The long rod-shaped Sr2MgSi2O7:Eu2+,Dy3+ with ultrahigh afterglow performance

The afterglow properties of long afterglow luminescent materials are greatly affected by their defects, which are distributed on the grain surface. Increasing the exposed surface area is an important method to improve the afterglow performance. In this research, long rod-shaped long afterglow materials Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were prepared using the hydrothermal-coprecipitation method. When the reaction time reached 96 h, the length of the afterglow materials could grow to 2 mm, and the sintering temperature was just 1150°C. The emission spectra of all obtained samples upon excitation at 397 nm had a maximum of 465 nm, which belonged to the representative transition of Eu²⁺. The initial brightness was 1.35 cd/m². The afterglow time could reach 19 h, giving a good afterglow performance. The research on this kind of material has essential significance in the exploration of luminescence mechanisms and their applications.     

Luminescence studies on Ba2ZnSi2O7 : Eu2+ phosphors crystals

A novel blue green‐emitting phosphor Ba₂ZnSi₂O₇ : Eu²⁺ was prepared by combustion synthesis method and an efficient bluish green emission under from ultraviolet to visible light was observed. The emission spectrum shows a single intensive band centered at 503 nm, which corresponds to the 4f⁶5d¹ → 4f⁷ transition of Eu²⁺. The excitation spectrum is a broad band extending from 260 to 465 nm, which matches the emission of ultraviolet light‐emitting diodes (UV‐LEDs). The effect of doped Eu²⁺ concentration on the emission intensity of Ba₂ZnSi₂O₇ : Eu²⁺ was also investigated. The result indicates that Ba₂ZnSi₂O₇ : Eu²⁺ can be potentially useful as a UV radiation‐converting phosphor for white light‐emitting diodes. Copyright © 2009 John Wiley & Sons, Ltd.     

UV or blue light excited red persistent perovskite phosphor with millisecond lifetime for use in AC‐LEDs

Energy storage phosphors with millisecond period afterglow that compensate for the diming time of alternating current light‐emitting diodes (AC‐LEDs) have promising application. To obtain a persistent luminescence (PersL) white colour in AC‐LEDs, we focussed on a red afterglow with short period phosphorescence. Ca₄Ti₃O₁₀ forms a type of perovskite‐related Ruddlesden–Popper phase structure. Doping Pr³⁺ ions into Ca₄Ti₃O₁₀, an ideal red PersL was obtained. X‐ray diffraction and element analysis demonstrated that our target samples were crystallized well. Steady‐state and afterglow luminescence properties were investigated in detail. Notably, the PersL intensity was dependent on various excitation wavelengths. By measuring three‐dimensional thermoluminescence spectra, we found that the trap depths showed a continuous distribution and that the shallowest trap contributed to the millisecond afterglow. Two PersL mechanism models were used to elucidate the electron charging and de‐trapping processes under UV or blue light activation.     

Photoluminescence properties of Ca2Al2O5:RE3+ (RE = Eu,Dy and Tb) phosphors for solid state lighting

Ca₂Al₂O₅:Eu³⁺, Ca₂Al₂O₅:Dy³⁺ and Ca₂Al₂O₅:Tb³⁺ phosphors were synthesized using a combustion synthesis method. The prepared phosphors were characterized by X‐ray powder diffraction for phase purity, by scanning electron microscopy for morphology, and by photoluminescence for emission and excitation measurements. The Ca₂Al₂O₅:Eu³⁺ phosphors could be efficiently excited at 396 nm and showed red emission at 594 nm and 616 nm due to ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions. Dy³⁺‐doped phosphors showed blue emission at 482 nm and yellow emission at 573 nm. Ca₂Al₂O₅:Tb³⁺ phosphors showed emission at 545 nm when excited at 352 nm. Concentration quenching occurred in both Eu³⁺ and Dy³⁺phosphors at 0.5 mol%. Photoluminescence results suggested that the aluminate‐based phosphor could be a potential candidate for application in environmentally friendly based lighting technologies.     

