Oxide Phosphors Research Articles

Photoluminescence properties of Er3+ and Eu3+ ions based on oxide host for optical temperature sensing with high sensitivity

Motivated from increasing demands of non-contact optical temperature sensing, the Yb3+-Er3+ and Eu3+ doped NaY9Si6O26 (NYS) oxide phosphors were designed by high-temperature solid-state reaction method. The phase purity of the as-prepared samples was checked from XRD patterns. For the upconversion luminescence in NYS:Yb3+,Er3+, the optimal Er3+ doping content was determined to be 1 mol%, and the characteristic emission peaks of Er3+ were observed in the region of 500–700 nm. In Eu3+ activated NYS phosphors, it has been found that the emissions originating in 5D1 and 5D0 levels demonstrate different change tendencies in intensity with Eu3+ doping concentration. By studying the temperature-dependent luminescent spectra, it was indicated that the emissions intensities from different excited states of Er3+ change differently with temperature. Two kinds of fluorescence intensity ratio (FIR) strategies were used in NYS:10%Yb3+,1%Er3+, containing thermally-coupled levels and non-thermally-coupled levels. In the NYS:3%Eu3+ phosphor, it was found that the FIR for 577 and 536 nm emissions follows a linear relation with temperature. The high sensitivities in the present phosphors indicate the potential application in optical temperature sensing.

Luminescence spectroscopy of Cr3+ in an oxide: A strong or weak crystal-field phosphor?

Various Cr3+-activated oxide phosphors can be classified into two groups: a strong crystal field group [E(2Eg)ZPL < E(4T2g)ZPL] and a weak crystal field group [E(2Eg)ZPL > E(4T2g)ZPL] from an equality relation of the zero-phonon line (ZPL) energies of 2Eg and 4T2g. Obtaining reliable Racah parameters for the 3d3 ion (Cr3+) usually needs accurate information on the three excited-state ZPL energies, E(2Eg)ZPL, E(4T2g)ZPL, and E(4T1g,a)ZPL. However, an exact determination of such ZPL energies is a very difficult problem. Because of an accumulation with adjacent excited states along with the presence of charge transfer band, this is especially for E(4T1g,a)ZPL. An importance of accurate determination of the excited-state energies to be used in the Racah parameter calculation is discussed in detail with demonstrating a risk of erroneous conclusion of whether Cr3+-activated oxide phosphor belongs to a strong or weak crystal-field phosphor.

Structural and optical studies of cerium doped gadolinium oxide phosphor

This research aims to study the influence of variation of doping concentration on various properties of Ce3+ doped Gd2O3 phosphor. The phosphors (Gd1−xCex)2O3 (0 ≤ x ≤ 0.15) were successfully synthesized by the solution combustion method. The structural and optical properties of the prepared phosphors were studied. Rietveld refinement confirms the formation of the cubic phase. Fourier transform infrared spectra further confirm the formation of the phosphor. It is found that an enhancement in doping concentration of Ce3+ results in the expansion of the crystal lattice, leading to a reduction in crystallite size as well as in the optical band gap. Photoluminescence emission spectra are studied, and the exact emission colour is confirmed using 1931 Commission Internationale de l’Eclairage (CIE) chromaticity coordinates. The prepared phosphor exhibits bluish green emission corresponding to 5d–4f transitions of the trivalent cerium ion and can be used as a promising candidate in optical display applications and LED applications.

Synthesis and luminescence properties of double perovskite Bi3+/Mn4+ co-doped Ca2GdTaO6 phosphor

