Preparation,luminescence properties,and application of temperature sensing and anti-counterfeiting of La2MgTiO6:Yb3+/Ln3+/Mn4+

The doping of transition metal ions in the up-conversion (UC) luminescent material doped with Yb³⁺/Ln³⁺ is a facile way to increase their UC luminescence intensities and alter their colors. In this study, La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ (Ln³⁺ = Er³⁺, Ho³⁺, and Tm³⁺) phosphors showing excellent luminescence properties were prepared by a solid-state method. The sensitivity of the La₂MgTiO₆:Yb³⁺/Ln³⁺/Mn⁴⁺ phosphor was double that without Mn⁴⁺, because Mn⁴⁺ affects the UC emissions of Ln³⁺ via energy transfer between these ions. Moreover, Mn⁴⁺ also acts as a down-conversion activator, which can combine with UC ions to achieve multi-mode luminescence at different wavelengths. Under 980 nm excitation, these samples emit green light (from Er³⁺ and Ho³⁺) and blue light (from Tm³⁺). In contrast, under 365 nm excitation, they emit red light (from Mn⁴⁺). Further testing revealed that the La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ phosphors have potential applications in temperature sensing and anti-counterfeiting.     

Enhanced luminescence properties of Li2MgTiO4: Mn4+, Ge4+ phosphor via single cation substitution for indoor plant cultivation

Red and far-red emitting phosphors have been widely used in phosphor-converted light emitting diode (pc-LED) devices to provide lighting for indoor plant growth, thus achieving desired product qualities. Among the many ways to optimize phosphors’ optical performance, cationic substitution is one of the most effective methods. In this study, red phosphors (Li₂MgTi_1-x-yO₄: xMn⁴⁺, yGe⁴⁺) were synthesized by high temperature solid state method and the optical performance of phosphors were improved with increasing Ge⁴⁺ constituents. In particular, luminescence intensity of Li₂MgTiO₄: 0.002Mn⁴⁺, 0.1Ge⁴⁺ increased by 152% under 468 nm excitation, and the thermostability of emission intensity increases from 22% (y = 0) to 43% (y = 0.1), which is about twice as much. Finally, pc-LED device was fabricated via the red phosphor Li₂MgTiO₄: 0.002Mn⁴⁺,0.1Ge⁴⁺ coated on a 470 nm ultraviolet chip. By changing the proportion of the phosphor, the electroluminescence spectra of pc-LED device could match well with the absorption regions of plant pigments. Therefore, Li₂MgTiO₄: 0.002Mn⁴⁺, 0.1Ge⁴⁺ phosphor has potential application in plant lighting. Furthermore, this work can offer some helpful references for improving luminescent efficiency by simply modulating the chemical composition.     

Bi3+/Mn4+ co-doped dual-emission phosphors for potential plant lighting

Developing environment-friendly dual-emission phosphors of both blue–cyan and deep-red lights is desirable for the utilized indoor plant lighting research. Notably, the naked 6s and 6p Bi³⁺ ions are sensitive to the lattice sites, which emit from Ultraviolet (UV) to red lights in various crystal compounds. Meanwhile, the ²E → ⁴A_2g transition of Mn⁴⁺ ions promises its deep-red light emissions, which satisfies the demand for specific wavelength lights for plants growth. Hence, a Bi³⁺/Mn⁴⁺ co-doped Sr₂LaGaO₅: Bi³⁺, Mn⁴⁺ (SLGO:Bi³⁺:Mn⁴⁺) phosphor was finally synthesized. The phase, micromorphology and luminescent properties were systematically evaluated. Upon excitation at 350 nm light, dual emissions of both blue–cyan (470 nm) and deep-red (718 nm) lights were observed. Besides, due to the pronounced photoluminescence (PL) spectral overlap between Bi³⁺ and Mn⁴⁺ ions, a potential energy transfer process from Bi³⁺ to Mn⁴⁺ ions was confirmed. The relative PL intensities between Bi³⁺ and Mn⁴⁺ ions can be tuned just by adjusting the Mn⁴⁺ ion concentration. Besides, Li⁺ co-doping has been evidenced to improve the deep-red emissions (718 nm) of SLGO:0.005Mn⁴⁺ due to charge compensation and rationally designed lattice distortion, together with the improved thermal stability. Finally, the emissions of SLGO:Bi³⁺, Mn⁴⁺, Li⁺ phosphor suit properly with the absorption of the four fundamental pigments for plant growth, indicating that the prepared phosphorescent materials may have a prospect in plant light-emitting diodes lighting.     

