Controlling the energy transfer via multi luminescent centers to achieve white light/tunable emissions in a single-phased X2-type Y2SiO5:Eu(3+),Bi(3+) phosphor for ultraviolet converted LEDs

Structural and luminescence properties of novel Eu3+-doped Na3Ba2LaNb10O30 phosphors with high quantum efficiency and excellent color purity for w-LED applications

In this study, we report the successful synthesis and thorough characterization of Eu3+-doped Na3Ba2LaNb10O30 phosphors, targeting their application in white-light-emitting diodes (w-LEDs). The phosphors were synthesized using a high-temperature solid-state method, ensuring robust incorporation of Eu3+ ions into the host lattice. Comprehensive analyses were performed, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy, confirming the phase purity, crystallinity, morphology, and elemental composition of the phosphors. We have also studied the electronic structure using diffuse reflectance spectroscopy (DRS). Photoluminescence studies revealed strong red emissions under near-ultraviolet light excitation, with the optimal Eu3+ doping concentration identified to be 9 mol%. Quantum-yield measurements demonstrated high luminescence efficiency, while chromaticity coordinates indicated excellent color purity suitable for w-LED applications. These findings contribute significantly to the advancement of phosphor materials for solid-state lighting, suggesting promising prospects for their integration into commercial LED devices.

The synthesis and properties of Ca3 Sc2 Si3 O12 :Ce3+ (CSSG) phosphor are utilized for the development of human-centric lighting light-emitting diodes (HCL-LEDs)

In this study, cerium ion (Ce3+ )-doped calcium scandium silicate garnet (Ca3 Sc2 Si3 O12 , abbreviated CSSG) phosphors were successfully synthesized using the sol-gel method. The crystal phase, morphology, and photoluminescence properties of the synthesized phosphors were thoroughly investigated. Under excitation by a blue light-emitting diode (LED) chip (450 nm), the CSSG phosphor displayed a wide emission spectrum spanning from green to yellow. Remarkably, the material exhibited exceptional thermal stability, with an emissivity ratio at 150°C to that at 25°C reaching approximately 85%. Additionally, the material showcased impressive optical performance when tested with a blue LED chip, including a color rendering index (CRI) exceeding 90, an R9 value surpassing 50, and a biological impact ratio (M/P) above 0.6. These noteworthy findings underscore the potential applications of CSSG as a white light-converting phosphor, particularly in the realm of human-centered lighting.

Novel bandpass filter for far UV-C emitting radiation sources

Disinfection with far UV-C radiation (<230 nm) is an effective method to inactivate harmful microorganisms like the SARS-CoV2 virus. Due to the stronger absorption than regular UV-C radiation (254 nm) and hence limited penetration into human tissues, it has the promise of enabling disinfection in occupied spaces. The best far-UV sources so far are discharge lamps based on the KrCl* excimer discharge peaking at 222 nm, however they produce longer wavelength radiation as a by-product. In current KrCl* excimer lamps usually a dichroic filter is used to suppress these undesired longer wavelengths. A phosphor-based filter is an alternative which is cheaper and easier to apply. This paper describes the results of our exploration of this opportunity. Various compounds were synthesized and characterized to find a replacement for the dichroic filter. It was found that Bi3+-doped ortho-borates with the pseudo-vaterite crystal structure exhibit the best absorption spectrum i.e. high transmission around 222 nm and strong absorption in the 235-280 nm range. Y0.24Lu0.75Bi0.01BO3 showed the best absorption spectrum in the UV-C. To suppress the unwanted Bi3+ emission (UV-B), the excitation energy can be transferred to a co-dopant. Ho3+ turned out to be the best co-dopant, and Ho0.24Lu0.75Bi0.01BO3 appeared to be the best overall candidate for the phosphor filter material. A suitable formulation for a coating suspension containing this material was found, and quite homogeneous coatings were achieved. The efficiency of these filter layers was investigated and the results in terms of exposure limit increase i.e. gain factor vs. no filter were compared with the dichroic filter. We achieved a gain factor for the Ho3+ containing sample of up to 2.33, i.e. not as good as that of the dichroic filter (∼4.6), but a very relevant improvement, making Ho0.24Lu0.75Bi0.01BO3 an interesting material for a cost-effective filter for KrCl* far UV-C lamps.

