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Poor water stability is the main problem of commercialized Mn4+-doped fluorides for white light emitting diode (WLED) application. This work proposes a surface engineering strategy to rebuild a Mn4+-free fluoride shell on fluorides to effectively resist the destruction from water molecules. By simple processing using glyoxylic acid (GA) solution, the moisture resistance of the red-emitting fluorides can be significantly improved. The photoluminescence (PL) quantum efficiency (QE) of the surface-engineered K2SiF6:Mn4+ (KSFM-GA) still maintain 98.43% after water immersion for 360 h, in sharp contrary to the untreated one (its PLQE decreases to 59.79%). Additionally, PL intensity of the hydrolysed KSFM can be recovered to 99.1% through the treatment of the reducing GA solution. By using the high-stability KSFM-GA red phosphor, the as-fabricated high-performance warm-WLED device can still maintain 84.6% in luminous efficacy, higher than that (79.6%) with the untreated KSFM, after 500 hours of aging in a high temperature (85 oC) and high humidity (85%) environment.

Tb3+/Eu2+,3+-doped zinc aluminoborosilicate glasses were prepared using a conventional high temperature melt-quenching method. Infrared spectra and physical properties of as-prepared glasses verified that the addition of Tb/Eu causes structural weakness in the glass. Tuning of blue, green, and red emission bands achieves white light for the zinc aluminoborosilicate glasses. The broad blue emission band is attributed to the 5d-4f transition of Eu2+ due to partial reduction of Eu3+ during calcination in ambient atmosphere. The reduction of Eu3+ is related to the formation of Eu Zn • and V Zn '' defects and host alkalinity decreases with the addition of Eu3+. Emission spectra and decay curves confirm energy transfer from Tb3+ to Eu3+ in the zinc aluminoborosilicate glasses, and relative intensities of green and red luminescence can be tuned through concentrations changes of Tb3+ and Eu2+,3+. When the concentrations of Tb3+ and Eu2+,3+ are equal to 6% and 1.2%, respectively, a neutral white light emitting glass is obtained. Furthermore, the white-emitting glass shows very high thermal stability compared to a commercial Y3Al5O12:Ce3+ phosphor. Therefore, luminescence tuning of glasses through changing activator concentrations and energy transfer is expected to achieve high-powered white LEDs.

To pursue green ecological agriculture, long-life functionalized green house is looking for solar spectrum conversions with well spectral match, outstanding thermal and chemical stabilities, excellent anti-photobleaching and UV-conversion performance. CaS:Eu2+-based phosphors are widely known as a candidate for agricultural films with remarkable green-to-red conversion performance while they are also notorious for poor stabilities. In this work, a core-shell structured CaS:Eu2+@CaZnOS:Mn2+ composite phosphor was synthesized by a two-step solid state method. The coating layer of thermally and chemically inert oxysulfide prevents the sulfide core phosphor from hydrophilic, air-sensitive and heat-induced decompositions. Moreover, the addition of Mn2+ in CaZnOS shell qualifies the composite phosphor with strong UV absorption, which contributes to the improvement of the anti-photodegradation of the inner CaS:Eu2+ and the anti-aging of practical polymer films. The additional UV-to-orange red conversion resulting from CaZnOS:Mn2+ further extends the red components for the indoor plants. As a result, this dual UV/green excited and dual red-emitting super stable chalcogenide phosphor can be used as a general spectral conversion for plant cultivation.

Cationic substitution is a prevalent strategy to tune the luminescence spectra of phosphors. In this work, we reported a series of Eu2+-activated whitlockite type Ca7Sr3.5-0.5xAx(PO4)7 (CSPA; A =Li, Na, K) (x = 0–1.00) phosphors. The substitution by Na+ for both half occupied/vacant M(4) site was verified via Raman spectra, Reitveld refinement and HR-TEM, whereas a similar accommodation of K+ into the Ca2Sr(PO4)2 (CSP) host cannot be realized due to the significant size mismatch. A continuous increase of Na+ contents led to the progressively structural contraction, promoting the migration of Eu2+ activator from looser M(4) to other sites, and regulating the luminescence behaviors. Consequently, the gradual red-shift of emission band terminated at a new yellow phosphor Ca7Sr3Na(PO4)7:0.04Eu2+. The cation vacancy repair developed in this work can not only migrate the Eu2+ activator among different cation sites, but also serves as a new strategy for tuning the luminescence properties of phosphor.