pH dependent hydrothermal synthesis of Ca14Al10Zn6O35:0.15Mn4+ phosphor with enhanced photoluminescence performance and high thermal resistance for indoor plant growth lighting

Artificial light source for indoor cultivation has been vastly impeded by the lack of high far red emitting phosphors. Recently, Mn⁴⁺ activated phosphors were reported to be promising luminescent materials to solve above matter. In this study, controllable design of Ca₁₄Al₁₀Zn₆O₃₅:0.15Mn⁴⁺ (CAZO:0.15Mn⁴⁺) far red emitting phosphors was realized via pH assisted hydrothermal approach. The pure CAZO:0.15Mn⁴⁺ phosphors were obtained merely when the reaction pH was 1 or 2. Meanwhile, by adjusting the pH value of the reaction solution, far red emission CAZO:0.15Mn⁴⁺ phosphors with grains, sphere-like as well as aggregated bulk particles can be achieved at pH =?4, pH =?6 and pH =?10, respectively. Furthermore, the structures and morphologies depended photoluminescence (PL) performances of CAZO:0.15Mn⁴⁺ were checked. The best PL performance was found for the phosphor produced at pH =?6, while over acidic or alkaline conditions would lower the emission intensity. In addition, this phosphor also exhibit good thermal resistance which can maintain 78% initial intensity at 150?°C. The practical indoor tobacco cultivation demonstrated that CAZO:0.15Mn⁴⁺ obtained through this pH adjusted hydrothermal route is a promising phosphor for indoor plant growth lighting.     

Tuning the luminescence properties of blue and far-red dual emitting Gd2MgTiO6: Bi3+, Cr3+ phosphor for LED plant lamp

Blue and far-red light play a key role in plant growth, so it is necessary to develop blue and far-red dual emitting phosphors. However, the match between phosphors and plant pigments is not satisfactory. In this work, we synthesized a series of blue and far-red dual emission Gd₂MgTiO₆: Bi³⁺, Cr³⁺ (GMTO: Bi³⁺, Cr³⁺) phosphors and discussed the luminescence performance. The blue emission at 430 nm is ascribed to ³P₁ → ¹S₀ transition of Bi³⁺ and the far-red emission is ascribed to ⁴T₂ → ⁴A₂ and ²E → ⁴A₂ transitions of Cr³⁺. Notably, because of the energy competition between Cr³⁺ ions and host materials, the luminescence tuning realized with the content of Cr³⁺ doping. In addition, an energy-transfer performance occurred from Bi³⁺ ions to Cr³⁺ ions and the photoluminescence intensity of Cr³⁺ can be enhanced by Bi³⁺. The pc-LEDs devices were synthesized by GMTO: Bi³⁺, Cr³⁺ phosphor, and ultraviolet (UV) chips. Finally, the emission of GMTO: Bi³⁺, Cr³⁺ phosphor matched well with the absorption spectra of plant pigments which indicated the potential applications in LED plant lamp.     

Structure analysis,tuning photoluminescence and enhancing thermal stability on Mn4+-doped La2-xYxMgTiO6 red phosphor for agricultural lighting

Currently, phosphor-converted LEDs (pc-LEDs) are revolutionizing the industry of plant growth lighting. To meet the requirements of this technology, phosphors with tunable photoluminescence, high thermal stability and luminous intensity are required. Herein, we found that the simple substitution of yttrium for lanthanum in La₂MgTiO₆:Mn⁴⁺ (LMT:Mn⁴⁺) system could satisfy above three criteria simultaneously. The photoluminescence properties can be regulated by continuously controlling the chemical composition of La_2-xY_xMgTiO₆:Mn⁴⁺ solid solution. The La sites are occupied by Y ions, causing a significant blue shift in the emission spectra which owing to the change of local crystal field strengthen. Meanwhile, the thermal stability and decay lifetimes are also varied due to the variation of local structure and band gap energy. The thermal stability of the material reaches 83.5% at 150 °C, which is better than the reported La₂MgTiO₆:Mn⁴⁺ and Y₂MgTiO₆:Mn⁴⁺ phosphors. The electronic luminescence (EL) of pc-LED devices using La_2-xY_xMgTiO₆:Mn⁴⁺ red phosphor is evaluated, which matching the absorption regions of plant pigments well, reflecting the superiority of the studied phosphors in plant growth lighting areas.     