Luminescence and spectroscopic studies of halosulfate phosphors: a review

This review discusses the photoluminescence (PL) characteristics of halosulfate phosphors developed by us. Halosulfate phosphors KCaSO₄Cl:X,Y (X = Eu or Ce; Y = Dy or Mn) and Na₆(SO₄)₂FCl (doped with Dy, Ce or Eu) were prepared using a solid‐state diffusion method. The mechanism of energy transfer from Eu²⁺→Dy³⁺, Ce³⁺→Dy³⁺ and Ce³⁺→Mn²⁺ has also been studied. Dy³⁺ emission in the host at 475 and 570 nm is observed due to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transition, whereas the PL emission spectra of Na₆(SO₄)₂FCl:Ce phosphor shows Ce³⁺ emission at 322 nm due to 5d→4f transition of the Ce³⁺ ion. The main property of KCaSO₄Cl is its very high sensitivity, particularly when doped by Dy, Mn or Pb activators. This review also discusses the PL characteristics of some new phosphors such as LiMgSO₄F, Na₆Pb₄(SO₄)₆Cl₂, Na₂₁Mg(SO₄)₁₀Cl₃ and Na₁₅(SO₄)₅F₄Cl. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of cooling rate on the microstructure and luminescence properties of Sr2MgSi2O7:Eu2+,Dy3+ materials

Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ long afterglow materials were prepared by a high‐temperature solid‐state reaction method with different cooling rates. The cooling rate had a slight effect on X‐ray diffraction patterns and photoluminescence performance, but significantly modified the grain boundaries and long afterglow properties of the Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ materials. When the cooling rate was 1°C/min, grains remained intact with clear grain boundaries. As the cooling rate increased from 1°C/min to 5°C/min, some grain boundaries became indistinguishable. The afterglow properties were optimized, presenting best performance at the cooling rate of 3°C/min. The trap state was investigated and illustrated through thermoluminescence curves. The depths of the traps of all the samples were unchanged, whereas densities changed to a large extent, leading to different afterglow properties. The retrapping process is discussed based on the afterglow curves.     

A database on natural and transgenic luminous microorganisms: BiolumBase

The database BiolumBase was designed for the collection and systematization of available information on microorganisms containing bioluminescent systems; it includes two sections: natural and transgenic luminous microorganisms. By now, logic schemes of these sections have been developed, classification of the objects has been performed, ways of presentation of characteristics and structure of fields for input of information have been elaborated, and the necessary program modules have been developed. The database is filled on the basis of published data and our own experimental results; subsequent linkage of the database to the Internet is envisaged. Users will be able to obtain not only catalogues of strains but also information concerning the properties and functions of the known species of luminous bacteria, the structure, regulatory mechanisms, and application of bioluminescent systems and genetically engineered constructions with lux genes, as well as to find references and to search strains by using any set of attributes. The database will provide information that is of interest for the development of microbial ecology and biotechnology, in particular, for the prediction of biological hazard from the application of transgenic strains.__________Translated from Mikrobiologiya, Vol. 74, No. 2, 2005, pp. 278–286.Original Russian Text Copyright © 2005 by Medvedeva, Boyandin, Lankin, Kotov, Kargatova, Rodicheva, Popova.     

Energy transfer in M5(PO4)3 F:Eu2+,Ce3+ (M = Ca and Ba) phosphors

M₅(PO₄)₃ F:Eu²⁺ (M = Ca and Ba) co‐doped with Ce³⁺ phosphors were successfully prepared by the combustion synthesis method. The introduction of co‐dopant (Ce³⁺) into the host enhanced the luminescent intensity of the M₅(PO₄)₃ F:Eu²⁺ (M = Ca and Ba) efficiently. Previously, we have reported the synthesis and photoluminescence properties of same phosphors. The aim of this article is to report energy transfer mechanism between Ce³⁺?Eu²⁺ ions in M₅(PO₄)₃ F:Eu²⁺ (M = Ca and Ba) phosphors, where Ce³⁺ ions act as sensitizers and Eu²⁺ ions act as activators. The M₅(PO₄)₃ F:Eu²⁺ (M = Ca and Ba) co‐doped with Ce³⁺ phosphor exhibits great potential for use in white ultraviolet (UV) light‐emitting diode applications to serve as a single‐phased phosphor that can be pumped with near‐UV or UV light‐emitting diodes. Copyright © 2013 John Wiley & Sons, Ltd.     