A series of emission color tunable Ce3+, Tb3+, and Eu3+ co-doped La2Si2O7 (LSO) phosphors have been prepared via a solid state reaction. The crystal structure, luminescence properties, and thermal stability of the phosphors were studied in this paper. There exists two kinds of energy transfer (ET) modes under UV excitation, namely, electric dipole-dipole interaction for Ce3+→Tb3+ and terbium bridge model [Ce3+→(Tb3+)n→Eu3+] for LSO:Ce3+,Tb3+,Eu3+ system. The emitting color of the phosphors can be tuned from green to yellow and eventually to orange-red through the Ce3+→Tb3+→Eu3+ energy transfer. Although codoping Tb3+ and Eu3+ into La2Si2O7:Ce3+ leads to the reduction of thermal stability, it still remains 80% for LSO:0.05Ce3+,0.8 Tb3+,0.02Eu3+ at 150 °C when compared to that at room temperature. The absolute quantum yield (QY) increases from 71.04% (LSO:0.05Ce3+) to 95.60% (LSO:0.05Ce3+, 0.6 Tb3+), while those of LSO:0.05Ce3+,yTb3+,0.02Eu3+ samples remain more than 70%. These results indicate that the phosphors can be candidates for application in phosphor-converted white light-emitting diodes (pc-WLEDs).

The Pr3+ doped CaTiO3 red emitting phosphor with enhanced PL and ultrahigh temperature sensing was prepared via NaF flux assisted solid-state reaction. All samples had the orthorhombic perovskite phase and no impurity was found. The typical sample mainly had sphere-like morphology with particle size of ∼670 nm. The optical bandgap values were ∼3.62–3.63eV. The Pr3+ quenching content was 0.6 mol% and the ET mechanism for quenching was the d-d interaction with the critical distance of 26.09 A. A certain amount of NaF flux could enhance red emission attributed to 1D2→3H4 transition owing to improving the crystallinity of phosphors and reducing point defects near Pr3+ through the substitution of O2− by F− and Ca2+ by Na+. The energy storage trap (oxygen vacancy) near IVCT state played the key role for trapping electrons, accounting for the LAG emission and the average depth of trap was 0.39 eV. The CIE chromaticity coordinates were very close to that of the ideal red light and the CP was as high as 99.98%. The maximal Sa and Sr was as high as ∼0.015 K-1 and∼ 5.2% K−1, respectively. The thermal induced relaxation between the 3Pj levels and 1D2 level through the IVCT state was supposed to account for the excellent optical temperature sensing. Our work may provide a useful inspiration for developing ultrahigh sensitive optical temperature sensors.

The Eu3+-doped α-Al2O3 micro/nano-biscuits were prepared via microwave/starch- assisted sol-gel approach. The typical sample had the pure hexagonal α-Al2O3 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 Al2O3 (~ 8.7 eV), assigned to appearance of some defect levels and incorporation of impurity ions. The critical distance was ∼ 15.95 A 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.

The designed Ce3+-doped alkaline-earth silicate phosphors CamSr2–m–nBanSiO4:Ce3+,Li+ (CSBS:Ce3+) were synthesized by a high temperature solid-state reaction. The crystal field splitting and the centroid shift from the free ion energy of 5d configuration were approximated from the spectrum for Ca2SiO4, Sr2SiO4 and Ba2SiO4 phosphors. The single-phase purity was checked by means of X-ray diffraction. Here, when the doped concentration of Ca2+ is less than 80% (m ≤ 1.6), we report the structural phase transformation from monoclinic system β-Ca2SiO4 to orthorhombic system α׳-Ca2SiO4. The phosphors excited by near-ultraviolet (NUV) light at wavelengths ranging from 200 to 400 nm demonstrate a broad asymmetric blue emission band. The emission peak wavelength redshifts firstly from 417 nm of Ca2SiO4 to 438 nm of Sr0.3Ca1.6SiO4, and then blueshifts to 411 nm of Sr2SiO4, and the end of 401 nm of Ba2SiO4. These results indicate that the tunable blue-emission of the phosphors can be realized through changing the solid solution components, which has a potential use as a blue component for fabricated precision modulation LEDs light sources and auxiliaries of SSC plastics films for different plant growths. We discuss in detail the possible mechanism and energy diagram of the tunable blue luminescence in CamSr2–m–nBanSiO4:Ce3+,Li+ phosphors.