LED-pumped intense red luminescence based on Ba2LaTaO6: Mn4+ double perovskite phosphor

Non-rare earth Mn⁴⁺ ion-doped red oxide phosphors have great potential for applications in warm white light-emitting diodes (wLEDs) due to their low cost and stable physicochemical properties. Herein, a series of Ba₂LaTaO₆ (BLTO): Mn⁴⁺ phosphors were successfully synthesized by the high-temperature solid-state method. The theoretical values of the band gap calculated by the density functional theory are close to the experimental values obtained by the absorption spectroscopy. In addition, the phosphors have a broad excitation band in the wavelength range of 280–550 nm and emit red light at the peak wavelength of 681 nm under excitation. The concentration quenching of the BLTO: Mn⁴⁺ phosphor was caused by dipole-dipole interactions. The activation energy and the average decay lifetimes of the samples were calculated. Meanwhile, the effects of synthesis temperature and Li⁺ ion doping on the luminescence performance of the samples were also investigated. Satisfactorily, the color purity and internal quantum efficiency of the phosphor reached 98.3% and 26.8%, respectively. Further, the samples were prepared as red-light components for warm wLEDs. The correlated color temperature, color rendering index, and luminous efficiency of the representative devices driven by 60 mA current were 5190 K, 83.3, and 81.59 lm/W, respectively. This work shows that the BLTO: Mn⁴⁺ red phosphor with excellent luminescence performance can be well applied to warm wLEDs.     

Achieving highly efficient far-red emission from luminescence-ignorable Ca2MgTeO6:Mn4+ to Ca2-zLnzMgTe1-yWyO6:Mn4+ (Ln = La,Y, Gd) phosphors via solid solution and impurity doping strategies

The Mn⁴⁺-doped Ca2MgTeO6 (CMTO) far-red emitting phosphors with double perovskite-type structure were successfully synthesized. Upon near-ultraviolet (n-UV, 300 nm) light excitation, the as-prepared phosphors showed far-red light at 700 nm attributed to the ²E_g→⁴A_2g transition of Mn⁴⁺ ion. The doping concentration of the CMTO:xMn⁴⁺ samples was optimized to be 0.8 mol%. The relevant mechanism of concentration quenching was demonstrated as the dipole-dipole interaction. Furthermore, solid solution and impurity doping strategies were adopted to improve the far-red emission of the luminescence-ignorable CMTO:Mn⁴⁺ phosphor. Series of Ca₂MgTe_(1−y)W_yO₆:0.8 mol%Mn⁴⁺ (y = 0–100 mol%) solid solution and Ca_2−zLn_zMgTe_0.6W_0.4O₆:Mn⁴⁺ (Ln = La, Y, and Gd, z = 10 mol%) phosphors were synthesized through the above two strategies. The luminescence intensity of the optimal Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphor was 13.7 times that of the CMTO:Mn⁴⁺ phosphor and 2.51 times that of red commercial phosphor K₂SiF₆:Mn⁴⁺. Notably, both CMTO:Mn⁴⁺ and Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphors exhibited remarkable thermal stability compared with most Mn⁴⁺-doped phosphors. Finally, the highly efficient Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphor was successfully applied in fabricating the warm white light diode (w-LED). This working along both lines strategy exhibited great potential for luminescence optimization of Mn⁴⁺-doped oxide phosphors.     

