A new Eu2+ activated, G-type La2Si2O7 phosphor was synthesized successfully via a novel SiC-reduction route. The valence state of the Eu2+ ions was identified with XRD and XPS analysis and the luminescence spectrum presented Eu2+ broad bands. The G-La2Si2O7:Eu2+ (LPS:Eu2+) phosphor exhibited tunable emission colors depending on the excitation wavelength or the Eu concentration, enabling the production of white light. The color tunable property is ascribed to the component ratio of the two specific luminescent centers, Eu(1) and Eu(2). Eu2+ ions prefer to occupy the La3+ crystallographic sites selectively, which was identified by electron paramagnetic resonance (EPR) spectroscopy. Furthermore, the relative emission intensity of the phosphor at 100 °C and 160 °C can maintain 89% and 76% of the value measured at room temperature, which is much better than that of most of Eu2+ doped silicon oxides phosphors. The Eu(1) emission possesses a better fluorescence thermal stability than the Eu(2) emission, and an energy transition from Eu(1) to Eu(2) occurs. This better thermal stability and energy transition have been explained by the schematic configuration coordination. A w-LED device was fabricated by combining the prepared La2Si2O7:Eu2+ and commercial BaMgAl10O17:Eu2+ phosphors with a 365 nm n-UV chip. The w-LED device generates white light (color rendering index Ra = 93.9), and its CIE chromaticity coordinates and correlated color temperature (CCT) are (x, y) = (0.3429, 0.3523) and 5090 K, respectively. These results suggest that LPS:Eu2+ has a great potential for use in UV-LED-driven white emitting diodes.

The luminous efficiency of radiation (LER) and colour rendering indices (CRIs) are two key technological parameters for white light-emission diodes (WLEDs), but there is always a trade-off between them, especially between LER and R9 (the 9th CRI for red colour). It is therefore necessary to find ways to solve this problem by choosing appropriate red phosphors as well as the phosphor blend. In this work, we attempted to apply both a narrow-band (K2SiF6:Mn4+,KSF) and a broad-band ((Sr,Ca)AlSiN3:Eu2+, SCASN) red phosphors together with a green phosphor (Lu3Al5O12:Ce3+, LuAG) to minimize the trade-off. For a warm white LED with the correlated colour temperature of 3000 K, the combination of a single red phosphor (either KSF or SCASN) and LuAG led to high LERs (92.4 lm W−1 for KSF and 95 lm W−1 for SCASN) but low Ra (average of the first eight CRIs) and R9 (Ra = 60.9 and R9 = −28.2 for KSF; Ra = 83.7 and R9 = 16.6 for SCASN). On the other hand, by using dual red phosphors instead of one, CRIs and even LERs are significantly increased, which is dominantly ascribed to the narrow emission band and the absence of re-absorption of green light of KSF. A superior WLED with LER = 115.4 lm W−1, Ra = 96.9 and R9 = 95.8 was attained when pumping the phosphor blend of (KSF:SCASN:LuAG = 6 : 0.75 : 5.1 in weight ratio) by a blue InGaN LED, which enables it to be used broadly for high quality solid state lighting.

•Phase purity adjustable LSN: Ce and MLSN: Ce phosphor were obtained.•Phase and PL properties can be adjusted by control of alkaline-earth metal ions.•Raw material ration of La/Si played a key role in LSN phase purity.•Warm-light white LEDs fabricated showed relatively low CCT and high CRI.The high correlated colour temperature (CCT) and deficient thermal stability of widely-used YAG:Ce and InGaN white light systems prompt an urgent need for more outstanding succedaneum phosphors, among which Ce-doped La3Si6N11 (LSN:Ce) phosphor has the best performance in the yellow-orange area. However, it still has not gained popularity due to its low quantum efficiency and luminance quality, caused by many factors such as irregular particle morphology and impure chemical composition, especially the difficulty of obtaining a single phase without LaSi3N5 impurity. By doping with different alkaline-earth metal elements and adjustment of the lanthanum/silicon ratio in the raw materials, LSN:Ce and MLSN:Ce (M = Ca, Ba and Sr) phosphors with high purity were synthesised in this work. Compared to Ca and Sr, doping with Ba produced a better result, not only in the crystallisation of the LSN phase, but also in the red shift of the phosphor emission. To further improve the purity of LSN phosphors, the Si/La molar ratio was increased from 2:1 to 1:1.5, and finally resulting in a single phase when the ratio reached 1:1. The white LEDs fabricated with the LSN:Ce & BaLSN:Ce phosphors and InGaN blue light chips had lower CCTs at 3900 K and 3300 K, indicating the great potential of the phosphor for application in high power and display lighting.

Newly emerged phosphor ceramics play key roles in high-brightness solid-state laser lighting technologies. Recently, we developed a translucent CaAlSiN3:Eu2+ red-emitting ceramic, with high quantum efficiency (up to 60%) and thermal robustness (15% higher than the powders). In the current work, detailed structural analyses are carried out by advanced analytical techniques, such as TEM and EPMA, in tandem with the CL, to reveal the correlation between the optical properties and the microstructure, especially the contribution of the interface. It was found that the ceramics consist of many core–shell structured phosphor particles. The shell is coated by a highly crystallized Ca-α-Sialon thin layer to reduce the surface defects. Such core–shell particles are embedded in a non-luminescent matrix of nano-sized Ca-α-Sialon particles tightly surrounded by an amorphous phase, both of which have little influence on the light propagation. Thanks to the unique core–shell structure of phosphor particles and the tight interfaces in the matrix, the bulk CaAlSiN3:Eu2+ ceramic shows record high performance under blue laser irradiation. The output luminous flux increases linearly as the incident power density increases from 20 to 150 W cm−2 with a constant high luminous efficacy of 42.2 lm W−1, demonstrating its promising application in solid-state laser lighting.