Ce3+ single-doped Ca3(SiO3)3 phosphors were synthesized by a traditional solid-state reaction at elevated temperature. The phase impurities of phosphors prepared at different conditions were characterized and analyzed and an optimal one was obtained. The synthesis and luminescent properties of the phosphors were studied in detail. As a result, two different emission bands can be observed under excitations at 330 and 360 nm, which peak at 380 and ∼400 nm, respectively. Further analyses of emission spectra reveal that there should exist four different emission bands originating from four Ce3+ luminescence centers on different Ca2+ sites. The phosphor with optimal Ce3+ content [Ca2.82(SiO3)3:0.18Ce3+] exhibits high absolute quantum efficiencies up to 90.1% and 79.5% for emission bands at 380 and 400 nm, respectively. Moreover, the emission intensity of Ca2.82(SiO3)3:0.18Ce3+ at 150 °C remains ∼65% of that at room temperature. The phosphor deserves further investigation for the purpose of application in pc-WLEDs.

Commercial phosphors always require fewer impurities and higher crystallinity, but sometimes it is difficult or strict to synthesize a pure phase compound. Indeed, if the practical application is not influenced, it is acceptable to synthesize a kind of phosphors with diphase matrix that have similar structure and photoluminescence properties. In present work, we designed and synthesized a series of (1–x)BaMSiO4·xBa2MSi2O7:Eu (M = Zn2+, Mg2+) diphase phosphors which contained two phases BaMSiO4 (hexagonal, P63) and Ba2MSi2O7 (monoclinic, C2/c) by a high temperature solid-state reaction in air condition. The structures and luminescence properties related to the phase transform from BaMSiO4 to Ba2MSi2O7 were analyzed carefully. The results show that the self-reduction ability of Eu3+ is not the best in above four compounds, respectively. But it reaches the maximum and gets the green emission under the UV lamp when the matrix is in a proper ratio of two phases, which suggests that the heterostructure between the two crystals (BaMSiO4 and Ba2MSi2O7) improves the self-reduction process of the diphase. The possible mechanism of the tunable europium valence and the luminescent properties in (1–x)BaMSiO4·xBa2MSi2O7:Eu phosphors were discussed in detail.

CaAl12O19: Mn4+ has been reported as a red phosphor with good color purity. A quaternary-doping strategy was adopted to improve the optical properties in this work. Phosphors of general formula Ca1-mAl12-x-y-nO19: xMn4+, yMg2+, mBi3+, nB3+ (CAO:MMBB) were synthesized by high-temperature solid-state method. A broad band deep-red emission from Mn4+ centered at 654 nm was observed, and two strong absorption bands within the ultraviolet range (350–400 nm) and blue-green region peaked at 460 nm were confirmed. The incorporation of co-dopants brought about a remarkable enhancement of the luminescence intensity. The quantum yield of CAO:MMBB reached 84.9%, which is approximately 1.35 times higher than that of as-reported binary-doping phosphors CaAl12-x-yO19: xMn4+, yMg2+ (CAO:MM). The possible mechanism of co-doping Bi3+ and B3+ ions was discussed in detailed. CAO:MMBB phosphor shows a dual application in agriculture either as solar spectral conversion auxiliary in greenhouse plastic films or as a red component in blue-chip based plant growth light emitting diodes (PG-LEDs).

Discovery of highly efficient and thermal stable phosphors is a major topic in phosphor-converted white light-emitting diodes (LEDs). A highly efficient and zero-thermal quenching blue-emitting phosphor is realized in nominal Km-0.4Al11O17+δ:0.2Eu2+, which benefits from rigid aluminate structure with space group P63/mmc and the introduction of trap energy levels. The internal and external quantum efficiencies of optimal nominal K1.6Al11O17+δ:0.2Eu2+ are 97.1% and 61.8%, respectively. The phosphor exhibits zero-thermal-quenching behavior within 150 °C. Further increasing K content results in even better thermal stability, however, lower quantum efficiency. The relationship between luminescence properties and crystal structure was discussed. Results suggest that the blue-emitting phosphor is a candidate for white phosphor-converted LEDs based on near-UV or violet chip.