Bi3+-doped, Mn4+-doped, and Bi3+/Mn4+ co-doped oxide phosphors Ca2GdTaO6 (CGT) are prepared via the solid-state reaction method. The phase purity and morphology of CGT: Bi3+, Mn4+ phosphors are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The band structure and density of state for CGT are calculated based on density functional theory (DFT). The bandgap of the CGT host is 3.72 eV. The photoluminescence (PL) and photoluminescence excitation (PLE) spectra of CGT: Bi3+ and CGT: Mn4+ is investigated in detail. The overlap between the emission spectra of Bi3+ and the excitation of Mn4+ proves energy transfer from Bi3+ to Mn4+. The corresponding mechanism of the Bi3+→Mn4+ energy transfer process is investigated in detail based on the decay time and PL spectra. Energy transfer efficiency is also calculated. Upon excitation at 320 nm, Bi3+/Mn4+ co-doped CGT phosphors show dual emission attributed to the blue-violet emission (429 nm) of 3P1→1S0 transition of Bi3+ and red emission (679 nm) of 2Eg→4A2g of Mn4+. The intensity of the blue-violet and red emission peaks can be easily adjusted by controlling the concentration of Bi3+ and Mn4+ in the CGT host. The emission band is well-matched with the absorption bands of chlorophylls a and phytochrome PR under the near-ultraviolet to blue excitation, suggesting that the phosphors have great potential applications in light-emitting diodes (LEDs) to modulate plant growth.

Short review on recent progress in Mn4+ -activated oxide phosphors for indoor plant light-emitting diodes.

In the modern era, growing number of indoor plants for various purposes, such as vegetation, flowering, and decorations, has increased over the traditional follow-up trends for plantation. However, the indoor plantation requires different parameters for their growth; among these, light plays a significant role. In order to control the growth of plants using light-emitting diodes, Mn-doped oxide phosphors have emerged as promising candidates due to their broad and intense emission bands in the red and far-red spectral range. In this review article, recent progress on Mn-doped oxides for indoor plant growth has been reviewed. This review article is mainly divided into three parts. In the first part, different reaction conditions for the synthesis of Mn-doped oxide phosphors are compared. In the second part, the luminescent and other photometric parameters of these are discussed. The influence of different co-dopants on the luminescent characteristics has been elucidated in detail. The third part discusses the properties of light-emitting diodes fabricated using these phosphors for plant growth. The present review article elucidates the synthesis parameters, luminescent properties, and light-emitting diodes fabricated using Mn-doped oxide materials for plant growth applications.

A review on the structural dependent optical properties and energy transfer of Mn4+ and multiple ion-codoped complex oxide phosphors

The tetravalent manganese Mn4+ ions with a 3d3 electron configuration as luminescence centers in solid-state inorganic compounds have been widely investigated because they emit bright light in the red to far-red region when they are excited by light with a wavelength in the UV to blue light region. Herein, we present an overview of the recent developments of Mn4+ and multiple ion such as Bi3+ and rare earth ion Dy3+, Nd3+, Yb3+, Er3+, Ho3+, and Tm3+ codoped complex oxide phosphors. Most of the specified host lattices of these complex oxide phosphors possess multiple metallic cations, which provide possible substitutions with different codopants and form various luminescence centers with diverse spectra. The luminescence of Mn4+ and multiple ion-codoped materials spans almost the whole visible light to near infrared (NIR) region. The crystal structures of complex oxide phosphors, the spectroscopic properties of Mn4+, and the energy transfer between Mn4+ and multiple ions are introduced and summarized in detail with regard to their practical applications. This review provides an insight into the optical properties of Mn4+ and the energy transfer process in multiple ion-codoped luminescence materials, which will be helpful in the development of novel excellent materials for applications in the lighting industry.

Temperature dependent photoluminescence studies of NUV excited Gd2O3: Eu phosphor

Europium doped gadolinium oxide phosphor was successfully synthesized by the solution combustion method. The influence of temperature on the structural and optical properties of Gd2(1-x)Eu2xO3 (x = 0,0.01) phosphor is studied. The phase and the crystal structure of the phosphor are estimated by the XRD analysis. An enhancement in the calcination temperature results in the better crystallinity of the phosphor in the pure phase. The formation of the phosphor is further confirmed by the FTIR spectra. The optical band gap energy is estimated using Wood and Tauc relation. The effect of calcination temperature on the photoluminescence emission spectra is studied. Two most intense emissions are observed at ~614 and 623 nm corresponding to the 5D0 → 7F2 forbidden electric dipole transition of europium ion. Based on the 1931 CIE chromaticity diagram, the chromaticity coordinates are calculated and the formation of a red phosphor is confirmed. The synthesized phosphor can be used as a potential candidate in lighting applications.

