Toward Ultra-High Sensitivity Optical Thermometers and Bright Yellow LEDs Based on Phonon-Assisted Energy Transfer in Rare Earth-Doped La2ZnTiO6 Double Perovskite

Double perovskites, a class of ceramic oxides with unique crystal structures and diverse physical properties, show promise for various technological applications including solar cells, photodetectors, and light-emitting diodes (LEDs). Despite limited research on rare earth-doped double perovskites, leveraging their ultrahigh luminous efficiency to achieve bright yellow LED emission and addressing energy transfer challenges between Yb3+ and Nd3+ ions in double perovskite La2ZnTiO6 with moderate phonon energy are explored in this work. Through phonon-assisted energy transfer, an ultrasensitive optical thermometer covering a wide temperature range is developed by utilizing the different temperature responses of Er3+ emission in the visible light region and Nd3+ emission in the near-infrared region based on the luminescence intensity ratio (LIR). All the results demonstrate that the rare earth (Yb-Er, Yb-Nd, and Yb-Nd-Er)-doped La2ZnTiO6 phosphors can be effectively utilized for ultrabright LED illumination and ultrahigh sensitivity self-calibrated temperature sensing. This research underscores the significance of phonon-assisted energy transfer in improving material properties and provides valuable insights for the advancement of multifunctional materials.

High-efficiency upconversion process in cobalt and neodymium doped graphene QDs for biomedical applications

Multiphoton absorbing upconversion nanoparticles are emerging as bioimaging materials but are limited by the low quantum yield of their visible fluorescence. This article contains colloids of graphene quantum dots (GQDs), Neodymium, and Cobalt doped Graphene Quantum dots (Co-GQDs and Nd-GQDs) surrounded by carboxylic acids are synthesized which especially are suitable for bio applications; in this way, carboxylic acid groups exchanged by Amoxicillin as an antibiotic with bactericidal activity. The XRD diffraction method, TEM microscope, UV-Vis, and photoluminescence spectroscopies characterize the synthesized materials. The synthesized Quantum dots (QDs) exhibit upconversion properties and their emission is centered at 480 nm, but a red shift was observed with the increase of the excitation wavelength. In the emission spectra of synthesized QDs that can be related to the defect levels introduced by passivation of the QDs in the structure, the results show that with the interaction of the surface QDs with more carboxylic groups, the redshift is not observed. As the results indicate an increase in the intensity of upconversion emission is recorded for Co-GQDs and Nd-GQDs. The absolute quantum efficiency (QY) for Co-GQDs and Nd-GQDs were determined to be 41% and 100% more than GQDs respectively. DFT calculations indicate a strong bond between graphene and cobalt and Neodymium atoms. In doped materials, there are trap levels between the band gap of the GQDs which are responsible for increasing the intensity of the upconversion phenomenon.

Eu3+ Single-Doped Phosphor with Antithermal Quenching Behavior and Multicolor-Tunable Properties for Luminescence Thermometry

To date, non-contact luminescence thermometry methods based on fluorescence intensity ratio (FIR) technology have been studied extensively. However, designing phosphors with high relative sensitivity (S_r) has become a research hotspot. In this work, Eu³⁺ single-doped Ca₂Sb₂O₇:Eu³⁺ phosphors with a high S_r value for dual-emitting-center luminescence thermometry are developed and proposed. The anti-thermal quenching behavior of Eu³⁺ originating from the energy transfer (ET) of host → Eu³⁺ is found and proved in the designed phosphors. Interestingly, adjustable color emission from blue to orange can be achieved. Surprisingly, the degree of the anti-thermal quenching behavior of Eu³⁺ gradually reduces from 240 to 127% as the Eu³⁺ doping content increases from 0.005 to 0.05 mol, attributed to most Eu³⁺ being located in the low symmetrical [Ca1O₈] dodecahedral site. According to the differentiable responses of the host and Eu³⁺ to temperature, the maximal S_r value reaches 3.369% K^-1 (383 K). Moreover, the ambient temperature can be intuitively predicted by observing the emitting color. Owing to the excellent performance in optical thermometry, color-tunable properties, and outstanding acid and alkali resistance for polydimethylsiloxane (PDMS) films, the developed Eu³⁺ single-doped Ca₂Sb₂O₇:Eu³⁺ phosphors are expected to be prospective candidates in luminescence thermometers and LED devices in various conditions.