Tunable lanthanide/transition metal ion‐doped novel phosphors for possible application in w‐LEDs: a review

Lanthanide‐based phosphors have been extensively investigated for their possible applications in solid‐state lighting technologies especially for white‐light‐emitting diodes. In this review article emphasis has been laid on discussing the recent developments of phosphors for warm white‐light production based on various optical characteristics such as quantum efficiency, thermal stability, short emission decay time, long‐term stability, facile synthesis, and low cost of production. We have tried to cover the essential and latest discoveries of the lanthanide/rare earth‐doped phosphors after 2010. New generations of narrow‐band phosphors have also been included. The optical and material properties of several novel phosphors and their luminescence characteristics have been thoroughly discussed.     

The high thermal stability of white emitting phosphor Mg2Y2Al2Si2O12:Dy3+,Eu3+,La3+/Lu3+ for white light emitting diodes

A series of Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺ was prepared using a solid-state method, and the phosphor emitted white light by tuning the ratio of Dy³⁺/Eu³⁺. The effects of La³⁺/Lu³⁺ on the structure and luminescence properties of Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺ were explored. Under the influence of bond length and twist, the luminescence intensity of the materials increased first and then decreased under excitation with ultraviolet light. The lattice distortion of the trivalent cation La³⁺-substituted Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺ and Eu³⁺ phosphors was reduced, the symmetry of polyhedron occupied by the luminescence centre improved, and the thermal stability of the luminescence centre improved to a certain extent. White light emitting diodes (LEDs) were fabricated by combining a 370 nm LED chip and the Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺,La³⁺ (Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺,Lu³⁺) phosphor. The results showed that Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺,La³⁺/Lu³⁺ may have potential application in the area of white LEDs.     

A pilot experiment on a method for evaluating acceptability of a daylit luminous environment

1. 1. We propose a hierarchical model as a hypothesis to evaluate comfort in lighting environments.

2. 2. The model consists of physical quantities such as stimuli, and visual sensations as the first response, and then overall evaluation.

3. 3. A pilot experiment in a side-lit classroom usng 147 subjects was made to examine this model.

4. 4. It was found that in the side-lit classroom the most effective answers for discrimination between “acceptable” and “not acceptable” were “the surface of desk was not considered dark” and “not to experience any reflectance of lighting on the sheet of paper on which they wrote”.

5. 5. Moreover all of the effective items relate to the task area, namely desk and blackboard, and this meant that subjects gave priority to workability in the classroom.

Synthesis and luminescence characterization of Y2BaZnO5:RE (RE = Eu3+, Tb3+, Pr3+ and Sm3+) phosphors

Modified synthesis and luminescence of Y₂BaZnO₅ phosphors activated with the rare earths (RE) Eu³⁺, Tb³⁺, Pr³⁺ and Sm³⁺ are reported. RE₂BaZnO₅ phosphors have attracted attention because of their interesting magnetic and optical properties; and are usually prepared using a two‐step solid‐state reaction. In the first step, carbonates or similar precursors are thoroughly mixed and heated at 900°C to decompose them to oxides. To eliminate the unwanted phases like BaRE₂O₄, the resulting powders are reheated at 1100°C for a long time. We prepared Y₂BaZnO₅ phosphors activated with various activators by replacing the first step with combustion synthesis. The photoluminescence results are presented. The photoluminescence results for Eu³⁺, Tb³⁺ and Pr³⁺ are in good agreement with the literature. However, photoluminescence emission from Sm³⁺ has not been documented previously. The excitation spectrum of Eu³⁺ is dominated by a charge transfer band around 261 nm, and an additional band around 238 nm is always present, irrespective of the type of activator. The presence of this band for all these different types of activators was interpreted as host absorption.     