In this work we reported novel Yb-doped (Ba1−xSrx)AlSi5O2N7 phosphors showing intense persistent luminescence (PersL) in the visible and near-infrared (NIR) regions simultaneously. Both Yb2+ and Yb3+ were found to be PersL emitters, which presented a broad emission band centered at 664 nm and a sharp emission at 980 nm, respectively. The radiance of PersL in the Ba0.8Sr0.2AlSi5O2N7:Yb phosphor at 60 min after ceasing UV irradiation was 4.82 × 10−3 mW Sr−1 m−2, approximately one-third of the well-known ZnGa2O4:Cr3+ PersL phosphor. The results demonstrate that Yb could be a promising red-to-NIR PersL emitter and more Yb-activated phosphors could be developed for red-to-NIR PersL.

A red-emitting nitridosilicate phosphor, Sr2Si5N8:Eu2+, shows very promising photoluminescence properties but exhibits serious thermal degradation, thus making it difficult to be used practically as a color converter in white light-emitting diodes (wLEDs). To alleviate this problem, we introduce carbon into the Sr2Si5N8 lattice to form thermally robust carbidonitride phosphors (Sr2Si5CxN8−4x/3:Eu2+). The carbon doping, evidenced by a variety of analytical techniques, leads to structural evolutions including lattice shrinkage, shortening of the average bond length of Eu–(C,N), and the removal of Eu3+ ions from the lattice. The photoluminescence intensity and quantum efficiency of phosphors are greatly improved by the carbon doping and reach the maximum at x = 0.5, dominantly owing to the enhanced absorption of Eu2+. Thanks to the increased oxidation resistance of Eu2+ due to the stronger covalency of Si–(C,N) and Sr(Eu)–(C,N) bonds, thermal degradation is significantly reduced from 16 to 0.8% when the carbon doping increases from x = 0 to 1.25. In addition, thermal quenching is also reduced by 10% at 300 °C and the quantum efficiency declines slowly with increasing temperature when carbon is substituted for nitrogen. At 300 °C, the internal quantum efficiencies are 55% and 62% for x = 0 and 0.5, respectively. The enhanced thermal stability of the carbon-doped sample is also confirmed by smaller variations in the luminous efficacy and color coordinates of monochromatic red LEDs.

Luminescent materials play an important role in making solid state white light-emitting diodes (w-LEDs) more affordable home lighting applications. To realize the next generation of solid-state w-LEDs with high color-rendering index (CRI), the discovery of broad band and long emission wavelength luminescent materials is an urgent mission. Regarding this, the oxonitridosilicate Y3Si5N9O with a high nitrogen concentration should be a suitable host material to achieve those promising luminescent properties. In this work, a phase-pure Ce3+-doped Y3Si5N9O was successfully synthesized through the carbothermal reduction and nitridation method. Y3Si5N9O:Ce3+ shows an emission maximum at 620 nm and an extremely broad emission band with a full-width at half-maximum (fwhm) of 178 nm. The electronic and crystal structure calculations indicate an indirect band gap of 2.6 eV (experimental value: 4.0 eV), and identify two Ce3+ sites with different local environments that determine the luminescence properties. The orange-emitting phosphor has the absorption, internal and external quantum efficiencies of 89.5, 17.2, and 15.6% under 450 nm excitation, respectively. The valence state of Ce, cathodoluminescence, decay time, and thermal quenching of the phosphor were also investigated to understand the structure–property relationships.

New garnet phosphors, Lu3−xYxMgAl3SiO12:Ce3+ (x = 0–3), which can be efficiently excited by blue light and emit the yellow-orange light, were developed using the solid solution design strategy combining the chemical unit substitution and the cation substitution. Crystal structures of the four compounds were reported for the first time via the Rietveld refinement of their powder XRD patterns. All phosphors show the general cubic garnet structure with the space group Iad. The specific occupancy of Lu/Y, Al/Mg, Al/Si and O atoms in different positions was identified. The evolution of cell parameters and Y/Lu/Ce–O bond lengths were identified. Photoluminescence properties were evaluated on aspects of emission/excitation spectra, internal/external quantum efficiency and thermal emission stability. Under the 450 nm blue light excitation, the phosphors exhibit bright yellow color emission, peaking in the 575–597 nm spectral range. The internal and external quantum efficiency can reach 83% and 58%, respectively. The emission red-shift in response to the Y/Lu ratio variation was discussed in relation to the local structure evolution. The phosphors are relatively promising to act as wavelength converter of blue light in white light emitting diodes.

Novel Sr2–yEuyB2–2xSi2+3xAl2–xN8+x phosphors were investigated as a function of the boron and aluminum over silicon ratio and as a function of the Eu2+ concentration. Samples were prepared via solid-state reaction synthesis by carefully controlling the synthesis conditions and composition. At high boron and aluminum content, that is, x = 0, a Eu2+ 5d–4f emission is observed of which the maximum shifts from 595 nm for low Eu concentrations (y = 0.005) toward 623 nm for high Eu concentrations (y = 0.5). The samples can be excited by UV or blue light up to ∼475 nm. Substitution of [B2Al]9+ units by [Si3N]9+ units, increasing x up to 0.15, greatly improves the luminescence efficiency up to 46% and shows a very large redshift of the excitation bands with ∼100 nm, while the emission band shifts with ∼10 nm. The shifts are attributed to the lowering of the 5d level as a result of the decreased Eu–N distance upon substitution. Temperature-dependent measurements show that the Eu2+ 5d–4f emission is largely thermally quenched at room temperature for x = 0 due to thermal ionization toward the conduction band, explaining the low luminescence efficiency. The lowering of the 5d level at larger values of x reduces the thermal ionization and consequently increases the thermal stability and quantum efficiency, resulting in strongly luminescent blue-to-orange conversion phosphors that are interesting for light-emitting diode applications.