Highly precise FIR thermometer based on the thermally enhanced upconversion luminescence for temperature feedback photothermal therapy

A highly precise temperature-feedback photothermal therapy platform in deep tissue is proposed based on all-fiber fluorescence intensity ratio (FIR) thermometry, which provides a promising route to realize real-time temperature monitoring in the minimally invasive treatment of tumors. Highly disordered double perovskite Li₂Zn₂Mo₃O₁₂ (LZMO) phosphors doped with rare earth ions were prepared and intense green upconversion emissions were observed with an ultra-low excitation power. The thermal enhancement of the upconversion luminescence was achieved up to 423 K, which is very beneficial to achieve a good signal-to-noise performance during the temperature-rise period. Superior temperature sensing performance was demonstrated with the maximum absolute sensitivity of 89.9 × 10⁻⁴ at 423 K. The strong upconversion emissions and high temperature sensitivity result in a small temperature error (±0.4 K). The integrated bifunctional needle could simultaneously realize temperature measurement and laser heating, which was exhibited in the denaturation of egg white and laser ablation of the porcine liver in vitro.

A highly precise temperature-feedback photothermal therapy platform is proposed based on all-fiber fluorescence intensity ratio (FIR) thermometry.

BaAl2O4:Eu2+-Al2O3 ceramics for wide range optical temperature sensing

In this paper, BaAl₂O₄:Eu²⁺-Al₂O₃ ceramics were successfully prepared by spark plasma sintering (SPS). The optical properties of the multiphase ceramics doped with different concentrations of alumina were studied. Under excitation with 365 nm ultraviolet light, the luminescent color of the samples can be adjusted by changing the sintering temperature and the contents of alumina addition. The temperature dependent fluorescence spectra in the temperature range of 4 K-434 K were measured, and the temperature dependent fluorescence intensity ratio (FIR) was calculated. The FIR monotonically increased with the increase of temperature, indicating that the material could be used for temperature sensing. The absolute sensitivity S_a of the temperature sensing fluorescent material is larger than 0.005 K^-1 at 334 K-434 K, and the relative sensitivity S_r is larger than 0.75% K^-1 at 304 K-434 K. The results show that the BaAl₂O₄:Eu²⁺-Al₂O₃ ceramic is a promising non-contact temperature sensing material.

Highly sensitive optical temperature sensing based on pump-power-dependent upconversion luminescence in LiZnPO4:Yb3+-Er3+/Ho3+ phosphors

In this work, various LiZnPO₄:0.5 mol% Ln³⁺ (Ln = Ho, Er) phosphors with different Yb³⁺ ion doping concentrations were synthesized by a sol–gel/Pechini method. X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques were used to evaluate the phase and morphology of the samples. The UC process was mentioned as the typical emission peaks of Er³⁺ and Ho³⁺. For Er³⁺ and Ho³⁺, different optical temperature sensing methods are included. The Boltzmann distribution was accompanied by the fluorescence intensity ratio (FIR) for the two green Er³⁺ emissions originating from thermally-coupled levels. The effect of pump power on sensor sensitivities was extensively studied. The temperature uncertainty is also evaluated. The red and green emissions generated from non-thermally-coupled levels were used for temperature sensing in the Ho³⁺-activated LiZnPO₄. High sensitivities were obtained in the phosphors, and the LiZnPO₄:Yb³⁺/Ho³⁺ showed the largest absolute sensitivities. LiZnPO₄:Yb³⁺–Er³⁺/Ho³⁺ phosphors may be useful in the development of new luminescent materials for optical temperature sensing.

Novel orthophosphate LiZnPO4:Yb³⁺–Er³⁺/Ho³⁺ with tunable luminescence have been synthesized via sol–gel/Pechini method for optical thermometry.

Controllable crystal form transformation and luminescence properties of up-conversion luminescent material K3Sc0.5Lu0.5F6: Er3+, Yb3+ with cryolite structure

In this paper, a novel cryolite-type up-conversion luminescent material K3Sc0.5Lu0.5F6: Er3+, Yb3+ with controllable crystal form was synthesized by a high temperature solid state method. K3Sc0.5Lu0.5F6: Er3+, Yb3+ can crystallize in monoclinic or cubic form at different temperatures. The composition, structure and up-conversion luminescence (UCL) properties of K3Sc0.5Lu0.5F6: Er3+, Yb3+ samples with different crystal form were investigated in detail. It is impressive that both monoclinic and cubic forms of K3Sc0.5Lu0.5F6: Er3+, Yb3+ show green emission (2H11/2/4S3/2→4I15/2). The luminescence intensity of cubic K3Sc0.5Lu0.5F6 is much higher than that of the monoclinic form, and the reasons are also discussed in detail. The results show that the luminescence intensity of up-conversion materials can be effectively tuned by controlling the crystal form. According to the power dependent UCL intensity, the UCL mechanism and electronic transition process were discussed. In addition, the fluorescence decay curves were characterized and the thermal coupling levels (TCLs) of Er3+ (2H11/2/4S3/2 → 4I15/2) in the range of 304-574 k were used to study the optical temperature sensing characteristics. All the results show that K3Sc0.5Lu0.5F6: Er3+, Yb3+ can be used in electronic components and have potential application value in temperature sensing fields.

