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Here we report a novel quadrilayer structure glass/ceramic with multicolor emission, which has a great potential to be used as a light converter for laser lighting with low blue light and high color rendering index. The multilayer glass/ceramic was prepared by controlling the crystallization of the double-layer Sr 1.07 Eu 0.03 Al 2.2 Si 1.8 O 8 /Sr 1.09 Sm 0.01 Al 2.2 Si 1.8 O 8 glass. The outer layers of the glass/ceramic are the ceramic layers and the inner layers are the glass layers. Hexagonal Sr 1.1 Al 2.2 Si 1.8 O 8 is the only crystal phase precipitated during the crystallization process and these crystals are highly oriented in growth. The Ra and CRI values of the white light-emitting LD prepared by employing the multi-layer glass/ceramic as the light converter and a 405 nm LD as the pump source are both more than 90. This work provides a novel and enlightening idea for the design and preparation of the multilayer glass/ceramic with multicolor emission. [ABSTRACT FROM AUTHOR]

Abstract A single-phase white light emitting NaBi(WO 4) 2 :Dy3+, Tm3+ phosphor has been successfully prepared by conventional high-temperature solid-state method. First-principles calculations were used to investigate the electronic structures of NaBi(WO 4) 2. The calculation results show that NaBi(WO 4) 2 has an indirect band gap with 3.02 eV. The crystal structure and PL properties of the obtained phosphor are characterized by SEM, powder X-ray and photoluminescence spectra, respectively. The results demonstrate that all as-prepared crystalline in a tetragonal crystal system with a space group of I 4 ¯ . PL results confirmed that the obtained phosphors can be efficiently excited by 365 nm and generated white light emission. Then the energy transfer between Dy3+ and Tm3+ in the host NaBi(WO 4) 2 was investigated. Finally, the chromaticity coordinates of preferred NaBi 0.91-x (WO 4) 2 :0.09Dy3+, 0.11 Tm3+ (0.3319, 0.3395) were close to the standard white light point (0.333, 0.333). All these results reveal that NaBi(WO 4) 2 :Dy3+/Tm3+ was a potential single phase white light-emitting phosphor candidate for NUV-based w-LEDs. Highlights • Single-phase white light emitting phosphors NaBi(WO 4) 2 :Dy3+/Tm3+ have been synthesized by solid-state reaction method. • Electronic structure of NaBi(WO 4) 2 has a indirect band gap with 3.02 eV which attribute to the O 2 p and W 5 d. • White light was achieved from Dy3+/Tm3+ co-doped NaBi(WO 4) 2 phosphor excited at 365 nm. [ABSTRACT FROM AUTHOR]

Y 2 Ce 2 O 7 powders doped with different Yb 3+ and Er 3+ concentrations were synthesized via the sol-gel method. The structure and upconversion properties were investigated. The results indicated that a single phase was obtained and that the structure was cubic. The green and red upconversion emissions were detected with excitation at 980 nm, and the emission intensities could be tuned by the Yb 3+ and Er 3+ concentrations. The mechanism of the upconversion process was evaluated on the basis of the emission intensities and lifetimes of the 4 S 3/2 , 4 F 9/2 and 4 I 13/2 levels. The results demonstrated that cross-relaxation was responsible for the dependence of green and red upconversion emissions on the dopant concentration. [ABSTRACT FROM AUTHOR]

Eu-doped BaAlO red phosphors were synthesized by high-temperature solid-state reaction. The crystal structure, morphology and luminescence properties were investigated by XRD, TEM and photoluminescence spectroscopy. The effect of calcination temperature, Eu concentration as well as charge compensators on the luminescence properties was also investigated. Characteristic orange-red emission at 589 nm was detected under 394 nm excitation. The best performance could be derived for the sample calcined at 1450 °C. With the increase of Eu concentration, the emission intensities increased gradually up to the Eu concentration of 12 %. The emission intensities could be enhanced with Li, Na and K introduced as charge compensators. The results showed that BaAlO:Eu phosphors with charge compensator had potential application in the fields of near-UV-excited WLEDs. [ABSTRACT FROM AUTHOR]

Yb and Er co-doped YAB powders were prepared by sol-gel method. The structure and fluorescence properties were investigated. XRD pattern indicated that the single phase was obtained at 1150°C and the structure belonged to rhombohedral. Under 379 nm excitation, two emissions around 983 nm and 1531 nm were observed and the effect of Yb ion concentration on the emission intensity was discussed. The energy transfer was observed under 930 nm excitation and the energy transfer efficiencies for all samples were calculated. The lifetimes of F level of Yb ion and I level of Er ion were measured and the effect of Yb ion concentration on the lifetime was also discussed. The results indicated that there was an additional mechanism for the decay of I level in powder samples. The Yb and Er co-doped YAB powders should be a potential candidate for ceramic laser materials. [ABSTRACT FROM AUTHOR]

Yb and Erco-doped YCeO nanoparticles sintered at different temperatures were prepared by homogeneous co-precipitation method. The products were characterized by X-ray powder diffraction (XRD), energy-dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicated that the particle sizes and morphologies of the samples were heavily influenced by the sintering temperature. As temperature increased, the particle sizes became gradually larger and more agglomerate. The emissions including green and red upconversion emissions were investigated under 980 nm excitation. The emission intensities of the samples also depended on the sintering temperature. Two photon processes were mainly responsible for green and red upconversion emissions. [ABSTRACT FROM AUTHOR]

Abstract: Er3+ doped and Yb3+/Er3+ co-doped Y4Al2O9 phosphors are prepared by the sol–gel method. The effect of dopant concentration on the structure and up-conversion properties is investigated by X-ray diffraction (XRD) and photoluminescence, respectively. XRD pattern indicates that the sample structure belongs to monoclinic. Under 980nm excitation, the green and red up-conversion emissions are observed and the emission intensities depended on the Yb3+ ion concentration. The green up-conversion emissions decrease with the increase of Yb3+ concentration, while red emission increases as Yb3+ concentration increases from 0 to 8at% and then decreases at high Yb3+ concentration. The mechanisms of the up-conversion emissions are discussed and results shows that in Er3+ and Yb3+/Er3+ co-doped system, cross-relaxation (CR) and energy transfer (ET) processes play an important role for the green and red up-conversion emissions. [Copyright &y& Elsevier]

Abstract: The effect of Yb3+ concentrations on the properties of Yb3+ and Er3+ co-doped YAB crystals has been investigated in this paper. The dependence of the emission intensity on the Yb3+ concentration has been depicted according to the energy transfer model. The decay curves of 2F5/2 level of Yb3+ ion and 4I13/2 level of Er3+ ion in the different Yb3+ concentration crystals have been measured. The results show that the lifetime of 2F5/2 level of Yb3+ ion is heavily affected by Yb3+ concentration, contrary to that of 4I13/2 level of Er3+ in the crystals. [Copyright &y& Elsevier]

Abstract: The Yb3+ to Er3+ energy transfer in yttrium aluminum borate (YAB) crystal is investigated with the rate equation without considering the back energy transfer. The energy transfer coefficients (W 25) in the crystals with different Yb3+ concentrations are determined and compared with those in other crystals. The transfer efficiencies and the micro-parameters of energy transfer and migration are also determined. The results show that the energy transfer from Yb3+ to Er3+ in YAB crystal is very efficient and the Yb3+–Er3+ co-doped YAB crystal may be a good candidate for the 1.55μm laser media. [Copyright &y& Elsevier]

