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Eu3+-doped germanate based red emitting phosphors SrGe4O9: xEu3+ (0 ≤ x ≤ 0.5 mol%) were prepared by high-temperature solid-state procedure. Moreover, the Density Functional Theory (DFT) calculation, X-ray diffraction (XRD) Rietveld refinement, scanning electron microscopy (SEM), and photoluminescence (PL) measurement were discussed in detail to fully investigate the crystal structure and PL properties of SrGe4O9: xEu3+. Furthermore, the Judd–Ofelt (J–O) analysis demonstrated that the Eu3+ ions in the SrGe4O9 host possessed lower sites symmetry. In addition, the phosphor SrGe4O9: 0.35%Eu3+ displayed superior thermal stability with PL intensity at 423 K is around 90% of its initial value at 298 K. As a result, the white light emitting diodes (WLED) device based on SrGe4O9: 0.35%Eu3+ achieved an expected result of a correlated color temperature (CCT) of 4573 K and a color rendering index (CRI) of 80.8 under a voltage of 3 V and a driven current of 20 mA. [ABSTRACT FROM AUTHOR]

In this study, SrMoO 4 :Tb3+ phosphors were successfully synthesized for a single-band ratiometric (SBR) thermometry utilizing the redshift of CTB. The SrMoO 4 :Tb3+ phosphors have a tetragonal system owing to I 4 1 /a space group and irregular microparticles possessing a mean size of 20 μm. The incorporation of Tb3+ ions into the SrMoO 4 matrix lattice leads to a reduction in the bandgap energy owing to occurrence of defects level in gap-band. Thermal quenching concentration of Tb3+ is 1%, due to the dipole-dipole interaction between Tb3+ and Tb3+ ions. This study observed an interesting redshift in the edge of the CTB with increasing temperature, which can be explained using the configurational coordinate diagram. This phenomenon can be utilized to construct this SBR temperature measurement strategy by selecting appropriate excitation peaks or bands with different thermal responses. The study also demonstrated that SrMoO 4 : 1%Tb3+ has higher S a value of 13.31 × 10−2 K−1 @573 K and S r value of 3.54 K-1@298 K in optical thermometry, making it a suitable candidate for optical temperature measurement. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have exhibited tremendous potential in spectroscopic technology, promoting the demand of developing novel NIR materials with excellent properties. In this paper, a series of germanate based NIR phosphors Sr 3 ZnGe 5 O 14 : xCr3+ (0 ≤ x ≤ 0.05) were synthesized by high temperature solid state reaction. The X-ray diffraction (XRD), scanning electron microscopy (SEM), Ultraviolet diffuse reflection, photoluminescence spectra and PL decay were measured to analyze the crystal structure, morphology properties and elements composition, PL emission properties and lifetimes of these NIR phosphors. Results demonstrated that phosphors Sr 3 ZnGe 5 O 14 : xCr3+ (0 ≤ x ≤ 0.05) crystallized in a trigonal with a space group of P 321(150) with a broad band gap (E g) of 4.70–4.59 eV. Sample Sr 3 ZnGe 5 O 14 : 0.03Cr3+ with the best PL emission properties showed a good thermal stability with the PL emission intensity remains 69 % of its initial value at 420 K. It's worth noting that the NIR device based on Sr 3 ZnGe 5 O 14 : 0.03Cr3+ displays an impressive electroluminescent emission stability, for example, the electroluminescent emission intensity is still about 92.3 % of its initial value when the NIR pc-LED light up for 18 h. These research results provided an important guidance for developing novel Cr3+ doped germanate based NIR phosphors with excellent thermal and electroluminescent emission stability. [ABSTRACT FROM AUTHOR]