Yb3+, Er3+ Codoped Cerium Oxide Upconversion Nanoparticles Enhanced the Enzymelike Catalytic Activity and Antioxidative Activity for Parkinson's Disease Treatment

Oxidative stress plays an important role in Parkinson's disease (PD) and is considered a therapeutic target for PD. However, most therapeutic antioxidants show limitations due to their low reactive oxygen species (ROS) catalytic properties and low crossing of blood-brain barrier. Herein, the antioxidative activity of Yb3+ and Er3+ double-doped CeO2-x (Yb/Er/CeO2-x) upconversion nanoparticles (UCNPs) is obtained for PD treatment. Doping of Yb3+ and Er3+ ions increases oxygen vacancies, which leads to higher enzymelike catalytic activities compared to CeO2-x nanoparticles alone. Tyrosine hydroxylase protein and glial fibrillary acidic protein expression in substantia nigra and striatum as well as the open-field activity test indicates that Yb/Er/CeO2-x is effective for treatment of PD. The activities of glutathione peroxidase and total antioxidant capacity increase and the production of ROS decreases with Yb/Er/CeO2-x UCNP treatment compared with MPTP-induced injury. This indicates that the mechanism of PD treatment is to catalyze ROS products. There have been no reports to date on the usage of Yb/Er/CeO2-x as an antioxidant for PD treatment. Yb/Er/CeO2-x UCNPs cross the blood-brain barrier and exhibit biocompatibility and antioxidant catalytic properties, which decrease the ROS and effectively help in treating PD.

Optical Temperature Sensing of YbNbO4:Er3+ Phosphors Synthesized by Hydrothermal Method

The novel YbNbO4:Er3+ phosphors were firstly synthesized through the hydrothermal method by adding LiOH·H2O as flux in the H2O/EG system. YbNbO4:Er3+ phosphors showed the agglomerated irregular polygons coexisting with some tiny grains. XRD and Raman spectra were measured to understand the phase structure and the crystal growth mechanism of YbNbO4:Er3+ phosphors. The upconversion (UC) emission spectra, the pump power dependency and UC mechanism were studied under 980 nm excitation. Based on the fluorescence intensity ratio technique, YbNbO4:Er3+ exhibited the maximum sensor sensitivity of 0.00712 K−1 at 220 K, providing a promising application in optical low-temperature sensors.

Rapid aqueous-phase synthesis of highly stable K0.3Bi0.7F2.4 upconversion nanocrystalline particles at low temperature

Lanthanide-doped K_0.3Bi_0.7F_2.4 nanocrystalline particles are synthesized through an ultrafast (only 1 min) and aqueous-phase chemical method at low temperature (room temperature ∼ 90 °C), which can be used as pigments for anti-counterfeiting.

A lanthanide ion-doped Ba3Sc2F12 phosphor: hydrothermal synthesis, morphological control, energy transfer, and temperature-sensing performance

Ba₃Sc₂F₁₂ crystals were synthesized by a facile one-step hydrothermal method with Ba/Sc raw material in a ratio of 3 : 2. With the F/Sc ratio increasing from 4 to 8, the obtained crystal's morphology evolved gradually from a strip to a chocolate shape; further, the use of the additives, such as CTAB and EDTA, the obtained crystal's morphology changed from strip to cubic. The energy transfer of Ce³⁺→ Tb³⁺ in the Ba₃Sc₂F₁₂ host was also explored, and it was found to belong to a dipole-dipole interaction mechanism; the color of the light could be adjusted from blue-violet to green due to the different energy transfer efficiencies at different Ce³⁺ and Tb³⁺ ion-doping concentrations. Because of the thermal coupling level of Er³⁺ (²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2), Ba₃Sc₂F₁₂:14%Yb³⁺,2%Er³⁺ phosphors showed an excellent temperature-sensing ability with S_A(max) = 0.0043 K^-1 and T_max = 523 K, which are much better than the previously reported values for Yb³⁺/Er³⁺ co-doped systems. The as-prepared lanthanide ion-doped phosphors might have potential to serve as color light/displays and temperature control/sensors.

Yolk–shell structured Bi2SiO5:Yb3+,Ln3+ (Ln = Er, Ho, Tm) upconversion nanophosphors for optical thermometry and solid-state lighting

Bi₂SiO₅:Yb³⁺,Er³⁺ yolk–shell nanophosphors have been successfully synthesized, which are expected to find important applications in optical thermometry and solid-state lighting.