A series of ZnS:KBr,x%Mn2+ (x = 0–0.25) phosphors with dynamic multicolor luminescence are obtained by simultaneously constructing strong host luminescence and heterochromatic doping emissive center in ZnS lattice. Under a fixed ultraviolet irradiation, the phosphors emit tunable colors ranging from cyan to yellow-orange with increasing x values gradually. Besides, those Mn2+-doped phosphor (x > 0) emits different colors under different UV excitations. After removal of the UV lamp, all ZnS:KBr,Mn2+ phosphors exhibit an orange afterglow that is different from its photoluminescence (PL) color. The dynamic PL and afterglow is associated with the interactions between two PL centers and traps in the material. Therefore, spatially and temporally resolved dynamic multicolor luminescence is realized by tuning doping concentration, excitation wavelength, and observation time, which features the ZnS:KBr,Mn2+ phosphors a great application potential in high-level secure anti-counterfeiting.

Poor humidity resistance is a bottleneck problem to be solved urgently for Mn4+ activated fluoride red phosphors. At present, some strategies such as outer coating, cation exchange (CE), and surface passivation (SP) have been developed, but the effect is limited. The key reason is that the easily hydrolyzed Mn4+ ions on the surface are difficult to be completely removed. With the goal of achieving a significant improvement in the moisture resistance of fluoride, this work proposes a new idea of using the reduction-assisted surface recrystallization (RSRC) strategy to construct a real core-shell structure without Mn4+ in the shell. The quantum efficiency (QE) of the K2SiF6:Mn4+ treated by the RSRC method is 99.95%. After boiling in water, the QE can even be maintained at 96.7%, which is significantly higher than that of the fluorides treated by CE (15.53%) or SP (62.64%) methods. The Mn-free shell is further determined by a combination of in-situ lift-out and STEM-EDX techniques. Finally, the aging results of LED devices in high temperature (85 °C) and high humidity (85%) environments further confirmed that the color stability of the K2SiF6:Mn4+ was significantly improved.

A range of Ca 10.5-1.5 x La x (PO 4 ) 7 :Eu 2+ phosphors were synthesized by high temperature solid state method. Subsequently we studied the crystal structures and luminescent properties through X-ray diffraction, photoluminescence and photoluminescence excitation, diffuse reflection spectra, Raman spectra and decay curves systematically. Based on the special crystal structure of β -Ca 3 (PO 4 ) 2 :Eu 2+ , its emission undergoes a variation from violet–blue to cyan through introducing La 3+ . The substitution of La 3+ for Ca 2+ could form some cation vacancies in Ca(4) sites according to the scheme 3Ca 2+ = 2La 3+ + □ due to the different ion valence, which compels Eu 2+ to migrate from Ca(4) site to other sites. Additionally, the formation of the cation vacancies can further reduce the thermal stability of phosphors.

Nominal composition phosphors BaZnSiO 4 :RE (RE = Eu, Tm, Sm, Yb) were synthesized by the conventional solid-state method in air (oxidizing atmosphere, OA) and under 10%H 2 /90%N 2 flow (reductive atmosphere, RA) conditions, respectively. Self-reduction phenomenon, which is a valence change from trivalent rare-earth ions (RE 3+ ) to corresponding divalent state (RE 2+ ) without reducing agent, were observed in the samples of Eu/Tm/Yb-doped BaZnSiO 4 but have not observed in Sm-doped samples. Compared with RA condition, the ca. percent of the reductive concentration of Eu 2+ /Tm 2+ /Yb 2+ in the phosphors BaZnSiO 4 prepared in OA condition are 21%, 15% and 35%, respectively. It was found that both of BaZnSiO 4 :Eu and BaZnSiO 4 :Tm prepared in air show greatly broad band emission peak at 500 nm under the excitation of ultraviolet (UV), which indicated they are potential phosphors for UV-based LED. The factors which are related to self-reduction degree have been also discussed. The successful synthesis of BaZnSiO 4 :RE 2+/3+ phosphors in air provides a new route to obtain other novel orthosilicate-based materials.