Abstract: Er3+-doped YAl3(BO3)4 (YAB) crystal has been grown by the top-seeded solution method. The Judd–Ofelt (J–O) theory has been applied to analyze the polarized absorption spectra of Er3+ ions in the uniaxial crystal measured at room temperature, and the effective J–O parameters have been determined as: Ω 2 =8.38×10−20 cm2, Ω 4 =1.61×10−20 cm2, Ω 6 =1.50×10−20 cm2. The parameters have been used to calculate the spontaneous emission probability and radiative lifetime of 4I13/2 manifold for the Er3+ ions. The fluorescence lifetime of this manifold has been measured and the quantum efficiency has been estimated. The emission cross-sections for the 4I13/2 → 4I15/2 transition calculated using the Fuchtbauer–Ladenburg and the reciprocity methods are compared. [Copyright &y& Elsevier]

Abstract: Er3+-doped and Er3+–Yb3+ co-doped yttrium aluminum borate (YAB) single crystals have been grown by the top-seeded solution growth method using a new flux system, namely NaF–MoO3–B2O3. The Er3+ concentrations were 1.3mol% for both single doped and co-doped crystals and the Yb3+ concentration in the Er3+–Yb3+ co-doped crystal was 20.0mol% in the raw materials. The distribution coefficients of Er3+ single doped and Er3+–Yb3+ co-doped crystals were measured. The polarized absorption and fluorescence spectra of Er3+–Yb3+ co-doped crystal were recorded and compared with those of Er3+ single doped crystal. The results demonstrate that Er3+–Yb3+ co-doped YAB crystal is a potential candidate for 1.55μm laser materials. [Copyright &y& Elsevier]

The In‐based double perovskite halides have been widely studied for promising optical‐electric applications. The halide hexagonal perovskite Cs2LiInCl6 was isolated using solid‐state reactions and investigated using X‐ray diffraction and solid‐state NMR spectra. The material adopts a 12‐layered hexagonal structure (12R) consisting of layered cationic orders driven by the cationic charge difference and has Li+ cations in the terminal site and In3+ in the central site of face‐shared octahedron trimers. Such a cationic ordering pattern is stabilized by electrostatic repulsions between the next‐nearest neighboring cations in the trimers. The LiCl6 octahedron displays large distortion and is confirmed by 7Li SS NMR in the Cs2LiInCl6. The Cs2LiInCl6 material has a direct bandgap of ~4.98 eV. The Cs2LiInCl6: Mn2+ displays redshift luminescence (centered at ~610–622 nm) from the substituted Mn2+ emission in octahedron with larger PLQY (17.8 %–48 %) compared with that of Cs2NaInCl6: Mn2+. The Mn‐doped materials show luminescent concentration quenching and thermal quenching. The composition Cs2Li0.99In0.99Mn0.02Cl6 exhibits the highest PL intensity, a maximum PLQY of 48 %, and high luminescent retention rate of ~86 % below 400 K and is suitable for application for pc‐LED. These findings contribute to our understanding of the chloride perovskites and hold potential for widespread optical applications. [ABSTRACT FROM AUTHOR]

Cr3+‐activated near‐infrared (NIR) phosphors have gained extensive attention for use in NIR phosphor‐converted light‐emitting diodes (pc‐LEDs), which are required for smart NIR spectroscopy techniques. Nevertheless, obtaining broadband NIR‐emitting phosphors with outstanding thermal stabilities and photoluminescence (PL) efficiencies remains a significant challenge. Herein, considering NaSr2XGe5O14 (X = Al, Ga, Sc, and In) as hosts, which possess a large band gap and multiple sites for the substitution of Cr3+ ions. NaSr2XGe5O14:Cr3+ phosphors are successfully prepared using a solid‐state reaction technology. Upon blue light excitation, the phosphors cover a broad NIR emission band in 650–1100 nm region. Notably, an abnormal blueshift and PL enhancement are observed following the substitution of Al/Ga with Sc/In. In particular, the PL internal quantum efficiency is improved from 34.5% (NaSr2GaGe5O14: Cr3+) to 87.5% (NaSr2ScGe5O14: Cr3+). Moreover, the manufactured NIR pc‐LED exhibited an exceptional photoelectric efficiency of 17.7% with an NIR output power of 10.2 mW at 20 mA, and its potential application in nondestructive detection is demonstrated. [ABSTRACT FROM AUTHOR]

Quasi-zero-dimensional quantum dots (QDs) have garnered significant attention owing to their distinct structural attributes, quantum confinement behaviors, optoelectronic characteristics, etc. Regrettably, their susceptibility to stability poses a challenge. In this context, leveraging rational component regulation and crystallization process optimization strategies, we presented the successful preparation of CdS QDs silicate glass through the amalgamation of melt-quenching and controlled crystallization. The optical and morphological analysis substantiated the accomplishment of in-situ precipitation of CdS QDs within the glass matrix, with grain sizes <20 nm. Integrating CdS QDs into an inorganic glass matrix remarkably augmented its fluorescence thermal stability, enabling the preservation of 85.1 % of the room-temperature luminescent intensity even at an elevated temperature of 150 °C. Moreover, the encapsulated W-LED device by near-UV LED chip, CdS QDs glass, and BaMgAl 10 O 17 :Eu2+ phosphor exhibited a warm white-light emission characterized by suitable chromaticity coordinates (0.3741, 0.3452) and a notably high color rendering index (CRI = 93). Ultimately, the radioluminescence behavior of CdS QDs glass was unveiled by utilizing it as the scintillator wafer in an X-ray imaging system, which clearly demonstrated the structure of spring encapsulated within an opaque capsule. In a nutshell, these demonstrations unequivocally emphasize the substantial potential merits of CdS QDs glass, particularly in the domains of long-term W-LED lighting and X-ray imaging applications. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) spectroscopy has gained widespread application in food analysis, disease diagnosis, fingerprint analysis, and security monitoring. However, the lack of efficient, broadband NIR luminescent materials hinders the full potential of this technology. Here, an ultra-broadband and high-efficiency Cr3+-doped multi-phase glass-ceramics containing MgAl 2 O 4 , Al 2 SiO 5 , and SiO 2 nanocrystals was discovered, which exhibited an ultra-broadband NIR emission (λ em ∼ 900 nm) with a full width at half maximum more than 300 nm and a high internal quantum yield of 50.9% under the excitation of 465 nm blue light. Moreover, the integrated emission intensity at 100 °C and 150 °C can keep 88% and 77% of that at room temperature. The ultra-broadband, high efficiency, and thermally robust luminescence of this Cr3+-doped multi-phase glass-ceramics can be attributed to the selective enrichment of Cr3+ ions into different nanocrystals with octahedral sites, and medium electron-photon coupling effect. The NIR glass-ceramics-converted light-emitting diode constructed by the glass-ceramics combined with 465 blue LED chip produced an excellent NIR output and photoelectric conversion efficiency of 274 mW/1007 mW and 3.43%/2.79% at 100 mA/320 mA drive current, which demonstrated superior overall performance to the NIR device built by using the well-known NIR phosphors. Additionally, the NIR camera can capture the image of license plate and nectarine, as well as identify the residual drug content in the bottle under the irradiation of the NIR device constructed by the glass-ceramics. This work not only presented an ultra-broadband and high-efficiency NIR material but also highlights a design strategy to effectively enhance the efficiency and broadband characteristics of NIR glass-ceramics. [ABSTRACT FROM AUTHOR]