Defect-induced abnormal enhanced upconversion luminescence in BiOBr:Yb3+/Er3+ ultrathin nanosheets and its influence on visible-NIR light photocatalysis

In oxygen vacancy-rich BiOBr:Yb³⁺/Er³⁺ ultrathin nanosheets, the oxygen vacancy induced intermediate band effectively enhances UC luminescence.

Anti-Stokes Ultraviolet Luminescence and Exciton Detrapping in the Two-Dimensional Perovskite (C6H5C2H4NH3)2PbCl4

Recently, it has been found that low-dimensional organometallic halide perovskites can be adopted as nonlinear monolayer emitters because of their efficient spontaneous anti-Stokes visual luminescence under visual or near-infrared laser excitation. Herein, we demonstrate a luminescence up-conversion process from the visible self-trapped exciton (STE) to an ultraviolet (UV) free exciton (FE) in the two-dimensional perovskite (C₆H₅C₂H₄NH₃)₂PbCl₄ quantum wells excited by nanosecond pulse laser excitation. An ultraviolet 347 nm near-band-edge FE emission is obtained under the excitation of 579 nm dye laser at 10 K by a two-step, two-photon absorption process from the real intermediate exciton state. In addition, the decay rise time of higher-laying states of STE indicates the excitonic detrapping procedure could occur by the annihilation of phonons. Our results suggest that the low-dimensional halide perovskites with deformable structure are able to be applied in visible light-pumped UV-emitting devices.

One-pot synthesis of SiO2-coated Gd2(WO4)3:Yb3+/Ho3+ nanoparticles for simultaneous multi-imaging, temperature sensing and tumor inhibition

Rare earth ion-doped fluoride upconversion nanoparticles (UCNPs), emerging as a novel class of probes and drug carriers, exhibit superior promise for bio-applications in diagnostics and treatment on account of their strong luminescence, fine biocompatibility, and high drug loading. However, the fine control and manipulation of particle size and the distribution of rare earth ion-doped oxides has remained an insurmountable challenge to date. In this work, we construct and synthesize silica-coated Gd2(WO4)3:Yb3+/Ho3+ nanoparticles by one-pot co-precipitation, with uniform distribution (∼130 nm) and enhanced yellow fluorescence. Particularly, the nanoparticles not only possess outstanding temperature sensing performance at biological temperatures in water by utilizing the fluorescence intensity ratio (FIR) method, but also allow a further serviceable contrast effect in vitro and in vivo based on the prominent T1-weighted magnetic resonance (MR) signal of Gd3+. Compared with cisplatin and platinum(iv) (DSP), the Gd2(WO4)3@SiO2 nanoparticles functionalized with DSP (Gd2(WO4)3@SiO2-Pt-PEG) exert higher lethality against CT26 cells and significantly inhibit the growth of tumors at the same concentration of Pt. This effect occurs through the greater level of cell endocytosis. The lethality value of the latter is 10 times higher than the former after the same length of time according to inductively coupled plasma-mass spectrometry (ICP-MS) results. In short, the monodisperse and strongly fluorescent Gd2(WO4)3@SiO2-Pt-PEG nanoparticles are endowed with dual-mode imaging, temperature sensing and anticancer functions, which provide a significant guide for synthesis and bio-application of lanthanide ion-doped oxides.

Upconversion luminescence enhancement and lifetime based thermometry of Na(Gd/Lu)F4 solid solutions

Upconversion luminescence and lifetime based thermal sensing performance enhancements of NaGdF₄ are achieved by a simple solid solution strategy.

Enhanced upconversion luminescence of GdVO4:Er3+/Yb3+ prepared by spray pyrolysis using organic additives

Spray pyrolysis was applied to prepare Er³⁺/Yb³⁺-doped GdVO₄ particles, and their emission properties were investigated by varying the Er³⁺/Yb³⁺ content and the calcination temperature from 900 to 1400 °C. Ethylene glycol (EG), citric acid (CA) and N,N-dimethylformamide (DMF) were used as organic additives in order to improve the upconversion of GdVO₄:Er³⁺/Yb³⁺. The resulting GdVO₄:Er³⁺/Yb³⁺ particles show strong green emission due to ²H_11/2/⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ and weak red peak due to the ⁴F_9/2 → ⁴I_15/2 transition of Er³⁺. From the result observed by changing the pumping power of the near-infrared (NIR, 980 nm) laser, the observed green emission is caused by a typical two-photon process. In terms of achieving the highest upconversion luminescence, the optimal Er³⁺ and Yb³⁺ contents are 1.5% and 20% with respect to Gd, respectively. The luminescence intensity steadily increased as the calcination temperature was elevated up to 1200 °C due to the increment of crystallinity. The upconversion intensity showed a linear relationship with the crystallite size in all the calcination temperature range. Using the EG/CA/DMF mixture as organic additives improves the upconversion emission about 4.3 times higher than when no organic additives are used, due to the enhancement of crystallinity as well as the enlargement of primary particle size.