Tunable luminescence and efficient energy transfer investigation of a borosilicate phosphor KBSi2O6: Bi3+, Eu3+ with hypersensitive thermal quenching

Energy transfer between Bi³⁺ and Eu³⁺ has undergone substantial research but Bi³⁺ and Eu³⁺ co-doped luminescent materials with high energy transfer efficiency for temperature sensing are rarely investigated until now. Herein, Eu³⁺ and Bi³⁺ co-doped KBSi₂O₆ phosphors were successfully synthesized by solid-state reaction method. The phase purity structure as well as the element distribution were carefully investigated through X-ray diffraction structural refinement and energy dispersive spectrometer analysis. The characteristic luminescence property and luminescence kinetics of KBSi₂O₆: Bi³⁺, Eu³⁺ were investigated. By the large spectra overlap between the emission spectrum of Bi³⁺ and excitation spectrum of Eu³⁺, the energy transfer from Bi³⁺ to Eu³⁺ can be inferred. The corresponding decrease of the emission intensity and decay time of Bi³⁺ in KBSi₂O₆: Bi³⁺, Eu³⁺ provided direct evidence for the effective energy transfer from Bi³⁺ to Eu³⁺. The interaction and energy transfer mechanism between Bi³⁺ and Eu³⁺ ions were also studied. By increasing the Eu³⁺ concentration in KBSi₂O₆: Bi³⁺, Eu³⁺, the color-tunable emission from blue to red can be realized. KBSi₂O₆: Bi³⁺, Eu³⁺ shows hypersensitive thermal quenching behavior and the maximum absolute sensitivity (S_a) and relative sensitivity (S_r) are determined to be 1.87 %K^-1 and 2.895 %K^-1, respectively. All of the above results imply that KBSi₂O₆: Bi³⁺, Eu³⁺ phosphor can be a color-tunable phosphor for optical temperature sensing.

Second-phase-induced fluorescence quenching in non-equivalent substituted red phosphors

Concentration quenching, which generally originates from serious energy migrations among the uniformly distributed luminescent centers in the host matrix, is a key factor to influence the luminescence properties of materials. Different from previous reports, we demonstrate a novel fluorescence-quenching mechanism attributable to the second-phase Eu₂W₂O₉ in non-equivalent substituted SrWO₄:xEu³⁺ phosphors. The crystal structure, elemental distribution, and luminescence properties of the as-prepared SrWO₄:xEu³⁺ phosphors are systematically investigated. A second-phase Eu₂W₂O₉ is confirmed when the Eu³⁺-doping concentration exceeds 20%, which produces the new structure defects and energy-transfer paths, resulting in fluorescence quenching in this material. This finding gives a new perspective to analyze the concentration-quenching mechanism of the non-equivalent substituted phosphors and can help in the design of new, efficient luminescence materials. In addition, the as-prepared SrWO₄:xEu³⁺ phosphors exhibit a strong intrinsic excitation in the range of 355-425 nm, which is accompanied by the Commission Internationale de I'Eclairage (CIE) coordinates at (0.653, 0.347) and stable color purity of up to 94.52%. A packaged white light-emitting diode with CIE chromaticity coordinates of (0.398, 0.335), correlated color temperature of 3132 K, and color rendering index of 84.3 is fabricated by SrWO₄:20%Eu³⁺ phosphors with blue BAM:Eu²⁺ and green YAGB:Tb³⁺ phosphors in a near-ultraviolet chip.

Tuning of the thermal quenching performance of Bi3+-doped scheelite Ca(Mo/W)O4 solid solution phosphors

The utilization of phosphor materials has always been a significant challenge in terms of improving thermal quenching performance. In this work, the thermal quenching performance tuning mechanism which establishes the band gap and thermal quenching correlation patterns is proposed. The crystal field splitting energy D_q was decreased by changing the surrounding crystal lattice environment of Bi³⁺ through a solid solution replacement, and the thermal quenching activation energy ΔE of Bi³⁺ was tuned from 0.117 eV to 0.182 eV accordingly. At 423 K, the luminous intensity increases from 0.101 to 0.396 of the preliminary intensity at 303 K with increasing substitution. In addition, the band gap value of Bi³⁺ calculated by diffuse reflectance spectroscopy increased from 4.40 eV to 4.72 eV, which corresponds to a linear positive correlation between the band gap and the thermal quenching properties. Furthermore, a monophase white-emitting phosphor with good thermal stability was prepared by constructing a Bi³⁺-Eu³⁺ co-doping system. In particular, the relative sensitivity of S_r for temperature measurement applications reached 3.17% K^-1 based on the double-luminescence fluorescence intensity ratio. Thus, this modulation scheme can be used as a reference for the design of various phosphor materials with tunable thermal quenching properties in the future.

A novel cyan emitting phosphor KScSrSi2-yGeyO7:0.07Bi3+ for high color-rendering index and low correlated color temperature white LEDs

To make up for the cyan gap (480-520nm) in traditional tricolor (blue, green and red) phosphor-converted white light-emitting diodes (LEDs), it is highly important to find efficient cyan phosphors with...