Influence of Additional Doping of Divalent Ions on Emission Intensity of Mn-Doped CaAl12O19

In recent years, phosphor-converted white light-emitting diodes (pc-WLED) have great attention due to long lifetime and low power consumption compared to traditional lighting source. The most popular method to fabricate the pc-WLEDs is a combination of blue LED chips (GaN) and yellow phosphor (Y3Al5O12:Ce3+), which shows high luminescence intensity. However, such pc-WLED does not have high color rendering property due to the lack of red color emission component. In order to solve the problem and obtain warmer colored pc-WLEDs, it is efficient to incorporate a red phosphor in the pc-WLED. It is known that Mn-doped phosphor have been studied because of their broad excitation band in UV-blue region and their deep red emission. Among the oxide basis phosphors, several materials such as Mn-doped CaAl12O19 [1] and Mg2TiO4 [2] were reported with good luminescence property. To increase the emission efficiency, additional doping into such Mn-doped oxide phosphors were examined. The remarkable enhancement of the emission intensity was reported for Mg co-doping in Mn-doped CaAl12O19 [3]. However, the mechanism why such enhancement was achieved by co-doping has not yet been fully understood. In this study, influence of additional doping of divalent ions, such as Mg2+, Zn2+ and Cd2+, on the red-emission intensity of Mn-doped CaAl12O19 is investigated. All the samples were synthesized with conventional solid-state reaction method by changing divalent ions concentration. Crystal structure of the synthesized samples was characterized with the powder X-ray diffraction (XRD) technique. To determine the charge state and the local environment of Mn ions, the Electron Spin Resonance (ESR) spectra were observed.The observed photoluminescence spectra of non-doped and Cd2+, Mg2+, Zn2+ co-doped CaAl12O19:Mn are shown in Fig. 1. In all cases, it is shown that divalent ions dopings could enhance the emission intensity, among which Mg2+ doping shows the largest enhancement. In the observed ESR spectra of non-doped and Cd2+, Mg2+, Zn2+ co-doped CaAl12O19:Mn, six peaks derived from hyper fine structure of Mn4+ could be seen in all the samples. It is noted that Mg and Zn co-doping significantly affects the spectral profiles, whereas only slight change was observed in Cd co-doped one. This indicates that Mg and Zn co-doping influence on local structure of Mn. In order to understand the effect of divalent ions doping on the enhancement of the red emission intensity, the first principles calculations within a density functional theory (DFT) have been also performed. As it is well known that the local environment of Mn ions is quite important on the emission intensity, local environment of Mn ions in CaAl12O19 were examined by substituting Mn ions at five crystallographically independent Al sites using the Vienna Ab initio Simulation Package (VASP)[4]. Using the same method, influence of additional dopings of divalent ions are investigated. In the conventional DFT calculations with local density approximation (LDA) or generalized gradient approximation (GGA) the band gap is always underestimated. As there are some methods developed recently to obtain more accurate band gap, for the electronic structure analysis, the modified Becke-Johnson potential by Tran and Blaha (TB-mBJ) [5] implemented in WIEN2k package [6] was employed here. In addition, Hubbard U correction on the d electron state is adopted to represent the strong correlation between d-electrons on Mn ions, which cannot be fully included in TB-mBJ.AcknowledgementThis work was partially supported by the Joint Research Center for Environmentally Conscious Technologies in Materials Science (project No. 30009, 30012, 31008, and 31017) at ZAIKEN, Waseda University.

Experimental and Theoretical Analysis of Photoluminescence from Mn-Doped Oxide Phosphors

