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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.

Spectral modification is crucial for luminescent materials. A variety of strategies have been proposed in the literature, including the selection of activator ions with characteristic electron configurations, the modification of the local crystal field, and the design of an emissive center pair and energy transfer. Eu2+-activated haloapatites are considered as candidates for phosphor converted light emitting devices due to their excellent stabilities, easy preparation, and high efficiency. In this work, single-phased, single-doped (Ba,Sr)5(PO4)3Br:Eu2+ is selected and multiple approaches are applied, leading to multicolor tunabilities of the phosphors, including a crystal field strength controlled spectral shift, occupancy selectivity induced spectral saltation, defect-driven color tunability, and irradiation dependent dynamic chromaticity. In the high Eu2+ concentration doped Ba5−mSrm(PO4)3Br phosphor, the main emission band shifts from 448 to 452 nm with increasing Sr2+/Ba2+ ratio, and a second emission band around the green region uplifts in the binary metal solid solution phosphors, leading to variable emission colors from blue to cyan under near UV excitation. Moreover, oxygen vacancy (VO) defects formed under synthetic reducing conditions endow the bromoapatites with bright self-activated luminescence. In the low Eu2+ concentration doped Ba2Sr3(PO4)3Br, the combination of the broad yellow-green emission from VO and bluish emission from Eu2+ contributes to a full spectrum feature. The gradual increase of Eu2+ concentrations regulates the tunable emission from yellow-green, through white, to blue under short UV excitation. Furthermore, due to the different absorption preferences of these two centers, Ba2Sr3(PO4)3Br:0.01Eu2+ shows white light emission under 254 nm irradiation while blue emission when exposed to 365 nm irradiation. The materials with multicolor luminescence show promising versatile applications in lighting, biological detection and anti-counterfeiting. The cooperative effects of multiple strategies provide a promising approach to regulate the optical properties of inorganic phosphors.

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.

Due to the wide compositional variability and structural tolerance, Eu2+-doped whitlockite β-Ca3(PO4)2 (TCP)-type phosphors with different visible emissions have been realized by manipulating the chemical compositions. However, the site preference of the dopant Eu2+ at the multi-cation sites has been a dispute recently. In this study, a combination of experimental and theoretical calculations was applied to identify the preferential occupancy and variable optical behavior of Eu2+ through the evolution of Ca10.5−0.5xKx(PO4)7 (0 ≤ x ≤ 1) isostructures. Both spectral analysis and theoretical calculations reveal that Eu2+ prefers to occupy the loose Ca(4) sites and produce a narrow band emission around 420 nm. Moreover, a continuous increase in the K content compels the redistribution of dopants from the Ca(4) into the Ca(3) site, resulting in an abrupt spectral shift to 470 nm. Moreover, a vacancy defect repair effect was proposed for the enhancement in the luminescence of Ca10.5−0.5xKx(PO4)7:Eu2+, in which the incorporation of K+ repaired the half-unoccupied Ca(4) sites and benefitted the reduction of Eu3+ to Eu2+. Moreover, to further prove the significant vacancy repair and dopant redistribution effects, Na+- and Li+-doped systems were investigated. In addition, together with the reported Sr2+- or Gd3+-doped systems, the preferential occupancy and saltatory spectral variations of Eu2+ in whitlockite-type phosphors were uniformly clarified by cationic modification events.

With outstanding green-to-red spectral conversion ability, CaS:Eu2+ is notorious for its poor chemical and thermal stabilities, which seriously limit its practical applications. Herein, we structure core–shell CaS:Eu2+@CaZnOS phosphors by a convenient solid-state method. The oxysulfide protection layer was formed due to inward incorporation of ZnO into the surface lattice of the CaS substrate. As a result, the surface modified chalcogenide red phosphor shows super stability toward acidic/basic solutions and retains its brightly emissive activity in aqueous solutions with pH = 1–14. Moreover, it exhibits the best thermal resistance behavior for alkaline earth sulfide-based phosphors up to now, maintaining over 95% of the emission intensity till 150 °C. In addition, the QE of the optimal core–shell phosphor in the green region reached 68.78%, which is elevated by ∼23% compared to that of the starting CaS:Eu2+. This is the first time to simultaneously realize a chemically and thermally stable sulfide phosphor, along with high QE, which exhibits good suitability for solar spectral conversion films and light-emitting diodes for facilitating plant growth.

