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Quenching of lanthanide-doped upconversion nanoparticle (UCNP) luminescence at high dopant concentrations is an existing challenge that hampers their desired applications. It has already been reported that concentration quenching is strongly coupled to surface quenching. However, in this study we found that surface quenching is not the only cause for concentration quenching and concentration quenching was still observed in UCNPs with a well-protected surface. By using a mathematical model to better understand the processes, we proposed that this concentration quenching could be minimized by moving the extra sensitizers (Yb3+) to a different layer. To achieve this, a new tri-layer UCNP structure with sensitizers isolated in the middle layer was developed. It was observed that the quenching was reduced, and the luminescence intensity was enhanced up to 11.8 times in comparison with the brightest UCNPs without the sensitizing layer.

The light-harvesting efficiency of luminescent solar concentrators (LSCs) is encumbered by reabsorption of emission and concentration quenching. Energy transfer from a high-concentration donor to a low-concentration energy trap can reduce reabsorption losses while maintaining efficient light collection. Emissive aggregates enable this approach by reducing the impact of concentration quenching, which is detrimental to the entire energy transfer process. Here we describe a LSC that utilizes emissive aggregates as energy-transfer pairs for downconversion. We characterize the photophysics of a benzothiadiazole-based emissive aggregate, PITBT-TPE, that complements a highly emissive donor, DPATPAN, and functions as a highly emissive energy-transfer acceptor even at high concentrations in excess of 180 mM in the PMMA matrix. Monte Carlo simulations of LSCs that leverage these emissive aggregates as energy-transfer pairs predicted notable optical efficiencies at large concentrator dimensions. We demonstrate for the first time a LSC that utilizes donor and acceptor AIE chromophores to reduce reabsorption.

Herein, a series of GdSr2AlO5:Tb3+,Eu3+ phosphors were successfully synthesized through a high temperature solid-state reaction, and their crystal structures as well as photoluminescence properties were investigated in detail. Compared to the intense emission of 5D0 → 7F1 or 5D0 → 7F2 transition of Eu3+, another strong emission corresponding to 5D0 → 7F4 was observed. Concentration quenching is not obvious in Tb3+ or Eu3+-doped GdSr2AlO5 because structure isolation and energy transfer (ET) of Gd3+ → Eu3+ and Gd3+ → Tb3+ were found. Moreover, the energy transfer process from Tb3+ to Eu3+ was verified by the overlap of luminescence spectra and the variation of lifetime. Energy transfer mechanism was determined to be a dipole–dipole interaction, and ET efficiency as well as quantum efficiency were also obtained. Moreover, the emission color of GdSr2AlO5:Tb3+,Eu3+ can be tuned from green to red by altering the ratio of Tb3+/Eu3+. These results indicate that the GdSr2AlO5:Tb3+,Eu3+ phosphor is a promising single-component white light-emitting phosphor.

Organic solid fluorophores with a tunable emission color have been widely applied in multiple areas. However, rational design and efficient crafting of these fluorophores from a simple core skeleton is still a formidable challenge because of the undesirable concentration quenching emission effect. Herein, we present the development of two series of organic solid fluorophores based on a backbone of p-bis(2,2-dicyanovinyl)benzene. Notably, the introduction of either non-aromatic or aromatic substituents provides fluorophores with a tunable emission color. Moreover, the fluorophores with aromatic substituents exhibit additional unique optical phenomena, such as aggregation-induced emission, polymorphism-dependent emission, and reversible mechanochromic luminescence.

Y2−xErxMo4O15 (x = 0.04, 0.08, 0.16, 0.32, 0.64, 2.0) phosphors were synthesised at 700 °C through a solid-state reaction method. The samples were characterised by XRD and emission spectra analysis. Y2−xErxMo4O15 samples showed a strong green emission (2H11/2, 4S3/2 → 4I15/2) and a weak red emission (4F9/2 → 4I15/2) under 1550 and 980 nm excitation. The green emission intensity was enhanced increasing the Er3+ ion doping content, whereas the red emission was basically unchanged. Thus, Er2Mo4O15 exhibited an abnormal green up-conversion luminescence without concentration quenching under 1550 and 980 nm excitation. The dominating green up-conversion luminescence was due to the larger adjacent Er3+⋯Er3+ distance caused by the special structure of Er2Mo4O15, which limited the energy-transfer process and cross-relaxation responsible for the red up-conversion emission. Therefore, the up-conversion luminescence mechanism was excited-state absorption under 1550 nm excitation.

A series of single-doped Ca9Y(PO4)5(SiO4)F1.5O0.25:Ln3+ (Ln3+ = Eu3+/Tb3+/Dy3+/Sm3+) phosphors have been prepared via conventional high-temperature solid–state reaction. The structural refinement, photoluminescence properties, and decay curves were studied in detail. Under near-UV excitation, the Ca9Y(PO4)5(SiO4)F1.5O0.25:Eu3+/Tb3+/Dy3+/Sm3+ phosphors show the characteristic emissions of Eu3+ (5D0–7F2, red), Tb3+ (5D4–7F5, green), Sm3+ (4G5/2–6H7/2, red), and Dy3+ (4F9/2–6H13/2, yellow). The emission intensities of Ca9Y(1−x/z)(PO4)5(SiO4)F1.5O0.25:xEu3+/zSm3+ are maximized when x = 0.16 and z = 0.10, and the concentration quenching mechanisms are both dominated by dipole–dipole interactions. The excitation spectra of the Ca9Y(PO4)5(SiO4)F1.5O0.25:Eu3+/Sm3+ phosphors show the strongest absorption at about 400 nm, which matches well with the commercially available near-UV-emitting InGaN-based light emitting-diode (LED) chip. Finally, a red LED was fabricated using the present phosphors (with the composition of Ca9Y(PO4)5(SiO4)F1.5O0.25:Eu3+/Sm3+) and exhibited a red emission with high color purity. All the results indicate that Ca9Y(PO4)5(SiO4)F1.5O0.25:Ln3+ phosphors are promising phosphors for white LEDs.