Most of the current phosphor materials are prepared by doping dilute amount of rare-earth or transition metal ions, which act as emission center, in matrix materials. Among such phosphors, rare-earth doped oxides show good properties such as high luminescence and high stability for long term use, etc. However, due to the limitation of the rare-earth elements in the earth, rare-earth free phosphor materials have been strongly demanding, and therefore such materials have been extensively investigated these years. Although there are wide varieties of dopants for such rare-earth free phosphors, Mn4+ doped phosphor materials, which show red emission, are one of the most attractive materials. In order to design new phosphors doped with Mn ions, it is essential to know the local environment of the doped Mn ions in an atomic scale and the electronic structures of Mn-doped materials. Although the local environment analysis is mandatory, such analysis is very difficult for dilute dopants. In the current study, local environment analysis of Mn ions doped in some oxides were carried out by using the X-ray absorption near edge structure (XANES) measurements and the electronic structure calculations for such materials have been performed with the first principles calculations.All the samples were fabricated with the conventional solid-state reaction method changing the concentration of Mn ions and/or matrix oxides, such as CaTiO3, CaZrO3, CaSnO3, CaAl12O19, Mg2TiO4 and so on. Crystal structures of the synthesized materials were characterized with powder X-ray diffraction technique. Mn K- and L- XANES spectra were observed at BL9C of KEK-PF in the transmission mode and BL4B in UVSOR in total electron yield mode, respectively. Theoretical XANES spectra to be compared with the experimental ones were prepared with the WIEN2k package [1]. Prior to the detailed electronic structure calculations, geometry optimizations were carried out computationally to investigate the local environment of the doped Mn ions in the matrix oxides by the first principles calculations within a density functional theory level using the Vienna Ab-initio Simulation Package, VASP [2]. The electronic structures of the Mn-doped materials after above geometry optimizations were investigated with modified Becke-Johnson potential [3], which was recently developed electron-electron correlation functional and implemented in WIEN2k package is accurate for the band-gap estimation of the wide variety of semiconductors.AcknowledgementThis work was partially supported by the Joint Research Center for Environmentally Conscious Technologies in Materials Science (project No. 30009, 30012, 31008, and 31017) at ZAIKEN, Waseda University.

Zero-thermal-quenching and improved chemical stability of a UCr4C4-type phosphor via crystal site engineering

• CsNa 2 K(Li 3 SiO 4 ) 4 :Ce 3+ phosphor was synthesized with 80% quantum efficiency. • First zero-thermal-quenching phosphor among other Ce 3+ -doped phosphors. • Upon Ce 3+ doping in host shows excellent chemical stability than Eu 2+ doping. • CsNa 2 K(Li 3 SiO 4 ) 4 :Ce 3+ shows high color rendering index value of 95 at 1000 mA. Europium-doped UCr 4 C 4 cuboid phosphors with narrow and tunable emission show promise for application in designing light-emitting diodes with high color purity and thermal stability. Nevertheless, their poor chemical stability bottlenecks their use in lighting applications. Herein, a dual narrow-band blue-emitting Ce 3+ -doped CsNa 2 K(Li 3 SiO 4 ) 4 (CNKLSO) cuboid phosphor with a quantum yield of 80% is synthesized. The dual-band emission is attributed to the occupation of Ce 3+ at two distinct sites of CNKLSO, which is consistent with the density functional theory outcomes. Ce 3+ doping produces stable emission characteristics, in contrast to Eu 2+ incorporation, because of the improved site stability, as realized from bond valence sum calculations. Remarkably, no drop in the emission intensity is observed even at 200 °C, making CNKLSO:Ce 3+ the first Ce 3+ -based zero-thermal-quenching phosphor. A CNKLSO:Ce 3+ -based white light-emitting diode displays an excellent color rendering index (~95) at a high flux current of 1000 mA. The proposed study indicates that Ce 3+ doping in other UCr 4 C 4 - type oxide phosphors may improve the site stability, which in turn the chemical stability of the phosphor materials can be boosted.

P‐213: Late‐News‐Poster: Electroluminescence of Oxide Phosphor in Metal‐Oxide‐Semiconductor Structure

The green Zn2SiO4:Mn2+ phosphor film for electroluminescence (EL) was fabricated through a thermal annealing process of spin coated film on n‐type silicon wafer as a semiconductor electrode. The oxide phosphor was placed in metal‐oxide‐semiconductor (MOS) structure, where indium tin oxide was used as a top transparent electrode. The EL device showed the high‐purity green emission spectrum at 525 nm. Its luminance‐voltage and frequency dependence showed the increasing trend up to 100 V and 1 kHz.