Bifunctional application of La3BWO9:Bi3+,Sm3+ phosphors with strong orange-red emission and sensitive temperature sensing properties

Through a solid-phase reaction technique, Sm³⁺ and Bi³⁺ co-doped La₃BWO₉ phosphors with high emission intensity and sensitive temperature sensing properties have been successfully synthesized. Based on XRD Rietveld refinement, the optimized crystal structure was used as the original model to calculate the band structure and partial density of states (PDOS) by density functional theory (DFT) calculations. The luminescence characteristics of Sm³⁺ and Bi³⁺ co-doped La₃BWO₉ phosphors were measured and analyzed. In addition, the optimal doping concentrations of Sm³⁺ and Bi³⁺ were investigated. The luminescence properties of Sm³⁺ doped phosphors were optimized by introducing Bi³⁺ ions. Efficient energy transfer from Bi³⁺ to Sm³⁺ ions was observed in La₃BWO₉:Sm³⁺, Bi³⁺ phosphors. An optical temperature sensor with high sensitivity was designed based on the different thermal quenching properties of Sm³⁺ and Bi³⁺ ions. In the temperature range of 293-498 K, the optimum absolute sensitivity (S_a) and maximum relative sensitivity (S_r) were 2.88 %K^-1 and 1.32 %K^-1, respectively. These results indicated that the prepared La₃BWO₉:Bi³⁺, Sm³⁺ phosphors have wide application prospects as solid state lighting materials and optical temperature sensors.

A highly sensitive ratiometric optical cryothermometer using a new broadband emitting trivalent bismuth singly activated Ba2ZnSc(BO3)3 microcrystal

Motivated by the growing demand for noncontact temperature sensing in cryogenic environments, the development of a high performance low temperature optical thermometer has become more and more urgent. Herein, we demonstrate a new broadband emitting bismuth singly activated Ba₂ZnSc(BO₃)₃ optical thermometric material that exhibits a remarkable temperature-dependent emission color variation and a good low temperature sensing performance. First, Bi³⁺ doped Ba₂ZnSc(BO₃)₃ phosphors were successfully synthesized by a high-temperature solid-state reaction. Upon excitation at 320 nm, the emission spectra of Ba₂ZnSc(BO₃)₃:Bi³⁺ cover almost the entire visible region from 350 to 720 nm because of the multiple crystallographic sites occupied by Bi³⁺ ions, which have been verified by structure analysis and time-resolved emission spectroscopy. Interestingly, the temperature dependent emission characteristics indicated that the thermal quenching phenomena of Bi³⁺ at different lattice sites were different, resulting in a very sensitive emission color variation from orange to cyan. Further analysis indicated that these Bi³⁺ doped luminescent materials showed a good performance in temperature sensing over a wide temperature range from 10 to 374 K, with a maximum relative sensitivity of 3.076% K^-1 at 210 K. Finally, this study provides a new perspective for the design of superior thermosensitive phosphors, aimed toward non-rare earth ion doped thermosensitive phosphors for optical cryothermometry applications.

Synthesis of a Bi3+-Doped Cs2HfCl6 Double Perovskite with Highly Efficient Blue Light Emission at Room Temperature

Lead-free perovskites have been widely studied due to their environmental friendliness and high stability. In this study, Bi³⁺-doped Cs₂HfCl₆ has been synthesized at room temperature. Different from the emission of the Cs₂HfCl₆ host (452 nm), Bi³⁺:Cs₂HfCl₆ can produce a bright blue emission at an excitation wavelength of 350 nm, which is derived from the ³P₁ → ¹S₀ transition of Bi ions and accompanied by the properties of self-trapped excitons. Moreover, 7%Bi³⁺:Cs₂HfCl₆ shows excellent stability with the photoluminescence quantum yield reaching up to 69.08%. Meanwhile, a light-emitting diode that is close to pure white light has been fabricated by using 7%Bi³⁺:Cs₂HfCl₆, which has a high color rendering index of 92.5. These results show that Bi³⁺:Cs₂HfCl₆ would be a potential candidate in the field of inorganic luminescent materials.

Synthesis and characterization of a Eu3+ -activated Ba2-x V2 O7 :xEu3+ phosphor using a hydrothermal method: a potential material for near-UV-WLED applications

Eu³⁺ -activated Ba₂ V₂ O₇ (Ba_2-x V₂ O₇ :xEu³⁺ ) phosphor materials were synthesized using a hydrothermal method and different concentrations of europium (x = 0.01, 0.02, 0.03, 0.04, and 0.05%). Phase purity, structural, morphological, optical, and luminescence characteristics of the as-synthesized phosphors were studied using powder X-ray diffraction (XRD), high resolution scanning electron microscopy, UV-visible spectroscopy, and fluorescence spectrometry. The recorded XRD patterns of the as-synthesized phosphors were indexed and predicted to be a triclinic structure. A cube-like morphology was obtained for the as-prepared samples. Broad absorption in the UV region from 200 nm to 380 nm was observed and the good transparency in the visible region at 400-800 nm originated from the [VO₄ ]^3- group charge transfer (CT) transition. The broad emission peak centred at 499 nm was due to the CT band of the [VO₄ ]^3- group. Also, a sharp peak observed at 613 nm was due to the electric dipole transition of ⁵ D₀ →⁷ F₂ of Eu³⁺ ions that occupied the lattice sites without inversion symmetry for all concentrations. The colour qualities of the as-prepared samples were calculated using Commission International de l'Eclairage coordinates. The colour-rending index (CRI) value was 86 for the Ba_1.97 V₂ O₇ :0.03Eu³⁺ phosphor. Furthermore, a WLED with a high CRI value of 95 was achieved by coupling the 3 W 356 nm near-UV light-emitting diode (LED) chip with the Ba_2-x V₂ O₇ :xEu³⁺ phosphor. These results suggested that the as-prepared phosphor materials are potential candidates for fabrication of near-UV chip excited WLEDs.