Ce 3+ , Mn 2+ codoped and Ce 3+ , RE 3+ , Mn 2+ (RE 3+ = Tb 3+ , La 3+ , Gd 3+ , Lu 3+ ) codoped Ca 5 (BO 3 ) 3 F phosphors have been synthesized by a high-temperature solid-state reaction. Crystal structure and site occupancy of the doped ions were determined by Rietveld refinement. Photoluminescence (PL) spectra as well as fluorescence lifetimes were investigated. Under the excitation of 360 nm, Ca 5 (BO 3 ) 3 F:Ce 3+ , Mn 2+ phosphors show a strong emission band at 392 nm and a very weak emission band at ∼630 nm, which belong to Ce 3+ and Mn 2+ , respectively. The introduction of Tb 3+ and even non-luminescent ions such as La 3+ , Gd 3+ and Lu 3+ to the Ce 3+ , Mn 2+ codoped phosphors leads to the enhancement of Mn 2+ emission. The analyses of fluorescence lifetimes suggest that there is energy transfer from Ce 3+ and especially Tb 3+ to Mn 2+ . However, Rietveld refinement results indicate that the introduction of RE 3+ ions leads to the adjustment of Mn 2+ ions from Ca(3) site to Ca(2) site, which is the key factor for the enhancement of Mn 2+ emission. The crystal-site engineering is expected to provide a promising route to tune the luminescent properties of phosphors with more than one site for activators.

Thermal stability and quantum efficiency are crucial parameters for phosphors when they act as components in phosphor-converted white light-emitting diodes (pc-wLEDs). Therefore, it is important to explore phosphors with highly thermal stability and quantum efficiency. Blue-emitting Ce3+-activated (Ba1-xSrx)3Y2(BO3)4 phosphors were synthesized through high-temperature solid-state reaction. X-ray powder diffraction suggests the success of complete solid solution in the phosphor series. Scanning electron microscope (SEM) image and elemental mapping suggest uniform distribution of Ba and Sr atoms in the phosphor particles. Rietveld refinement indicates that cell volume decreases with increasing the content of Sr2+, while the related emission peak exhibits a slight blue shift, which implies the existence of remote control effect. Both thermal stability and quantum efficiency increase with the evolution of solid solution from Ba3Y2(BO3)4:Ce3+ to Sr3Y2(BO3)4:Ce3+, which is due to the increase of structural rigidity. The emission intensity of Sr3Y1.94(BO3)4:0.06Ce3+ at 423 K remains ∼56% of the room-temperature value. The internal and external quantum efficiencies of Sr3Y1.94(BO3)4:0.06Ce3+ are ∼93% and ∼67%, respectively. A pc-wLED was fabricated with a 365 nm UV chip, Sr3Y1.94(BO3)4:0.06Ce3+, commercial green phosphor, and commercial red phosphor, which exhibits a color rendering index of 94.5. This work provides an example on the adjustment of luminescent properties through solid solution.

Perovskite quantum dots (QDs) have the sensing applications only in organic solution because of their instability in water. In this communication, we report an ingenious way to detect Cu2+ in aqueous solution based on the CsPbBr3 (CPB) QDs. The idea is that adding strong organic ligand (oleylamine, OAm) to selectively transfer Cu2+ ions from water to cyclohexane to quench fluorescence of CPB QDs. Due to the strong interaction between the amine ligands and the metal ions, OAm in cyclohexane can capture Cu2+ from water to form OAm-Cu2+ complexes at the interface of cyclohexane/water. These Cu2+ complexes can rapidly diffuse into cyclohexane and finally quench PL of the CPB QDs. The linear range, high selectivity, response time and quenching mechanism of the probe were studied.

SnO2: Eu3+ phosphors were prepared via egg albumin assisted sol-gel method. The typical sample SnO2: Eu3+ had tetragonal rutile structure. The sample SnO2: 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 SnO2: 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.

Thermally stable phosphors are crucial for the application in phosphor-converted white light-emitting diodes. This paper reports the evolution of phase compositions in nominal Na2−xAl2B2O7:xEu (x = 0.02–2.0) upon replacing Na atoms by Eu atoms. Eu2+-activated blue-emitting phosphor was discovered through phase segregation combined with related analyses. The structure, phase composition and related luminescent properties were investigated by X-ray powder diffraction, backscattered electron image combined with elemental mapping, cathodoluminescence-combined scanning electron microscope, and temperature-dependent emission spectra, etc. Analyses results suggest that EuBO3 phase segregates upon the gradual replacement of Na by Eu atoms, which is accompanied by phase transformation from Na2Al2B2O7:Eu2+ to NaAl11O17:Eu2+ and dramatic enhancement of blue emission. The broad emission band is peaking at around 470 nm under UV irradiation. The internal quantum efficiencies of nominal Na0.4Al2B2O7:1.6Eu and Na0.2Al2B2O7:1.8Eu are 58.6% and 60.2%, respectively, which contain both NaAl11O17 and EuBO3 phase. The emission intensity for these two samples at 150 °C remains 96% (x = 1.6) and 83% (x = 1.8) of the room-temperature values, respectively.