GdVO₄:Er/Yb fine particles with good upconversion luminescence was prepared by spray pyrolysis using organic additives.

Synthesis, structure, and luminescence characteristics of far-red emitting Mn4+-activated LaScO3 perovskite phosphors for plant growth

Far-red emitting phosphors LaScO₃:Mn⁴⁺ were successfully synthesized via a high-temperature solid-state reaction method. The X-ray powder diffraction confirmed that the pure-phase LaScO₃:Mn⁴⁺ phosphors had formed. Under 398 nm excitation, the LaScO₃:Mn⁴⁺ phosphors emitted far red light within the range of 650–800 nm peaking at 703 nm (14 225 cm⁻¹) due to the ²E_g → ⁴A_2g transition, which was close to the spectral absorption center of phytochrome P_FR located at around 730 nm. The optimal doping concentration and luminescence concentration quenching mechanism of LaScO₃:Mn⁴⁺ phosphors was found to be 0.001 and electric dipole–dipole interaction, respectively. And the CIE chromaticity coordinates of the LaScO₃:0.001Mn⁴⁺ phosphor were (0.7324, 0.2676). The decay lifetimes of the LaScO₃:Mn⁴⁺ phosphors gradually decreased from 0.149 to 0.126 ms when the Mn⁴⁺ doping concentration increased from 0.05 to 0.9 mol%. Crystal field analysis showed that the Mn⁴⁺ ions experienced a strong crystal field in the LaScO₃ host. The research conducted on the LaScO₃:Mn⁴⁺ phosphors illustrated their potential application in plant lighting to control or regulate plant growth.

Far-red emitting Mn⁴⁺-activated LaScO₃ perovskite phosphors were investigated for indoor plant growth lighting.

Novel SrMg2La2W2O12:Mn4+ far-red phosphors with high quantum efficiency and thermal stability towards applications in indoor plant cultivation LEDs

Novel Mn4+-activated far-red emitting SrMg2La2W2O12 (SMLW) phosphors were prepared by a conventional high-temperature solid-state reaction method. The SMLW:Mn4+ phosphors showed a broad excitation band peaking at around 344 nm and 469 nm in the range of 300-550 nm. Under 344 nm near-ultraviolet light or 469 nm blue light, the phosphors exhibited a far-red emission band in the 650-780 nm range centered at about 708 nm. The optimal Mn4+ doping concentration in the SMLW host was 0.2 mol% and the CIE chromaticity coordinates of SMLW:0.2% Mn4+ phosphors were calculated to be (0.7322, 0.2678). In addition, the influences of crystal field strength and nephelauxetic effect on the emission energy of Mn4+ ions were also investigated. Moreover, the internal quantum efficiency of SMLW:0.2% Mn4+ phosphors reached as high as 88% and they also possessed good thermal stability. Specifically, the emission intensity at 423 K still maintained about 57.5% of the initial value at 303 K. Finally, a far-red light-emitting diode (LED) lamp was fabricated by using a 365 nm near-ultraviolet emitting LED chip combined with the as-obtained SMLW:0.2% Mn4+ far-red phosphors.

Near-Infrared Ratiometric Luminescent Thermometer Based on a New Lanthanide Silicate

A new lanthanide silicate system, Na₂ K[Ln₃ Si₆ O₁₈ ] (Ln=Lu, Yb/ Er, Lu/Eu, or Lu/Yb/Er), comprising microcrystals embedded in an amorphous siliceous matrix, obtained by sintering at 1373 K a Na₃ K[Ln₂ Si₆ O₁₇ ]⋅3 H₂ O nano-crystalline precursor, is reported. The crystal structure of these lanthanide silicates was solved from high-resolution synchrotron power X-ray diffraction data collected at 110 K, and further supported by ²⁹ Si MAS NMR and Eu³⁺ luminescence. The materials crystallize in the Pī triclinic centrosymmetric space group, exhibiting a dense framework consisting of hexameric [Si₆ O₁₈ ]^12- cyclosilicate units, and chains of two distinct {LnO₆ } octahedra. Na₂ K[(Lu_0.75 Yb_0.20 Er_0.05 )₃ Si₆ O₁₈ ] is the first example of a lanthanide silicate operative as a near-infrared ratiometric luminescent thermometer, with good sensitivity at cryogenic temperatures (<100 K). Upon excitation at 903 nm, the ratio between the ² F_7/2 →² F_5/2 (Yb³⁺ ) and ⁴ I_13/2 →⁴ I_15/2 (Er³⁺ ) emissions was used for sensing temperature in the 12-450 K range, reaching a maximum thermal sensitivity of 2.6 % K^-1 at 26.8 K.