Photoluminescence properties of aeschynite‐type LaNbTiO6:RE3+ (RE = Tb,Dy, Ho) down‐converting phosphors

In this study, a series of LaNbTiO₆:RE³⁺ (RE = Tb, Dy, Ho) down‐converting phosphors were synthesized using a modified sol–gel combustion method, and their photoluminescence (PL) properties were investigated as a function of activator concentration and annealing temperature. The resultant particles were characterized using X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, UV/Vis diffuse reflectance spectroscopy and PL spectra. The highly crystalline LaNbTiO₆:RE³⁺ (RE = Tb, Dy, Ho) phosphors with an average size of 200–300 nm obtained at 1100°C have an orthorhombic aeschynite‐type structure and exhibit the highest luminescent intensity in our study range. The emission spectra of LaNbTiO₆:RE³⁺ (RE = Tb, Dy, Ho) phosphors under excitations at UV/blue sources are mainly composed of characteristic peaks arising from the f–f transitions of RE³⁺, including 489 nm (⁵D₄ → ⁷F₆) and 545 nm (⁵D₄ → ⁷F₅) for Tb³⁺, 476 and 482 nm (⁴F_9/2 → ⁶H_15/2) and 571 nm (⁴F_9/2 → ⁶H_13/2) for Dy³⁺, and 545 nm (⁵F₄ + ⁵S₂ → ⁵I₈) for Ho³⁺, respectively. The luminescent mechanisms were further investigated. It can be expected that these phosphors are of intense interest and potential importance for many optical applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Persistent luminescence of CaMgSi2O6:Eu2+,Dy3+ and CaMgSi2O6:Eu2+,Ce3+ phosphors prepared using the solid‐state reaction method

CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors were synthesized using the solid‐state reaction method. X‐Ray diffraction (XRD) and photoluminescence (PL) analyses were used to characterize the phosphors. The XRD results revealed that the synthesized CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors were crystalline and are assigned to the monoclinic structure with a space group C2/c. The calculated crystal sizes of CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors with a main (221) diffraction peak were 44.87 and 53.51 nm, respectively. Energy‐dispersive X‐ray spectroscopy (EDX) confirmed the proper preparation of the sample. The PL emission spectra of CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors have a broad band peak at 444.5 and 466 nm, respectively, which is due to electronic transition from 4f⁶5d¹ to 4f⁷. The afterglow results indicate that the CaMgSi₂O₆:Eu²⁺,Dy³⁺ phosphor has better persistence luminescence than the CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphor. Copyright © 2015 John Wiley & Sons, Ltd.     

Photoluminescence property of A9B(VO4)7 [A = Ca,Sr, Ba and B = La,Gd] phosphors

A new efficient phosphor, A₉B(VO₄)₇ [A = Ca, Sr, Ba and B = La, Gd] has been synthesized by the solid‐state method at high temperature. X‐ray diffraction analysis confirmed the formation of the compound. Photoluminescence excitation measurements show that the phosphor can be efficiently excited by near‐ultraviolet light from 300 nm to 400 nm to realize emission covering the 397–647 nm region of visible spectrum. Therefore, newly synthesized novel phosphor may be useful as green‐emitting phosphor in solid‐state lighting. Copyright © 2012 John Wiley & Sons, Ltd.     

Study on the preparation and luminescence properties of SrGe4O9:Mn4+ red phosphors for plant illumination

In this study, SrGe₄O₉:Mn⁴⁺ red phosphors for plant illumination were prepared using a high-temperature solid-phase method. The samples were characterized and analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), fluorescence spectroscopy, and other techniques. The phase structure, apparent morphology, and luminescence properties of the SrGe₄O₉:Mn⁴⁺ red phosphors were investigated. The results indicated that the dopant Mn⁴⁺ was incorporated into the matrix structure by substituting some Ge⁴⁺ ions without any changes in the crystal structure of the SrGe₄O₉ matrix. The samples comprised micron-scale particles and exhibited high purity and uniform distribution of elements. The SrGe₄O₉:Mn⁴⁺ phosphors exhibited relatively strong red light emission at 660 nm under the excitation of a 430-nm blue light, and the luminescence intensity was the highest when the Mn⁴⁺ doping amount was 1%. Proper doping of Ti⁴⁺ or Sn⁴⁺ could effectively improve the luminescence intensity of the SrGe₄O₉:Mn⁴⁺ phosphors. The light-emitting diode (LED) device packaging showed that the SrGe₄O₉:Mn⁴⁺ red phosphors could be used for plant growth illumination.     

