhibiting obvious “red” and “green” patterns by varying the doping rare earth ion concentrations.

Study on Er3+-Yb3+ co-doped La2O3–Al2O3 glasses for C-band optical waveguide amplifier with high luminous efficiency and low pump threshold

Efficient planar optical waveguide amplifiers at C-band are critical to the development of silicon photonics. In order to overcome the problem of low utilization efficiency of 980 nm pump for erbium-based planar optical waveguide amplifiers, an Er3+-Yb3+ co-doped La2O3–Al2O3 glass material for optical waveguide amplifiers was developed in this paper. While maintaining a high Er3+ doping concentration (∼1021 cm−3), the utilization efficiency of the material for 980 nm pumping is improved, so that the pump threshold of the waveguide amplifier fabricated with this material is lowered. Moreover, up-conversion and down-conversion luminescence are also suppressed in the material, resulting in a significant increase in the luminescence intensity of the C-band. A simple ridge waveguide simulation suggests that waveguide amplifiers fabricated by this material are expected to surpass the highest net gain reported so far for erbium-based planar waveguide amplifiers.

Designing Optical Thermometers Using Down/Upconversion Ca14Al10Zn6O35: Ti4+, Eu3+/Yb3+, Er3+ Thermosensitive Phosphors.

Down/upconversion Ca14Al10Zn6O35 inorganic phosphors codoped with Ti4+/Eu3+ or Yb3+/Er3+ were prepared. The crystal structure and downconversion luminescence properties of Ca14Al10Zn6O35:Ti4+, Eu3+ phosphors were studied in detail. Ti4+ and Eu3+ occupied Al3+ and Ca2+ sites in the host lattice, respectively. Under the excitation of 273 nm, the emission peak in the 300-570 nm band originated from the 2T2 → O2- transition of Ti4+. The f-f transition of Eu3+ ions generated multiple peaks in the 570-800 nm range. The emission intensity of Ti4+ and Eu3+ ions can be used as a fluorescence intensity ratio (FIR) signal. Based on the FIR technology, the maximum relative sensitivity (Sr) and the minimum temperature uncertainty (δT) reached 1.41% K-1 and 0.07 K, respectively. Meanwhile, the temperature-sensing behaviors were explored by the temperature-dependent upconversion spectra of Er3+- and Yb3+-codoped Ca14Al10Zn6O35 phosphors. Based on the fluorescence intensity ratio of thermal coupling levels (Er3+:2H11/2/4S3/2), the maximum Sr and minimum δT of upconversion phosphors reached 1.28% K-1 and 0.08 K in the temperature range of 293-473 K, respectively. Ca14Al10Zn6O35:Ti4+/Eu3+ (Yb3+/Er3+) phosphors realize temperature sensors with higher relative sensitivity, and it is a good candidate material for optical temperature measurement.

Tunable concentration-dependent upconversion and downconversion luminescence in NaYF4: Yb3+, Er3+@ NaYF4: Yb3+, Nd3+ core-shell nanocrystals for a dual-mode anti-counterfeiting imaging application.

Lanthanide-doped luminescent nanocrystals display both upconversion luminescence (UCL) and downconversion luminescence (DCL) properties, which offer potential applications in the second near-infrared window (NIR-II) images and biology sensors. Both UCL and DCL are sensitive to concentrations of activators. However, few works reveal the mechanism of concentration-dependent UCL and DCL. Herein, we synthesize core-shell upconversion nanocrystals (UCNCs) NaYF4: Yb3+(20%), Er3+ (2%)@NaYF4: Yb3+ (x%), Nd3+ (y%) with varying concentration of Nd and Yb ions. The UCL and DCL spectra are recorded under excitation of 980 nm and 808 nm lasers. The results indicate that the luminescence of core-shell UCNCs is influenced by the non-radiative rate between activators (Yb3+ and Nd3+) and the back energy transfer rate from Er3+ ions to activators. UCL tends to be obtained at a relatively low concentration of Yb3+ and Nd3+ ions (about 5%), whereas NIR emission tends to be obtained at a relatively high concentration of Yb3+ and Nd3+ ions (not higher than 20%). Dual-mode anti-counterfeiting imaging is successfully fabricated using core-shell UCNCs, which can be detected and distinguished by visible and infrared detectors. The visible versus infrared brightness of dual-mode anti-counterfeiting imaging can be tuned by varying the concentration of activators (Yb3+, Nd3+). Our work demonstrates concentration-dependent UCL and DCL in core-shell UCNCs, which provides reference to obtain NIR emission in the NIR-II region and adds encrypted dimensions for anti-counterfeiting patterns in the field of file encryption.