A red phosphor of Sr2Si5N8:Eu2+ powder was synthesized by a solid state reaction. The synthesized phosphor was thermally post-treated in an inert and reductive N2–H2 mixed-gas atmosphere at 300–1200 °C. The main phase of the resultant phosphor was identified as Sr2Si5N8. A passivation layer of ∼0.2 μm thickness was formed around the phosphor surface via thermal treatment. Moreover, two different luminescence centers of Eu(SrI) and Eu(SrII) in the synthesized Sr2Si5N8:Eu2+ phosphor were proposed to be responsible for 620 nm and 670 nm emissions, respectively. More interestingly, thermal- and moisture-induced degradation of PL intensity was effectively reduced by the formation of a passivation layer around the phosphor surface, that is, the relative PL intensity recovered 99.8% of the initial intensity even after encountering thermal degradation; both moisture-induced degraded external and internal QEs were merely 1% of the initial QEs. The formed surface layer was concluded to primarily prevent the Eu2+ activator from being oxidized, based on the systemic analysis of the mechanisms of thermal- and moisture-induced degradation.

Eu2+ doped La2.5Ca1.5Si12O4.5N16.5 powders have been prepared via a solid-state reaction synthesis and have been studied as a function of the Eu concentration. A large shift of the position of the Eu2+ 5d–4f emission band from 495 to 575 nm was observed with increasing Eu concentration, which changes the emission colour of the phosphors from blue-green for low Eu concentrations towards orange for highly concentrated samples. Similarly, the maximum in the excitation spectrum shifted from 388 to 511 nm. The shifts are due to the two distinct crystallographic sites on which the Eu2+ ions are substituted, which give rise to a high and a low energy emission band. Increased energy transfer at higher Eu concentration from the high to the low energy sites results in a relative increase of the low energy site emission. Temperature dependent luminescence measurements reveal a slight blue shift of the luminescence with increasing temperature due to energy back-transfer and show that the emission is temperature stable with half of the luminescence maintained up to 600 K.

The single-particle-diagnosis approach allows for the fast discovery of novel luminescent materials using powdered samples. This paper reports a new blue-emitting Sr3Si8–xAlxO7+xN8–x:Eu2+ phosphor for solid state lighting and its scale-up synthesis. The structure-, composition-, and temperature-dependent luminescence were investigated and discussed by means of various analytic techniques including single-crystal XRD diffractometer, single-particle fluorescence spectroscopy, FTIR spectra, decay time, low-temperature luminescence, and computed energy level scheme. Sr3Si8–xAlxO7+xN8–x crystallizes in the monoclinic system (space group C2/c, no. 15) with a = 18.1828 (13) Å, b = 4.9721 (4) Å, c = 15.9557 (12) Å, β = 115.994 (10)ο, and Z = 2. The Sr atoms are coordinated to 8 and 6 O/N atoms and located in the voids along [010] formed by vertex-sharing (Si,Al)-(O,N)4 tetrahedra. Phase-pure powder samples of Sr3Si8–xAlxO7+xN8–x:Eu2+ were synthesized from the chemical composition of the single particle by controlling the x value. Luminescence of both a single particle and powders show a broad Eu2+ emission band centered at ∼465 nm and a fwhm of ∼70 nm, under the UV light irradiation. The title phosphor has a band gap of 5.39 eV determined from the UV–vis spectrum, absorption efficiency of 83%, internal quantum efficiency of 44.9%, and external quantum efficiency of 37.4% under the 355 nm excitation. An abnormal thermal quenching behavior is observed in Sr3Si8–xAlxO7+xN8–x:Eu2+ that has a high activation energy for thermal quenching (0.294 eV) but a low thermal quenching temperature (∼370 K), which is ascribed to the partial overlap between the Eu2+ excited energy level and the conduction band of the host.

As an extension of nitride luminescent materials, carbidonitride phosphors are also attracting great attention due to their superior thermal stability. This paper reports a blue-emitting carbidonitride phosphor Al1–xSixCxN1–x:Eu2+ suitable for near ultraviolet (UV) light emitting diodes (LEDs), which is formulated by introducing SiC into AlN:Eu2+. With the introduction of carbon (silicon), the lattice abnormally shrinks along both a- and c-axes at low x values (x ≤ 0.08), due to the formation of a dense interlayer for accommodating the luminescence center Eu2+. Both of the Raman spectra and solid state NMR spectroscopy show that both Si and C are dissolved in the AlN lattice. A single blue emission band (λem = 472–477 nm) is observed for compositions of x > 0.05 by cathodoluminescence measurements. Under the 365 nm excitation, the maximum luminescence is attained for the composition of x = 0.06 that has an external quantum efficiency of 61% and absorption efficiency of 74.4%, which is about 11–15% higher than the corresponding carbon-free nitride sample. The thermal quenching of Al1–xSixCxN1–x:Eu2+ reduces with increasing C (SiC) content, and the sample of x = 0.06 shows a small loss of ∼4.0% in quantum efficiency even at 200 °C. Using this phosphor in a near UV-driven white LED, a superhigh color rendering index of Ra = 95.3 and R9 = 72 as well as a color temperature of 3533 K are achieved.