In this work, a series of Dy3+ and Dy3+/Tm3+ ion activated Ca 3 NbGa 3 Si 2 O 14 glass-ceramics were prepared by traditional melt crystallization method, and report on the structural, optical, and energy transfer (ET)-based photoluminescence (PL) properties of glass-ceramics co-doped Dy3+/Tm3+. The preparation of glass-ceramics was studied by DTA, XRD, SEM, and UV–vis photometer technology, phase composition, transmittance, optimum heat treatment conditions, and luminescence properties. The best heat treatment procedure for obtaining transparent and well-formed glass-ceramics is crystallization at 820 °C for 5 h. The spectra excited by Tm3+ and Dy3+ have intersections at 352 nm and 365 nm, which means that CNGS: Dy3+/Tm3+ can be effectively excited by 352 nm and 365 nm ultraviolet light. Under the excitation of 352 nm ultraviolet light, four main emission peaks corresponding to 1 D 2 →3 F 4 , 4 F 9/2 → 6 H 15/2 , 4 F 9/2 → 6 H 13/2 , 4 F 9/2 → 6 H 11/2 were found at 456 nm, 484 nm, 577 nm, and 663 nm, respectively. When the optimal concentration (4 at.%) of Dy3+ is Co-doped with a different amount of Tm3+, the luminous color can be adjusted by adjusting the doping amount of Tm3+ and changing the excitation wavelength. There is an overlapping region between the emission spectrum of Tm3+ doped glass and the excitation spectrum of Dy3+ doped glass, which indicates that there is energy transfer between Tm3+ and Dy3+. In addition, CNGS: Dy3+/Tm3+ CIE coordinates show that the color coordinates (0.3324, 0.3352) when y = 0.02 under 365 nm excitation are closest to the standard white light (0.333, 0.333), indicating that this glass has potential applications in WLED devices. [ABSTRACT FROM AUTHOR]

Efficient ultra-broadband near-infrared (NIR) phosphors with long-wavelength (λ max > 850 nm) and wide full width at half-maximum (FWHM, >200 nm) have sparked tremendous interest, demonstrating their immense potential in NIR spectroscopy technology. Nevertheless, the development of NIR spectroscopy technology suffers from the restricted capability to efficiently emit the ultra-broadband NIR light. Herein, the synergetic enhancement strategy of heterogeneous substitution and compositional modulation was applied to create a novel Cr3+ doped long-wavelength ultra-broadband MgO: Cr3+, Ga3+ phosphor, which exhibited a long-wavelength ultra-broadband NIR emission (λ max = 850 nm) covering the range of 650–1300 nm on the electromagnetic spectrum with the FWHM of more than 200 nm under the excitation of 468 nm light. Furthermore, the tunable NIR emission from 818 nm to 862 nm with an optimized quantum efficiency of 30% was accomplished by the Ga3+ ions substitution and Cr3+ ions modulation. The phosphor exhibited remarkable thermal stability up to 100 °C, remaining 83% of the integrated emission intensity at room temperature. A prototype of the NIR phosphor-converted LED (pc-LED) demonstrated that the novel MgO: Cr3+, Ga3+ phosphor possessed a relatively strong NIR output power (15.05 mW at 100 mA driven current) with a photoelectric conversion efficiency of 5.53%, which is impressive compared with other Cr3+-doped long-wavelength ultra-broadband phosphors. This work not only proposes a novel long-wavelength ultra-broadband NIR phosphors with industrialization and great application prospect in night vision but highlights a synergetic enhancement strategy to effectively boost the performance of long-wavelength ultra-broadband NIR pc-LED light sources. [ABSTRACT FROM AUTHOR]

The near‐infrared (NIR) phosphor‐converted light‐emitting diode (pc‐LED) is a new NIR light source with both compact structure and high efficiency, and its performances is greatly depended on the NIR phosphors. Herein, this work presents a Cr3+‐doped gadolinium aluminum gallium garnet (GAGG:Cr3+) NIR ceramic phosphor with a broadband emission in the range of 650–850 nm, and optical performances that can be regulated via crystal‐field engineering. By optimizing the Al/Ga ratio, an external quantum efficiency as high as 65% is observed. The thermal stability is enhanced with the increase of Al content, which is attributed to the broadening of bandgap and the weakening of electron–phonon coupling effect. The NIR light output powers of the fabricated device based on the GAGG:Cr3+ ceramic are up to 88.9 mW @ 10 mA and 1247.7 mW @ 200 mA, while the electro‐optical conversion efficiencies were 28.5% @ 10 mA and 17.7% @ 200 mA, respectively. In addition, the NIR pc‐LED exhibited a strong penetrability such that the veins in a palm could be clearly identified, allowing for its potential use in biosecurity applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Sm3+ doped silica-aluminum-gallium glasses for orange-red LEDs has been prepared. • The effect of Al 2 O 3 /Ga 2 O 3 ratio on the luminescence properties of Sm3+ ions was investigated. • Compared with gallium silicate glass, the addition of Al 2 O 3 significantly improves the luminescence performance of Sm3+ ions. The Sm3+ doped SrO-Nb 2 O 5 -Al 2 O 3 -Ga 2 O 3 -SiO 2 glasses in this work were prepared using the conventional melt quenching method. The effects of Al 2 O 3 /Ga 2 O 3 ratio on the structure and orange light emission properties were studied by XRD, Raman spectroscopy, spectrophotometer and J-O theory, respectively. With the increase of Al 2 O 3 content, the absorption coefficient of the glass sample gradually increases, which might be attributed to an increase in non-bridged oxygen bonds caused by a change in the glass network structure. Under 403 nm excitation, the emission spectra show clear peaks at 602 nm and 649 nm, representing the 4G 5/2 → 6H 7/2 , and 4G 5/2 → 6H 9/2 transitions, respectively. When the Al 2 O 3 /Ga 2 O 3 ratio is 0.25, the sample luminescence intensity is the highest, and the emission cross section of A2 glass sample is 4.34 × 10−22 cm2. The CIE color coordinates, color purity, and color temperature values of all samples were determined, and they were all located in the orange-red light region. The experiments results reveal that the prepared silica-aluminum-gallium glasses has a potential application prospect in orange-red LEDs, solid state lasers and other fields. [ABSTRACT FROM AUTHOR]

Red long afterglow phosphors have significant implications for the realization of multicolor long-afterglow phosphors, but their insufficient luminescence intensity and afterglow duration still cannot meet the demands of practical applications. In this study, a novel orange-red phosphor, Y 2 Ge 2 O 7 :Pr3+, was synthesized for the first time. This phosphor not only exhibits exceptional thermal resistance but also shows a marked enhancement in long-afterglow performance upon co-doping with Sm3+. Remarkably, an orange-red afterglow can still be distinctly observed with the naked eye even 5 min after the removal of the excitation source in darkness. Further investigations involving thermoluminescence spectrum tests and the construction of an independent host-referred binding energy (HRBE) diagram reveal that the introduction of Sm3+ effectively mitigates the trap depth (1.02 eV) of the Y 2 Ge 2 O 7 :Pr3+ phosphor and significantly augments the quantity of electrons in shallow traps. This modification facilitates the effective release of electrons under room temperature conditions by the improved phosphor, thereby actualizing the long-afterglow luminescence phenomenon. Additionally, our findings indicate that a trap depth within the range of 0.60–0.80 eV is the optimal range for releasing electrons at room temperature. This research offers a crucial reference for future endeavors aimed at enhancing the performance of long-afterglow phosphors. • A novel orange-red long afterglow phosphor, Y 2 Ge 2 O 7 :Pr3+, Sm3+, was successfully synthesized using the high-temperature solid-state method. • Co-doping with Sm3+ successfully reduces the trap depth of Y 2 Ge 2 O 7 :Pr3+, increases the number of electrons in shallow traps, and exhibits long afterglow luminescence. • Both YGO:Pr3+ and YGO:Pr3+, Sm3+ phosphors exhibit excellent thermal stability, indicating potential application value in information storage. [ABSTRACT FROM AUTHOR]