A Novel Gd<Superscript>3+</Superscript>–Pb<Superscript>2+</Superscript> Doped LiSrPO<Subscript>4</Subscript> Phosphor for Phototherapy Lamp Applications

The phosphors LiSrPO₄:Gd³⁺ and LiSrPO₄:Gd³⁺, Pb²⁺ with different concentration of Gd³⁺ and Pb²⁺ were synthesized by combination of re-crystallization and modified solid state diffusion method. The synthesized phosphors were characterized using XRD, SEM and PL spectroscopies. The PL excitation spectra of LiSrPO₄:Gd³⁺ phosphor exhibit peak at 275 nm due to the ⁸S_7/2 →⁴I_J transition of Gd³⁺ ions and gave narrow UVB emission at 312 nm. The effect of Pb²⁺ ions on the PL properties of LiSrPO₄:Gd³⁺have also been investigated. Upon the addition of Pb²⁺ ions, the excitation of phosphors shows broad peak with maximum at 247 nm, overlapping the Hg 253.7 nm line. This addition of Pb²⁺ ions improved the emission intensity of narrow band UVB i.e. 312 nm under the excitation of 247 nm. The phosphor could be good candidate as phototherapy lamp phosphor material.     

Insight into a novel rare-earth-free red-emitting phosphor Li3Mg2NbO6:Mn4+: Structure and luminescence properties

Red phosphor is indispensable to achieve warm white light in the white light diode (WLED) application. However, the current red phosphors suffer from high cost and harsh synthesis conditions. In this study, an oxide-based rare-earth-free red-emitting phosphor Li₃Mg₂NbO₆:Mn⁴⁺ (LMN:Mn⁴⁺) has been successfully synthesized by a simple solid-state reaction method. The relationship between crystal structure and luminescence was investigated in detail. The site occupancy of the doping Mn⁴⁺ ion in the LMN host has been discussed from the point of bond valence sum. How the coordination environment of doping Mn⁴⁺ affects the energy level of doping Mn⁴⁺ ion has been illustrated via the Tanabe-Sugano energy-level diagram. Moreover, warm white light has been obtained using LMN:Mn⁴⁺ as compensator to the YAG:Ce³⁺.     

Trap engineering in ZnGa2O4:Tb3+ through Bi3+ doping for multi-modal luminescence and advanced anti-counterfeiting strategy

Optical information encryption based on luminescence materials have received much attention recently. However, the single luminescence mode of the luminescence materials greatly limits its anti-counterfeiting application with high safety level. Here, a series of luminescence materials of Tb³⁺ and Bi³⁺ co-doped ZnGa₂O₄ phosphors with great correspondence in photoluminescence (PL), persistent luminescence (PersL), and thermoluminescence (TL) modes was synthesized by the conventional solid-phase method for the application in multi-modal anti-counterfeiting fields. Under the excitation of 254 nm, ZnGa_1.99O₄:0.01 Tb³⁺, yBi³⁺ (y = 0.001,0.002) sample exhibited a broad blue emission band (the transition from [GaO₆]) at 440 nm and the characteristic emission peaks of Tb³⁺ at 495 nm, 550 nm, 591 nm and 625 nm, corresponding to the transitions of ⁵D₄-⁷F_n (n = 6, 5, 4, 3), respectively. Interestingly, the co-doping of Bi³⁺ ions improve the crystallinity and particle size of the phosphor, subsequently enhanced the PL intensity of Tb³⁺ to 6 times that of Tb³⁺ singly doped ZnGa₂O₄ phosphor. Further, the flexible films with multi-modal luminescence properties have been fabricated through the unique TL and PersL characteristics of ZnGa₂O₄: Tb³⁺, Bi³⁺ phosphors, including “Optical information storage film”, “snowflake and characters” and “QR code”. Moreover, a set of optical information encryption is obtained by combining ZnGa₂O₄:Tb³⁺, Bi³⁺ phosphor and red emitting phosphor. The results indicate that ZnGa₂O₄:Tb³⁺, Bi³⁺ phosphor with multi-modal stimulus response can be expected to be potentially used in the applications of optical information storage and anti-counterfeiting fields.     