Abstract A series of Bi3+ ions activated blue-emitting phosphors Gd 2-x ZnTiO 6 :xBi3+ (0 ≤ x ≤ 0.015) were synthesized by high-temperature solid-state procedure. The Density Functional Theory (DFT) calculations demonstrated that the host lattice Gd 2 ZnTiO 6 possessed a direct band gap of 3.07 eV which agreed well with the optical band gap of about 3.80 eV obtained from the diffuse reflection spectrum. Moreover, the Gd 2-x ZnTiO 6 :x Bi3+ crystallizes in a monoclinic space group P 2 1 / n (# 14) and the representative Gd 1.9925 ZnTiO 6 :0.0075Bi3+ phosphor presents an irregular crystal shape with smooth surface, clear edges and corner. All of them emit bright blue light with the emission peak at 419 nm under 375 nm excitation and the optimum Bi3+ ion doping concentration is 0.0075. In addition, the thermal quenching properties and PL decay test show that the Gd 1.9925 ZnTiO 6 :0.0075Bi3+ possess good thermal stability and an efficient energy transfer between Bi3+ ions. Finally, we explored the application of Gd 1.9925 ZnTiO 6 :0.0075Bi3+ phosphor by fabricating the warm pc-WLED device. Notably, the device presents good luminescence properties with the International Commission on Illumination (CIE) coordinates of (0.4485, 0.4222), a high color rendering index (CRI) of 89.4 and low corresponding color temperature (CCT) of 2956 K under 60 mA current. Graphical abstract Image 1 Highlights • Gd 2 ZnTiO 6 :Bi3+ were synthesized as blue-emitting phosphors. • Gd 1.9925 ZnTiO 6 :0.0075Bi3+ possess efficient energy transfer between Bi3+ ions. • The Gd 1.9925 ZnTiO 6 :0.0075Bi3+ based WLED presents excellent luminescence properties. [ABSTRACT FROM AUTHOR]

Abstract The Eu3+-doped α-Al 2 O 3 micro/nano-biscuits were prepared via microwave/starch- assisted sol-gel approach. The typical sample had the pure hexagonal α-Al 2 O 3 phase. The solubility limit of Eu3+ ions was ~ 2 mol%. The micro/nano-biscuits consisted of the outer layers paved with nanoparticles of 50–70 nm and inner layers arranged with nanoparticles of 100–200 nm in a brick-upon-tile pattern. The forming mechanism was proposed. Optical bandgap values were apparently lower than that of bulk Al 2 O 3 (~ 8.7 eV), assigned to appearance of some defect levels and incorporation of impurity ions. The critical distance was ∼ 15.95 Å and ET mechanism was the d-d interaction. The integrated strength at 423 K dropped to 68% of the original value at 298 K and the E a was ~ 0.259 eV. Moreover, the CIE coordinate of the typical sample with good thermal stability was close to that of the commercial red phosphor, having promising applications in pc-WLEDs as a red-emitting phosphor. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

The photoluminescence and temperature sensitivities of Ca 3 Y 2 Si 3 O 12 :Pr3+ thermo-phosphors with silico-carnotite structure obtained by solid state reaction method were investigated. Pr3+ ions were accommodated in the A sites having coordination number of 9 in AB 2 C 2 (SiO 4) 3 to replace Y3+ ions. The typical sample consisted of microcrystals with an irregular structure and the surface of particles was smooth, which could enhance the luminescence due to reducing the scattering and non-radiation produced by rough surfaces. The band gap value of typical sample was about 4.01 eV. Dipole-dipole interaction could account for concentration quenching. The two thermometry strategies including normalized intensities from 3P 0 →3H 4 transition and Fluorescence intensity ration (FIR) of 3P 0 →3H 4 /3P 1 →3H 5 transitions were employed for temperature sensing in 298–573 K. The results revealed that Ca 3 Y 2 Si 3 O 12 :Pr3+ thermo-phosphors had good temperature sensitivity performance with maximum S r of 0.59% K−1@573 K and 0.762% K−1@298 K in the above two methods, respectively. Hence, Ca 3 Y 2 Si 3 O 12 :Pr3+ would be a promising candidate in the field of optical thermometry. [ABSTRACT FROM AUTHOR]

• Egg albumin assisted sol-gel synthesis of Eu3+ doped SnO 2 phosphor. • The concentration quenching mechanism was attributed to the dipole-quadrupole interaction type. • SnO 2 : 2%Eu3+ had high relative sensitivity of 3.214 % K−1 at 298 K (2854.42/T2 K−1). • A promising phosphor for possible applications in temperature sensing. SnO 2 : Eu3+ phosphors were prepared via egg albumin assisted sol-gel method. The typical sample SnO 2 : Eu3+ had tetragonal rutile structure. The sample SnO 2 : Eu3+ had irregular lamellar structure and serious agglomeration. The optical bandgap values of samples were in the range of ∼3.92–4.36 eV. When Eu3+ concentration was 2.0 %, concentration quenching of dipole-quadrupole (d-q) interaction type occurred. Based on the non-thermally coupled energy level fluorescence intensity ratio, the sample SnO 2 : 2%Eu3+ had the maximum absolute sensitivity of ∼0.87565 K−1 at 373 K. The relative sensitivity was estimated to be 2854.42/T2 K−1, and the maximum relative sensitivity was 3.214 % K−1 at 298 K, which had great potential application in the field of temperature sensing. [ABSTRACT FROM AUTHOR]