(Sr,Ca)AlSiN3:Eu2+ (SCASN) is a very promising red phosphor used as a down-conversion luminescent material in solid state lighting. In this study, the moisture-induced degradation of SCASN was comprehensively investigated by treating it under severe conditions with high-pressure water steam. The degradation initiated at 150 °C, and the luminescence of SCASN was quenched quickly, with the powder sample being bleached after the treatment. Both the microstructure and phase changed obviously with oxidation, and the host turned finally into NH3, (Sr,Ca)Al2Si2O8 and Ca(OH)2. Using a variety of spectroscopic, surface and microstructure analytical techniques, the degradation mechanism was clarified and proposed to occur via the oxidant-gas penetration mechanism through the moisture-enhanced oxidation of both the SCASN host and divalent europium. The activation energy for the moisture-induced degradation was about 66.32 kJ mol−1.

The red phosphor of Sr2Si5N8:Eu2+ was synthesized by a solid state reaction. The as-synthesized phosphor powders were post-treated in a N2 atmosphere. The prepared samples were analyzed by XRD, FE-SEM, TG-DTA, FT-IR, zeta potential, cathodoluminescence (CL), photoluminescence (PL), quantum efficiencies (QEs), and temperature-dependent PL and QE techniques. After the thermal treatment in N2, it was found that the N2-treatment caused a negligible influence on the phase purity and particle morphology; the surface of the phosphor particle became more hydrophilic; the isoelectric point (IEP) of the suspension containing phosphor powder shifted to a higher pH value; the edge area (formed surface layer) of the phosphor particle had lower CL intensity than the inner part but it inhibited the surface damage caused by e-beam irradiation; more significantly, the formed surface layer plays a passivating role in preventing the Eu2+ activator from being oxidized, consequently, effectively reducing thermal degradation that deteriorates the PL intensity of the Sr2Si5N8:Eu2+ phosphor.

Solid state laser lighting is superior to white light-emitting diodes in brightness, efficiency and color gamut, which require thermally robust color converters that can be endured by high power blue laser irradiation. Due to this, the application of bulk phosphor-in-glass (PiG) luminescent materials could be of great interest. Here, we report a green-emitting PiG material by co-firing β-Sialon:Eu phosphor powders with the ZnO–B2O3–BaO–Al2O3 glass frits at 630–660 °C for 20–80 min in air. The microstructure, photoluminescence spectra, quantum efficiency, transmittance and thermal quenching of the β-Sialon:Eu PiG materials were investigated. The microstructural analysis indicated that β-Sialon:Eu phosphor powders were uniformly dispersed in the glass matrix without any interfacial reactions. The luminescence efficiency and transparency of the PiG materials were largely dependent on the phosphor concentration, firing temperature and dwell time. Under the blue laser excitation, the optimized PiG sample consisting of 5 wt% β-Sialon:Eu showed a linear relationship between the luminous flux and the incident laser power when the blue laser flux density was below 0.7 W mm−2, indicating its potential applications in solid state laser lighting.

A series of Eu2+- and Mn2+-codoped γ-AlON (Al1.7O2.1N0.3) phosphors was synthesized at 1800 °C under 0.5 MPa N2 by using the gas-pressure sintering method (GPS). Eu2+ and Mn2+ ions were proved to enter into γ-AlON host lattice by means of XRD, CL, and EDS measurements. Under 365 nm excitation, two emission peaks located at 472 and 517 nm, resulting from 4f65d1 → 4f7 and 4T1(4G) → 6A1 electron transitions of Eu2+ and Mn2+, respectively, can be observed. Energy transfer from Eu2+ to Mn2+ was evidenced by directly observing appreciable overlap between the excitation spectrum of Mn2+ and the emission spectrum of Eu2+ as well as by the decreased decay time of Eu2+ with increasing Mn2+ concentration. The critical energy-transfer distance between Eu2+ and Mn2+ and the energy-transfer efficiency were also calculated. The mechanism of energy transfer was identified as a resonant type via a dipole–dipole mechanism. The external quantum efficiency was increased 7 times (from 7% for γ-AlON:Mn2+ to 49% for γ-AlON:Mn2+,Eu2+ under 365 nm excitation), and color-tunable emissions from blue-green to green-yellow were also realized with the Eu2+ → Mn2+ energy transfer in γ-AlON.

Knowing the physicochemical properties of a material is of great importance to design and utilize it in a suitable way. In this paper, we conduct a comprehensive survey of photoluminescence spectra, localized cathodoluminescence, temperature-dependent luminescence efficiency, and applications of Eu2+-doped Sr0.5Ba0.5Si2O2N2 in solid-state lighting. This phosphor exhibits a broad emission band with a maximum at 560–580 nm and a full-width at half maximum of 92–103 nm upon blue light excitation, whereas a dual-band emission (i.e., 470 nm and 550 nm) is observed under electron beam irradiation due to perhaps the intergrowth of BaSi2O2N2:Eu2+ and Sr0.5+σBa0.5−σSi2O2N2:Eu2+ in each phosphor particle. Under 450 nm blue light irradiation, this yellow phosphor exhibits excellent luminescence properties with absorption, internal and external efficiencies of 83.2, 87.7 and 72.6%, respectively. Furthermore, it also possesses high thermal stability, with the quantum efficiency being decreased by only 4.2% at 150 °C and a high quenching temperature of 450 °C. High-efficiency white LEDs using the title phosphor have a luminous efficacy, color temperature and color rendition of ∼120 lm W−1, 6000 K and 61, respectively, validating its suitability for use in solid-state white lighting.

