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Colloidal synthesis of CsPbBr3 nanoparticles (NPs) by polar-solvent-free ultrasonic bath.

A BaY2 F8 :Yb3+ ,Ho3+ phosphor was synthesized using a simple precipitation method. The temperature-sensing properties of BaY2 F8 :Yb3+ ,Ho3+ phosphor were investigated using the fluorescence intensity ratio (FIR) of the thermally coupled energy levels (5 F4 and 5 S2 ) of Ho3+ . Energy transitions 5 F4 →5 I8 and 5 S2 →5 I8 gave rise to emission peaks at 538 nm and 549 nm, respectively. The areas under these two emission peaks were used to calculate the FIR. Temperature-dependent upconversion luminescence was recorded in the temperature range 303-623 K using a 980 nm laser excitation source. The results suggested that the BaY2 F8 :Yb3+ , Ho3+ phosphor has the potential to be used as a non-contact optical temperature sensor.

This work focuses on the charge-compensation effects produced by different monovalent alkali ions, viz. Li+, Na+, K+, and the vacancy defects in the Eu3+-activated Ca3Mg3(PO4)4 host. To compensate the extra charge produced due to doping of Eu3+ ions in the Ca2+ site, two approaches were adopted. In the first approach, a Ca2+ vacancy (□+) was deliberately created in such a way that three Ca2+ ions were removed for doping of every two Eu3+ ions. In the second case, a monovalent alkali ion (Li+, Na+ or K+) was incorporated along with one Eu3+ ion to replace two Ca2+ sites in the host. Sol-gel/Pechini method was employed for the synthesis. The luminescence emissions of Ca3Mg3(PO4)4;Eu3+ phosphor significantly improved with the introduction of charge-compensators. The remarkable enhancement in the emission intensity of the charge-compensated samples was accompanied by noteworthy improvement in the color purity of their emissions.

Monoclinic phase of BaY2F8:0.2Yb3+, xHo3+ (x = 0.005, 0.01, 0.02, 0.05 and 0.1 mol) and BaY2F8:yYb3+, 0.02Ho3+ (y = 0.01, 0.02, 0.05, 0.1 and 0.2 mol) phosphors were prepared by a facile precipitation method. Rietveld analysis was employed to carry out the structural refinement. The upconversion (UC) luminescence properties of BaY2F8:Yb3+, Ho3+ phosphor were investigated under near infra-red (NIR) excitation and the influence of dopant concentration on their spectra was also accessed. The possible UC processes and the energy transfer mechanisms between Yb3+ and Ho3+ were discussed on the basis of UC decay curves and the UC spectra obtained from a laser-pump power variation. The thermal stability of the BaY2F8:0.2Yb3+, 0.02Ho3+ phosphor was studied in the range of 30–300 °C. The color coordinates of the phosphor were located in the green region with very high color purity.

Dy3+ -doped CaAl12 O19 phosphors were synthesized utilizing a combustion method. Crystal structure and morphological examinations were performed respectively using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques to identify the phase and morphology of the synthesized samples. Fourier transform infrared spectroscopy (FTIR) estimations were carried out using the KBr method. Photoluminescence properties (excitation and emission) were recorded at room temperature. CaAl12 O19 :Dy3+ phosphor showed two emission peaks respectively under a 350-nm excitation wavelength, centered at 477 nm and 573 nm. Dipole-dipole interaction via nonradiative energy shifting has been considered as the major cause of concentration quenching when Dy3+ concentration was more than 3 mol%. The CIE chromaticity coordinates positioned at (0.3185, 0.3580) for the CaAl12 O19 :0.03Dy3+ phosphor had a correlated color temperature (CCT) of 6057 K, which is situated in the cool white area. Existing results point out that the CaAl12 O19 :0.03Dy3+ phosphor could be a favorable candidate for use in white light-emitting diodes (WLEDs).

An energy transfer process from Ce3+ to Tb3+ ions was successfully achieved in a Li2 SO4 -Al2 (SO4 )3 mixed-sulphate system. A wet-chemical synthesis was employed to prepare the Li2 SO4 -Al2 (SO4 )3 system by doping Ce3+ and Tb3+ ions individually as well as collectively. The phases were identified using X-ray diffraction studies. The as-prepared samples were characterized by FT-IR and photoluminescence measurements. Green-light emission was exhibited by Ce3+ , Tb3+ co-doped Li2 SO4 -Al2 (SO4 )3 system, thus, indicating its potential as a material for display devices or in the lamp industry.