Up and down conversion photoluminescence and structural properties from hafnium doped with different lanthanides and lithium

The structural and photoluminescent results of the lanthanum, erbium, ytterbium and lithium doped hafnium oxide phosphors; are presented. These powders were synthesized by the solvent evaporation technique, different percentages of doping of the lanthanides were carried out, obtaining monoclinic and cubic phases, also a cubic phase is present when doping lanthanides with 28% mol. Up-conversion (UC) and down-conversion (DC) luminescence spectra when excited with a 980 nm laser, three emission regions are presented; two in the visible (up-conversion) and one in the infrared (downshift), are observed. The green emission located at 528 nm, 543 nm and 559 nm; associated whit transitions of erbium ion (2H11/2 + 4S3/2) → 4I15/2 and in the red emission located at 653 nm and 678 nm; associated whit transitions of erbium ion (4F9/2 + 4I9/2) → 4I15/2. In 1532 nm, the infrared down conversion associated electronic transition 4I13/2 → 4I15/2 of erbium ion. The luminescence emission intensity increase in green is 336 times and in red is 105 times when doping with lithium in comparison with samples without lithium co-doped.In the XRD diffractograms shown the monoclinic, cubic and mix of the phases in the phosphors; these are confirmed with the TEM diffraction patterns. The EDS result indicates the presence of HfO2, Er3+ and Yb3+, in the phosphorus; hafnium decreases due to the presence of ions lanthanides. XPS showed changes in energy values due to doping of lanthanides. The CIE diagram indicates that HfO2 doped phosphors have a variety of shades from red to yellow.

Achieving Efficient Red-Emitting Sr2Ca1−δLnδWO6:Mn4+ (Ln = La, Gd, Y, Lu, δ = 0.10) Phosphors with Extraordinary Luminescence Thermal Stability for Potential UV-LEDs Application via Facile Ion Substitution in Luminescence-Ignorable Sr2CaWO6:Mn4+

In this work, we adopt a facile rare earth ions Ln3+ (Ln = La, Gd, Y, Lu) substitution strategy to achieve the efficient red luminescence Sr2Ca1−δLnδWO6:Mn4+ (δ = 0.10), which extremely improves the luminescence properties of luminescence-ignorable Sr2CaWO6:Mn4+. It is demonstrated that the substitution of Ln3+ for Ca2+ can stabilize the Mn in tetravalent state, which would like to occupy W6+ site and generate the luminescence. It is also found that the emission profile of original Sr2CaWO6:Mn4+ changes manifestly after different Ln3+ ions substitution, which is mainly attributed to the synergistic effect of lattice distortion, Mn4+ transition 2Eg → 4A2g and lattice vibration. Most fascinatingly, the Sr2Ca0.9Ln0.1WO6:0.005Mn4+ (SC0.9Ln0.1WO:0.005Mn4+, Ln = La, Gd) show extraordinary luminescence thermal stability, whose integrated emission intensity still maintains about 95% (Gd, 96.8%; La, 94.8%) at 478 K of its original value at room temperature (298 K), much better than those in most reported Mn4+-activated oxide phosphors so far. It is confirmed that the traps may play an important role for this phenomenon. Best of all, this work gives us a facile strategy to achieve efficient Mn4+-activated red-emitting materials with extraordinary luminescence thermal stabilities derived from luminescence-ignorable ones.

Frequency conversion in lanthanide-doped sol-gel derived materials for energy applications