Sol‐gel synthesis and luminescent properties of red‐emitting Y(P,V)O4:Eu3+ phosphors

Eu³⁺‐activated Y(P,V)O₄ phosphors were prepared by the EDTA sol‐gel method, and the corresponding morphologies and luminescent properties were investigated. The sample particles were relatively spheroid with size of 2–3 µm and had a smooth surface. The excitation spectra for Y(P,V)O₄:Eu³⁺ consisted of three strong excitation bands in the 200–350 nm range, which were attributed to a Eu³⁺‐ O^2? charge‐transfer band and ¹A₁?¹ T₁/¹ T₂ transitions in VO₄^3?. The as‐synthesized phosphors exhibited a highly efficient red luminescence at 613 nm due to the Eu^{3+ 5}D₀?⁷ F₂ electric dipole transition. With the increase in the V⁵⁺/P⁵⁺ ratio, the luminescence intensity of the red phosphor under UV excitation was greatly improved due to enhanced VO₄^3? → Eu³⁺ energy transfer. Copyright © 2015 John Wiley & Sons, Ltd.     

A new Pr3+‐activated molybdate‐based phosphor for application to white LEDs with blue excitation

The novel red‐emitting phosphors K_xSr_1?2xMoO₄:Pr³⁺_x (0.00 ≤ x ≤ 0.04) were prepared by solid‐state reaction. The crystallization and particle sizes of samples were investigated by powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). TEM images were in good agreement with the theoretical calculation data from the XRD patterns. Photoluminescence analysis indicated that there were three excitation peaks under 430–500 nm, and all samples showed the intensely red emission at 648 nm corresponding to the ³P₀ → ³F₂ transition of Pr³⁺. The concentrations of doping ions, temperature and polyethylene glycol in the phosphor system can significantly influence the intensity of the red emission. The photoluminescence spectral intensity reached its maximum at x = 0.02. The results showed that the investigated phosphor is a potential red phosphor for white light‐emitting diodes. Copyright © 2010 John Wiley & Sons, Ltd.     

Optical analysis of Sr3Gd(PO4)3:Pr3+ phosphors for lighting applications

A series of praseodymium (Pr³⁺) ion activated Sr₃Gd_(1−x)(PO₄)₃:xPr³⁺ (0 ≤ x ≤ 2.0 mol%) phosphors were prepared and their structural, compositional and luminescence properties were investigated. The X-ray diffraction profiles indicate that the studied phosphors crystallized into body centred cubic structure and the Pr³⁺ ions have no influence on Sr₃Gd(PO₄)₃ phase. The high-resolution scanning electron microscopy images show the agglomeration of particles that are inter-connected and form irregular shape Sr₃Gd(PO₄)₃ structures. The excitation transitions corresponding to Pr³⁺:³H₄ → ³P_2,1,0 transitions at 445, 471 and 483 nm, respectively, matched well with the emission of blue-light-emitting diode (LED) chip. The emission spectra show strong reddish-orange luminescence through ¹D₂ → ³H₄ transition when excited at 445 nm blue wavelength. The synthesized phosphors have the potential to be used as reddish-orange lighting devices.     

A novel red‐emitting phosphor,KAl1‐xPO4Cl:Eux3+ (0.1 ≤ x ≤ 1.0)

A series of phosphors KAl_1‐xPO₄Cl:Eu_x³⁺ (0.1 ≤ x ≤ 1.0) was synthesized using a facile combustion method using urea as a fuel and their structural, morphological and photoluminescence properties were investigated. It was found that the particle size was in the range of 1–2 µm with an irregular shape. The f–f transitions of Eu³⁺ in the host lattice were assigned and discussed. The excitation and emission spectra indicated that this phosphor can be efficiently excited by ultraviolet (395 nm), and exhibit reddish orange emission corresponding to the ⁵D₀→⁷F_J (J = 0, 1, 2) transitions of Eu³⁺. The impact of the Eu³⁺ concentration on the relative emission intensity was investigated, and the best doping concentration is 0.5. The present study suggests that the KAl_0.5PO₄Cl: Eu_0.5³⁺ phosphor is a strong candidate as a red component for phosphor‐ converted white light‐emitting diodes (LEDs). Copyright © 2015 John Wiley & Sons, Ltd.