The effects of different calcium sources and the non-stoichiometric calcium addition on the preparation and photoluminescence properties of the red-emitting nitride phosphor CaAlSiN3:Eu2+ were studied. Better crystallinity, enhanced emission intensity, and improved photoluminescence thermal stability of the phosphors were obtained when 10% of the calcium source (Ca3N2) was substituted by CaCO3. The partial substitution for Ca3N2 by CaCO3 resulted in the formation of more transient liquid phases at high temperature, which suppressed the evaporation of Ca/Eu elements to some extent. In order to effectively compensate for the calcium deficiency, excess initial Ca source was added, resulting in a narrower emission band and faster decay rate. Furthermore, the as-synthesized CaAlSiN3:Eu2+ was employed as a red-emitting component to fabricate the two-phosphor-converted white LEDs, which exhibited high color rendering index Ra of ∼98 and warm correlated color temperature of 3000 K, and the narrower emission band with 140% initial Ca content gave an increase of 15% in luminous efficiency.

Discovery of novel luminescent materials is of fundamental importance in the advancement of solid state lighting and flat panel display technologies. In this work, we report a single-particle-diagnosis method for the discovery of new phosphors by just characterizing a luminescent crystalline particle as small as 10 μm in diameter. We explored single-particle fluorescence imaging and spectroscopy techniques to evaluate the photoluminescence of a phosphor particle distinguished from a complex powder mixture and applied a high-resolution single-crystal X-ray diffractometer to determine its crystal structure. The approach enabled us to discover two new phosphors in the Ba3N2–Si3N4–AlN ternary system: Ba5Si11Al7N25:Eu2+ and BaSi4Al3N9:Eu2+. Ba5Si11Al7N25:Eu2+ crystallizes in the space group of Pnnm (no. 58) with a = 9.5923(2), b = 21.3991(5), c = 5.8889 (2) Å and Z = 2, while BaSi4Al3N9:Eu2+ in the space group of P21/C (no.14) with a = 5.8465(4), b = 26.7255(18), c = 5.8386(4) Å, β = 118.897° and Z = 4. The single-particle photoluminescence of Ba5Si11Al7N25:Eu2+ shows yellow emission (λem = 568 nm, fwhm = 98 nm) and a quantum efficiency of 36% under the 405 nm excitation. BaSi4Al3N9:Eu2+ shows blue emission (λem = 500 nm, fwhm = 67 nm) upon the 365 nm excitation.

A phase pure SrSi2O2N2:Eu2+ green phosphor was synthesized by a solid state reaction through careful control of the Sr:Si ratio in the starting powder consisting of SrCO3, Si3N4 and Eu2O3. The thermal degradation of the phosphor was investigated by baking it at high temperatures for 2 h. The surface states of the samples before and after baking were analyzed by SEM, HRTEM, XPS, TGA/DTA, and high temperature in situ X-ray diffraction. The results showed that the thermal degradation became intense when the temperature was higher than 500 °C, and the degradation was caused by the formation of SrSiO3 on the particle surface and the oxidation of Eu2+ to Eu3+. It is suggested that the thermal stability can be enhanced by achieving high crystallinity as well as high phase purity of the phosphor.

The promising green oxynitride phosphor, Ba3Si6O12N2:Eu2+, was synthesized at 1350 °C for 5 hours under a reducing N2/H2 (5%) atmosphere by using the solid-state reaction method. The phase purity was investigated by varying the nominal compositions, and the pure phase was achieved by carefully controlling the Si/Ba and O/Ba ratios. The phosphor displayed a broad excitation band spanning from the ultraviolet (UV) to the blue spectral region, and showed a single symmetrical emission band peaking at 525 nm with a full width at half maximum (FWHM) of ∼68 nm. The as-prepared green phosphor exhibited a small thermal quenching, which remained 90% of the initial emission intensity when measured at 200 °C. The internal and external quantum efficiencies measured under 450 nm excitation were 68 and 38%, respectively. Color temperature-tunable white LEDs with a high color rendering index of Ra = 88–94 were attained by combining the prepared green phosphor and a red phosphor Sr2Si5N8:Eu2+ with a blue LED chip.

Mn2+ doped-AlN red phosphors were prepared by the solid-state reaction method. X-ray diffraction, SEM-EDS, photoluminescence and cathodoluminescence were utilized to characterize the prepared phosphor. Under UV light or electron beam excitation, the AlN:Mn2+ phosphors exhibit a strong red emission centered at 600 nm, which is ascribed to the characteristic 4T1(4G)–6A1(6S) transition of Mn2+. Energy level diagrams were constructed to discuss the photoluminescence and cathodoluminescence processes of the AlN:1% Mn2+ phosphor. The oxygen-related defects in AlN have great influence on the photoluminescence and cathodoluminescence properties of the AlN:1% Mn2+ phosphor. The dependence of brightness on accelerating voltage or electric current, the decay behavior of CL intensity under the electron bombardment, and the stability of CIE chromaticity coordinates were investigated in detail. The results indicate that the AlN:Mn2+ phosphor exhibits a higher brightness, higher color purity, and lower saturation compared to the red Y2O3:Eu3+ phosphor, which gives the AlN:Mn2+ phosphor great potential as a red phosphor for full color FEDs.

Eu2+-doped BaSi6N8O phosphors (Ba1−xEuxSi6N8O, 0.005≤x≤0.2) were synthesized by gas-pressure sintering of the powder mixture of BaCO3, Si3N4, and Eu2O3 at 1750 °C under 0.5 MPa N2. The fired powder consists of a major BaSi6N8O phase and a trace amount of impurity phases. The structural result of the BaSi6N8O powder, refined by the Rietveld method, agrees well with that of single crystals. A wide blue luminescence band peaking at about 500 nm is observed in BaSi6N8O:Eu2+, upon excitation with the ultraviolet light of 310 nm. Although Eu is covalently bonded to six nearest neighbor nitrogen atoms, the luminescence of Eu2+ is not significantly redshifted but shows a very narrow excitation spectrum at high energies. The origin of the short-wavelength luminescence is mainly ascribed to a small crystal-field splitting as a result of extremely long distances between europium and nitrogen ligands in BaSi6N8O:Eu2+.