Phosphor-converted white light-emitting diodes (w-LEDs) have become the new generation of lighting. Several strategies have been introduced to realize a high CRI value for illumination. However, these strategies suffer from new problem(s), such as reabsorption, different deterioration rates among the phosphors, different thermal stability for diverse emission bands, and/or the decrease of quantum efficiency for the phosphor. Therefore, it is desired to develop new phosphors that not only realize a high CRI value for w-LEDs, but also resolve the above problems. In this work, a site-preference driven color-tunable Eu2+-activated K2Ca(PO4)F phosphor was prepared. The color-tunable phosphor exhibits two broad emission bands peaking at 485 and 660 nm upon UV excitation. White emission is realized in K2Ca(PO4)F:0.006Eu2+. The internal and external quantum efficiencies of the white-emitting phosphor are 91.5 and 66.9%, respectively. The phosphor also exhibits good thermal stability, namely, the emission intensity at 423 K maintains >80% of that at room temperature, and the intensity ratio between the two emission bands remains nearly unchanged within 423 K. A white LED device has also been fabricated using a 365 nm LED chip and K2Ca(PO4)F:0.006Eu2+, showing a high color rendering index (Ra = 87.6). These results indicate that the K2Ca(PO4)F:Eu2+ phosphor is a promising candidate for UV-pumped w-LEDs.

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).

Ba1.8–xSrxSiO4:0.1Ce3+,0.1Na+ (x = 0–1.8) phosphors were prepared by a high-temperature solid-state reaction. The emission peaks of Ba1.8–xSrxSiO4:0.1Ce3+,0.1Na+ shift from 391 to 411 nm with increasing Sr2+ content under excitation by a UV light at around 360 nm. Ba0.4Sr1.4SiO4:0.1Ce3+,0.1Na+ phosphor exhibits the best performance of luminescence, whose absolute quantum efficiency is 97.2%, and the emission intensity at 150 °C remains 90% of that at room temperature. The effect of replacing Ba2+ by Sr2+ on the red shift of the emission band and the increase of quantum efficiency (QE) and thermal stability (TS) was investigated in detail based on the Rietveld refinements, Raman spectra, thermoluminescence, and decay curves, etc. The performance of UV chip-based pc-LEDs indicates that Ba0.4Sr1.4SiO4:0.1Ce3+,0.1Na+ can be a promising blue phosphor for white-emitting pc-LEDs.

Many approaches have contributed to improving the luminescence properties of phosphors, including surface coating, direct reduction and charge compensation, which are involved in reducing the inner or surface defects of luminescent particles. In this study, we propose a cation vacancy repair strategy to successfully improve the orange-yellow luminescence properties of the Sr9Mg1.5(PO4)7:Eu2+ phosphor. The main idea of the strategy is that introducing K+ repairs the vacancy at the Mg(1) site according to the formula . The preferred substitution of the large Mg(1) site by K+ is supported by theoretical calculations. As a result, the luminescence of the repaired phosphate phosphor was enhanced by 2.5 times, and the internal and external quantum efficiency significantly increased by 50.5% and 55.4%, respectively. Additionally, the thermal stability was also a little improved. The enhancement mechanisms for luminescence are discussed in detail based on investigations of the microstructure, luminescence spectra, decay curves and concentration using various analysis techniques. We find that low luminescence efficiency is due to the existence of vacancy defects in the phosphor. Through using the repaired Sr9MgK(PO4)7:Eu2+ phosphor, a white LED package demonstrated a low correlated color temperature (∼2900 K), high color rendering index (∼90) and R9 > 91. We expect that the strategy proposed herein would improve luminescence for other phosphors with vacancy defects.

SnO2 micro/nano-structured biscuits had been successfully prepared via egg albumin-assisted sol–gel procedure. The typical sample calcined at 900 °C was pure SnO2 with a tetragonal rutile structure, constructed by the numerous pomegranate seed-like irregular nanoparticles in the range of ~100 to ~400 nm. The complexation of egg albumin and tin ions and the bonding characteristics of functional groups had been confirmed. The band gap energy values of samples were apparently higher than the reference value of bulk matter, which could be assigned to a well-known effect that small particles tended to exhibit increased band gaps. It was revealed that with the increase of the calcined temperature the photoluminescence efficiency increased. The sample at 500 °C had the higher photocatalytic activity and the higher mean photo-degradation rate of MO was 88.1 ± 1.2% as compared to other samples, which could be assigned to the lower value of band gap due to the defect levels in the band gap from the impurities formed during the growth and the lower photoluminescence efficiency, beneficial to electrons transfer and reducing the combination of electron and hole, which resulted in better photocatalytic activity.