Preparation of zero-thermal-quenching tunable emission bismuth-containing phosphors through the topochemical design of ligand configuration

We report a high performance bismuth-containing phosphor with zero-thermal-quenching, which can be used for white light illumination and non-contact temperature sensing.

Bi3+ and Eu3+ Activated Luminescent Behaviors in Non-Stoichiometric LaO0.65F1.7 Structure

Optical materials composed of La_1-p-qBi_pEu_qO_0.65F_1.7 (p = 0.001–0.05, q = 0–0.1) were prepared via a solid-state reaction using La(Bi,Eu)₂O₃ and NH₄F precursors at 1050 °C for two hours. X-ray diffraction patterns of the phosphors were obtained permitting the calculation of unit-cell parameters. The two La³⁺ cation sites were clearly distinguished by exploiting the photoluminescence excitation and emission spectra through Bi³⁺ and Eu³⁺ transitions in the non-stoichiometric host lattice. Energy transfer from Bi³⁺ to Eu³⁺ upon excitation with 286 nm radiation and its mechanism in the Bi³⁺- and Eu³⁺-doped host structures is discussed. The desired Commission Internationale de l’Eclairage values, including emissions in blue-green, white, and red wavelength regions, were obtained from the Bi³⁺- and Eu³⁺-doped LaO_0.65F_1.7 phosphors.

Luminescence Spectroscopy and Origin of Luminescence Centers in Bi-Doped Materials

Bi-doped compounds recently became the subject of an extensive research due to their possible applications as scintillator and phosphor materials. The oxides co-doped with Bi3+ and trivalent rare-earth ions were proposed as prospective phosphors for white light-emitting diodes and quantum cutting down-converting materials applicable for enhancement of silicon solar cells. Luminescence characteristics of different Bi3+-doped materials were found to be strongly different and ascribed to electronic transitions from the excited levels of a Bi3+ ion to its ground state, charge-transfer transitions, Bi3+ dimers or clusters, radiative decay of Bi3+-related localized or trapped excitons, etc. In this review, we compare the characteristics of the Bi3+-related luminescence in various compounds; discuss the possible origin of the corresponding luminescence centers as well as the processes resulting in their luminescence; consider the phenomenological models proposed to describe the excited-state dynamics of the Bi3+-related centers and determine the structure and parameters of their relaxed excited states; address an influence of different interactions (e.g., spin-orbit, electron-phonon, hyperfine) as well as the Bi3+ ion charge and volume compensating defects on the luminescence characteristics. The Bi-related luminescence arising from lower charge states (namely, Bi2+, Bi+, Bi0) is also reviewed.

A new strategy of interlayer doping of Li ions for the photoluminescence enhancement of Eu3+-doped bismuth oxychloride layered semiconductors

The interlayer doping of Li⁺ ions significantly improves the IEF in layered BiOCl, which modifies the photoluminescence of Eu³⁺ ions via its local field effect and photocarrier separation role.

Tuning the Doping of Europium in Gadolinium Borate Microparticles at Mesoscale Toward Efficient Production of Red Phosphors

The ideal product of rare-earth-doped phosphors should have uniform particle size distribution and homogeneous doping ions in each particle, and therefore, intensified micromixing at mesoscale is highly required. In this article, inspired by the concept of "mesoscience", we demonstrate the tuning of Eu³⁺ doping in GdBO₃ microparticles at mesoscale by a high-gravity-assisted reactive precipitation-coupled calcination process. The high-gravity environment and tiny droplets generated by the high-gravity rotating packed bed (RPB) reactor lead to significant intensification of mass transfer and micromixing, which are beneficial for the homogeneous doping of Eu³⁺ in the host material during reactive precipitation in liquid solution. Under excitation at 395 nm, the emission spectra of the Eu³⁺-doped phosphors exhibit a narrow-band red emission centered at 625 nm and the highest intensity was observed at x = 0.2. The RPB products show higher intensity than that of the control group even when the reaction time was shortened to 1/6. After calculation, the quenching in the sample most likely results from dipole-dipole interactions. The chromaticity coordinates for the RPB sample was measured as (0.598, 0.341) with a quantum yield of up to 78.11%, and the phosphors exhibit good thermal stability at 423 K. The phosphors were used as the luminescent materials for light-emitting diodes (LEDs), and the devices showed good performance. Our preliminary study illustrated that high-gravity-assisted approaches are promising for tuning the doping of rare-earth ions in microparticles at mesoscale toward efficient production of phosphors for LEDs.