An Eu2+-activated AlN phosphor was synthesized by firing the powder mixture of AlN, α-Si3N4, and Eu2O3 at 1500−2050 °C for 4 h under 1.0 MPa N2. The phase purity, photoluminescent properties, thermal quenching, and quantum efficiency of the fired samples were investigated. A single AlN wurtzite phase was formed at low doping concentrations of Eu2+ (≤0.1 mol %) and Si (≤2.2 mol %). The introduction of Si is essential for the solubility of Eu2+ in the AlN lattice. Intense blue luminescence with a peak emission wavelength of 465 nm was observed in AlN:Eu2+, when Si was doped simultaneously. This blue phosphor shows a small thermal quenching, retaining the luminance of 90% at 150 °C. The absorption and external quantum efficiencies of AlN:Eu2+ are 63%μ and 46% upon 365 nm excitation, respectively. These results indicate that AlN:Eu2+ has great potential as a blue phosphor for white light-emitting diodes (LEDs) utilizing UV chips as the light source.

•CaAlSiN3:Eu2+ PiG is prepared and discussed for laser lighting technology.•Optical properties of achieved PiG under the blue laser irradiation are clarified.•PiG shows suitability as a red color converter in low incident laser power range.A red-emitting phosphor-in-glass (PiG) material was synthesized by dispersing CaAlSiN3:Eu2+ phosphor powders in a ZnO-B2O3-BaO-Al2O3 glass matrix. A fully densified translucent CaAlSiN3:Eu2+ PiG material was achieved at 650 °C for 40 min with an external quantum efficiency (QE) of 43%, transmittance of 30% at 640 nm and thermal conductivity of 1.12 Wm−1K−1. The CaAlSiN3:Eu2+ particles were distributed in the glass matrix uniformly, and no serious interfacial reactions occurred between the glass matrix and the contained phosphor particles. Under the excitation of blue laser, the maximum luminous flux of CaAlSiN3:Eu2+ PiG sample is 39 lm at the laser flux density of 0.5 W/mm2. Although luminous saturation was observed at high laser incident density, the PiG material would be a promising red color converter for use in white lighting sources pumped by blue laser diodes.Red-emitting phosphor-in-glass (PiG) material, where CaAlSiN3:Eu2+ phosphor powders are uniformly distributed in a ZnO-B2O3-BaO-Al2O3 glass matrix, as a promising red color converter for laser lighting and display technologies.Figure optionsDownload full-size imageDownload high-quality image (248 K)Download as PowerPoint slide

CaAlSiN3:Eu2+ is a very promising red phosphor for high color rendering white light-emitting diodes (wLEDs), but a large part of its emission covers wavelengths longer than 700 nm, which is not detectable by the human eye and thus wasted. Optimizing its luminescence properties will allow us to further enhance the overall optical properties of wLEDs. In this contribution, the luminescence spectra of Ce3+ or Eu2+-activated CaAlSiN3 were tuned and tailored by introducing isostructural Si2N2O to form solid solutions of Ca1−xAl1−xSi1+xN3−xOx (x = 0–0.22). The structural evolutions, microstructure, luminescence, thermal quenching and quantum efficiency of Ca1−xAl1−xSi1+xN3−xOx:RE (RE = Ce3+, Eu2+) were investigated and clarified by using various analytic techniques. Upon introducing Si2N2O into CaAlSiN3, the Ce3+-doped CaAl1−xSi1+xN3−xOx shifted its peak emission from 606 to 575 nm and retained the band width of 145 nm, whereas the Eu2+-doped one blue-shifted its emission from 650 to 638 nm and broadened its band width from 90 to 122 nm, owing to the structural distortion and disorder as well as the band gap broadening associated with the solid solution formation. By combining these phosphors with a blue LED, high color rendering (Ra) and luminous efficacy (η) white LEDs were realized (Ra = 82.5 and η = 104 lm W−1 for the Ce3+-doped phosphors, and Ra = 97 and η = 101 lm W−1 for the Eu2+-doped phosphors).

In this work we reported novel Yb-doped (Ba1−xSrx)AlSi5O2N7 phosphors showing intense persistent luminescence (PersL) in the visible and near-infrared (NIR) regions simultaneously. Both Yb2+ and Yb3+ were found to be PersL emitters, which presented a broad emission band centered at 664 nm and a sharp emission at 980 nm, respectively. The radiance of PersL in the Ba0.8Sr0.2AlSi5O2N7:Yb phosphor at 60 min after ceasing UV irradiation was 4.82 × 10−3 mW Sr−1 m−2, approximately one-third of the well-known ZnGa2O4:Cr3+ PersL phosphor. The results demonstrate that Yb could be a promising red-to-NIR PersL emitter and more Yb-activated phosphors could be developed for red-to-NIR PersL.