Photoluminescence quantum efficiency (QE) and thermal stability are important for phosphors used in phosphor-converted light-emitting diodes (pc-LEDs). Li4Sr1+xCa0.97-x(SiO4)2:0.03Ce3+ (-0.7 ≤ x ≤ 1.0) phosphors were designed from the initial model of Li4SrCa(SiO4)2:Ce3+, and their single-phased crystal structures were found to be located in the composition range of -0.4 ≤ x ≤ 0.7. Depending on the substitution of Sr2+ for Ca2+ ions, the absolute QE value of blue-emitting composition-optimized Li4Sr1.4Ca0.57(SiO4)2:0.03Ce3+ reaches ∼94%, and the emission intensity at 200 °C remains 95% of that at room temperature. Rietveld refinements and Raman spectral analyses suggest the increase of crystal rigidity, increase of force constant in CeO6, and decrease of vibrational frequency by increasing Sr2+ content, which are responsible for the enhanced quantum efficiency and thermal stability. The present study points to a new strategy for future development of the pc-LEDs phosphors based on local structures correlation via composition screening.

Eu2+-activated Ba2ZnS3 has been reported as a red phosphor with a broad emission band peaking at 650 nm under blue excitation for white-LED. In this study, Ba2ZnS3:Eu2+, X– (X = F, Cl, Br, I) phosphors doped with halide ions were prepared by traditional high-temperature solid-state reaction. Phase identification of powders was performed by X-ray powder diffraction analysis, confirming the existence of single-phase Ba2ZnS3 crystals without dopant. The corresponding excitation spectra showed an additional broad band in the green region peaking at 550 nm when the phosphor was halogenated except by the smallest F–. It was proved that the green-excitation efficiency successively strengthened from Cl–, to Br–, to I–, which suggested larger halide ions made a greater contribution to the further splitting of the t2g energy level of the doped Eu2+ ions in the host Ba2ZnS3, and the optimized formula Ba1.995ZnS2.82:Eu2+0.005, I–0.18 showed a potential application in solar spectral conversion for agricultural greenho...

Tb3+-doped and Eu2+, Tb3+ co-doped Ca9Y(PO4)7 phosphors were synthesized by conventional solid-state method. Additionally, the luminescence properties, decay behavior and energy transfer mechanism have already been investigated in detail. The green emission intensity of Tb3+ ions under NUV excitation is weak due to its spin-forbidden f-f transition. While Eu2+ can efficiently absorb NUV light and yield broad blue emission, most of which can be absorbed by Tb3+ ions. Thus, the emission color can be easily tuned from cyan to green through the energy transfer of Eu2+→Tb3+ in Ca9Y(PO4)7:Eu2+,Tb3+ phosphor. In this work, the phenomenon of cross-relaxation between 5D3 and 5D4 are also mentioned. The energy transfer is confirmed to be resulted from a quadrupole-quadrupole mechanism.

The red-emitting phosphor Ca0.8 Zn0.2 TiO3 :Pr3+ was synthesized using an ethylene glycol (EG)-assisted hydrothermal method. The effects of additional amounts of and order of adding EG, plus hydrothermal temperature, time, and pH on the composition, morphology and optical properties of the titanate phosphors were studied. The crystalline phases of the titanate phosphors were confirmed to be constituted of a series of co-existing CaTiO3 , Zn2 TiO4 and Ca2 Zn4 Ti16 O38 compounds in various proportions that were visualized using an X-ray diffractometer (XRD). The optical properties of the phosphors were studied using photoluminescence spectra and UV-visible spectroscopy. The results show that the impurities Zn2 TiO4 :Pr3+ and Ca2 Zn4 Ti16 O38 :Pr3+ significantly contributed to the enhancement of an absorption band around 380 nm. The optimum Ca0.8 Zn0.2 TiO3 :Pr3+ phosphor consisting of appropriate amounts of CaTiO3 , Ca2 Zn4 Ti16 O38 and Zn2 TiO4 in three phases was achieved by controlling the hydrothermal conditions, and the obtained red phosphor exhibited the highest red emission (1 D2 → 3 H4 transition of Pr3+ ) with an ideal chromaticity coordinate located at (x = 0.667, y = 0.332) under 380 nm excitation.