Visible Quantum Cutting and Energy Transfer in Tb3+‐Doped KSr(Gd,Y)(PO4)2 Under VUV–UV Excitation

KSr(Gd,Y)(PO₄)₂: Tb³⁺ phosphors were synthesized using the high‐temperature solid‐state reaction method. The VUV–UV spectroscopic properties of these phosphors were studied. The results show that efficient energy transfer (ET) from Gd³⁺ to Tb³⁺ occurs in this system, and the ET efficiency increases with increasing of Tb³⁺ doping concentrations, which is evidenced that both the emission intensity and decay time of Gd³⁺ decreases with increasing Tb³⁺ doping concentrations. Visible quantum cutting via cross relaxation between the neighboring Tb³⁺ ions was observed in the high Tb³⁺ concentration doped sample. In addition, the emission color of KSr(Gd,Y)(PO₄)₂: Tb³⁺ phosphors can be tuned from blue to yellowish‐green by varying the doping concentration of Tb³⁺. Under 147 nm excitation, the sample KSrGd_0.5(PO₄)₂: 0.5Tb³⁺ exhibits the strongest emission, which is about 70% of the commercial green‐emitting phosphor Zn₂SiO₄: Mn²⁺ indicating the potential application of this phosphor for plasma display panels, Hg‐free lamps, and three‐dimensional displays.     

Effects of HfO2 dopant on characteristics of Li2MgTiO4-based red phosphors: Thermal stability,photoluminescence intensity and quantum efficiency improvement

To produce natural and vivid color, the color rendering index of white light-emitting diodes (WLEDs) with single phosphors is usually lower than 70, which is problematic for LED applications. A commonly used method to resolve this issue is to enhance the red component of WLEDs. In the present study, Hf⁴⁺ and Mn⁴⁺ co-doped Li₂MgTiO₄ red phosphors are synthesized using a solid-state reaction method. When this red phosphor is excited at 397 and 468?nm, it exhibits weak reabsorption in the blue region and emits a broad and deep red emission band in the range of 640–750?nm, which is attributed to the ²E_g → ⁴A_2?g transition. With 5?mol% HfO₂ dopant, the photoluminescence intensity is enhanced by 1.45-fold and thermal stability is increased by 7.7%. Moreover, this red phosphor was applied to a red phosphor-in-glass (RPiG) optical device with a low-melting TeO₂-B₂O₃-ZnO-Na₂O-WO₃ glass system. In the RPiG melting process, Li₂MgTiO₄:Mn⁴⁺, Hf⁴⁺ red phosphor triggered neither a chemical reaction nor severe degradation, indicating good thermal stability. Li₂MgTiO₄:Mn⁴⁺, Hf⁴⁺ has potential as a red emission material for warm WLED applications.     

Cation and polyhedron substitution strategies: Effects on local crystal structure and on Bi3+ and Eu3+ co-doped inverse garnet phosphors’ luminescence property

Following the rapid growth of lightning technology, the development of red-emitting phosphors is effective for improving color temperature and color rendering index for w-LEDs devices. Herein, a single phased garnet phosphor with cation and polyhedron substitution modification was firstly prepared. For Mg₃Gd₂Ge₃O₁₂: Bi³⁺, Eu³⁺, the intensity has been remarkably improved by about 16% compared to the one without Bi³⁺ sensitization. The energy transfer mechanism is identified in this work. Based on cation and polyhedron substitution strategies, novel phosphors with different compositions were obtained and further modified the PL properties. With Lu³⁺ substitution, the bond lengths between Bi³⁺ ion and anion ligands are decreased and the site symmetry has been strengthened, which leads to a 21 nm blue shift when Lu³⁺ totally replaced Gd³⁺ ions. In addition, Lu³⁺ and [SiO₄] substitution strategies both effectively increased symmetric rigid structure, which leads to a significant improvement in thermal stability, indicating the samples own great potential in optical applications This work provides a new insight to synthesis red-emitting phosphors for warm white-LEDs.     