Dual-mode multicolor luminescence based on lanthanide-doped Na2CaGe2O6 phosphor for anticounterfeiting application

The lanthanide doped luminescent materials have been of great importance to the anticounterfeiting applications. At present, these materials combing with the up/down-conversion luminescence could provide a promising assumption to design an advanced anticounterfeiting. Herein, a series of distinct combinations of rare earth (RE3+) doped Na2CaGe2O6 phosphors are synthesized for dual-mode anticounterfeiting. An up-conversion luminescent phosphor Na2CaGe2O6: Ln3+, Yb3+ (Ln3+ = Er3+, Ho3+, Tm3+) is reported, which could emit green, red and blue light under 980 nm excitation, respectively. Based on the up-conversion luminescence of Na2CaGe2O6: Ln3+, Yb3+ phosphor, these samples could simultaneously possess three luminescent modes of up-conversion, down-conversion and persistent luminescence with rich emission colors due to the co-doping Tb3+ ions. Furthermore, the Na2CaGe2O6: Eu3+ phosphor could be efficiently excited by ultraviolet lamp around 393 nm and exhibits intense red down-conversion luminescence. These outstanding luminescent properties make as-prepared phosphors particularly attractive for multilevel anticounterfeiting.

Hybrid Mesoporous MnO2-Upconversion Nanoparticles for Image-Guided Lung Cancer Spinal Metastasis Therapy.

Upconversion nanoparticles (UCNPs) and MnO2 composite materials have broad prospects in biological applications due to their near-infrared (NIR) imaging capability and tumor microenvironment-responsive features. Nevertheless, the synthesis of such composite nanoplatforms still faces many hurdles such as redundant processing and uneven coatings. Here, we explored a simple, rapid, and universal method for precisely controlled coating of mesoporous MnO2 (mMnO2) using poly(ethylene imine) as a reducing agent and potassium permanganate as a manganese source. Using this strategy, a mMnO2 shell was successfully coated on UCNPs. We further modified the mMnO2-coated UCNPs (UCNP@mMnO2) with a photosensitizer (Ce6), cisplatin drug (DSP), and tumor targeting pentapeptide (TFA) to obtain a nanoplatform UCNP/Ce6@mMnO2/DSP-TFA for treating spinal metastasis of nonsmall cell lung cancer (NSCLC-SM). The utilization of both upconversion and downconversion luminescence of UCNPs with different NIR wavelengths can avoid the simultaneous initiation of NIR-II in vivo imaging and tumor photodynamic therapy, thus reducing damage to normal tissues. This platform achieved a high synergistic effect of photodynamic therapy and chemotherapy. This leads to beneficial antitumor effects on the therapy of NSCLC-SM.

Distinctive Sandwich-Type Composite Film and Deuterogenic Three-Dimensional Triwall Tubes Affording Concurrent Aeolotropic Conduction, Magnetism, and Up-/Down-Conversion Luminescence.

Compared to single functional materials, multifunctional materials with electrical conduction, magnetism, and luminescence are more attractive and promising, so it has become an important subject. A distinctive sandwich-type composite film (STCF) with dual-color up- and down-conversion luminescence, magnetism, and aeolotropic conduction is prepared by layer-by-layer electrospinning technology. Macroscopically, STCF is assembled by three tightly bonded layers, including a [polypyrrole (PPy)/poly(methyl methacrylate) (PMMA)]//[NaYF4:Yb3+, Er3+/PMMA] Janus nanobelt array layer as the first layer, a CoFe2O4/polyacrylonitrile (PAN) nanofiber nonarray layer as the second layer, and a Na2GeF6:Mn4+/polyvinylpyrrolidone (PVP) nanofiber nonarray layer as the third layer. This unique macropartition effectually confines conductive aeolotropy, magnetism, and luminescence in different layers. Microscopically, a Janus nanobelt is used as a construction unit to restrict the luminescent and conductive materials to their microregions, thus achieving highly conductive aeolotropy and green luminescence. The high integration of the micro-subarea and macro-subarea in the STCF can efficaciously avoid the mutual disadvantageous effects among different materials to obtain splendid polyfunctional performance. The conductive anisotropy and magnetism of the STCF can be adjusted by changing the contents of PPy and CoFe2O4. When the PPy content reaches 70%, the conductance ratio in the conductive direction to insulative direction is 108. The 2D STCF can be crimped by four different methods, and the 3D TWTs have the same excellent polyfunctional performances as 2D STCF. This unique design idea and construction technology can be applied to the preparation of other multifunctional materials to avoid harmful interference among various functions.