Blue-light activated long afterglow luminescence phosphors have attracted much attention because of their potential application in many fields. Herein, the influence of trap depth and the quantity of electrons captured by the traps on the long afterglow luminescence properties were systematically revealed through a comparative analysis of the long afterglow luminescence performance of the series of Y 3 Al 5-x Ga x O 12 (YAGG):Ce3+, Cr3+ (x = 0, 1, 2, 3, 4, 5) phosphors. To achieve long afterglow luminescence, it requires that the traps can effectively capture electrons, and possess an appropriate trap depth. Additionally, it is discovered that the quantity of electrons captured by the traps is the main factor affecting the duration of long afterglow luminescence. The more electrons are captured, the longer the afterglow lasts. The quantity of trapped electrons is inversely proportional to the energy differences between CB M -Ce 5d and trap depth. The sample exhibits the high quantity of trapped electrons attributable to its small energy differences which allows electrons to be directly captured by traps through the tunneling effect. On this basis, the effects of crystal field splitting (ε cfs), centroid shift (ε c), and the degree of dodecahedral distortion (D (YO)) on trap depth (E T) were discussed to manipulate the trap depth, demonstrating there is a significant positive correlation between ε c -ε cfs (2(1-10D(YO))) and E T values for the garnet structure A 3 B 2 C 3 O 12 , when the ion doped at the A-position remains constant and the ions at the B and C positions vary. Notably, A larger D (YO) value corresponds to a deeper trap depth. This study provides a new perspective toward the development and design of long afterglow materials with superior afterglow emission. • The effect of trap depth and the quantity of trapped electrons in mechanism processes of persistent luminescence properties were systematically demonstrated. • The quantity of trapped electrons is inversely proportional to the energy differences between CB M -Ce 5d and trap depth. • A mathematical model is developed to reveal the effects of crystal field splitting (ε cfs), centroid shift (ε c), and the degree of dodecahedral distortion (D (YO)) on trap depth (E T) to manipulate the trap depth. [ABSTRACT FROM AUTHOR]

In this work, the glass 42AO-7Nb 2 O 5 -21Ga 2 O 3 –29SiO 2 -1Sm 2 O 3 (A = Ca,Sr,Ba) are prepared by the conventional melt quenching technique. The effects of modifiers on the glass network structure and luminescence properties were investigated by XRD, Raman spectroscopy, spectrophotometry, and J-O theory, respectively. The J-O intensity parameters which were calculated though the absorption spectra were used to evaluate the laser parameters such as the radiative excursion probability of Sm3+ ions in different samples at each energy level, the emission cross section, the radiative lifetime, and the optical gain parameter. When BaO is used as a network modifier, the emission cross section is maximized at the 4G 5/2 → 6H 7/2 transition, with σ em = 9.47 × 10−22 cm2. The experiments results reveal that altering the network modifier can effectively improves the laser emission performance of the samples, and the Sm3+ ions doped gallium silicate glasses has prospective applications in solid state orange lasers. [Display omitted] • A novel glass 42AO-7Nb 2 O 5 -21Ga 2 O 3 –29SiO 2 -1Sm 2 O 3 (A = Ca,Sr,Ba) was prepared. • The influence of network modifier's cation radius on the wave number of Raman peak is small, but the peak intensity increases with the increase of cation radius. • Sm3+ ions doped gallium silicate glasses has prospective applications in solid state orange lasers. [ABSTRACT FROM AUTHOR]

• ScP 3 O 9 : Cr3+, shows a broadband NIR emission and peaking at ∼900 nm. • The PL intensity of ScP 3 O 9 : Cr3+ can be enhanced by phase transition. • ScP 3 O 9 : Cr3+, Nd3+, Pr3+ exhibits an excellent PL thermal stability (86 % at 423 K). • The NIR pc-LED device can be applied in non-destructive analysis. Near-infrared (NIR) phosphors play an important role in NIR pc-LEDs. However, NIR phosphor with long wavelength are still suffered from low efficiency and poor thermal stability. Herein, a blue light excitable ScP 3 O 9 : Cr3+ NIR phosphor with an emission peak > 880 nm is reported. Significantly, the PL intensity of ScP 3 O 9 : Cr3+ increased to 241 % when the monoclinic phase changes to cubic. Moreover, by co-doping the cubic ScP 3 O 9 : Cr3+ with Nd3+, Pr3+ ions, the PL internal quantum efficiency (IQE) of the phosphors increased from 62 % to 74 %, and the thermal quenching of the phosphor is suppressed effectively (86 % at 423 K). The energy transfer processes between Cr3+ and Nd3+, Pr3+ ions are proposed to be responsible for the enhancement. Furthermore, an efficient NIR pc-LED was fabricated, and gives a high photoelectric efficiency of 16.5 % (26.8 mW at 60 mA). Finally, multifunctional applications of the NIR device in night-vision and nondestructive analysis were demonstrated. An efficient broadband NIR phosphor ScP 3 O 9 : Cr3+, Nd3+, Pr3+ with excellent thermal stability is prepared to fabricate compact NIR pc-LED based on commercial blue diode chips. The NIR pc-LED device is promising for the applications in non-destructive analysis. [Display omitted] [ABSTRACT FROM AUTHOR]

We report a "multidentate polymer microreactor" method for the creation of secondary structures of colloidal nanocrystals. Using NaYF4:Yb,Er as an example, we demonstrate that the use of sodium polyacrylate (PAAS) as a "multidentate polymer microreactor" allows the controllable growth of primary nanocrystals and induces aggregation of the nanocrystals into well-defined mesoporous clusters. [ABSTRACT FROM AUTHOR]

W-LED lighting is a green and environment-friendly lighting method in today's society, and red phosphors play an irreplaceable role in W-LED lighting. In this work, a series of rare-earth-doped phosphors, Ba2-aSiO4: aEu3+ (a = 0.02 ~ 0.10), Ba2-a-bSiO4: aEu3+, bBi3+ (b = 0.01 ~ 0.08) and Ba2-a-cSiO4: aEu3+, cSm3+ (c = 0.005 ~ 0.02), were successfully synthesized by traditional high-temperature solid-state reaction method. The experimental results showed that the concentration quenching occurred in the case of the doping concentration of Eu3+ exceeding 0.08 mol, and the main mechanism of concentration quenching was based on the multipole interaction. Under the excitation of 392 nm light, all phosphors emitted strong reddish orange light. The doping of Sm3+ and Bi3+ ions can effectively improve the luminescence properties of Ba2-aSiO4: aEu3+ phosphor, and the optimal doping concentration for Bi3+ and Sm3+ ions was 4 mol.% and 1 mol.%, respectively. The results mentioned above indicate that these phosphors have a potential application in the W-LED field. [ABSTRACT FROM AUTHOR]

Tricolor phosphors play a pivotal role in the application of white-light-emitting diode (W-LED). Herein, we successfully prepared a series of Y2Zr2O7:Eu3+ phosphors via sol–gel method. Structural analysis showed that the phosphor was fluorite structure (space group Fm–3 m), and the elements of Y, Zr, O, and Eu were uniformly distributed within each particle. From the emission spectra, five distinctive peaks can be found in the wavelength of 500–700 nm excited by 393 nm UV light, and in the case of increase of Eu3+ contents, the luminescence intensities of phosphors increased first and then decreased. And the chromaticity coordinates fell into the reddish orange zone. For different calcination temperatures, they did not seriously affect the crystal structure, chromaticity coordinates, and CCTs except for crystallinity. Meanwhile, the phosphor has excellent thermal stability at working temperature of 150 °C. The above-mentioned excellent properties indicate that this phosphor has potential applications in W-LED devices. [ABSTRACT FROM AUTHOR]