Series of Sr2MgAl22O36:Ce3+, Sr2MgAl22O36:Dy3+ and Sr2MgAl22O36:Ce3+,Dy3+ phosphors were synthesized by urea-assisted combustion method. The identification of phase and morphology of the prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Photoluminescence excitation (PLE) and emission spectra of the as-prepared samples were investigated. Photoluminescence studies revealed that the luminescence intensity of Ce3+ ion increases with increasing concentration in Sr2MgAl22O36:Ce3+ and no concentration quenching have been witnessed. Similar trend was observed for Sr2MgAl22O36:Dy3+ with increasing Dy3+ concentration. The energy transfer from Ce3+ to Dy3+ in Sr2MgAl22O36 host has been achieved successfully to produce white light emission. The calculated Commission Internationale de L′Eclairage (CIE) chromaticity coordinates for the Sr2MgAl22O36:Ce3+, Dy3+ phosphor are (x = 0.302, y = 0.357). The values of CIE chromaticity coordinates and correlated color temperature (CCT) of 6798 K endorse Sr2MgAl22O36:Ce3+, Dy3+ phosphor as potential candidate for cool white-light emission.

Light-emitting diodes (LEDs) have taken the world by surprise with its flair and application in almost every field that can come from human imagination. To understand the imperative presence of LEDs in today’s world, it is essential to know the complete journey from the prehistoric period that slowly and gradually led to the development of this outstanding technology. The history of lighting is broadly classified into four generations and LEDs have dominated the fourth and the latest generation of lighting. This chapter takes through the different phases of lighting that started with the burning of firewood and oil lamps, followed by the lamps working on the principles of incandescence, fluorescence, and, finally, the LEDs. Here, the concepts associated with the luminescence phenomenon and its mechanisms are also highlighted.

Light-emitting diode (LED) technology has moved ahead with several breakthrough innovations in a span of 50 years. Giant leaps were made in the lighting and display industries with the introduction of new variants of LEDs. LEDs have evolved from the traditional semiconductor technology to several new branches that have opened up prospects to achieve more efficiency and feasibility for applications. This has enabled the devices to appear with a more compact and flexible design, which can be molded as per the need. This chapter delivers the advances made in the LED industry and the revolution that is being offered by the new entrants in the field of lighting and display devices.

Light-emitting diodes (LEDs) have penetrated the lighting industry by creating a huge difference in the energy savings. The luminaires that existed before LEDs consumed an enormous amount of energy with poor luminescence efficiency. This facilitated LED to put a mark in the lighting industry with loads of advantages over its predecessors. This chapter reflects those advantages that LEDs have gained over other artificial light sources. This is followed by a briefing on the general construction and working principle of semiconductor LEDs. The materials used for the fabrication of LEDs are also discussed in brief. This discussion covers the integration of semiconductor LEDs with inorganic phosphors along with certain encapsulation materials to form an LED package. This chapter also involves the discussion on the characteristics that determine the quality of LED phosphors.

Light-emitting diodes (LEDs) have established a strong base in the digital communication and display industries. In the communication sector, LEDs have steered the technology from the traditional wireless fidelity towards light fidelity (Li-Fi) for high-speed data transmission. Li-Fi is a coming-of-age technology that has boosted the use of visible light for communication. The display market has also witnessed a surge in the recent past with the induction of LEDs in the display devices. LEDs have come in the form of organic LEDs, microLEDs, and quantum dots to provide a completely different outlook on the shape, brightness, and efficiency of the display devices. It has also made possible to fabricate displays of all sizes, which were earlier impossible with the cathode ray tube or liquid crystal displays.

LEDs achieved success in creating a mesmerizing life for humans. LEDs with low output are relatively cheap, and hence, they are used for many temporary purposes such as glow sticks, photonic textiles, and LED art by artists. Besides the basic applications, LEDs have made strong strides in several new fields of applications and emerged as leaders in the technological growth. The LED industry has experienced tremendous change since its inception in the commercial market. In over a decade, the LED efficiencies have improved and their cost has lowered down. This has created numerous growth opportunities to implement LEDs for multiple businesses and newer products.