A new Eu2+ activated, G-type La2Si2O7 phosphor was synthesized successfully via a novel SiC-reduction route. The valence state of the Eu2+ ions was identified with XRD and XPS analysis and the luminescence spectrum presented Eu2+ broad bands. The G-La2Si2O7:Eu2+ (LPS:Eu2+) phosphor exhibited tunable emission colors depending on the excitation wavelength or the Eu concentration, enabling the production of white light. The color tunable property is ascribed to the component ratio of the two specific luminescent centers, Eu(1) and Eu(2). Eu2+ ions prefer to occupy the La3+ crystallographic sites selectively, which was identified by electron paramagnetic resonance (EPR) spectroscopy. Furthermore, the relative emission intensity of the phosphor at 100 °C and 160 °C can maintain 89% and 76% of the value measured at room temperature, which is much better than that of most of Eu2+ doped silicon oxides phosphors. The Eu(1) emission possesses a better fluorescence thermal stability than the Eu(2) emission, and an energy transition from Eu(1) to Eu(2) occurs. This better thermal stability and energy transition have been explained by the schematic configuration coordination. A w-LED device was fabricated by combining the prepared La2Si2O7:Eu2+ and commercial BaMgAl10O17:Eu2+ phosphors with a 365 nm n-UV chip. The w-LED device generates white light (color rendering index Ra = 93.9), and its CIE chromaticity coordinates and correlated color temperature (CCT) are (x, y) = (0.3429, 0.3523) and 5090 K, respectively. These results suggest that LPS:Eu2+ has a great potential for use in UV-LED-driven white emitting diodes.

Newly emerged phosphor ceramics play key roles in high-brightness solid-state laser lighting technologies. Recently, we developed a translucent CaAlSiN3:Eu2+ red-emitting ceramic, with high quantum efficiency (up to 60%) and thermal robustness (15% higher than the powders). In the current work, detailed structural analyses are carried out by advanced analytical techniques, such as TEM and EPMA, in tandem with the CL, to reveal the correlation between the optical properties and the microstructure, especially the contribution of the interface. It was found that the ceramics consist of many core–shell structured phosphor particles. The shell is coated by a highly crystallized Ca-α-Sialon thin layer to reduce the surface defects. Such core–shell particles are embedded in a non-luminescent matrix of nano-sized Ca-α-Sialon particles tightly surrounded by an amorphous phase, both of which have little influence on the light propagation. Thanks to the unique core–shell structure of phosphor particles and the tight interfaces in the matrix, the bulk CaAlSiN3:Eu2+ ceramic shows record high performance under blue laser irradiation. The output luminous flux increases linearly as the incident power density increases from 20 to 150 W cm−2 with a constant high luminous efficacy of 42.2 lm W−1, demonstrating its promising application in solid-state laser lighting.

The red phosphor of Sr2Si5N8:Eu2+ was synthesized by a solid state reaction. The as-synthesized phosphor powders were post-treated in a N2 atmosphere. The prepared samples were analyzed by XRD, FE-SEM, TG-DTA, FT-IR, zeta potential, cathodoluminescence (CL), photoluminescence (PL), quantum efficiencies (QEs), and temperature-dependent PL and QE techniques. After the thermal treatment in N2, it was found that the N2-treatment caused a negligible influence on the phase purity and particle morphology; the surface of the phosphor particle became more hydrophilic; the isoelectric point (IEP) of the suspension containing phosphor powder shifted to a higher pH value; the edge area (formed surface layer) of the phosphor particle had lower CL intensity than the inner part but it inhibited the surface damage caused by e-beam irradiation; more significantly, the formed surface layer plays a passivating role in preventing the Eu2+ activator from being oxidized, consequently, effectively reducing thermal degradation that deteriorates the PL intensity of the Sr2Si5N8:Eu2+ phosphor.

A red phosphor of Sr2Si5N8:Eu2+ powder was synthesized by a solid state reaction. The synthesized phosphor was thermally post-treated in an inert and reductive N2–H2 mixed-gas atmosphere at 300–1200 °C. The main phase of the resultant phosphor was identified as Sr2Si5N8. A passivation layer of ∼0.2 μm thickness was formed around the phosphor surface via thermal treatment. Moreover, two different luminescence centers of Eu(SrI) and Eu(SrII) in the synthesized Sr2Si5N8:Eu2+ phosphor were proposed to be responsible for 620 nm and 670 nm emissions, respectively. More interestingly, thermal- and moisture-induced degradation of PL intensity was effectively reduced by the formation of a passivation layer around the phosphor surface, that is, the relative PL intensity recovered 99.8% of the initial intensity even after encountering thermal degradation; both moisture-induced degraded external and internal QEs were merely 1% of the initial QEs. The formed surface layer was concluded to primarily prevent the Eu2+ activator from being oxidized, based on the systemic analysis of the mechanisms of thermal- and moisture-induced degradation.

Knowing the physicochemical properties of a material is of great importance to design and utilize it in a suitable way. In this paper, we conduct a comprehensive survey of photoluminescence spectra, localized cathodoluminescence, temperature-dependent luminescence efficiency, and applications of Eu2+-doped Sr0.5Ba0.5Si2O2N2 in solid-state lighting. This phosphor exhibits a broad emission band with a maximum at 560–580 nm and a full-width at half maximum of 92–103 nm upon blue light excitation, whereas a dual-band emission (i.e., 470 nm and 550 nm) is observed under electron beam irradiation due to perhaps the intergrowth of BaSi2O2N2:Eu2+ and Sr0.5+σBa0.5−σSi2O2N2:Eu2+ in each phosphor particle. Under 450 nm blue light irradiation, this yellow phosphor exhibits excellent luminescence properties with absorption, internal and external efficiencies of 83.2, 87.7 and 72.6%, respectively. Furthermore, it also possesses high thermal stability, with the quantum efficiency being decreased by only 4.2% at 150 °C and a high quenching temperature of 450 °C. High-efficiency white LEDs using the title phosphor have a luminous efficacy, color temperature and color rendition of ∼120 lm W−1, 6000 K and 61, respectively, validating its suitability for use in solid-state white lighting.