Fast and simultaneous doping of Sr0.9-x-y-zCa0.1In2O4:(xEu3+, yTm3+, zTb3+) superstructure by ultrasonic spray pyrolysis

In the present work, Sr_0.9-x-y-zCa_0.1In₂O₄:(xEu³⁺, yTm³⁺, zTb³⁺) particles were synthesized by the ultrasonic spray pyrolysis (USP) method to obtain a single-phase white phosphorus formed by six different cations in solution within the lattice (superstructure). The samples were also structurally and morphologically characterized by X-ray diffraction (XRD) techniques and by field emission scanning electron microscopy (FE-SEM). The photoluminescent behavior and the characteristics of the emitted colors were studied by the variation in the co-doping of the rare earth elements. The Sr_0.9Ca_0.1In₂O₄ sample showed a near blue color emission, but all co-doped samples showed emission in white with very close chromaticity coordinates to the standard white (x = 0.33 and y = 0.33). The Tm³⁺ → Tb³⁺ (ET1), Tm³⁺ → Eu³⁺ (ET2) and Tb³⁺ → Eu³⁺ (ET3) Energy Transfers were proposed and are considered necessary for adjusting and controlling the desired color properties.

New strategy for designing orangish-red-emitting phosphor via oxygen-vacancy-induced electronic localization

Phosphor-converted white-light-emitting diodes (pc-WLED) have been extensively employed as solid-state lighting sources, which have a very important role in people's daily lives. However, due to the scarcity of the red component, it is difficult to realize warm white light efficiently. Hence, red-emitting phosphors are urgently required for improving the illumination quality. In this work, we develop a novel orangish-red La₄GeO₈:Bi³⁺ phosphor, the emission peak of which is located at 600 nm under near-ultraviolet (n-UV) light excitation. The full width at half maximum (fwhm) is 103 nm, the internal quantum efficiency (IQE) exceeds 88%, and the external quantum efficiency (EQE) is 69%. According to Rietveld refinement analysis and density functional theory (DFT) calculations, Bi³⁺ ions randomly occupy all La sites in orthorhombic La₄GeO₈. Importantly, the oxygen-vacancy-induced electronic localization around the Bi³⁺ ions is the main reason for the highly efficient orangish-red luminescence. These results provide a new perspective and insight from the local electron structure for designing inorganic phosphor materials that realize the unique luminescence performance of Bi³⁺ ions.

Mixing the valence control of Eu2+/Eu3+ and energy transfer construction of Eu2+/Mn2+ in the solid solution (1 − x)Ca3(PO4)2–xCa9Y(PO4)7 for multichannel photoluminescence tuning

Multichannel photoluminescence control from blue-to-green to red across the white region was achieved by solid solution evolution, valence mixing of Eu²⁺/³⁺ and Eu²⁺ → Mn²⁺ energy transfer.

Investigation of local structure distortion and electron cloud interaction on emission-band broadening induced by the concentration perturbation effect of cation substitution in BaY2Si3O10:Eu phosphors

Here, we conceived a concentration perturbation effect to obtain cyan-emitting phosphors based on local structure distortion and electron cloud interaction.

Novel orange-yellow-green color-tunable Bi3+-doped Ba3Y4−wLuwO9 (0 ≤ w ≤ 4) luminescent materials: site migration and photoluminescence control

The site migration of Bi³⁺ induced orange-yellow-green photoluminescence control in Ba₃Y_4−wLu_wO₉ (0 ≤ w ≤ 4).

An energy self-compensating phosphosilicate material applied to temperature sensors

For years, researchers have been exploring effective methods of sustaining the emission intensity of phosphors with increasing temperature by suppressing emission loss. In this work, we developed a multi-cationic site and lattice-distorted phosphosilicate phosphor, Ca₈Al₂P₆SiO₂₈:Ce, Eu. To obtain luminous-self-healing properties, we attempted to change the energy depths and density distributions of the traps to achieve self-suppression of emission loss by energy compensation from the traps or energy transfer between Ce³⁺ and Eu²⁺/Eu³⁺. The temperature-dependent emission spectra indicate that the luminescence of Ce³⁺ presents similar change trends in both single and co-doped samples. Meanwhile, the change trends of the Eu²⁺/Eu³⁺ emission intensities show obvious differences. Combined with the thermoluminescence curves, decay times, temperature-dependent fluorescence characteristics and cathodoluminescence spectra, we speculate that the traps play an important role in the luminescence of Ce³⁺ due to the smaller energy difference of the Ce³⁺ excited states and the conduction band. The abnormal luminescence of Eu²⁺/Eu³⁺ mainly results from the energy transfer of Ce³⁺ to Eu²⁺/Eu³⁺. For this phenomenon, a high thermal sensitive fluorescence intensity ratio is obtained in a broad temperature range, which implies that this material can be applied in temperature sensors.