In order to increase the efficiency of photovoltaic solar cells, photon absorption in an extended range of the solar spectrum is necessary, for example by means of up-conversion (UC) of sub-bandgap photons to minimize transparency losses. While lanthanide (Ln)-doped luminescent layers may be deposited on cell materials to achieve spectral conversion by methods like CVD or PVD, sol-gel (SG) processing is a low-cost technology which may be a good alternative for this purpose. In this work, Ln-doped SG-derived active layers have been deposited by spin-coating onto c-Si substrates for frequency conversion, with particular emphasis on UC, involving host matrices like aluminosilicate glass and titania ceramic doped with the activator/sensitizer pair Er/Yb. White light emitting diodes (WLEDs) based on Ln-doped phosphors still have efficiency limitations, namely because the Stokes shift from UV/blue LED excitation to the emitted lower frequency visible light converts some of the pump energy into heat. However, if white light generation (WLG) is achieved through IR-pumped UC instead, the cost of the LED lamp will be reduced, while the energy loss from Stokes shift can be minimized. SG synthesis of Ln-doped oxide phosphors for UC in WLG has been achieved (Er/Yb and Tm/Er/Yb doping), based on aluminosilicate glass matrices. Photonic crystal-assisted UC emission has also been demonstrated in a Tm/Yb-doped Fabry–Perot microcavity (MC). The different materials have been characterized by XRD, SEM, ellipsometry and photoluminescence (PL) spectroscopies and their light emission has been analyzed with the help of CIE chromaticity diagrams.

Near-infrared luminescence spectroscopy in yttrium oxide phosphor activated with Er3+, Li+ and Yb3+ ions for application in photovoltaic systems

Near-infrared emission from phosphors Y2O3 doped with Er3+, Li+ and Yb3+ ions under continuous excitation at 523 nm is reported. The downshifting emissions from 950 to 1090 nm correspond to transitions 4I11/2 → 4I15/2 of Er3+ ions and 2F5/2 → 2F7/2 of Yb3+ ions; the emissions from 1500 to 1600 nm correspond to transitions 4I13/2 → 4I15/2 of Er3+. The role of Yb3+ ions in phosphors of Y2O3 doped with 4 at.% of Er, 2 at.% of Li and 2 at.% of Yb was to enhance the 950–1090 nm emissions around 3.5 times in comparison with Yb3+ free samples, through an energy transfer from the erbium 4I11/2 level to the ytterbium 2F5/2 level. Li+ plays an important role in such energy transfer process. With addition of Li+ an erbium 4I13/2 and ytterbium 2F5/2 level decay time increasing is also observed. A peak intensity increase in XRD patterns of the sample tri-doped revealed that the incorporation of lithium increases the phosphor crystallinity. FT-IR and SIMS studies confirmed that Li+ ions are incorporated into the Y2O3 host. According to the optical and structural properties of these phosphors, they could be used to increase the photon absorption in photovoltaic systems.

Enhanced emission of Eu3+ in lutetium tungsten molybdenum oxide phosphors: Synthesis, optical properties, thermal behavior, and LED packaging

By adjusting molar ratios of raw materials of Lu2O3 (Eu2O3) to WO3 and MoO3 as well as WO3 to MoO3, several lutetium tungsten molybdenum oxide phosphors Lu2W0·5Mo0·5O6, Lu2WxMoyO9 (x + y = 2), Lu2W1·5Mo1·5O12, and Lu6W0·5Mo0·5O12 were synthesized through a solid-state reaction method. The materials were characterized by X-ray diffraction (XRD) patterns, scanning electron microscope (SEM) images, energy-dispersive spectra (EDS), diffuse reflection (DR) spectra, room temperature photoluminescence (PL) excitation and emission spectra, luminescence decay curves, and temperature dependent PL spectra. Red shift excitation bands were recorded in Lu2WxMoyO9 (x + y = 2) phosphors with the concentration of Mo6+ increasing. Enhanced Eu3+ excitation and emission spectra were observed in the Lu2WxMoyO9 (x + y = 2) phosphors with the concentration of W6+ increasing. Possible energy transfer processes were proposed to explain the PL excitation and emission spectra. By combining phosphors with 365 nm ultraviolet (UV) chips, the obtained light emitting diodes (LEDs) gave bright red light under forward bias current. The results suggest that the obtained Eu3+ doped Lu2WMoO9 have potential applications in phosphor converted based UV LEDs.