A BaY

A series of new silicate phosphors, Ba 1-x Eu x KYSi 2 O 7 (BKY: Eu 2+ ) (x = 0.005, 0.01, 0.02, 0.05, 0.07) have been synthesized from a water-soluble propylene glycol modified silane (PGMS) based silicon precursor by a solution approach. This phosphor can be efficiently excited by near-UV light and generates a broadband bright blue emission with internal Quantum Efficiency 34%. The detailed crystal structure of monoclinic BKY:Eu 2+ was determined from the XRD profile using Rietveld refinement. Band gap was determined from Diffuse Reflectance Spectra using Kubelka Munk function. Steady state and time resolved Photoluminescence measurement as well as the thermal quenching properties of the phosphor have been investigated in detail. A highly efficient broadband blue emission centered at λ max ~ 460 nm with a full-width at half-maximum of 72 nm shows very low thermal quenching; 83.2% at 150 °C with respect to that measured at room temperature. Moreover, a white LED device has been fabricated by coating the as-synthesized phosphor with a standard red emitting CaAlSiN 3 :Eu 2+ phosphor and a standard green emitting Ba 2 SiO 4 :Eu 2+ phosphor. The LED device exhibited an excellent color-rendering index CRI of 84.0564 at a correlated color temperature of 3752.4 K with CIE color coordinates of (0.363, 0.293) under a 350 mA forward-bias current. The interesting excitation profile and robust thermal performance reflect the potential application of this phosphor for near UV- LED driven solid state lighting.

Cu+-doped Na5Ca4(PO4)4F fluorophosphate was synthesized by wet-chemical method. This blue-emitting phosphor was characterized by XRD, FTIR and photoluminescence measurements. Rietveld refinement method was employed to analyse the phase formation of the as-prepared phosphor. The electron-vibrational interaction (EVI) parameters were calculated by the spectrum-fitting method. Na2Ca4(PO4)3F:Cu+ phosphor demonstrated blue emission under near-UV excitation and its CIE coordinates were found at (0.151, 0.037).

A series of samples with the compositions Sr2(1−x-z/2)Eu2xLazSi1−zGazO4 were synthesized by an advanced solution method employing a water-soluble silicon (WSS) compound. It has been observed that the substitution of Si4+ by Ga3+ in charge compensated Sr2(1−x-z/2)Eu2xLazSi1−zGazO4 samples causes a phase transition from β-phase to the α-phase of Sr2SiO4 accompanied by a considerable red shift in the photoluminescence emission spectra. Internal quantum efficiencies are found to be 95% and 77% for Sr1.98Eu0.02SiO4 and Sr1.93Eu0.02La0.05Si0.95Ga0.05O4 respectively. The high quantum efficiency of the phosphors owe to the synthesis procedure as well as use of SrCl2 as flux during the heat treatment in H2/Ar atmosphere. To demonstrate its potential application, we fabricated a warm white light-emitting diode (WLED) using the Sr1.93Eu0.02La0.05Si0.95Ga0.05O4 phosphor, pumped with a 365 nm n-UV LED chip, which reflects the good color rendering index and color temperature.

A series of BaB 8 O 13 phosphors doped with different concentrations of Gd 3+ ions and co-doped with Pr 3+ ions were synthesized by solid state synthesis method. X-ray powder diffraction (XRD) analysis confirmed the formation of the compound in a crystalline and homogeneous form. Scanning Electron Microscopy (SEM) was performed to study the surface morphology of the compound and Fourier Transform Infrared (FT-IR) spectroscopy measurements determined the nature of bonding between elements of the compounds. The photoluminescence (PL) excitation spectra of BaB 8 O 13 :Gd 3+ phosphor showed excitation peaks at 246 nm, 252 nm and 274 nm. The prominent emission peak was observed at 313 nm which is in narrow band ultraviolet B (NB-UVB) range. Energy transfer was achieved by co-doping Pr 3+ ions with Gd 3+ ions. PL decay time was also measured for BaB 8 O 13 : Gd 3+ , Pr 3+ phosphor. Emission at 313 nm can be used for the treatment of skin diseases.