The YAG single crystals doped with 10 at.%, 20 at.% and 50 at.% Er3+ were successfully grown by the micro-pulling down method and spectroscopic properties of the crystals were investigated. The main interest was focus on the relation between the Er3+ concentration and ∼3.5 μm emission of Er3+:YAG crystals. Room temperature absorption spectra were analyzed by the Judd-Ofelt theory. The stimulated emission cross-sections were calculated by the Füchtbauer-Ladenburg equation. The fluorescence intensities and peak emission cross-sections of the crystals at ∼3.5 μm are slightly decreasing with the increase of Er3+ concentration. The results indicate that the highly doped Er3+ concentration is beneficial to realize the ∼3.5 µm laser output. [Display omitted] • The YAG single crystals doped with 10 at.%, 20 at.% and 50 at.% Er3+ were successfully grown by the micro-pulling down method. • Room temperature absorption spectra were analyzed by the Judd-Ofelt theory and the stimulated emission cross-sections were calculated by the Füchtbauer-Ladenburg equation. • The fluorescence intensities and peak emission cross-sections of the Er3+:YAG crystals at ∼3.5 μm are slightly decreasing with the increase of Er3+ concentration. The YAG single crystals doped with 10 at.%, 20 at.% and 50 at.% Er3+ were successfully grown by the micro-pulling down method and spectroscopic properties of the crystals were investigated. The main interest was focus on the relation between the Er3+ concentration and ∼3.5 μm emission of Er3+:YAG crystals. Room temperature absorption spectra were analyzed by the Judd-Ofelt theory. The stimulated emission cross-sections were calculated by the Füchtbauer-Ladenburg equation. The fluorescence intensities and peak emission cross-sections of the crystals at ∼3.5 μm are slightly decreasing with the increase of Er3+ concentration. The trend of the emission properties in NIR and visible region with the Er3+ concentration was also discussed and compared. The results indicate that the highly doped Er3+ concentration is beneficial to realize the ∼3.5 µm laser output. [ABSTRACT FROM AUTHOR]

• A novel Dy3+/Sm3+ co-doped gallium silicate glass-ceramic for indoor warm white light illumination was prepared. The matrix components are 43SrCO 3 +7Nb 2 O 5 +21Ga 2 O 3 +29SiO 2. • The glass-ceramic has good thermal stability. • This glass-ceramic maintains good transparency in the visible light range (The transmittance is about 60 %, after the heat treatment at 830℃/ 2 h). • Multiple energy transfer channels exist between Dy3+ and Sm3+ ions. • These glass-ceramics have potential applications in indoor warm white lighting. In this paper, a series of Dy3+ and Dy3+ /Sm3+ ions co-doped gallium silicate glass–ceramics prepared by conventional melt crystallization method. The best heat treatment conditions and the luminescence properties of the glass–ceramics were systematically investigated by XRD, DSC, SEM and spectrophotometer, respectively. To obtain glass-ceramic samples with high transmittance and good luminescence performance, the best heat treatment procedure should be 830℃/4 h. The energy transfer relationship between Dy3+ ions and Sm3+ ions is discussed through emission decay curves and energy level diagrams. The Dy3+/Sm3+ ions co-doped samples have good thermal stability, maintaining 67.9 % of the emission intensity at 150 °C. The CCT of the SNGSDy 4.0 Sm 0.6 sample was 3330 K under 402 nm excitation. The results indicate that the sample is suitable for solid state lighting technology, and the warm white light source can be used for indoor lighting in halls and corridors. [ABSTRACT FROM AUTHOR]

• Er3+/Yb3+ co-doped CaYAlO 4 , CaGdAlO 4 , and CaLaAlO 4 upconversion phosphors were synthesized. • The energy band structures and density of states distributions of three samples before and after Er3+/Yb3+ doping were investigated by density functional theory. • By eliminating the influence of variables as much as possible, the main factors affecting the upconversion luminescence performance are obtained. In recent years, trivalent rare-earth ion (RE3+) doped upconversion luminescent (UCL) materials have been studied extensively owing to their potential applications. The structure of the material is the main factor affecting the UCL performance. In this study, three structurally identical Er3+/Yb3+ co-doped aluminates CaYAlO 4 , CaGdAlO 4 , and CaLaAlO 4 (CYA, CGA, and CLA) phosphors were synthesized, and the effects of the local environment on the UCL performance of Er3+ ions were investigated. The morphology and phonon energy of the samples were not the main factors affecting the luminescence performance in the same structural material. The difference in the crystal field strength was the main reason for the difference in the UCL of the three phosphors, which was attributed mainly to the difference in the crystal field strength and the difference in the degree of distortion of the Al–O octahedra that changes the transition probabilities of the parity forbidden intra-4fN–4fN electronic transitions of Er3+. A comparison of the distances between the RE3+ and the lifetimes of the 4I 11/2 and 4I 13/2 energy levels in the three materials showed that the red–green ratio of the materials was affected by the energy transfer. Finally, an analysis of the changes in the energy band structure and density of states (DOS) distribution before and after Er3+/Yb3+ doping of CYA, CGA, and CLA found that the effect of the bandgap on the UCL can be neglected when the bandgap of the matrix is larger than the energy difference from the 4I 15/2 energy level to the 2H 11/2 energy level of the Er3+ ion. [ABSTRACT FROM AUTHOR]

• Phosphate phosphors were prepared using the traditional high-temperature solid-state method. • The luminescence of Dy3+ ions was enhanced by co-doping with Bi3+ ions. • The luminescence enhancement effect was achieved using both near-ultraviolet excitation and blue LD pumping. Dy3+ ions are an efficient activator for achieving near-UV-excited single-phase white light and blue LD-pumped yellow laser output. However, weak luminescence intensity is one of the main factors affecting its application. Herein, a series of Dy3+-doped and Dy3+/Bi3+ co-doped YPO 4 phosphors were synthesized by high-temperature solid-phase method to enhance the luminescence of Dy3+ ions. The structure, morphology, and luminescence properties were studied using X-ray diffraction, scanning electron microscopy, and fluorescence spectroscopy. When excited at 353 nm and 450 nm, Dy3+ ions had three main emission peaks in the visible light range. When Bi3+/Dy3+ were co-doped, the emission intensity of the sample was significantly enhanced. The optimal doping concentration of Dy3+ was 4.0%. The energy transfer between Bi3+ and Dy3+ contribute to the enhancement of Dy3+ luminescence. The study indicates that Bi3+ co-doping can effectively enhance the visible light emission of Dy3+ ions. [ABSTRACT FROM AUTHOR]

Tailoring the local crystal environment around the activators is one of an important way to enhance the upconversion (UC) luminescence intensity. Herein, we substitute the Y3+ lattice with La3+ ion gradually in Y2Ti2O7:Yb3+, Er3+ phosphor and investigate the effect of La3+ concentration on the UC luminescent properties as well as the temperature sensing behaviors. During the phase transformation process from cubic Y2Ti2O7 to monoclinic La2Ti2O7, the La3+ ions also play an important role on the adjustment of size and morphology of particles. Furthermore, the cooperation of La3+ ion is in favor of the crystal growth toward the easy growth directions. The UC luminescence intensities can be enhanced efficiently with the increasing of La3+ concentration. The sensitivity for temperature sensing can be improved by the increasing of La3+ concentration in the Y2Ti2O7 and La2Ti2O7 two‐phase coexistence system and the maximum SA is 45.3 × 10−4 K−1 at 410K when the La3+ concentration is 80%. The maximum SA and corresponding temperature can be adjusted by controlling the La3+ concentration, which means that (Y0.94‐xLax)2Ti2O7: Er3+/Yb3+ phosphors may be applicable to different working environment. [ABSTRACT FROM AUTHOR]