High temperature sensitivity phosphor based on an old material red emitting CaTiO 3 : Pr3+ phosphor prepared via H 3 BO 3 flux assisted solid-state reaction is reported. The typical sample possesses the orthorhombic perovskite phase and no impurity is found. The optical bandgap value is ~3.59 eV. There exists a single red emission with ideal color purity. The average long-afterglow decay time is 87.7s, the average trap depth is 0.76 eV. The maximum absolute sensitivity at 473 K is equal to ~0.0258 K-1 and the maximum relative sensitivity is estimated to be 7.69% K−1 at 298 K with the resolution of 0.26–0.65 K, indicating the suitability of the material for temperature sensitivity application. A possible mechanism for the quenching of 3P j emission at room temperature and the thermal quenching process of 1D 2 level through intervalence charge transfer state are proposed from the configurational coordinate diagram. Image 1 • High temperature sensitivity phosphor based on H 3 BO 3 flux assisted CaTiO 3 : Pr3+. • The CIE chromaticity coordinates are very close to that of the ideal red light. • IVCT state interfered thermometers with maximal S a and S r is ~~0.0258 K-1 and~ 7.69% K−1. • Ranking among the highest ones for inorganic optical thermometric materials reported before. • Providing a promising pathway to develop high optical temperature sensitivity. [ABSTRACT FROM AUTHOR]

Abstract Novel BaGe 4 O 9 :Eu3+ red-emitting phosphors were synthesized by a high-temperature solid-state reaction. The crystal structures, morphological properties, elements analysis, optical properties and fluorescence decay time were investigated systematically. In contrast, the optimal Eu3+-doping concentration is 30 mol% when monitored at 591 nm with a 394 nm excitation. The energy transfer of Eu3+ ions in BaGe 4 O 9 host lattice is dominated by the exchange interaction with the critical distance (R c) of 5.28 Å. As expected, the red-emitting phosphor BaGe 3.7 O 9 :0.3Eu3+ exhibited a better quantum yield (QY) of 57.9% and an excellent lifetime of 2.25 ms. Consequently, the red-emitting phosphors BaGe 3.7 O 9 :0.3Eu3+ revealed a promising performance in warm WLED device with the CIE coordinates of (0.4365, 0.4130), the color temperature (T c) of 3079 K and the color rendering index (R a) of 85.8 under a driven current of 20 mA. These results indicate that the BaGe 4 O 9 :Eu3+ phosphors are prospective candidates as red-light component for warm white light-emitting diodes (WLEDs) devices. Graphical abstract Novel BaGe 4 O 9 :Eu3+ red-emitting phosphors for warm light-emitting diodes were synthesized by a high-temperature solid-state reaction. Image 1 Highlights • Novel BaGe 4 O 9 :Eu3+ red-emitting phosphors were synthesized by a high-temperature solid-state reaction. • The BaGe 4 O 9 :Eu3+ phosphors are prospective candidates as red-light component for warm white light-emitting diodes devices. [ABSTRACT FROM AUTHOR]

SrSnO 3 : Pr3+ phosphors with red long afterglow (LAG)and temperature sensing were prepared by albumin assisted sol-gel method. The typical sample had cubic structure. The mean particle size was about 2.02 μm. The band gap values of samples were in the range of about 4.06–4.09 eV. The luminescent properties and LAG behaviors of SrSnO 3 : Pr3+ phosphors were investigated and the luminescence mechanism of red LAG was discussed. Albumin assisted SrSnO 3 : Pr3+ phosphor with a red long afterglow had an average decay time of 74.25 s. Pr3+ ions not only act as an activator, emitting red long afterglow, but also act as a trap provider. Moreover, the temperature sensing property was studied based on the non-thermal coupling FIR of TE and 3P 0 →3H 4 transition emission. The relative sensitivity was as high as 3580.89/T2. The absolute sensitivity (S a) and relative sensitivity (S r) of SrSnO 3 : 0.5%Pr3+ were 0.0374 K-1 and 4.03% K−1, respectively. Its optical thermometry performance is better than that of most phosphors. It has the potential to be applied in the field of temperature sensing. [Display omitted] • Albumin assisted SrSnO 3 : Pr3+ phosphors with red long afterglow (LAG)and temperature sensing were prepared. • Pr3+ ions not only act as an activator, but also act as a trap provider, emitting red long afterglow. • The relative sensitivity was as high as 3580.89/T2. • It has the potential to be applied in the field of temperature sensing. [ABSTRACT FROM AUTHOR]