Color tunable Ba3Lu(PO4)3:Tb3+,Mn2+ phosphor via Tb3+→Mn2+ energy transfer for white LEDs

Series of UV excited Ba₃Lu(PO₄)₃:Tb³⁺,Mn²⁺ phosphors with tunable green to red emissions had been prepared using solid state reactions. Powder X-ray diffraction and Rietveld structure refinement were used to investigate the phase purity and crystal structure of the prepared samples. Under UV excitation, the Ba₃Lu(PO₄)₃:Tb³⁺,Mn²⁺ samples exhibited not only the typical Tb³⁺ emission peaks but also the broad emission band of Mn²⁺ ions due to the efficient Tb³⁺→Mn²⁺ energy transfer which had been verified by luminescence spectra and decay curves. Utilizing the Inokuti-Hirayama model, the Tb³⁺→Mn²⁺ energy transfer mechanism was determined to be the electronic dipole–quadrupole interaction. Moreover, the emission spectra of Ba₃Lu(PO₄)₃:0.80Tb³⁺,0.015Mn²⁺ sample at different temperatures manifested that our prepared phosphors possessed good thermal stability. The luminescence properties investigation results revealed the potential value of Ba₃Lu(PO₄)₃F:Tb³⁺,Mn²⁺ in application for UV excited phosphor converted white light emitting diodes.     

Highly sensitive optical thermometer of Sm3+, Mn4+ activated LaGaO3 phosphor for the regulated thermal behavior

Sm³⁺, Mn⁴⁺ co-activated LaGaO₃ phosphors, giving the characteristic emissions of orange and red emission simultaneously, were prepared by a solid-state reaction. Their luminescence properties, energy transfer behavior, thermal stability, and ratiometric temperature sensing performance were investigated. Thanks to the inhibition of energy transfer between Sm³⁺ and Mn⁴⁺ ions at high temperature and the reconstruction of the traps, the distinct optical behavior of the involved activators dependent on the ambient temperature was evaluated. Anti-thermal quenching performance of Sm³⁺ ions along with the emission declination of Mn⁴⁺ ions was observed. Hence, the optical thermometry characteristics of the resultant phosphor based on the fluorescent intensity ratio (orange/red) realize a recorded temperature sensitivity of 4.19% K⁻¹ and 2.09% K⁻¹. Moreover, the as-explored film combined with the LaGaO₃: Sm³⁺, Mn⁴⁺ phosphor is demonstrated to be a promising multi-color optical thermometer.     

Novel color tunable LaCaGaO4:Bi3+,Eu3+ phosphors for high color rendering warm white LEDs

A series of LaCaGaO₄:xBi³⁺,yEu³⁺ (x = 0.002–0.04, y = 0.02–0.45) phosphors with adjustable emission colors were synthesized by high-temperature solid-state reaction. The samples were identified as pure phases by X-ray diffraction and Rietveld refinement, and the crystal structures were analyzed in detail. The LaCaGaO₄:xBi³⁺ phosphor shows an intense blue emission under near-ultraviolet excitation, originating from the ³P₁ → ¹S₀ transition. The spectrum analysis reveals that the Bi³⁺ ions occupy two luminescence centers in the LaCaGaO₄ host and that energy transfer can occur. A model of the energy transfer between the Bi³⁺ and Eu³⁺ ions was also created and studied in detail. As the Eu³⁺-concentration increased, the emission color of the LaCaGaO₄:0.005Bi³⁺,yEu³⁺ phosphor changed from blue to pink to red. In addition, the fluorescence lifetime, quantum yield, thermal stability, and other properties of the phosphors were characterized and analyzed. Finally, two white light-emitting diode devices with R_a values of 96.6 and 95 and correlated color temperatures of 4578 and 3324 K were fabricated, indicating the potential of phosphors for warm white lighting applications.     

Synthesis and luminescence properties of broad band greenish-yellow emitting LnVO4:Bi3+ and (Ln1, Ln2)VO4:Bi3+ (Ln=La,Gd and Y) as down conversion phosphors