High quantum efficiency is a vital parameter of phosphors for practical application. An efficient near-UV and blue emitting phosphor Li4SrCa(SiO4)2:Ce3+ was synthesized by a traditional solid-state reaction, and luminescent properties were studied in detail. The Ce3+-activated phosphor can emit both a near-UV light centred at 345 nm and a blue light peaking at 420 nm when Ce3+ occupies the Sr and Ca site, respectively. The internal quantum efficiency (IQE) of Li4SrCa(SiO4)2:0.03Ce3+ is as high as 97% under the excitation at 288 nm, while the external quantum efficiency (EQE) is 66%. The IQE and EQE values of Li4SrCa(SiO4)2:0.03Ce3+ under the excitation at 360 nm are 82% and 31%, respectively.

The red, green and blue (R/G/B) tricolor emitting phosphors Ba 2 ZnSi 2 O 7 co-doped with Ce 3+ and Eu 3+ were synthesized in air atmosphere by a conventional high temperature solid-state reaction technique. All of the excitation spectrum of the phosphor Ba 2 ZnSi 2 O 7 :Ce, Eu showed a strong broad band absorption in the n-UV region whenever monitored by red (630 nm)-emitting or by green (500 nm)- and blue (402 nm)-emitting. Under the excitation of 330 nm, the emission spectrum containing a blue-violet emission band, a green emission and four sharp lines originated from the characteristic transitions of Ce 3+ , Eu 2+ and Eu 3+ ions, of which the relative intensities of the three emission bands could be controlled by the doping concentration of Ce 3+ . The ca. CIE chromaticity coordinates ( x =0.317, y =0.309) of the phosphor Ba 1.94 ZnSi 2 O 7 :0.03Eu,0.01Ce was very close to the standard white ( x =0.33, y =0.33), which suggested that it was a novel single-phased white-light emitting phosphor for LED-based near-UV chip. The mechanisms of energy transfer from Eu 2+ to Eu 3+ via Ce 3+ was also discussed.

The red phosphors Mg2TiO4:Mn4+, Bi3+, Li+ with strong absorption at blue region were synthesized. Through the excitation and emission spectra, diffuse reflection spectra and Raman spectra, it is proved that Bi3+ ion plays a role of sensitizer to the enhancement of optical property, especially the increased excitation intensity of blue light. It is the first time to report about asynchronous increases of different excitation bands with Bi3+ as a sensitizer, primarily resulting from the perturbation of symmetry and lattice vibration along with crystal defect in the host lattice with larger Bi3+ occupied at a small octahedral site of Mg2+. The sensitization of Bi3+ works not only in the case of powder phosphors but also even better in ceramic phosphors. For powder phosphor, the intensity of the blue excitation band of Mg2−2xTi0.999O4:0.1%Mn4+, xBi3+, xLi+ grows to at least 1.5 times than that of Mg2Ti0.999O4:0.1%Mn4+ when x = 0.5%, following with a uplift at about 410 nm. Meanwhile, Mg2TiO4:Mn4+, Bi3+, Li+-based luminescent ceramic manifests with a more than 2.5 times increase as x = 0.8%. The red phosphors with a broad emission band in the pure red light region show a promising application in blue LEDs as a red component.

In this paper, a cyan-emitting phosphor Ca 3 (PO 4 ) 2 :Eu 2+ (TCP:Eu 2+ ) was synthesized and evaluated as a candidate for white light emitting diodes (WLEDs). This phosphor shows strong and broad absorption in 250–450 nm region, but the emission spectrum is prominent at around 480 nm. The emission intensity of the TCP:Eu 2+ was found to be 60% and 82% of that of the commercial BaMgAl 10 O 17 :Eu 2+ (BAM) under excitation at 340 nm and 370 nm, respectively. Upon excitation at 370 nm, the absolute internal and external quantum efficiencies of the Ca 3 (PO 4 ) 2 :1.5%Eu 2+ are 60% and 42%, respectively. Moreover, a white LED lamp was fabricated by coating TCP:Eu 2+ with a blue-emitting BAM and a red-emitting CaAlSiN 3 :Eu 2+ on a near-ultraviolet (375 nm) LED chip, driven by a 350 mA forward bias current, and it produces an intense white light with a color rendering index of 75.