Sm3+ and Pr3+ ion co-doped phosphors Ca 3 Y 2 Ge 3 O 12 :0.04Sm3+:yPr3+ (0.001 ≤ y ≤ 0.006 mol%) were synthesized by high tempereture calcination process. The XRD results showed that samples Ca 3 Y 2 Ge 3 O 12 :0.04Sm3+:yPr3+ (0.001 ≤ y ≤ 0.006) were matched well with the standard profile Ca 3 Y 2 Ge 3 O 12 (PCSD No. 27–0092) which possessed a cubic structure with the space group I a-3d (230), and these synthesized samples exhibited irregular particles with large size of about 40 μm. The photoluminescence (PL) study demonstrated that the co-doped Pr3+ ions could improve the PL properties through the energy transition (ET) process between Pr3+ ions and Sm3+ ions, leading to a smaller liftimes of Ca 3 Y 2 Ge 3 O 12 :0.04Sm3+:0.003Pr3+ than Ca 3 Y 2 Ge 3 O 12 :0.04Sm3+. The optimum Pr3+ ions doping concentration was y = 0.003 and the CIE coordinates (0.5249, 0.4730) of Ca 3 Y 2 Ge 3 O 12 :0.04Sm3+:0.003Pr3+ lied in red light region. Notably, sample Ca 3 Y 2 Ge 3 O 12 :0.04Sm3+:0.003Pr3+ exhibited better thermal stability and larger activation energy (E a) by compariton of Ca 3 Y 2 Ge 3 O 12 :0.04Sm3+. Finally, the WLED device based on Ca 3 Y 2 Ge 3 O 12 :0.04Sm3+:0.003Pr3+, (Ba, Sr) 2 SiO 4 : Eu2+ and an ultraviolet chip of 395 nm exhibited a low correlated temperature (CCT) of 3929 K and a color rendering index (R a) of 89. Image 1 • Pr3+ can improve PL properties of Ca 3 Y 2 Ge 3 O 12 :0.04Sm3+:0.003Pr3+. • Phosphor Ca 3 Y 2 Ge 3 O 12 :0.04Sm3+:0.003Pr3+ exhibited a splendid thermal stability. • Ca 3 Y 2 Ge 3 O 12 :0.04Sm3+:0.003Pr3+ based WLED exhibited a low CCT and a high R a. [ABSTRACT FROM AUTHOR]

CaSnO 3 : Pr3+ phosphor for new application in temperature sensing was investigated. CaSnO 3 : 0.3%Pr3+ had distorted orthorhombic perovskite structure and Pr3+ occupied Ca2+ sites due to their similar ionic radii. CaSnO 3 : 0.3%Pr3+ had spherical particles with mean size of 0.816 μm. The electric dipole−dipole interaction could explain the concentration quenching mechanism. The chromaticity coordinates were (0.1324, 0.3847), located in greenish-blue region and the average afterglow decay time was 60.2 s for CaSnO 3 : 0.15%Pr3+, which had potential applications for LED and emergency lighting. CaSnO 3 : 0.3%Pr3+ had the activated energy of 0.380 eV. The maximum relative temperature sensitivity for CaSnO 3 : 0.3%Pr3+ was 7.57% K−1 at 298 K and relative sensitivity was as high as 6722.76/T2 K−1, which was better than that of most Pr3+ doped phosphors and had potential application in temperature sensing. Moreover, the possible luminescence and long afterglow mechanisms and thermal quenching process of 3P 0 level through IVCT state were proposed. Unlabelled Image • Pr3+ doped CaSnO 3 phosphor for new application in temperature sensing. • S r value of 6722.7557/T2 K−1 was better than that of most Pr3+ doped phosphors. • CaSnO 3 : 0.3%Pr3+ had spherical particles with mean particle size of 0.816 μm. • τ avg is 60.2 s for CaSnO 3 : 0.15%Pr3+, potential application in emergency lighting. • Possible luminescence and long afterglow mechanisms were proposed. [ABSTRACT FROM AUTHOR]