Recent Advances in Luminescent Downconversion: New Materials, Techniques, and Applications in Solar Cells

AbstractNumerous investigations have been done in pursuing phosphors with quantum yield (QY) greater than unity in terms of downconversion (DC) strategies, as well as applications in display, lighting, and particularly in novel solar cells with efficiency exceeding the Shockley–Queisser limit (≈30%). It is of significant interest that: i) DC of one high‐energy photon to two or more low‐energy photons is widely found in lanthanide and/or transition‐metal ions activated materials; ii) broadening of absorption spanning ultraviolet/blue range is achieved by introducing sensitizers with spin‐allowed transitions and especially by combining the advancing perovskite quantum dots, nanostructures, and organic dye molecules; iii) internal QY ≫ 1 and even measured QY > 1 are claimed in many near‐infrared (NIR) DC systems; iv) applications of downconverting layer atop commercial solar cells are performed to increase the photon conversion efficiency. In this review, the development of DC in theories, concepts, and experiments is first summarized, then the breakthrough in visible‐DC is briefly highlighted, NIR‐DC with latest progresses in models, materials, techniques as well as the corresponding optimizations and practices as effective downconverting layers is elaborated, and finally concluding remarks and perspectives in advancing NIR‐DC and applications in novel solar cells are given.

Excitation wavelength-dependent multi-color emitting phosphor Ba2GdTaO6: Mn4+, Er3+ for application in anti-counterfeiting

Developing multi-mode luminescent anti-counterfeiting materials is one of an efficient tactics to ensure the security of important documents and information. Herein, multi-mode luminescent material Ba2GdTaO6: Mn4+, Er3+ was synthesized via high temperature solid state method, which exhibits yellow-green and yellow up-conversion (UC) luminescence under the excitation of 980 and 1550 nm lasers as well as deep red light emission under 365 nm source, respectively. Furthermore, the influences of doping Mn4+ and Er3+ on the UC and down-conversion (DC) luminescence were discussed respectively, and possible luminescence mechanisms and energy transfer processes between them were also analyzed in detail. The potential application of Ba2GdTaO6: Mn4+, Er3+ in anti-counterfeiting was also achieved by screen printing fluorescent security patterns to demonstrate.

High-precision tumor resection down to few-cell level guided by NIR-IIb molecular fluorescence imaging

In vivo fluorescence/luminescence imaging in the near-infrared-IIb (NIR-IIb, 1,500 to 1,700 nm) window under <1,000 nm excitation can afford subcentimeter imaging depth without any tissue autofluorescence, promising high-precision intraoperative navigation in the clinic. Here, we developed a compact imager for concurrent visible photographic and NIR-II (1,000 to 3,000 nm) fluorescence imaging for preclinical image-guided surgery. Biocompatible erbium-based rare-earth nanoparticles (ErNPs) with bright down-conversion luminescence in the NIR-IIb window were conjugated to TRC105 antibody for molecular imaging of CD105 angiogenesis markers in 4T1 murine breast tumors. Under a ∼940 ± 38 nm light-emitting diode (LED) excitation, NIR-IIb imaging of 1,500- to 1,700-nm emission afforded noninvasive tumor–to–normal tissue (T/NT) signal ratios of ∼40 before surgery and an ultrahigh intraoperative tumor-to-muscle (T/M) ratio of ∼300, resolving tumor margin unambiguously without interfering background signal from surrounding healthy tissues. High-resolution imaging resolved small numbers of residual cancer cells during surgery, allowing thorough and nonexcessive tumor removal at the few-cell level. NIR-IIb molecular imaging afforded 10-times-higher and 100-times-higher T/NT and T/M ratios, respectively, than imaging with IRDye800CW-TRC105 in the ∼900- to 1,300-nm range. The vastly improved resolution of tumor margin and diminished background open a paradigm of molecular imaging-guided surgery.