Eu 2+ -doped Li 4 SrCa(SiO 4 ) 2 phosphor was synthesized by a high temperature solid-state reaction. There are two different crystallographic sites, namely, a Sr 2+ site and a Ca 2+ site in the cell of Li 4 SrCa(SiO 4 ) 2 , which can be occupied by Eu 2+ ions and will generate two emission bands. However, three different emission bands were observed in this phosphor. The first one is peaking at 433 nm with the corresponding excitation band at 250–400 nm. The second one is at 584 nm under the excitation at 395 nm, which shows lower emission intensity than that of the blue emission. The third one is at around 615 nm under the excitation at 460 nm. Analysis suggests that the 433 nm emission belongs to Eu 2+ on Sr 2+ site, and the 584 nm emission originates from Eu 2+ on isolated Ca 2+ site. The 615 nm emission may be related to Eu 2+ clusters.

Enhanced photoluminescence and high temperature sensitivity of a novel Pr3+ doped SrSnO3/SnO2 composite phosphor was investigated. The typical samples had SrSnO3 and SnO2 phases and spherical morphology with mean particle size of 421 nm. The presence of SnO2 phase could contribute to improving crystallinity of SrSnO3. The optical bandgap values of Pr3+ doped SrSnO3/SnO2 composite phosphors were in the range of ~3.85–~3.88 eV. Enhanced photoluminescence intensity of the typical Pr3+ doped SrSnO3/SnO2 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 SrSnO3: 0.6%Pr3+ phosphor and 0.429 eV for SrSnO3/SnO2: 0.16%Pr3+ composite phosphor. The maximum relative sensitivity of SrSnO3/SnO2: 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 SrSnO3: 0.6%Pr3+, for temperature sensitivity application. The possible mechanism for the greenish-blue emission and the thermal quenching process of 3P0 level through IVCT state were proposed from the configurational coordinate diagram.

High temperature sensitivity phosphor based on an old material red emitting CaTiO3: Pr3+ phosphor prepared via H3BO3 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 3Pj emission at room temperature and the thermal quenching process of 1D2 level through intervalence charge transfer state are proposed from the configurational coordinate diagram.

The red-emitting phosphor CaZnOS:Eu 2+ was synthesized from CaCO 3 , ZnS, Eu 2 O 3 and CeCl 3 by controlling the sintering condition. It was found that Ce 3+ ions can play a role of reductant to contribute to the formation of Eu 2+ in CaZnOS matrix under inert protective atmosphere. While the gas flow changed to H 2 /N 2 , the product turned to CaS easily. XRD, photoluminescence spectra, UV–vis and IR absorption spectra were evaluated to investigate the origin of the distinctions of the optical properties and stabilities between the two divalent europium ions doped phosphors CaZnOS:Eu 2+ and CaS:Eu 2+ . The similarities and differences between them were analyzed.

In this work, we report preparation, characterization and luminescent mechanism of a phosphor Sr 1.5 Ca 0.5 SiO 4 :Eu 3+ ,Tb 3+ ,Eu 2+ (SCS:ETE) for white-light emitting diode (W-LED)-based near-UV chip. Co-doped rare earth cations Eu 3+ , Tb 3+ and Eu 2+ as aggregated luminescent centers within the orthosilicate host in a controlled manner resulted in the white-light phosphors with tunable emission properties. Under the excitation of near-UV light (394 nm), the emission spectra of these phosphors exhibited three emission bands: one broad band in the blue area, a second band with sharp lines peaked in green (about 548 nm) and the third band in the orange–red region (588–720 nm). These bands originated from Eu 2+ 5d→4f, Tb 3+ 5 D 4 → 7 F J and Eu 3+ 5 D 0 → 7 F J transitions, respectively, with comparable intensities, which in return resulted in white light emission. With anincrease of Tb 3+ content, both broad Eu 2+ emission and sharp Eu 3+ emission increase. The former may be understood by the reduction mechanism due to the charge transfer process from Eu 3+ to Tb 3+ , whereas the latter is attributed to the energy transfer process from Eu 2+ to Tb 3+ . Tunable white-light emission resulted from the system of SCS:ETE as a result of the competition between these two processes when the Tb 3+ concentration varies. It was found that the nominal composition Sr 1.5 Ca 0.5 SiO 4 :1.0%Eu 3+ , 0.07%Tb 3+ is the optimal composition for single-phased white-light phosphor. The CIE chromaticity calculation demonstrated its potential as white LED-based near-UV chip.