Thermally stable La2LiSbO6:Mn4+,Mg2+far-red emitting phosphors with over 90% internal quantum efficiency for plant growth LEDs

In this paper, we reported on the high-efficiency and thermally-stable La₂LiSbO₆:Mn⁴⁺,Mg²⁺ (LLS:Mn⁴⁺,Mg²⁺) far-red emitting phosphors. Under 338 nm excitation, the composition-optimized LLS:0.3%Mn⁴⁺,1.6%Mg²⁺ phosphors which were made up of [SbO₆], [LiO₆], and [LaO₈] polyhedrons, showed intense far-red emissions peaking at 712 nm (²E_g → ⁴A_2g transition) with internal quantum efficiency as high as 92%. The LLS:0.3%Mn⁴⁺,1.6%Mg²⁺ phosphors also exhibited high thermal stability, and the emission intensity at 423 K only reduced by 42% compared with its initial value at 303 K. The far-red light-emitting device has also been made by using the LLS:0.3%Mn⁴⁺,1.6%Mg²⁺ phosphors and a 365 nm emitting InGaN chip, which can emit far-red light that is visible to the naked eye. Importantly, the emission spectrum of the LLS:0.3%Mn⁴⁺,1.6%Mg²⁺ phosphors can match well with the absorption spectrum of phytochrome P_FR, indicating the potential of these phosphors to be used in plant growth light-emitting diodes.

Double perovskite La₂LiSbO₆:Mn⁴⁺,Mg²⁺ far-red emitting phosphors with internal quantum efficiency as high as 92% and good thermal stability were developed for plant growth LEDs.

Lu3+ doping induced photoluminescence enhancement in novel high-efficiency Ba3Eu(BO3)3 red phosphors for near-UV-excited warm-white LEDs

Novel high-efficiency Ba₃Eu(BO₃)₃:Lu³⁺ red phosphors with internal quantum efficiency as great as 87% were developed for near-UV-excited warm-white LEDs.

Novel SrLaAlO4:Mn4+deep-red emitting phosphors with excellent responsiveness to phytochrome PFRfor plant cultivation LEDs: synthesis, photoluminescence properties, and thermal stability

Herein, novel rare-earth-free Mn⁴⁺-doped SrLaAlO₄ deep-red emitting phosphors were successfully synthesized via a traditional solid-state reaction method. The crystal structure and phase purity of the as-prepared samples were confirmed by XRD Rietveld refinement. Photoluminescence properties of SrLaAlO₄:Mn⁴⁺ phosphors were examined in detail using photoluminescence spectra, decay lifetimes, temperature-dependent emission spectra and internal quantum efficiency measurements. The excitation spectrum obtained by monitoring at 730 nm contained two excitation bands centered at 364 and 520 nm within the range of 200–550 nm due to the Mn⁴⁺–O²⁻ charge-transfer band and the ⁴A_2g → ⁴T_1g, ⁴T_2g transitions of the Mn⁴⁺ ions. Under the 364 nm excitation, the SrLaAlO₄:Mn⁴⁺ phosphors exhibited an intense deep-red emission band in 610–790 nm wavelength range peaking at 730 nm, which was assigned to the ²E_g → ⁴A_2g transition of Mn⁴⁺ ions. The deep red emission showed excellent responsiveness to phytochrome P_FR, revealing that the SrLaAlO₄:0.4% Mn⁴⁺ phosphors possessed a possible application in deep-red light-emitting diodes (LEDs) for plant cultivation. The optimal doping concentration of Mn⁴⁺ ions was found to be 0.4 mol%. The critical distance R_c for energy transfer among Mn⁴⁺ ions was determined to be 5.86 Å and the concentration quenching mechanism was confirmed to be the electric dipole–dipole interaction. In addition, the Commission International de I'Eclairage (CIE) colour coordinates of the SrLaAlO₄:0.4% Mn⁴⁺ phosphors (0.734, 0.266) were located in the deep red region and the corresponding internal quantum efficiency was measured to be about 29%. The above results confirmed that the as-prepared SrLaAlO₄:0.4% Mn⁴⁺ deep red emitting phosphors might be a potential candidate for plant cultivation LEDs.