Ln_0.97VO₄:Bi_0.03³⁺ and (Ln1_0.5, Ln2_0.5)_0.97VO₄:Bi_0.03³⁺ (where Ln=La, Gd and Y) down conversion (DC) phosphors have been synthesized by a novel co-precipitation technique followed by heat-treatment. The influence of lanthanide host composition on crystal structure, luminescence and pertinent optical properties have been investigated by various spectroscopic techniques: XRD, SEM, FT-IR and PL. The produced phosphors have exhibited an intense greenish-yellow emission, upon UV-irradiation. A broad band excitation (280–350 nm) ascribed to ¹S₀→³P₁ and an intense broad greenish-yellow emission band (400–700 nm) attributed to ³P₁→¹S₀ transition, owing to Bi³⁺ ions have been observed. PL spectra revealed that the phosphors with Gd – containing host has exhibited a better luminescence among the others. The luminescence intensity sequence in descending order was as follows: GdVO₄→(Gd, Y)VO₄→(La, Gd)VO₄→(La, Y)VO₄→YVO₄→LaVO₄: Bi³⁺. These phosphors can efficiently convert the UV-photons in a broad range from 280–350 nm of feckless UV-rays into the absorbable visible emission for c-Si solar cells, based on the spectral matching phenomena. In view of the better fluorescence and pertinent optical properties, the phosphor with composition Gd_0.97VO₄: Bi_0.03³⁺ is a suggestible sought UV-absorbing spectral converter, in its thin transparent DC form for c-Si solar cells for better harvesting the solar energy.     

Near-UV light excited Eu3+, Tb3+, Bi3+ co-doped LaPO4 phosphors: Synthesis and enhancement of red emission for WLEDs

A series of single-phase Eu³⁺, Tb³⁺, Bi³⁺ co-doped LaPO₄ phosphors were synthesized by solid-state reaction at 800 °C. Crystal structures of the phosphors were investigated by X-ray diffraction (XRD). A monoclinic phase was confirmed. The excitation (PLE) and emission (PL) spectra showed that the phosphors could emit red light centered at 591 nm under the 392 nm excitation, which is in good agreement with the emission wavelength from near-ultraviolet (n-UV) LED chip (370–410 nm). The results of PLE and PL indicated that the co-doped Tb³⁺ and Bi³⁺could enhance emission of Eu³⁺ and the fluorescent intensities of the phosphors excited at 392 nm could reach to a maximum value when the doping molar concentration of Tb³⁺ and Bi³⁺ is about 2.0% and 2.0%, respectively. The co-doping Tb³⁺ and Bi³⁺ ions can strengthen the absorption of near UV region. They can also be efficient to sensitize the emission of Eu³⁺, indicating that the energy transfer occurs from Tb³⁺ and Bi³⁺ to Eu³⁺ ions. From further investigation it can be found that co-doping Tb³⁺ and Bi³⁺ ions can also induce excitation energy reassignment between ⁵D₀–⁷F₁ and ⁵D₀–⁷F₂ in these phosphors, and result in more energy assignment to ⁵D₀–⁷F₂ emission in LaPO₄:Eu³⁺, Tb³⁺, Bi³⁺. Our research results displayed that La_0.94PO₄:Eu³⁺_0.02, Tb³⁺_0.02, Bi³⁺_0.02 could be a new one and could provide a potential red-emitting phosphor for UV-based white LED.     

Synthesis and photoluminescence properties of novel Ca2LaSbO6:Mn4+ double perovskite phosphor for plant growth LEDs

A novel Mn⁴⁺ activated Ca₂LaSbO₆ (CLS) far-red phosphor was synthesized by high temperature solid state reaction. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence spectra, ultraviolet-visible spectra, luminescence decay times, emission-temperature relationship and internal quantum efficiency (IQE). It is found that CLS:Mn⁴⁺ phosphor has a strong broad excitation band in the range of 200–550?nm. The samples can be excited by ultraviolet and blue light. There is a wide emission band centered at 685?nm between 600?nm and 760?nm. The optimum doping concentration of Mn⁴⁺ is approximately 0.5?mol%. In addition, all the CIE chromaticity coordinates of CLS:0.005Mn⁴⁺ located at far-red region. The concentration quenching mechanism is the dipole-dipole interaction of Mn⁴⁺ activator. Importantly, the CLS:0.005 Mn⁴⁺ sample has an IQE of up to 52.2%. Finally, a 365?nm ultraviolet light emitting diode (LED) chip combined with 0.5?mol% Mn⁴⁺ far-red phosphor was used to fabricate the LED device. All the results indicated that CLS:Mn⁴⁺ phosphors have potential applications in indoor plant cultivation.