A facile hydrothermal route has been demonstrated for the synthesis of Eu3+ doped LaPO4 with distinct and well-controlled morphologies (spherical and rod-like). Morphological control has been established by fine-tuning the pH of the precursor solution, and formation of different morphologies at different pH values has been explained by taking into consideration the chemical potentials of the various species present in the precursor solution. At constant pH of the mother liquor, an increase in the autoclaving temperature from 120 °C to 140 °C is seen to change the aspect ratio of the nanorods. A red shift in the charge transfer band is observed in the excitation spectra of the nanocrystalline samples (both nanorod and nanosphere) with respect to the bulk. A change in the (red/orange) peak intensity ratio in the photoluminescence emission spectra of bulk, spherical and rod-like nanocrystalline samples reveals that the host morphology plays a vital role in determining the local symmetry of Eu3+ in LaPO4 matrix. Decay-time measurement of the as-prepared morphologies at 620 nm (for 5D0–7F2 transition) leads to a maximum value for nanorods (3.7 ms), while the corresponding values for nanospheres and bulk samples are somewhat smaller (2.58 ms and 2.99 ms respectively). This clearly indicates the influence of shape anisotropy on the photoluminescence properties of the as-synthesized nanoarchitectures.

A series of Tm2−xWO6:xEr3+ (where x = 0.02–0.50 mol) phosphors were synthesized successfully by the solid-state reaction method. The powder X-ray diffraction patterns of the Tm2−xWO6:xEr3+ phosphors confirmed that the as-synthesized materials belonged to the monoclinic crystalline structure, which has a P2/c (13) space group. Due to a similar ionic size and valence state of the Er3+ ions, they can easily replace the Tm3+ in the Tm2WO6 crystal lattice. High-resolution X-ray photoelectron spectroscopy was used to explore the photoelectron binding energy and chemical state of all the elements. The XPS results confirmed that the W atom coordinated octahedrally to the oxygen atoms with its highest 6+ state in the Tm2WO6 material. The upconversion luminescence intensity at 657 nm [4F9/2→4I15/2 (Er3+)], when excited at 980 nm, was enhanced with higher magnitude when increasing the doping concentration from 0.02 mol to 0.20 mol of Er3+ ions. The dependence of the laser pump power with respect to the upconversion luminescence intensity depicts that the emission at 657 nm is due to a single-photon absorption process, and the possible reasons for the number of photons involved in the excitation of the emitting state, n ≤ 1 were discussed. The Commission Internationale del'Eclairage chromaticity coordinates and decay time measured for the Tm2WO6:Er3+ phosphors were investigated. Real-time latent-fingerprint detection using Tm2WO6:Er3+ upconversion phosphor without using Yb3+ ion showed an excellent marking agent for applications in forensic science and medical diagnostics.

Ca3La3-x(BO3)5:xTb (x = 0.005 to 0.10) phosphors were synthesized by the sol-gel process. The formation of the sol-gel products was confirmed by X-ray diffraction (XRD) analysis. The samples were also characterized by FTIR spectroscopy to study the nature of bonding between boron and oxygen ions. The luminescence properties of the synthesized products were examined under ultraviolet (UV) and vacuum UV (VUV) excitations. The phosphor exhibited green luminescence with the optimum emission peak centered at 544 nm for UV and VUV excitation. The color purity of the sample with optimum Tb concentration was 63.63 %. The prepared phosphors are a good option for the green-emitting component in plasma-display panels (PDPs).

In this work, we have comprehensively explored the energy transfer process between Ce3+ and Dy3+ ions doped in Ca3Mg3(PO4)4 host lattice. The phosphors were synthesized by facile urea-assisted combustion method. The charge imbalance, produced due to doping of trivalent lanthanides in the divalent sites of the host lattice, has been compensated by adding Li+ charge compensator. The structural characterization by Rietveld refinement, morphological and FTIR studies were performed on the as-prepared Ca2.96Mg3(PO4)4:0.01Ce3+, 0.01Dy3+, 0.02Li+ phosphor. The diffuse reflectance spectra and the photoluminescence spectra of the prepared phosphors and the electron-vibration interaction (EVI) parameters of Ca3Mg3(PO4)4:Ce3+,Li+ phosphor were thoroughly analysed. Ca3Mg3(PO4)4:Ce3+,Dy3+,Li+ phosphor exhibited its ability to produce white light emission at UV excitation wavelength 316 nm. The codoping of Ce3+ ions enhanced the PL emission intensity of Dy3+ by ten times as compared to the intensity obtained for the samples that were singly-doped with Dy3+. The results suggest the use of single-phased Ca2.96Mg3(PO4)4:0.01Ce3+, 0.01Dy3+, 0.02Li+ phosphor as potential white light emitting phosphor.

