Enriching the Deep-Red Emission in (Mg, Ba)3M2GeO8: Mn4+ (M = Al, Ga) Compositions for Light-Emitting Diodes

Structural Investigation and Energy Transfer of Eu3+/Mn4+ Co-Doped Mg3Ga2SnO8 Phosphors for Multifunctional Applications

In recent years, rare earth ion and transition metal ion co-doped fluorescent materials have attracted a lot of attention in the fields of WLEDs and optical temperature sensing. In this study, I successfully prepared the dual-emission Mg3Ga2SnO8:Eu3+,Mn4+ red phosphors and the XRD patterns and refinement results show that the prepared phosphors belong to the Fd-3m space group. The energy transfer process between Eu3+ and Mn4+ was systematically investigated by emission spectra and decay curves of Mg3Ga2SnO8:0.12Eu3+,yMn4+ (0.002 ≤ y ≤ 0.012) phosphors and the maximum value of transfer efficiency can reach 71.2%. Due to the weak thermal quenching effect of Eu3+, its emission provides a stable reference for the rapid thermal quenching of the Mn4+ emission peak, thereby achieving good temperature measurement performance. The relative thermometric sensitivities of the fluorescence intensity ratio and fluorescence lifetime methods reached a maximum value of 2.53% K-1 at 448 K and a maximum value of 3.38% K-1 at 473 K. In addition, the prepared WLEDs utilizing Mg3Ga2SnO8:0.12Eu3+ phosphor have a high color rendering index of 82.5 and correlated color temperature of 6170 K. The electroluminescence spectrum of the synthesized red LED device by Mg3Ga2SnO8:0.009Mn4+ phosphor highly overlaps with the absorption range of the phytochrome PFR and thus can effectively promote plant growth. Therefore, the Mg3Ga2SnO8:Eu3+,Mn4+ phosphors have good application prospects in WLEDs, temperature sensing, and plant growth illumination.

Temperature-dependent color-tunable persistent luminescence in Ba0.95Sr0.05Ga2-yGdyO4:Bi3+ phosphor for advanced anti-counterfeiting

As emerging anti-counterfeiting materials, persistent luminescence (PersL) materials have attracted much attention owing to their particular luminescent properties, including durable luminescence, facile identification, high security and environment-friendly. Especially, exploiting color-tunable dynamic afterglow materials that facilitate the use of advanced technology such as multi-mode dynamic anti-counterfeiting remains of great realistic significance. Herein, a series of Ba0.95Sr0.05Ga2-yGdyO4:Bi3+ phosphors with tunable photoluminescence and PersL were synthesized by the cationic substitution strategy. The displacement of Ga3+ by Gd3+ induces an additional blue emission owing to the generation of a new Bi3+ luminescence center. The pure white light is realized in Ba0.942Sr0.05Ga1.9Gd0.1O4:0.8 %Bi3+,0.25 %K+ when excited by 325 nm light. Besides, color-tunable emission is triggered by changing the excitation wavelength or temperature. Significantly, excellent room-temperature PersL and dramatically intensified PersL with tunable color output under thermal stimulation are clearly discernible. Such properties result from the existence of multiple Bi3+ luminescent centers and traps. These findings open up new ideas to produce color-tunable dynamic PersL materials for advanced anti-counterfeiting, information storage and encryption.

Defect Regulation Induced Luminescence Improvement of the Broadband Orange Phosphor Lu2CaMg2Si3O12:Ce3+ for WLED

Phosphors for white light emitting diode (WLED) have been attracting the attention of researchers to obtain devices with a high color rendering index (CRI) and low correlated color temperature (CCT). Herein, the broadband orange phosphor Lu2CaMg2Si3O12:Ce3+ is prepared, and Lu3+ vacancy is created in the lattice to regulate the structure of this phosphor. This orange phosphor can be excited well by blue light and emit orange light ranging from 500 to 750 nm. By decreasing Lu3+ content in the lattice, the band gap of the matrix is widened. Besides, the emission of Ce3+ in this garnet structure is improved, and the emission of Lu1.84CaMg2Si3O12:Ce3+ reached the maximum of all the samples. The thermal stability of this orange phosphor is improved, and the emission of the phosphor Lu1.84CaMg2Si3O12:Ce3+ maintains 75.5% at 423 K compared to that at 298 K. WLED device is fabricated via coating the mixtures of Lu1.84CaMg2Si3O12:Ce3+ and the cyan phosphor Ca3Sc2Si3O12:Ce3+ onto the blue chip. This WLED device shows a high CRI of 87.9 and a low CCT of 4167 K, verifying the great potential of this orange phosphor in WLED.

Novel efficient deep-red emitting phosphor SrCa2Ga2O6:Mn4+ with tululite-related structure