For years, researchers have been exploring effective methods of sustaining the emission intensity of phosphors with increasing temperature by suppressing emission loss.

Multicolor Tuning and Temperature-Triggered Anomalous Eu3+-Related Photoemission Enhancement via Interplay of Accelerated Energy Transfer and Release of Defect-Trapped Electrons in the Tb3+,Eu3+-Doped Strontium-Aluminum Chlorites

So far, a large number of rare earth (RE) and non-RE-doped emission-tunable crystals based on controllable energy transfer have become available, but numerous mechanistic issues, particularly for those that involve temperature-dependent energy transfer between the well-shielded 4f RE ions, lack comprehensive theoretical and experimental investigation, limiting greatly their development and applications in the future. Here, we design and report a type of Tb³⁺,Eu³⁺-doped Sr₃Al₂O₅Cl₂ phosphors capable of multiemissions upon excitation at 376 nm, through using the orthorhombic Sr₃Al₂O₅Cl₂ as the host lattice while the well-shielded 4f Tb³⁺ and Eu³⁺ ions as dual luminescent centers. Our results reveal that the energy transfer from Tb³⁺ to Eu³⁺ ions, happening via an electric dipole-quadrupole (d-q) interaction, can be controlled by the doping ratio of Tb³⁺ and Eu³⁺, leading to the tunable emissions from green (0.3159, 0.5572) to red (0.6579, 0.3046). It is found from time-resolved photoluminescence (PL) spectra that this energy transfer begins at t = 5 μs and gradually ends at t ≥ 200 μs. Moreover, from temperature-dependent PL results, we reveal that the Eu³⁺ emission features an anomalous intensity enhancement at the earlier heating state. With the density functional theory (DFT) calculations, we have screened the possibilities of site preferential substitution problem. By jointly taking into account the X-ray diffraction Rietveld refinement, DFT findings, and PL and thermoluminescence spectra, a mechanistic profile is proposed for illustrating the PL observations. In particular, our discussions reveal that the temperature-triggered Eu³⁺ emission enhancement is due to the interplay of the temperature-induced accelerated energy transfer and defect-trapped electrons that are released upon the thermal stimulation. Unlike most of reported phosphor materials that are always suggested for phosphor-converted white light-emitting diodes, we propose new application possibilities for Tb³⁺,Eu³⁺-doped Sr₃Al₂O₅Cl₂ phosphors, such as anticounterfeiting, temperature-controlled fluorescence sensor, data storage, and security devices.

Enhanced Efficiency of Functional Smart Window with Solar Wavelength Conversion Phosphor-Photochromic Hybrid Film

Here, the high sensitivity and enhanced photochromic efficiency of the hybrid film of solar wavelength conversion phosphor and photochromic film for functional smart window have been achieved by fabricating a double-layered hybrid structure of wavelength conversion phosphor and photochromic film. Y₂SiO₅:Pr³⁺ phosphor nanoparticles, which upconvert visible light to UV light, were synthesized by simple hydrothermal method. The synthesized Y₂SiO₅:Pr³⁺ nanoparticle was coated as layered structured film on photochromic H₃PW₁₂O₄₀ film. The Y₂SiO₅:Pr³⁺/H₃PW₁₂O₄₀ hybrid film showed an enhanced sensitivity and efficiency of photochromic process with solar light irradiation due to the increased UV portion of solar light through upconversion process of visible light by wavelength conversion phosphor layer. The increased UV portion by upconversion process of Y₂SiO₅:Pr³⁺ layer through excited-state absorption and energy transfer upconversion process, contributed to an enhancement of coloration rate of photochromic H₃PW₁₂O₄₀ film by 7 times with 50 min of 1 sun irradiation due to fast conversion of W⁶⁺ state to W⁵⁺ state in H₃PW₁₂O₄₀ film with 5 times enhanced photochromic sensitivity compared with pristine photochromic film.