The establishment of an approach to design tunable yellow emission through singly doped single-phased phosphors to obtain white LED-based InGaN chip was reported. BaY 2- x S 4 : x Ho 3+ phosphors were prepared by the high temperature solid state reaction and characterized by X-ray diffraction and photoluminescence spectra. Under the excitation of 465 nm, the emission spectra of these phosphors exhibited three sharp emission lines peaked at about 492, 543 and 661 nm of Ho 3+ corresponding to 5 F 3 , 5 F 4 ( 5 S 2 ) and 5 F 5 → 5 I 8 transitions, respectively, with comparable intensities, resulting in a yellow light emission. The luminescence mechanism for Ho 3+ in BaY 2 S 4 was explained.

Effects of ZrO 2 , La 2 O 3 , CeO 2 , Yb 2 O 3 and V 2 O 5 on the crystallization kinetics, microstructure and mechanical properties of mica glass–ceramics were investigated by the differential scanning calorimetry (DSC), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness tester. Results show that bulk crystallization can be obtained by introducing proper nucleation agents into the glass. Both Ozawa method and Kissinger method are suitable for analyzing the crystallization kinetics of mica glass–ceramic. The addition of nucleation agents has little influence on the value of n , keeping two-dimensional crystal growth mechanism. ZrO 2 and V 2 O 5 are best nucleation agents in mica system. The increase of crystallization temperature is helpful for the increase of aspect ratio, and the microstructure of the glass–ceramics becomes interconnected, which contributes the improvement of the machinability of the glass–ceramics. Microhardness ( H v ), cutting energy ( μ 1 ) and machinability parameter ( m ) can be used for estimating the machinability of mica glass–ceramics.

Using ferric-S-methyl-porphyrin as the prototype of heme-containing complexes, we address how to accurately and efficiently carry out density functional studies for systems of biological importance. Our results indicate that GGA and meta-GGA functionals bias the lower spin state by producing levitated frontier orbitals and often fail to provide a correct description of the ground spin state. Also, we propose composite double and triple zeta quality basis sets with polarization functions applied only to the transition metal and electronegative atoms. Accurate structural and electronic properties including DFT reactivity indices have been obtained and significant gain in computational efficiency has been achieved.

Nanophosphor with the nominal composition of Ca 0.8 Zn 0.2 TiO 3 :Pr 3+ , Na + (CZTOPN) was synthesized at relatively low temperature by the sol-gel method. Metal ions were dispersed by citric acid in ethylene glycol solvent and then react with Ti(OC 4 H 9 ) 4 to form sol and gel. The decomposition process of the precursor, and crystallization and particle size of CZTOPN were examined by thermal analysis (TG-DSC), powder X-ray diffraction (XRD), and scan election microscopy (SEM). Results of TG-DSC and XRD reveal that the composition of Ca 0.8 Zn 0.2 TiO 3 :Pr 3+ , Na + changes with the sintering temperature. SEM data indicate that the diameter of particles is under 50 nm even if the sintering temperature increases to 1000 °C. In contrast to a solid state reaction, the excitation spectra of samples synthesized by the sol-gel method shift blue about 10 nm and the emission intensity at 617 nm increases significantly.

A Eu2+ doped LiSrBO3 phosphor has been synthesized by a double-sintering process under a reducing atmosphere on the purpose of searching broad-band red phosphors. LiSrBO3: Eu2+ shows a broad emission band with a maximum at 618 nm under excitation of 460 nm-light, which is due to a large covalency and a high crystal field splitting. Although a phosphor-converted LED was fabricated with the synthesized LiSrBO3: Eu2+ and a 460 nm-emitting InGaN chip, this phosphor cannot be applied in LED until the quantum efficiency is improved.