Mn4+-activated phosphors have been attracted to replace the rare-earth-activated phosphors in the use of deep-red optical devices. Owing to their low toxicity and wide applications, oxide materials are promising hosts for Mn4+ phosphors. Exploration into novel oxides is important for developing new Mn4+-doped phosphors with high luminescent efficiencies. In this study, we discovered the deep-red emitting phosphor SrCa2Ga2O6:Mn4+ in the Sr3Ga2O6-Ca3Ga2O6 solid solution system. From the single crystal X-ray diffraction analysis, SrCa2Ga2O6:Mn4+ was found to crystallize in a cubic unit cell with space group F432. Furthermore, SrCa2Ga2O6:Mn4+ was revealed to be a new member of tululite structure-related phosphors, such as Ca14Zn6Al10O35:Mn4+, Ca14Zn6Ga10O35:Mn4+, and Ca14Mg4Ga12O36:Mn4+. To study the fundamental luminescence properties, we synthesized SrCa2Ga2O6:Mn4+ powder samples via the conventional solid-state reaction method. SrCa2Ga2O6:Mn4+ has an absorption band in the region of 250-550 nm, and shows a deep-red emission band peaks at 712 nm. The excitation band is well matched to the emission wavelength of near-ultraviolet and blue light emitting diodes. The optimized sample exhibited high quantum efficiency and good thermal quenching properties. This study revealed SrCa2Ga2O6:Mn4+ has excellent potential as a deep-red emitting phosphor and is expected to be used for commercial applications, such as indoor plant cultivation and wavelength down-convertor for solar-cells.

Realizing Near Infrared Mechanoluminescence Switch in LAGO:Cr Based on Oxygen Vacancy

Mechanoluminescence (ML) materials are featured with the characteristic of "force to light" in response to external stimuli, which have made great progress in artificial intelligence and optical sensing. However, how to effectively enable ML in the material is a daunting challenge. Here, a Lu3Al2Ga3O12:Cr3+ (LAGO: Cr3+) near infrared (NIR) ML material peaked at 706 nm is reported, which successfully realizes the key to unlock ML by the lattice-engineering strategy Ga3+ substitution for Al3+ to "grow" oxygen vacancy (Ov) defects. Combined with thermoluminescence measurements, the observed ML is due to the formation of defect levels and the ML intensity is proportional to it. It is confirmed by X-ray photoelectron spectroscopy and electron paramagnetic resonance that such a process is dominated by Ov, which plays a crucial role in turning on ML in this compound. In addition, potential ML emissions from 4T2 and 2E level transitions are discussed from both experimental and theoretical aspects. This study reveals the mechanism of the change in ML behavior after cation substitution, and it may have important implications for the practical application of Ov defect-regulated turn-on of ML.

A highly efficient deep red-emitting Mn4+-powered oxyfluoride nanophosphor developed for plant growth and optical thermometric applications

This research mainly highlighted an intense deep red-emitting and Mn4+-powered oxyfluoride nanophosphor, Mg14Ge4.99O16F8:0.01Mn4+ (MGOF:Mn), which was synthesized via adopting a scalable synthesis route for commercial temperature sensing and artificial plant growth applications. The electron microscopic analysis confirmed the formation of nanosized particles without any defined shape or size distribution. The obtained nanophosphor exhibited sharp emission peaks at 659 nm and 631 nm under UV (317 nm) and blue excitation (417 nm) owing to Mn4+:2Eg → 4A2g and Mn4+:2T1g → 4A2g transitions, respectively. The emission spectrum is situated in the deep red region of the CIE color diagram where the red color purity approached 100% under both the excitations. The absorption efficiency and the internal and external quantum efficiencies of this red-emitting system were calculated to be 53%, ∼77%, and ∼41%, respectively, under blue excitation of 417 nm, which indicated its potential for indoor plant cultivation. A prototype red LED was fabricated by pasting the red-emitting MGOF:Mn4+ nanophosphor powder on a 410 nm blue LED chip. The resulting electroluminescence spectrum overlapped with those of the important organic pigments of normal plants. Importantly, the thermometric properties of the nanophosphor were evaluated in detail for FIR and lifetime-based thermometry applications. The examined nanophosphor showed an extreme absolute sensitivity of 0.00326 K-1 at 373 K with excellent reproducibility and temperature resolution. Because of the small particle size and high luminescence efficiency, the nanophosphor could be implemented in various nano-devices where non-contact optical thermometry is necessary for high performance.

High-efficiency energy transfer in the strong orange-red-emitting phosphor CeO2:Sm3+, Eu3

High-efficiency energy transfer (ET) from Sm3+ to Eu3+ leads to dominant red emission in Sm3+, Eu3+ co-doped single-phase cubic CeO2 phosphors. In this work, a series of Sm3+ singly and Sm3+/Eu3+ co-doped CeO2 cubic phosphors was successfully synthesized by solution combustion followed by heat treatment at 800 °C in air. The crystal structure, morphology, chemical element composition, and luminescence properties of the obtained phosphors were investigated using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and photoluminescence analysis. Under 360 nm excitation, the Sm3+ singly doped CeO2 phosphor emitted strong yellow-red light at 573 nm (4G5/2-6H5/2) and 615 nm (4G5/2-6H7/2). Meanwhile, the CeO2:Sm3+, Eu3+ phosphors showed the emission characteristic of both Sm3+ and Eu3+, with the highest emission intensity at 631 nm. The emission intensity of Sm3+ decreased with increasing Eu3+ content, suggesting the ET from Sm3+ to Eu3+ in the CeO2:Sm3+, Eu3+ phosphors. The decay kinetics of the 4G5/2-6H5/2 transition of Sm3+ in the CeO2:Sm3+, Eu3+ phosphors were investigated, confirming the high-efficiency ET from Sm3+ to Eu3+ (reached 84%). The critical distance of energy transfer (RC = 13.7 Å) and the Dexter theory analysis confirmed the ET mechanism corresponding to the quadrupole-quadrupole interaction. These results indicate that the high-efficiency ET from Sm3+ to Eu3+ in CeO2:Sm3+, Eu3+ phosphors is an excellent strategy to improve the emission efficiency of Eu3+.