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.

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.

A series of Ca2Sr(PO4)2:Ce3+,Mn2+,Na+ phosphors were synthesized by a high-temperature solid-state reaction. Under ∼320 nm excitation, the Ce3+ and Mn2+ co-doped phosphors exhibit two emission bands peaking at 370 and 645 nm, which originate from 5d–4f and 3d–3d transitions of Ce3+ and Mn2+, respectively. Luminescence properties, diffuse reflectance spectra, and decay curves indicate that energy transfer (ET) occurs from Ce3+ to Mn2+, and the ET efficiency reaches its maximum (91%) at an Mn2+ content of 0.35. The diffuse reflectance spectrum shows that the co-doped phosphors have strong absorption around 320 nm, which is good for the anti-aging ability of an agricultural film. The absolute quantum efficiency of the Ca1.6Sr(PO4)2:0.15Ce3+,0.10Mn2+,0.15Na+ phosphor is ∼94%. And the co-doped phosphors exhibit good stability in water. Therefore, Ca2Sr(PO4)2:Ce3+,Mn2+,Na+ phosphors have potential application as a light conversion material in agricultural films.

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.

A series of color-tunable Ce3+ single-doped and Ce3+, Mn2+ codoped Ca2.5Sr0.5Al2O6 phosphors were synthesized by a high-temperature solid-state reaction. The crystal structure, luminescent properties, and energy transfer were studied. For Ca2.5Sr0.5Al2O6:Ce3+ phosphors obtained with Al(OH)3 as the raw material, three emission profiles were observed. The peak of photoluminescence (PL) spectra excited at ∼360 nm shifts from 470 to 420 nm, while that of the PL spectra excited at 305 nm stays unchanged at 470 nm with the increase of Ce3+ content. Furthermore, the peak of PL spectra is situated at 500 nm under excitation at ∼400 nm. The relationship between the luminescent properties and crystal structure was studied in detail. Ce3+, Mn2+ codoped Ca2.5Sr0.5Al2O6 phosphors also showed interesting luminescent properties when focused on the PL spectra excited at 365 nm. Obvious different decreasing trends of blue and cyan emission components were observed in Ca2.5Sr0.5Al2O6:0.11Ce3+,xMn2+ phosphors with the incre...

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.

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.

In this study, we used HF (as good solvent) to dissolve K2GeF6 and K2MnF6 and added ethanol (as poor solvent) to cause ultrafast self-crystallization of K2GeF6:Mn4+ crystals, which had an unprecedentedly high external quantum efficiency that reached 73%. By using the red phosphor, we achieved a high-quality warm white light-emitting diode with color-rendering index of Ra = 94, R9 = 95, luminous efficacy of 150 lm W–1, and correlated color temperature at 3652 K. Furthermore, the good–poor solvent strategy can be used to fast synthesize other fluorides.

An unexpected spectral blue shift of the emission from yellow to green is observed for the solid solution phosphors Sr3−mCamB2O6:Eu2+ (m = 0–3), when larger Sr2+ ions are substituted by smaller Ca2+ ions in Sr3B2O6 lattices. The powder X-ray patterns of all the phases indicate a structural similarity to the end compounds and show a smooth variation of the structural parameters with composition in the full range. The linear structural evolution of the iso-structural Sr3−mCamB2O6 solid solutions obeying Vegard's rule has also been examined and verified by Rietveld refinement, high resolution transmission electron microscopy and Fourier transform infrared spectroscopy. The average bond lengths of the central cations to the coordinating anions and the distortion indexes of the coordination polyhedra are investigated. As a result, the symmetry of the coordination crystal field is found to be higher with increasing Ca content in the solid solutions phosphors, which should be primarily responsible for the continuous blue shift of the emission spectra of Sr2.96−mCamB2O6:0.04Eu2+ with the growth of the m value.

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.