Two-Dimensional-Layered Perovskite ALaTa2O7:Bi3+ (A = K and Na) Phosphors with Versatile Structures and Tunable Photoluminescence

Topological chemical reaction methods are indispensable for fabricating new materials or optimizing their functional properties, which is particularly important for two-dimensional (2D)-layered compounds with versatile structures. Herein, we demonstrate a low-temperature (∼350 °C) ion exchange approach to prefabricate metastable phosphors ALa_{1- x}Ta₂O₇: xBi³⁺ (A = K and Na) with RbLa_{1- x}Ta₂O₇: xBi³⁺ serving as precursors. The as-prepared ALa_0.98Ta₂O₇:0.02 Bi³⁺ (A = Rb, K, and Na) share the same Dion-Jacobson type 2D-layered perovskite phase, and photoluminescence analyses show that ALa_0.98Ta₂O₇:0.02 Bi³⁺ (A = Rb, K, and Na) phosphors exhibit broad emission bands peaking at 540, 550, and 510 nm, respectively, which are attributed to the nonradiative transition of Bi³⁺ from excited state ³P₁ or ³P₀ to ground state ¹S₀. The various Bi³⁺ local environments at the crystallographic sites enable the different distributions of emission and excitation spectra, and the photoluminescence tuning of ALa_0.98Ta₂O₇:0.02 Bi³⁺ (A = Rb, K, and Na) phosphors are realized through alkali metal ion exchange. Notably, the combination of superior trivalent bismuth emission and low-temperature ion exchange synthesis leads to a novel yellow-emitting K(La_0.98Bi_0.02)Ta₂O₇ phosphor which is successfully applied in a white LED device based on a commercially available 365 nm LED chip. Our realizable cases of this low-temperature ion exchange strategy could promote exploration into metastable phosphors with intriguing properties.

Misconceptions in electronic energy transfer: bridging the gap between chemistry and physics

Many treatments of energy transfer (ET) phenomena in current literature employ incorrect arguments and formulae and are not quantitative enough. This is unfortunate because we witness important breakthroughs from ET experiments in nanoscience. This review aims to clarify basic principles by focusing upon Förster-Dexter electric dipole-electric dipole (ED-ED) ET. The roles of ET in upconversion, downconversion and the antenna effect are described and the clichés and simple formulae to be avoided in ET studies are highlighted with alternative treatments provided.

Tb3+, Eu3+ Co-doped CsPbBr3 QDs Glass with Highly Stable and Luminous Adjustable for White LEDs

Herein, we have introduced rare-earth cations Tb³⁺ and Eu³⁺ into CsPbBr₃ QDs glass by conventional melt-quenching. Rare-earth cations like Tb³⁺ emit green light, causing the main peak of bromide lead cesium to exhibit some redshift, owing to the energy transfer between CsPbBr₃ and Tb³⁺. To achieve adjustable light, Eu³⁺ emits red light, which was doped in this glass with different proportions to solve the problem of red deficiency. More importantly, Tb³⁺ and Eu³⁺ co-doped CsPbBr₃ QDs glass shows a series of desirable characteristics due to the energy transfer between Tb³⁺ and Eu³⁺. Interestingly, the blue light radiated by blue chip can excite Tb³⁺, Eu³⁺, and CsPbBr₃ perovskite effectively. We acquired high-performance white light-emitting diodes with color-rendering index, color coordinate transformation, and luminous efficiency of 85.7, 4945 K, and 63.21 lm/W under the current of 20 mA. This acquired Tb³⁺, Eu³⁺ co-doped CsPbBr₃ QDs glass proved the significant feasibility of luminescent materials in solid warm light source.

Simultaneous enhancement of photoluminescence and afterglow luminescence through Bi3+ co-doping in the Sr3Al2O5Cl2:Eu2+ phosphor

In this work, the Sr3Al2O5Cl2:Eu2+ and Sr3Al2O5Cl2:Eu2+,Bi3+ phosphors are synthesized by high temperature solid state reactions. Various characterization techniques, such as X-ray diffraction (XRD), Rietveld refinement, photoluminescence (PL) spectroscopy, afterglow spectroscopy, decay curves and thermoluminescence (TL) spectroscopy, are used to examine the phase purity and PL properties of all samples. The XRD results show that all samples belong to the targeted orthorhombic Sr3Al2O5Cl2 phase with the space group of P212121. Upon excitation with UV light, Eu2+-related reddish photoemission and afterglow luminescence are observed in the Sr3Al2O5Cl2:Eu2+ samples. More remarkably, we find that co-doping with Bi3+ ions can enhance the Eu2+-related photoemission and afterglow intensity as well the afterglow duration. For the optimal Sr3Al2O5Cl2:Eu2+,Bi3+ sample, the afterglow luminescence can continue for nearly 550 min in the dark, which is almost 3-fold the duration of the afterglow luminescence of the optimal Sr3Al2O5Cl2:Eu2+ sample. The TL spectra reveal that co-doping with Bi3+ ions can enhance the defect population that corresponds to trap depths at 63 °C, 75 °C and 150 °C, of which the former two trap depths may help to improve the Eu2+-related luminescence in addition to the afterglow property. Due to an increase in the trap concentration, there is an increase in the re-trapping possibility for the released carriers. This work not only achieves enhanced afterglow luminescence of the Sr3Al2O5Cl2:Eu2+ phosphor by co-doping with the non-rare earth (RE) Bi3+ ions, but also provides new insights into the design of RE and non-RE related enhanced afterglow photonic materials for the future.