A novel double-perovskite LiLaMgTeO6: Mn4+ far-red phosphor for indoor plant cultivation white LEDs: Crystal and electronic structure, and photoluminescence properties

Abstract Deep-red-emitting Mn4+ activated oxide phosphors are the hot research topic due to their potential applications in indoor plant cultivation LEDs. In this paper, a novel double-perovskite LiLaMgTeO6:Mn4+ phosphor was firstly prepared by high-temperature solid-state reaction method and its structure of the phosphor was determined by X-ray diffraction (XRD) and Rietveld refinement. Density functional theory (DFT) calculations using VASP provide an insight into the bandgap and electronic structures of the LiLaMgTeO6 host. Under UV or blue excitation, LiLaMgTeO6:Mn4+ shows a good stability and bright far-red light in the 540–800 nm range with the maximum at 708 nm, which matches well with the absorption band of phytochrome PFR, indicating its potential application in improving plant growth. The optimal Mn4+ doping concentration was approximately 0.6 mol%. Furthermore, a white-LEDs device made of a 365 nm chip coated with present phosphor and commercial green, blue phosphors was designed for indoor plant cultivation. The results indicate that the LiLaMgTeO6: Mn4+ phosphor possesses great application prospect in white-LEDs for plant cultivation.

Mn4+ and Cr3+ ions in red and deep red-emitting phosphors: Spectral analysis and Racah parameter determination

The luminescence properties of the Mn4+ and Cr3+-activated fluoride and oxide phosphors have been discussed in detail. The Mn4+ and Cr3+-activated fluoride and oxide phosphors can be classified into five types from an aspect of the different luminescence properties: F–Mn, F–Cr, O–Mn, O–Cr-A, and O–Cr–B. The representative phosphors considered here are: BaSiF6:Mn4+ (type F–Mn), K2NaScF6:Cr3+ (type F–Cr), Sr2MgGe2O7:Mn4+ (type O–Mn), MgAl2O4:Cr3+ (type O–Cr-A), and BaZrSi3O9:Cr3+ (type O–Cr–B). The photoluminescence (PL) and PL excitation spectra are analyzed based on the Franck−Condon analysis model with considering the electron−lattice vibration interaction (Huang−Rhys factors). The Racah and crystal-field-related parameters of such phosphors are determined and plotted very well on the Tanabe−Sugano energy-level diagram curve.

Synthesis and photoluminescent properties of Sm3+-activated La3Si6N11 as an orange-red emitting phosphor

A series of Sm3+-doped La3Si6N11 phosphor materials were synthesized by a high temperature solid-state reaction method. The crystal structure, microstructure, photoluminescence properties, decay curves as well as thermal quenching properties of the as-prepared phosphors were investigated systematically. The excitation spectra contain a wide asymmetric band below 350 nm originating from the host absorption, several sharp excitation peaks in the range of 300–550 nm corresponding to f-f transition of Sm3+. Under the excitation of 369 and 414 nm light, the phosphors exhibit strong narrow-band orange-red emission peaked at 605 nm. The average decay time of La2.99Si6N11:0.01Sm3+ sample is fitted to be 0.38 ms and the CIE coordinates were calculated to be (0.6105, 0.3833). For water resistance, La3Si6N11:Sm3+ is better than K2SiF6:Mn4+ phosphor. After soaking in deionized water for 300 min, the La3Si6N11:Sm3+ sample retains approximately 80% of its initial relative emission intensity. When the temperature rises to 423 K (150 °C), the emission intensity of La2.99Si6N11:0.01Sm3+ sample remains 85% in comparison to that of room temperature. The activation energy was calculated to be 0.63253 eV, which is higher than those of Sm3+-activated oxide phosphors, indicating that the phosphor has relatively good thermal stability.

Upconversion/downconversion luminescence of color-tunable Gd2O3:Er3+ phosphors under ultraviolet to near-infrared excitation

Multicolored luminescence tuning in a single rare earth ion (Er3+) activated rare earth oxide phosphors were achieved among green to red colors. The emission bands in visible light region corresponding to the transitions between 4F7/2 → 4I15/2 (487 nm), 2H11/2 → 4I15/2 (525 nm), 4S3/2 → 4I15/2 (550 nm) and 4F9/2 → 4I15/2 (667 nm) were demonstrated by luminescence spectroscopy under excitations at 379 nm and 980 nm. The dependence of upconversion/downconversion luminescence intensity on the firing temperature and Er3+ concentration were investigated, which is useful to tailor the color chromaticity coordinates under varied excitation wavelengths by adjusting the experimental conditions.