Simultaneous achievement of sensitivity enhancement and dual-mode luminescence through co-doping Eu3+ in Ca2MgWO6:Er3+/Yb3+ phosphor

Demands for temperature probe technologies and information security have driven the development of luminescent materials doped with lanthanide ions (Ln3+) because of their distinctive optical properties. Nevertheless, the problems of poor temperature sensing performance and single-mode luminescence restrict most materials' applications in the fields of temperature sensing and optical anti-counterfeiting. Herein, we have effectively achieved the enhancement of the temperature sensing sensitivity factor and the multi-mode anti-counterfeiting at the same time by co-doping Eu3+ in the up-conversion Ca2MgWO6:Er3+/Yb3+ material. The maximum absolute sensitivity based on the 2H11/2/4S3/2 couples of Er3+ increased from 81.83 × 10−4 K−1 at 423 K to 88.12 × 10−4 K−1 at 398 K, which was attributed to the energy transfer between Er3+ and Eu3+ which increases the fluorescence intensity ratio values. Utilizing the down-conversion luminescence characteristics of Eu3+ ion, phosphors exhibited color tunability under 980 nm and 365 nm excitations to achieve dual-mode anti-counterfeiting function. Meanwhile, the fluorescent anti-counterfeiting pattern prepared by screen printing technology helped materials towards emerging anti-counterfeiting applications. Therefore, the novel phosphors have potential applications in noncontact temperature sensing and optical anti-counterfeiting security fields.

Up/down-conversion luminescence of monoclinic Gd2O3:Er3+ nanoparticles prepared by laser ablation in liquid

Multifunctional luminescent materials are attracting attention nowadays. In this work, monoclinic Gd2O3:Er3+ nanoparticles, which possess up-conversion luminescence and down-conversion luminescence properties, were successfully synthesized by laser ablation in liquid (LAL) technique. Up-conversion luminescence and down-conversion luminescence of monoclinic Gd2O3:Er3+ nanoparticles were got under the excitation of 980 nm and 379 nm, respectively. In addition, tunable luminescence was got. Furthermore, the cytotoxicity of the nanoparticles is low and the fluorescence of the nanoparticles in cell is also strong enough. The results indicate that the Gd2O3:Er3+ nanoparticles synthesized by LAL technique are promising candidates for bio-imaging or other fields that require controllable fluorescence.

Correlation between local lattice distortions and up-/down-conversion luminescence of (Y,Al)NbO4:Yb3+/Er3+

The changes in the crystallographic parameters of Y 0.79- z Al z Yb 0.18 Er 0.03 NbO 4 powders prepared with varying Al content were determined by Rietveld refinement, and their effects on the up- (UC) and down-conversion (DC) spectra were studied. The findings confirmed that the Al 3+ , Yb 3+ , and Er 3+ ions were completely incorporated at the Y 3+ sites. The substitution of the small Al 3+ ions led to the modification of the interatomic distance. As a result, the highest polyhedral distortion index of the YO8 dodecahedron ( D YO ) could be achieved at z = 0.2. Under infrared radiation, UC spectra demonstrated that a two-photon energy transfer (ET) UC process from Yb 3+ to Er 3+ was responsible for the green and red emissions, whose intensities increased dramatically by 160 and 166% at z = 0.2, respectively. This enhancement was a consequence of a large crystal-field asymmetry surrounding the Yb 3+ and Er 3+ ions, which resulted from the highest D YO at z = 0.2. In addition to D , the Yb‒Er interatomic distance was responsible for the enhanced UC emission, affecting the ET probability from Yb 3+ to Er 3+ . Under 379 nm excitation, the DC green emission of Er 3+ also showed the maximal intensity at z = 0.2 owing to the largest D YO . However, a correlation between the crystallographic variations and the DC emissions activated by [NbO 4 ] 3- niobates could not be fully elucidated owing to the complexity of the emission mechanism.