Enhanced photoluminescence and high temperature sensitivity of a novel Pr3+ doped SrSnO 3 /SnO 2 composite phosphor was investigated. The typical samples had SrSnO 3 and SnO 2 phases and spherical morphology with mean particle size of 421 nm. The presence of SnO 2 phase could contribute to improving crystallinity of SrSnO 3. The optical bandgap values of Pr3+ doped SrSnO 3 /SnO 2 composite phosphors were in the range of ~3.85–~3.88 eV. Enhanced photoluminescence intensity of the typical Pr3+ doped SrSnO 3 /SnO 2 composite phosphor was attributed to the effective energy transfer from host material to Pr3+ ions. The typical samples had the greenish-blue emission. The d-d or d-p interaction could explain the Pr3+–Pr3+ energy transfer mechanism. The activated energy value was 0.206 eV for SrSnO 3 : 0.6%Pr3+ phosphor and 0.429 eV for SrSnO 3 /SnO 2 : 0.16%Pr3+ composite phosphor. The maximum relative sensitivity of SrSnO 3 /SnO 2 : 0.16%Pr3+ was estimated to be 5.727% K−1 at 303 K (5257.83/T2), which was very prominent and excellent, compared with that of SrSnO 3 : 0.6%Pr3+, for temperature sensitivity application. The possible mechanism for the greenish-blue emission and the thermal quenching process of 3P 0 level through IVCT state were proposed from the configurational coordinate diagram. Enhanced photoluminescence and high temperature sensitivity of Pr3+-doped SrSnO 3 /SnO 2 composite phosphor was investigated. Excessive SnO 2 did not quench the Pr3+ luminescence, but enhanced its photoluminescence. The possible mechanism for the greenish-blue emission and the thermal quenching process of 3P 0 level through IVCT state were proposed from the configurational coordinate diagram. The high S r of 5257.83/T2 was obtained. Our work expands the design thought on the optical thermometric material, which may provide a promising pathway to develop high optical temperature sensing. Image 1 • High temperature sensing and enhanced PL of Pr3+ doped SrSnO 3 /SnO 2 composite phosphor. • The CIE chromaticity coordinates are in the region of greenish-blue light. • IVCT state interfered thermometers with the high S r of 5.727% K−1 at 303 K (5257.83/T2). • Ranking among the highest ones for inorganic optical thermometric materials reported before. • Providing a promising pathway to develop high optical temperature sensing. [ABSTRACT FROM AUTHOR]

Two series of Eu3+ ions activated high performance red-emitting phosphors Ba 2(1-x) AGe 2 O 7 : 2xEu3+ (A = Mg, Zn, 0 ≤ x ≤ 0.2) were synthesized by high-temperature solid-state procedure. The research results showed that the host lattice Ba 2 MgGe 2 O 7 possess higher band gap than that of Ba 2 ZnGe 2 O 7 , and all the Ba 2(1-x) MgGe 2 O 7 : 2xEu3+ (BMGO: 2 xEu3+, 0 ≤ x ≤ 0.2) and Ba 2(1-x) ZnGe 2 O 7 : 2xEu3+ (BZGO: 2 xEu3+, 0 ≤ x ≤ 0.2) phosphors crystallized in a tetragonal unit cell with the space group of P 421 m (113). Compared with other phosphors in the same series, the samples BMGO: 0.30 Eu3+ and BZGO: 0.25 Eu3+ presented the highest absorption intensity when monitoring at 616 nm under 395 nm excited, respectively. Moreover, the samples BMGO: 0.30 Eu3+ and BZGO: 0.25 Eu3+ not only exhibited high color purity of 90% and 90.3%, respectively, but also possess excellent thermal stability. Unsurprisingly, the WLED devices based on BMGO: 0.30 Eu3+ and BZGO: 0.25 Eu3+ as the red-emitting components displayed good luminescence properties, especially the color rendering index (CRI, R a) R 9 represented the saturation of colour of illuminated objects exhibited a high value of 89.6 and 82.3, respectively. In contrast, the WLED device based on BMGO: 0.30 Eu3+ as red-emitting phosphors presented better electroluminescence performances than those of BZGO: 0.25 Eu3+ on account of its much favorable crystal structure, PL performance and thermal stability. Image 1 • Ba 2 AGe 2 O 7 : Eu3+ were synthesized as red-emitting phosphors. • BMGO:0.3Eu3+ and BZGO:0.25Eu3+ exhibit excellent color purity and thermal stability. • BMGO:0.3Eu3+ and BZGO:0.25Eu3+ based WLED present excellent luminescence properties. [ABSTRACT FROM AUTHOR]