It has been one of the hot issues to prepare the red‐emitting Mn4+‐doped fluoride phosphors with highly efficient and waterproofness for warm white‐light‐emitting diodes (WLEDs) by the green and environmentally friendly method. Herein, we design a novel green molten salt route to synthesize K2SiF6:Mn4+ red powder using molten NH4HF2 salt instead of HF liquor as the reaction medium. The results show that KMnO4 and MnF2 could produce Mn4+ in NH4HF2 molten salt through a reduction reaction, and the resulting Mn4+‐doped K2SiF6 exhibited a bright red emission peaked at 632 nm under blue light excitation. The luminescence intensity of the as‐obtained product after immersing into water for 24 hours maintain nearly 100% of that before soaking and emission peak shape remains unchanged. The thermal stability of the sample was evaluated by temperature‐dependent luminescence spectral intensity during heating and cooling. Furthermore, a warm white‐light‐emitting diodes (WLEDs) with an excellent color rendering index (Ra = 87.1), lower correlated color temperature (CCT = 3536K), and high luminous efficacy (116.99 lm·W−1) was fabricated based on blue chip and K2SiF6:Mn4+ and commercial yellow phosphor (Y3Al5O12:Ce3+). [ABSTRACT FROM AUTHOR]

Research on near-infrared (NIR) emission of Tm3+ and Yb3+ co-doped upconversion (UC) materials has accepted many interests owing to delightful features for frontier applications. In this work, we focus on the preparation of pure NIR emission and the improvement of absolute sensitivity (S A) on temperature in Tm3+ and Yb3+ co-doped novel double perovskite Gd 2 ZnTiO 6 (GZT) phosphors. Upon 980 nm excitation, these phosphors perform dramatical NIR emissions, and the integral intensity percentage of NIR emission versus total visible emissions reaches up to 99.88%. A high S A value with 1.7351 K−1 at 473 K for the I 801 /I 650 is obtained via introducing excellent NIR emission. Besides, the S A value of non-thermally coupled levels is higher than that of thermally coupled levels. These results suggest that this kind of UC material may be a candidate for NIR imaging and temperature detection applications. Image 1 High sensitivity based on non-thermally coupled levels is received via utilizing intense NIR emission in Tm3+ and Yb3+ co-doped double perovskite GZT phosphors. • Upconversion properties of Tm3+ and Yb3+ co-doped novel double perovskite Gd 2 ZnTiO 6 phosphors are investigated in detail. • Intense and nearly pure NIR emission with high integral intensity percentage that achieves 99.88% is obtained. • High S A with 1.7351 K−1 at 473 K for N-TCLs is received via utilizing intense near-infrared emission. [ABSTRACT FROM AUTHOR]

The applications in high-power fields of white light-emitting diodes (WLEDs) are restricted due to their poor thermal stability. Transparent Y 3 Al 5 O 12 :Ce3+ phosphor-in-glass (YAG-PiG) provides an efficient way to resolve this problem. In this work, novel transparent Te/Pb-free YAG-PiGs are successfully prepared via a facile screen-printing route. It is revealed that 5 mol% Eu 2 O 3 optimizes the concentration in substrate glass. Slight erosion of YAG particles occurs in the as-prepared samples. With increasing YAG concentration and film thickness, the intensities of photoluminescence spectra of YAG-PiGs increase. The energy transfer from Eu3+ to Ce3+ is greatly suppressed. Superior thermal stability and high quantum efficiency are obtained. The optimal optical performance values in terms of a luminous efficiency of 117.2 lm/W, a correlated color temperature of 5859 K and a color rendering index of 77.2 are achieved in YAG-PiGs. All of the results reveal that the as-prepared YAG-PiGs are promising candidates for high-power WLEDs. [ABSTRACT FROM AUTHOR]

Multilayered inorganic transparent materials have been widely used as laser materials, scintillators and phosphors due to their excellent combined properties or functions. However, owing to the limitation of the current preparation technology, only the ceramics with cubic crystal structure could be fabricated into multilayered transparent materials, which has greatly obstructed the diversity of multilayered transparent materials. Here we report a novel non-cubic multilayered transparent phosphor with a ceramic/glass/ceramic sandwich-like structure prepared by controlling crystallization from Eu 2 O 3 -SrO-Al 2 O 3 -SiO 2 bulk glass. The ceramic thicknesses, total transmittances, emission colors and the fluorescence quantum yields of the samples can be adjusted continuously within a certain range. The multilayered transparent phosphor could be used as a potential candidate for the white LEDs with high color rendering index. It can be anticipated that the controlled crystallization from bulk glass method is a simple, fast, cost-effective and promising synthesis approach to prepare non-cubic transparent materials with ceramic/glass/ceramic structures. [ABSTRACT FROM AUTHOR]

Yellow laser has been widely applied in various fields such as biomedicine, optical communication technology and chip processing. This study focuses on the preparation and characterization of a 3 at.% Dy3+:KGd(WO 4) 2 crystal. The crystal was grown by the top-seeded solution growth method. The absorption spectrum, excitation spectrum, emission spectrum, and fluorescence decay curve were measured at room temperature, and the fluorescence properties of the crystal in the yellow region were explored. Analysis of the absorption spectrum revealed an absorption cross-section σ abs of 4.81 × 10−21 cm2 at 453 nm (E//Y), corresponding to the 6H 15/2 → 4I 15/2 transition. Utilizing the Judd-Ofelt theory, the J-O intensity parameters Ω t , radiative transition probability, fluorescence branching ratio, and radiative lifetime were calculated. The F-L theory was used to calculate the emission cross-section σ em at 575 nm (E//Y), which was found to be 2.43 × 10−20 cm2, along with a fluorescence lifetime τ f of 148.5 μs and a fluorescence quantum efficiency of 80.35% for 4F 9/2. These findings suggest that Dy3+:KGd(WO 4) 2 crystal shows significant promise as a yellow laser material, with the potential to contribute to both commercial and scientific fields. • Dy3+:KGd(WO 4) 2 single crystal was grown successfully by top-seeded solution growth method. • Room temperature absorption spectra were analyzed by the Judd-Ofelt theory and the stimulated emission cross-sections were calculated by the Füchtbauer-Ladenburg equation. • The J-O intensity parameters Ω t (t = 2, 4, 6) of Dy3+:KGd(WO 4) 2 shows higher possibility to emit yellow laser under the excitation of pumping with blue semiconductor lasers. • Dy3+:KGd(WO 4) 2 crystal is a promising candidate for yellow laser. [ABSTRACT FROM AUTHOR]

Temperature detection based on the fluorescence intensity ratio (FIR) has been considered to be a promising technique for non-contact temperature measurement. Unfortunately, the FIR-based temperature sensor materials generally show low temperature sensitivity because of the narrow energy gap between the thermally coupled energy levels. In this work, lanthanide-doped Ba 3 Y 4 O 9 (BYO) upconversion luminescent materials were synthesized in order to explore their potential application in optical thermometer. The crystal structure of the present samples was investigated by XRD and further refined by the Rietveld method, which indicate that the dopant ions successfully enter the host lattice by occupying Y3+ sites. Excited by 980 nm, BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ present high-purity green and blue output colors, respectively. Based on the analysis of emission intensity ratio and pump-power dependence, the upconversion emission mechanisms are systematically investigated. Subsequently, the temperature sensing performances of BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ based on FIR technique are evaluated in the temperature range of 298–573 K under 980 nm excitation. Owing to the different temperature-dependent behaviors of different emission bands and larger energy gaps, the present materials display high sensitivity, good repeatability and excellent stability. The maximum absolute sensitivity of BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ reach as high as 79.62 × 10−4 K−1 and 193.51 × 10−4 K−1, respectively. Among them, the highest sensitivity of BYO:Tm3+/Yb3+ is far higher than those of other optical temperature sensors using the thermally coupled levels based on FIR technique. The results indicate that the present materials are promising for application as optical thermometer in non-contact temperature detection, and using FIR of 5F 1 /5G 6 and 5F 2,3 /3K 8 multiplets (Ho3+), and 3F 2,3 /1G 4 (Tm3+) are feasible methods for accurate temperature detection. [ABSTRACT FROM AUTHOR]