Nd-to-Yb energy transfer (ET) at the molecular level has been investigated in the novel heterobimetallic NdYb2Q9 (Q = 8-quinolinolate) complex where the Q ligand works as a high cross-sectional optical antenna. The remarkable ion size-driven templating effect of Nd3+ allows for good control of molecular speciation through a simple one-pot synthetic procedure. Short intermetallic distances and enhanced donor (Nd)/acceptor (Yb) spectral overlap in the molecular assembly strongly favor Nd-to-Yb energy transfer, which reaches nearly unitary efficiency, while detrimental processes such as concentration quenching and energy back transfer are ruled out. The devised approach allows us to obtain a controlled assembly of heterolanthanide compounds whose features hold potential for the development of highly performing Yb3+-based optical materials.

In the present work, rare earth (Eu3+, Dy3+ and Sm3+) activated Ca4Al6WO16 phosphors were synthesized by citrate complexation and combustion methods and their photoluminescence characterization was performed. The phase purity and morphology of the phosphors were characterized by XRD and SEM. The SEM micrographs of phosphor sample synthesized by citrate complexation method show a layer structure while sample synthesized by citrate combustion method show porous nature. Intense red emission of Eu3+ and yellow emission of Dy3+ in Ca4Al6WO16 host lattice show the occupation of a noncentrosymmetric site by the rare earth ions in the host lattice. The reddish orange emission from Sm3+ activated phosphor consists of three intense emission peaks in yellow, orange-red and red regions, respectively at 567, 604 and 650 nm. Intense characteristic emissions show no concentration quenching up to 2 mol% concentration of rare earth ions. The phosphors could be effectively excited by near UV (Dy3+ activated phosphor) and visible light (Eu3+ and Sm3+ activated phosphors) and give emission hues from orange-red to near white, demonstrating their potential suitability for application in solid state lighting.

Luminescence and excitation spectra of LiLa1−xDyxP4O12 nanocrystals are reported. In particular, the impact of dopant concentration on the luminescence properties of LiLa1−xDyxP4O12 nanocrystals was investigated. It was found that increase in Dy3+ concentration results in a strong quenching of luminescence. The mechanism of concentration quenching was discussed in terms of the Yokota–Tanimoto model. It is concluded that with increasing Dy3+ concentration, the donor–acceptor interaction leads to a significant concentration quenching resulting in nonexponential luminescence decay, whereas at a high concentration limit the donor–donor interaction becomes dominant and exponential decay is observed.

A novel reddish-orange phosphor, Ca3Y2−2x(Si3O9)2:2xDy3+, was synthesized via conventional solid-state reaction. Its photoluminescence properties were investigated. With increasing Dy3+ concentration, the luminescence intensity first increases, reaches the greatest, and then decreases. The concentration quenching mechanism is based on the electric dipole–dipole interaction. The decay times were also determined.

The past decade has seen extensive developments in the field of upconversion nanotechnology, which has found applications in various fields. Different applications require different emission wavelengths from nanoparticles, and significant research has been undertaken to fine tune individual emission peaks in shorter wavelengths without much success. Recently, a novel class of upconversion nanoparticles with an orthorhombic crystal structure has been developed, which enables high concentrations of activator ions to be used without concentration quenching and also allows for the excellent tuning of shorter emission wavelengths.

Ce(3+) and Ce(3+)/Tb(3+)-activated Y4Si2O7N2 phosphors are synthesized by the solid-state method, which can be efficiently excited by near ultraviolet (UV) light emitting diode (LED) chips. The PL spectrum of Y4Si2O7N2:Ce(3+) shows a broad hump between 380 and 650 nm, assigned to the electron transition from the 4f energy level to different 5d sub levels of the Ce(3+) ions at different Y(3+) sites. The color of the Y4Si2O7N2:Ce(3+) phosphor can shift from blue to green by introducing Tb(3+). In addition, the energy transfer process from Ce(3+) to Tb(3+) in the Y4Si2O7N2 host was investigated and discussed in terms of both the luminescence spectra and decay curves. The energy transfer critical distance has been calculated and evaluated by the concentration quenching method. Therefore, the Ce(3+) and Ce(3+)/Tb(3+)-activated Y4Si2O7N2 phosphors can serve as key materials for phosphor-converted white-light UV-LEDs.

A new class of rhodamine luminophores, 3',3''-bis(oxospiroisobenzofuran)-3,7-bis(dialkylamino)benzopyrano-xanthene derivatives (ABPX), have been successfully developed. The emission behavior of ABPX series is directly opposite to the concentration quenching of conventional rhodamine dyes. ABPX series exhibit aggregation-induced emission enhancement (AIEE).

A modification of Forster's equation for the quantum yield of heterogeneous radiationless energy transfer improves its description of homogeneous concentration quenching, at the expense of a new parameter which can be related to the number of steps taken by the excitation in its random walk and which seems to be independent of concentration.

The triplet yield of pyrene in poly(methylmethacrylate) decreases with increasing concentration in the same way as does total fluorescence yield, showing that concentration quenching of total fluorescence is to be attributed to enchanced internal conversion rather than intersystem crossing.