Synthesis, electronic structures, and photoluminescence properties of an efficient and thermally stable red-emitting phosphor Ca3ZrSi2O9:Eu3+,Bi3+ for deep UV-LEDs

A series of red-emitting Ca3ZrSi2O9:Eu3+,xBi3+ phosphors was synthesized using a conventional high temperature solid-state reaction method, for the purpose of promoting the emission efficiency of Eu3+ in a Ca3ZrSi2O9 host. The site preference of Bi3+ and Eu3+ in the Ca3ZrSi2O9 host was evaluated by formation energy. The effects of Bi3+ on electronic structure, luminescent properties, and related mechanisms were investigated. The inner quantum yield of the optimized sample increased to 72.9% (x = 0.08) from 34.6% (x = 0) at 300 nm ultraviolet light excitation. The optimized sample (x = 0.08) also showed excellent thermal stability, and typically, 84.2% of the initial emission intensity was maintained when the temperature increased to 150 °C from 25 °C, which is much higher than that without Bi3+ doping (70.1%). The mechanisms of emission properties and thermal stability enhancement, as well as the redshift of the charge transfer band (CTB) induced by Bi3+ doping in the Ca3ZrSi2O9:Eu3+ phosphor, were discussed. This study elucidates the photoluminescence properties of Bi3+-doped Ca3ZrSi2O9:Eu3+ phosphor, and indicates that it is a promising luminescent material that can be used in ultraviolet light-emitting diodes.

Broad color tuning and Eu3+-related photoemission enhancement via controllable energy transfer in the La2MgGeO6:Eu3+,Bi3+ phosphor

Herein, we provide the new UV converted tunable phosphors and increase the emission intensity via a controllable energy transfer.

Synthesis and photoluminescence properties of Eu3+-activated LiCa3ZnV3O12white-emitting phosphors

A novel high-efficiency white-emitting LiCa₃ZnV₃O₁₂:Eu³⁺phosphor was developed.

Structure and photoluminescence properties of red-emitting apatite-type phosphor NaY9(SiO4)6O2:Sm3+ with excellent quantum efficiency and thermal stability for solid-state lighting

A novel red-emitting phosphor NaY₉(SiO₄)₆O₂:Sm³⁺ (NYS:Sm³⁺) was synthesized and the X-ray diffraction and high-resolution TEM testified that the NYS compound belongs to the apatite structure which crystallized in a hexagonal unit cell with space group P6₃/m. The novel phosphor boasts of such three advantageous properties as perfect compatible match with the commercial UV chips, 73.2% quantum efficiency and 90.9% thermal stability at 150 °C. Details are as follows. NYS:Sm³⁺ phosphor showed obvious absorption in the UV regions centered at 407 nm, which can be perfectly compatible with the commercial UV chips. The property investigations showed that NYS:Sm³⁺ phosphor emitted reddish emission with CIE coordination of (0.563, 0.417). The optimum quenching concentration of Sm³⁺ in NYS phosphor was about 10%mol, and the corresponding concentration quenching mechanism was verified to be the electric dipole–dipole interaction. Upon excitation at 407 nm, the composition-optimized NYS:0.10Sm³⁺ exhibited a high quantum efficiency of 73.2%, and its luminescence intensity at 150 °C decreased simply to 90.9% of the initial value at room temperature. All of the results indicated that NYS:Sm³⁺ is a promising candidate as a reddish-emitting UV convertible phosphor for application in white light emitting diodes (w-LEDs).

Crystal structure, tunable luminescence and energy transfer properties of Na3La(PO4)2:Tb3+,Eu3+phosphors

A series of Tb³⁺and/or Eu³⁺doped Na₃La(PO₄)₂phosphors were successfully synthesized and their crystal structure and photoluminescence (PL) properties were investigated in detail.

Cation substitution induced novel gehlenite Ca2GaAlSiO7:Eu2+/Ce3+phosphor with green/blue emission for UV-WLEDs

We have investigated the structure and luminescence properties of a novel and efficient Ca₂GaAlSiO₇:Eu²⁺/Ce³⁺phosphor obtained by cation substitution for UV-WLEDs.

Structure and photoluminescence properties of novel Sr6Ca4(PO4)6F2:Re (Re = Eu2+, Mn2+) phosphors with energy transfer for white-emitting LEDs

A series of Sr₆Ca₄(PO₄)₆F₂:Eu²⁺,Mn²⁺ phosphors were synthesized by traditional solid state reaction. Through controlling the ratio of Eu²⁺ and Mn²⁺, emission colors can be tuned from blue to yellow, including white-light-emitting.