Energy transfer (ET) and cross-relaxation (CR) processes play significant roles in regulating emitting colors and intensity of upconversion (UC) materials. Calculating the coefficients in ET and CR processes can provide visual descriptions for evaluating the UC luminescence properties. Here, we find that those ET and CR processes are responsible for the color-tunable properties in Gd 2 Ce 2 O 7 : Yb3+, Er3+ phosphors. By solving the rate equation, mathematical expressions are established to calculate the ET and CR coefficients based on the experimental UC spectra and lifetimes. The results are benefit to evaluate the efficiencies of ET and CR processes in quantization in different Yb3+ ion concentrations doped samples. The coefficients of ET process arise from 1.05 to 7.93 × 1017 cm3s−1 while those of CR process increase from 2.69 to 72.01 × 1017 cm3s−1 with increasing the Yb3+ ion concentration, which suggest that the CR and ET processes are efficient in Gd 2 Ce 2 O 7 host. Furthermore, potential temperature sensing properties are also evaluated according to the fluorescence intensity ratio of 2H 11/2 and 4S 3/2 levels and the maximal sensitivity (S) is achieved about 0.00337 K−1 at 503 K. This work provides an insight into the evaluation of those UC processes and reveals the capacity in color-tunable and temperature sensing aspects. [ABSTRACT FROM AUTHOR]

A series of Mn4+ doped La 2 MgTiO 6 red-emitting materials with double-perovskite structure and high efficient red emission have been successfully prepared by molten salt assisted method which LiCl acting as molten salt at a relatively low temperature. The effects of the reaction temperature and the usage amounts of LiCl on the structure and photoluminescence properties of phosphors were studied. Experimental results indicate that the synthesis temperature of the Mn4+-doped La 2 MgTiO 6 by molten salt method is only 800 °C while the traditional solid phase method requires 1350 °C. The morphology and particle size of phosphors can be well controlled by adjusting the reaction temperature and the amount of molten salt. The thermal stability and quenching mechanism of phosphors were studied by temperature dependent emission spectra, which demonstrated that LiCl is benefit to improve the thermal stability of the Mn4+activated La 2 MgTiO 6 phosphors. [ABSTRACT FROM AUTHOR]

Current white light emitting diodes (WLEDs) have poor thermal stability and lack red‐light, which restrict their applications in high‐power and high‐color‐rendering‐index solid‐state lighting. YAG glass‐ceramics provide an efficient way to resolve these problems. Herein, novel YAG‐embedded calcium bismuth borate glass‐ceramics (YAG‐GCs) with Eu3+ doping were prepared using a rapid melt quenching technique. The precursor glass exhibits superior YAG refractive index matching and high transmittance. Differential scanning calorimeter simulations verify YAG particles react with the precursor glass. The degree of YAG erosion is slight but monotonously increases with the co‐sintering temperature from 640 to 700°C. The erosion products probably contain YAB (Al3Y(BO3)4), Al3Eu(BO3)4, Bi24B2O39, and Ca12Al14O33 phases, and the Bi ion valence state is maintained during the reaction process. The energy transfer from Ce3+ to Eu3+ is suppressed. The YAG‐GC PL intensities monotonously increase as the co‐sintering temperature decrease from 640 to 700°C and the YAG content increase from 2.5 to 7 wt.%. The optical parameters of a WLEDs packed by YAG‐GCs and blue chips are a luminous efficiency of 105.3 lm/W, correlated color temperature of 3940 K and color rendering index of 70.1. The as‐prepared YAG‐GCs are promising candidates for high‐power, warm WLEDs due to their superior thermal stability, high quantum efficiency, and low cost. [ABSTRACT FROM AUTHOR]

Abstract Upconversion (UC) optical thermometers using the fluorescence intensity ratio (FIR) technique arising from the thermally coupled energy levels (TCLs) are still suffering from low sensitivity owing to the restriction of small energy gap. In the present study, a strategy to strive for superior temperature sensitivity and signal discriminability is employed with the help of non-thermally coupled energy levels (NTCLs). A novel tri-doped Ba 3 Y 4 O 9 : Ho3+/Tm3+/Yb3+ phosphor with rhombohedral symmetry was successfully prepared via a solid-state reaction method, and the temperature sensing performance was evaluated by analyzing temperature-dependent upconversion emission spectra. The emission intensities of both Ho3+ and Tm3+ activators can be almost completely restored to their original values when the temperature of the sample is cooled to room temperature. The temperature-dependent FIR between NTCLs can be fitted well by a derived three-term equation with the correlation coefficient above 99.6%, and the FIR of NTCLs exhibits high temperature sensitivity over a wide temperature range owing to the different temperature responses of the NTCLs. The maximum absolute sensitivity S A and relative sensitivity S R values reaches as high as 0.0552 K−1 and 1.49% K−1, respectively, which are much higher than those of the previously reported bulk UC optical temperature sensing materials. Moreover, the emission bands of NTCLs are well separated, which endows the material a good signal discriminability for temperature detection. Excellent temperature sensing performance is also demonstrated in Er3+/Tm3+/Yb3+ tri-doped Ba 3 Y 4 O 9 , evidencing the validity of this strategy. These results indicate that the present UC materials can be potential candidates for optical temperature sensors, and the present strategy will provide a thought for developing other innovative UC temperature sensing materials. [ABSTRACT FROM AUTHOR]

BaLu 1.94 Al 4 SiO 12 :0.06Ce 3+ (BLASO:0.06Ce 3+ ) green-emitting phosphor could be easily obtained by a conventional solid-state reaction method at 1400 °C. BLASO:0.06Ce 3+ possesses the garnet structure ( Ia 3 ̅ d space group) with the lattice parameter a = 11.9222(0) Å. The emission peak of BLASO:0.06Ce 3+ is located at 513 nm and its photoluminescent quantum yield is determined to be 92.4% at 25 °C when excited at 450 nm. BLASO:0.06Ce 3+ presents excellent thermal properties, with the photoluminescence intensity at 200 °C only decreased to 91.5% of its room temperature value. A phosphor-converted white LED device fabricated by using BLASO:0.06Ce 3+ as the green phosphor exhibits good optical performance with Ra = 88.5, CCT = 3562 K and CIE1931 chromaticity coordinates as (x = 0.4041, y = 0.3951). The results indicate that BLASO:0.06Ce 3+ phosphor has strong potential applications in developing high color rendering, thermally stable, warm-white LEDs. [ABSTRACT FROM AUTHOR]

A series of Er3+, Tm3+, Yb3+ co-doped or tri-doped SrLu2O4 phosphors were synthesized by a high-temperature solid-state reaction method. The crystal structure was characterized by X-ray diffraction technique and further validated by Rietveld refinement. The chemical composition and elemental distribution of tri-doped sample were determined by the energy-dispersive spectrometry. It is worthwhile to note that the upconversion (UC) luminescence of as-prepared samples could be precisely controlled by adjusting the Yb3+ doping concentration and the excitation pump power. A bright UC white light in Er3+/Tm3+/Yb3+ tri-doped SrLu2O4 samples was observed by controlling the intensities of red, green and blue emissions. Under various pump powers in the range of 290-810 mW, the color coordinates could be effectively tuned in a quite broad white region. Particularly, the color coordinate of optimal sample under 630 mW at 980-nm excitation is (0.3336, 0.3244), which is very close to the standard white-light illumination (0.333, 0.333) and the corresponding correlated color temperature is 5442 K. Based on the UC emission spectra and luminescence decay curves, the energy transfer (ET) mechanisms involved in the different UC processes were proposed in detail. The results imply that ET processes of Yb3+ → Er3+, Yb3+ → Tm3+ and Tm3+ → Er3+ worked simultaneously in tri-doped system and produced white UC emissions by means of two- or three-photon processes. The Er3+/Tm3+/Yb3+ tri-doped SrLu2O4 phosphor can be a potential candidate for white UC material in displays, backlights and white-light sources. [ABSTRACT FROM AUTHOR]