Novel Mn⁴⁺ activated SrLaAlO₄ deep-red emitting phosphors with excellent responsiveness to phytochrome P_FR were developed for plant cultivation LEDs.

Synthesis and photoluminescence properties of novel far-red-emitting BaLaMgNbO6:Mn4+ phosphors for plant growth LEDs

A series of far-red-emitting BaLaMgNbO₆:Mn⁴⁺ (BLMN:Mn⁴⁺) phosphors were successfully synthesized by a high-temperature solid-state reaction method. Crystal structure and luminescence properties of the obtained samples were systematically investigated. The emission spectra exhibited a strong narrow far-red emission band peaking at 700 nm with a full width at half-maximum (FWHM) of ∼36 nm under 360 nm excitation. The optimal Mn⁴⁺ concentration was about 0.4 mol%. The internal quantum efficiency and CIE chromaticity coordinates of the BLMN:0.4% Mn⁴⁺ phosphor were 52% and (0.7222, 0.2777), respectively. In addition, the luminescence mechanism has been analyzed using a Tanabe–Sugano energy level diagram. Finally, by using a 365 nm near-ultraviolet InGaN chip combined with BLMN:0.4% Mn⁴⁺ phosphors, a far-red LED device was fabricated.

Mn⁴⁺-activated BaLaMgNbO₆ far-red emitting double-perovskite phosphors with internal quantum efficiency up to 52% were developed for potential application in plant growth LEDs.

Excitation power dependent optical temperature behaviors in Mn4+doped oxyfluoride Na2WO2F4

Optical temperature sensing behaviors of Na₂WO₂F₄:Mn⁴⁺under different excitation powers.

Structure, luminescence and temperature sensing in rare earth doped glass ceramics containing NaY(WO4)2 nanocrystals

A novel rare earth doped glass ceramic containing NaY(WO₄)₂ nanocrystals was fabricated and its temperature sensing properties were investigated.

Photoluminescence properties of novel Ba2Lu5B5O17:Eu3+ red emitting phosphors with high color purity for near-UV excited white light emitting diodes

A series of new red-emitting Ba₂Lu_4.98−xEu_xLa_0.02B₅O₁₇ (0.1 ≤ x ≤ 1.0) phosphors were synthesized via the high-temperature solid-state reaction method. The phase formation of the as-synthesized Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ phosphor was confirmed by powder X-ray diffraction analysis. It was found that La³⁺ doping resulted in the reduction of LuBO₃ impurities and thus pure phase Ba₂Lu₅B₅O₁₇ was realised. The morphology of Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ phosphors was studied by field emission scanning electron microscopy (FE-SEM). As a function of Eu³⁺ concentration the photoluminescence spectra and decay lifetimes were investigated in detail. Under excitation at 396 nm, a dominant red emission peak located at 616 nm (⁵D₀ → ⁷F₂) indicated that Eu³⁺ ions mainly occupied low symmetry sites with a non-inversion center in Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇. The optimal Eu³⁺ ion concentration was found to be x = 0.5 and the critical distance of Eu³⁺ was determined to be 6.55 Å. In addition, the concentration quenching takes place via dipole–dipole interactions. The phosphors exhibited good CIE (Commission International de I'Eclairage) color coordinates (x = 0.643, y = 0.356) situated in the red region and a high color purity of 97.8%. Furthermore, the internal quantum efficiency and the thermal stability of Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ phosphors were also investigated systematically. The results suggest that Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ may be a potential red phosphor for white light-emitting diodes.

Novel Ba₂Lu₅B₅O₁₇:Eu³⁺ red emitting phosphors with high color purity were prepared for near-UV excited white light emitting diodes.

Novel high-efficiency Eu3+-activated Na2Gd2B2O7 red-emitting phosphors with high color purity

Novel high-efficiency Eu³⁺-activated Na₂Gd₂B₂O₇ red-emitting phosphors with color purity as high as 99% were developed for warm white LEDs.

Morphology/dimensionality induced tunable upconversion luminescence of BiOCl:Yb3+/Er3+ nano/microcrystals: intense single-band red emission and underlying mechanisms

Different morphologies of BiOCl:Yb³⁺/Er³⁺ nano/microcrystals have been synthesized via solvothermal method, and the dependence of UC luminescence performance on morphology/dimension have been explored.