A phase pure SrSi2O2N2:Eu2+ green phosphor was synthesized by a solid state reaction through careful control of the Sr:Si ratio in the starting powder consisting of SrCO3, Si3N4 and Eu2O3. The thermal degradation of the phosphor was investigated by baking it at high temperatures for 2 h. The surface states of the samples before and after baking were analyzed by SEM, HRTEM, XPS, TGA/DTA, and high temperature in situ X-ray diffraction. The results showed that the thermal degradation became intense when the temperature was higher than 500 °C, and the degradation was caused by the formation of SrSiO3 on the particle surface and the oxidation of Eu2+ to Eu3+. It is suggested that the thermal stability can be enhanced by achieving high crystallinity as well as high phase purity of the phosphor.

(Sr,Ca)AlSiN3:Eu2+ (SCASN) is a very promising red phosphor used as a down-conversion luminescent material in solid state lighting. In this study, the moisture-induced degradation of SCASN was comprehensively investigated by treating it under severe conditions with high-pressure water steam. The degradation initiated at 150 °C, and the luminescence of SCASN was quenched quickly, with the powder sample being bleached after the treatment. Both the microstructure and phase changed obviously with oxidation, and the host turned finally into NH3, (Sr,Ca)Al2Si2O8 and Ca(OH)2. Using a variety of spectroscopic, surface and microstructure analytical techniques, the degradation mechanism was clarified and proposed to occur via the oxidant-gas penetration mechanism through the moisture-enhanced oxidation of both the SCASN host and divalent europium. The activation energy for the moisture-induced degradation was about 66.32 kJ mol−1.

Solid state laser lighting is superior to white light-emitting diodes in brightness, efficiency and color gamut, which require thermally robust color converters that can be endured by high power blue laser irradiation. Due to this, the application of bulk phosphor-in-glass (PiG) luminescent materials could be of great interest. Here, we report a green-emitting PiG material by co-firing β-Sialon:Eu phosphor powders with the ZnO–B2O3–BaO–Al2O3 glass frits at 630–660 °C for 20–80 min in air. The microstructure, photoluminescence spectra, quantum efficiency, transmittance and thermal quenching of the β-Sialon:Eu PiG materials were investigated. The microstructural analysis indicated that β-Sialon:Eu phosphor powders were uniformly dispersed in the glass matrix without any interfacial reactions. The luminescence efficiency and transparency of the PiG materials were largely dependent on the phosphor concentration, firing temperature and dwell time. Under the blue laser excitation, the optimized PiG sample consisting of 5 wt% β-Sialon:Eu showed a linear relationship between the luminous flux and the incident laser power when the blue laser flux density was below 0.7 W mm−2, indicating its potential applications in solid state laser lighting.

New garnet phosphors, Lu3−xYxMgAl3SiO12:Ce3+ (x = 0–3), which can be efficiently excited by blue light and emit the yellow-orange light, were developed using the solid solution design strategy combining the chemical unit substitution and the cation substitution. Crystal structures of the four compounds were reported for the first time via the Rietveld refinement of their powder XRD patterns. All phosphors show the general cubic garnet structure with the space group Iad. The specific occupancy of Lu/Y, Al/Mg, Al/Si and O atoms in different positions was identified. The evolution of cell parameters and Y/Lu/Ce–O bond lengths were identified. Photoluminescence properties were evaluated on aspects of emission/excitation spectra, internal/external quantum efficiency and thermal emission stability. Under the 450 nm blue light excitation, the phosphors exhibit bright yellow color emission, peaking in the 575–597 nm spectral range. The internal and external quantum efficiency can reach 83% and 58%, respectively. The emission red-shift in response to the Y/Lu ratio variation was discussed in relation to the local structure evolution. The phosphors are relatively promising to act as wavelength converter of blue light in white light emitting diodes.

The promising green oxynitride phosphor, Ba3Si6O12N2:Eu2+, was synthesized at 1350 °C for 5 hours under a reducing N2/H2 (5%) atmosphere by using the solid-state reaction method. The phase purity was investigated by varying the nominal compositions, and the pure phase was achieved by carefully controlling the Si/Ba and O/Ba ratios. The phosphor displayed a broad excitation band spanning from the ultraviolet (UV) to the blue spectral region, and showed a single symmetrical emission band peaking at 525 nm with a full width at half maximum (FWHM) of ∼68 nm. The as-prepared green phosphor exhibited a small thermal quenching, which remained 90% of the initial emission intensity when measured at 200 °C. The internal and external quantum efficiencies measured under 450 nm excitation were 68 and 38%, respectively. Color temperature-tunable white LEDs with a high color rendering index of Ra = 88–94 were attained by combining the prepared green phosphor and a red phosphor Sr2Si5N8:Eu2+ with a blue LED chip.

Mn2+ doped-AlN red phosphors were prepared by the solid-state reaction method. X-ray diffraction, SEM-EDS, photoluminescence and cathodoluminescence were utilized to characterize the prepared phosphor. Under UV light or electron beam excitation, the AlN:Mn2+ phosphors exhibit a strong red emission centered at 600 nm, which is ascribed to the characteristic 4T1(4G)–6A1(6S) transition of Mn2+. Energy level diagrams were constructed to discuss the photoluminescence and cathodoluminescence processes of the AlN:1% Mn2+ phosphor. The oxygen-related defects in AlN have great influence on the photoluminescence and cathodoluminescence properties of the AlN:1% Mn2+ phosphor. The dependence of brightness on accelerating voltage or electric current, the decay behavior of CL intensity under the electron bombardment, and the stability of CIE chromaticity coordinates were investigated in detail. The results indicate that the AlN:Mn2+ phosphor exhibits a higher brightness, higher color purity, and lower saturation compared to the red Y2O3:Eu3+ phosphor, which gives the AlN:Mn2+ phosphor great potential as a red phosphor for full color FEDs.