A series of Ba 3 Sc 4 O 9 :Ho 3+ /Yb 3+ phosphors were synthesized by a high-temperature solid-state reaction method. The phase purity and upconversion luminescence were characterized by X-ray diffraction and photoluminescence spectroscopy. The sintering temperature and doping concentrations were optimized to obtain the strongest emission intensity. Under 980 nm laser diode excitation, the green (545 nm, 5 F 4 / 5 S 2 → 5 I 8 ) and red (665 nm, 5 F 5 → 5 I 8 ) emissions were observed. The cross-relaxation and back-energy-transfer processes play an important role to adjust the emission intensity ratio of Green/Red at different dopant concentrations. Based on the energy level diagrams, the energy transfer mechanisms are investigated in detail according to the analysis of pump power dependence and luminescence decay curves. The upconversion luminescence properties of the phosphor were evaluated and the results show good color monochromaticity and relatively high upconversion luminescence intensity. The Ba 3 Sc 4 O 9 :Ho 3+ /Yb 3+ can be a good candidate for green upconversion material in display fields and fluorescent labeling. [ABSTRACT FROM AUTHOR]

Tetragonal $$\text {NaY}(\text {MoO}_{4})_{2}$$ (NYM) phosphors co-doped with $$\hbox {Yb}^{3+}$$ and $$\hbox {Tm}^{3+}$$ ions were synthesized through microwave hydrothermal method followed by calcining treatment. Powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and photoluminescence spectra were used to characterize the properties of as-prepared samples. The results show that $$\hbox {Yb}^{3+}$$ / $$\hbox {Tm}^{3+}$$ co-doped NYM displayed bright blue emission near 472 and 476 nm ( $$^{1}\hbox {G}_{4}\rightarrow {}^{3}\hbox {H}_{6}$$ transition), strong near-infrared upconversion (UC) emission around 795 nm ( $$^{3}\hbox {H}_{4}\rightarrow {}^{3}\hbox {H}_{6}$$ transition). The optimum doping concentrations of $$\hbox {Yb}^{3+}$$ and $$\hbox {Tm}^{3+}$$ for the most intense UC luminescence were obtained, and the related UC mechanism of $$\hbox {Yb}^{3+}$$ / $$\hbox {Tm}^{3+}$$ co-doped NYM depending on pump power was studied in detail. [ABSTRACT FROM AUTHOR]

Calcium bismuth borate glasses doped with Eu 3 + were prepared using a rapid melt quenching technique. The general physical properties of the glasses, including density, molar volume, and refractive index, were studied. Furthermore, the structural and optical properties as well as the thermal stability of the glasses were investigated. Eu 3 + melts homogeneously in the glass samples and acts as an effective activator. The largest absorption and excitation peak appears at 465 nm in the spectra, and intense emission occurs at 613 nm. The excited and emitted spectral intensities were observed to first increase and then decrease with increasing Eu 3 + concentration. The glass sample containing 3% (mole fraction) Eu 2 O 3 exhibited the optimum doped concentration, and it was determined that concentration quenching does not result from the non-relaxation of the 5 D 0 energy level. The glass structures were observed to become more compact with an increasing Eu 3 + concentration, and the symmetries decreased. Overall, the glasses maintained the amorphous states. [BO 3 ], [BiO 3 ], [BO 4 ] and [BiO 6 ] units appear in the glass samples, and the variation in the [BiO 6 ] units shows an inflection point. Briefly, the glass sample containing 3% Eu 2 O 3 exhibits many beneficial properties, such as high thermal stability, an appropriate refractive index and the ability to match the blue-light emission of LED chips. The glass therefore expected to be as candidate for white light emitting diode glass ceramic applications. [ABSTRACT FROM AUTHOR]

Pr3+ doped Al 2 O 3 –CaO based glasses were excellent candidate optical gain mediums for visible solid-state lasers due to its wide transmittance region and excellent mechanical properties. However, poor glass-forming ability limited its further application in visible fiber laser. In this work, B 2 O 3 , GeO 2 , Ga 2 O 3 were employed for modifying the glass-forming ability and lowing the melting temperature of the Al 2 O 3 –CaO based glasses. By introducing 15 mol% GeO 2 and Ga 2 O 3 , the thermal stability ΔT were enlarged to be 199 and 264 °C, respectively. The influence of glass composition on the fluorescence characteristic of Pr3+ were systematically investigated. For lower doping concentration, different multiphonon relaxation rare of 3P 0 and 1D 2 energy levels accounting for the different fluorescence spectra of Pr3+ doped Al–Ga, Al–Ge and Al–B glasses, while for the higher doping concentration, cross relaxation processes lead to the fluorescence was gradually dominated by the transition of 3P 0 with increasing Pr3+ concentration. [ABSTRACT FROM AUTHOR]

Upconversion materials with high green color purity are considered to have greater potential in the development and manufacturing of modern optoelectronic devices. However, the generation of high green color purity in Er3+-Yb3+ ions doped upconversion materials is usually a great challenge. Herein, we develop a series of Er3+ singly doped, and Er3+-Yb3+ co-doped La 4 Ti 9 O 24 phosphors with high green color purity under 980 nm irradiation. The green emission of the phosphor was not changed by increasing Yb3+ concentrations, and the material exhibited excellent color purity. We found that low phonon energy and layered structure are the main causes of high green color purity by analyzing Raman spectrum and crystal structure. Based on CIE chromaticity estimates from 1931 in terms of coordinates, dominant wavelength, and color purity, La 4 Ti 9 O 24 : 3 mol% Er3+ and La 4 Ti 9 O 24 : 3 mol% Er3+-16 mol% Yb3+ presents the color purity of 95.14% and 96.04%, respectively. • Titanate upconversion luminescent materials were synthesized via a conventional high-temperature solid state approach. • The La 4 Ti 9 O 24 is a direct band gap semiconductor by using the first-principle calculation based on DFT. • La 4 Ti 9 O 24 : 0.03 Er3+ and La 4 Ti 9 O 24 : 0.03 Er3+-0.16 Yb3+ presents the color purity of 95.14% and 96.04%, respectively. [ABSTRACT FROM AUTHOR]

A series of novel SrLu2O4: x Ho3+, y Yb3+ phosphors ( x=0.005-0.05, y=0.1-0.6) were synthesized by a simple solid-state reaction method. The phase purity, morphology, and upconversion luminescence were measured by X-ray diffraction ( XRD), scanning electron microscopy ( SEM), and photoluminescence ( PL) spectroscopy. The doping concentrations and sintering temperature were optimized to be x=0.01, y=0.5 and T=1400°C to obtain the strongest emission intensity. Under 980 nm laser diode excitation, the SrLu2O4:Ho3+, Yb3+ phosphors exhibit intense green upconversion ( UC) emission band centered at 541 nm (5F4,5S2→5I8) and weak red emission peaked at 673 nm (5F5→5I8). Under different pump-power excitation, the UC luminescence can be finely tuned from yellow-green to green light region to some extent. Based on energy level diagram, the energy-transfer mechanisms are investigated in detail according to the analysis of pump-power dependence and luminescence decay curves. The energy-transfer mechanisms for green and red UC emissions can be determined to be two-photon absorption processes. Compared with commercial NaYF4:Er3+, Yb3+ and common Y2O3:Ho3+, Yb3+ phosphors, the SrLu1.49Ho0.01Yb0.5O4 sample shows good color monochromaticity and relatively high UC luminescence intensity. The results imply that SrLu2O4:Ho3+, Yb3+ can be a good candidate for green UC material in display fields. [ABSTRACT FROM AUTHOR]