Preparation, characterization, and luminescence properties of double perovskite SrLaMgSbO6:Mn4+ far-red emitting phosphors for indoor plant growth lighting

Mn⁴⁺-activated SrLaMgSbO₆ far-red emitting phosphors with double perovskite structure were prepared by traditional solid-state reaction. The research on the crystal structure of the SrLaMgSbO₆:0.8%Mn⁴⁺ (SLMS:0.8%Mn⁴⁺) phosphors showed that the as-prepared sample was made up of two polyhedrons, [SbO₆] and [MgO₆]. Under the excitation of 333 nm, the SLMS:0.8%Mn⁴⁺ phosphors exhibited an intense far-red emission in the 625–800 nm wavelength range with CIE chromaticity coordinates of (0.733, 0.268), which could match well with the absorption spectrum of phytochrome P_FR. The optimal concentration of Mn⁴⁺ ions in the SLMS:Mn⁴⁺ phosphors was 0.8 mol%. Importantly, the as-prepared SLMS:0.8%Mn⁴⁺ phosphors had an internal quantum efficiency of 35%. The thermal stability of SLMS:0.8%Mn⁴⁺ phosphors was also investigated, and the activation energy was found to be 0.3 eV. Thus, the Mn⁴⁺-activated SLMS phosphors have great potential to serve as far-red emitting phosphors in indoor plant growth lighting.

Novel far-red emitting double perovskite SrLaMgSbO₆:Mn⁴⁺ phosphors were prepared and their photoluminescence properties were studied for applications in indoor plant growth lighting.

Ce3+ and Tb3+ doped Ca3Gd(AlO)3(BO3)4 phosphors: synthesis, tunable photoluminescence, thermal stability, and potential application in white LEDs

Novel blue-green-emitting Ca₃Gd(AlO)₃(BO₃)₄:Ce³⁺,Tb³⁺ phosphors were successfully synthesized via traditional high temperature solid reaction method. X-ray diffraction, luminescence spectroscopy, fluorescence decay time and fluorescent thermal stability tests have been used to characterize the as-prepared samples. The energy transfer from Ce³⁺ to Tb³⁺ ions in the Ca₃Gd(AlO)₃(BO₃)₄ host has been demonstrated to be by dipole–dipole interaction, and the energy transfer efficiency reached as high as 83.6% for Ca₃Gd_0.39(AlO)₃(BO₃)₄:0.01Ce³⁺,0.6Tb³⁺. The critical distance was calculated to be 9.44 Å according to the concentration quenching method. The emission colour of the obtained phosphors can be tuned appropriately from deep blue (0.169, 0.067) to green (0.347, 0.494) through increasing the doping concentrations of Tb³⁺. Moreover, the Ca₃Gd_0.39(AlO)₃(BO₃)₄:0.01Ce³⁺,0.6Tb³⁺ phosphor possessed excellent thermal stability at high temperature, and the emission intensity at 423 K was about 87% of that at 303 K. Finally, the fabricated prototype LED device with a BaMgAl₁₀O₇:Eu²⁺ blue phosphor, CaAlSiN₃:Eu²⁺ red phosphor, Ca₃Gd_0.39(AlO)₃(BO₃)₄:0.01Ce³⁺,0.6Tb³⁺ green phosphor and 365 nm-emitting InGaN chip exhibited bright warm white light. The current study shows that Ca₃Gd_0.39(AlO)₃(BO₃)₄:0.01Ce³⁺,0.6Tb³⁺ can be used as a potential green phosphor for white LEDs.

Novel thermal-stable blue-green-emitting Ca₃Gd(AlO)₃(BO₃)₄:Ce³⁺,Tb³⁺ phosphors were developed for near-ultraviolet-excited white LEDs.

Far-red-emitting double-perovskite CaLaMgSbO6:Mn4+ phosphors with high photoluminescence efficiency and thermal stability for indoor plant cultivation LEDs

A series of Mn⁴⁺-activated CaLaMgSbO₆ far-red-emitting phosphors were synthesized by a solid-state reaction route and the microstructure and optical characterizations were investigated in detail. Upon excitation at 370 and 469 nm, the samples showed intense far-red emission at about 708 nm originating from the ²E_g → ⁴A_2g transition and the optimal Mn⁴⁺ concentration was 0.7 mol%. The as-prepared phosphors also exhibited excellent internal quantum efficiency (88%) and high thermal stability. The emission intensity at room temperature dropped to 54% when the temperature rose to 423 K and the activation energy was 0.34 eV. The outstanding optical properties and the fact that the emission band of the obtained phosphors had a broad overlap with the absorption band of phytochrome P_FR demonstrated that the CaLaMgSbO₆:Mn⁴⁺ phosphors may be promising potential spectral converters for applying to indoor plant cultivation light-emitting diodes.

Far-red-emitting double-perovskite CaLaMgSbO₆:Mn⁴⁺ phosphors with high quantum efficiency and thermal stability were developed for potential applications in indoor plant cultivation LEDs.