The effect of NH 3 on the morphology evolution of single crystalline hexagonal-prism like Y 4 O(OH) 9 NO 3 and Y 2 O 3 has been systematically investigated, as a function of reaction time, by using a combination of powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Rational control over the morphology has been achieved by the choice of suitable electrolytes like NaNO 3 , KNO 3 , NH 4 NO 3 , KCl and NH 4 Cl in the presence of NH 4 OH. We report that the cross-sectional geometry of hydrothermally grown one-dimensional Y 4 O(OH) 9 NO 3 crystals can be tuned from spherical to hexagonal-prism like shape by introducing a particular reagent like NH 4 NO 3 in the presence of NH 4 OH. An ‘oriented attachment’ mediated growth process takes place along with the ‘dissolution-recrystallization’ route which eventually resulted in the generation of the single crystals with hexagonal-prism like morphology.

To facilitate the next generation of White Light Emitting Diodes (WLEDs) with higher color rendering and warm lighting, the development of inorganic phosphor for efficient conversion of photons from blue/near-UV light to other visible wavelengths is essential. In this regard, we demonstrate a systematic, cost effective, solution-processable, easily scalable and fully controllable synthesis of a series of RbBaScSi 3 O 9 :xEu 2+ (x = 0.2, 0.5, 2, 5, 7), a new cyan emitting scandium silicate based phosphor with 79% internal quantum efficiency under n-UV excitation with robust thermal performance. The concept as well as the methodology of using a “Mineral Inspired Approach” emerges as a new blueprint for the rational design of novel phosphor for phosphor converted WLEDs. The structural refinement, electronic structural calculation using “Density Functional Theory”, characteristic photoluminescence study, lifetime measurement as well as the thermal quenching properties of the phosphor has been investigated in detail. Owing to the highly efficient cyan emission at λ max ∼492 nm a full-width at half-maximum of 63 cm −1 that shows only very low thermal quenching (89.28% relative to the PL intensity at 150 °C with respect to that of measured at room temperature), reflects the great potential for the industrial application of this particular phosphor.

In the present manuscript, Calcium diphosphate phosphor doped with Cerium and capped with sodium hexametaphosphate has been reported. A theoretical analysis of electron vibration interactions in optical transitions of Ce3+ ions in Ca2P2O7 has been elaborated in brief. The main EVI parameters such as Huang’s Rhys factor and effective phonon energy were determined by evaluating the lowest 5d level of Ce3+ spectrum. The obtained values were used to model the shape of emission band along with estimation of zero phonon line. The fabricated nano phosphor was characterized by powder X-ray diffraction technique. Studies revealed that Ca2P2O7 crystallizes in tetragonal group with square anti prism symmetry. The crystal structure arrangement was found to be non linear in nature with two PO3 groups linked by bridging oxygen forming the diphosphate group. Transmission electron microscopy observations explored nano structural features of the synthesized nano phosphor compound. A study involving SAED and HRTEM on isolated particles was carried out to validate the stabilization of the tetragonal phase. The phosphate functional group of the host was probed by Fourier transform infrared microscopy. Optical properties were examined by evaluating the photoluminescence excitation and emission spectra. Broad emission peaks were observed around 326 nm and 347 nm because of 4f-5d transitions of rare earth activator Ce3+. With the help of TL glow curve measurements, the trap depths were calculated employing peak shape method. Lifetime calculation for the nano phosphor indicates that the aforementioned compound has promising potential for solid state lighting and optoelectronic applications.

Combustion synthesis method was employed for the synthesis of green-emitting monoclinic SrAl 2 O 4 :Eu 2+ , Dy 3+ phosphors. The phase-purity of the prepared phosphors were examined using X-ray diffraction (XRD). The prepared phosphors exhibited green light emission with the peak centred at 510 nm, under 350 nm UV excitation. The excitation and emission spectra were analysed and the parameters of electron-vibrational interaction (EVI), such as the Huang–Rhys factor, effective phonon energy and zero-phonon line position were estimated using the spectrum fitting method. Thermoluminescence (TL) behaviour of the as-prepared phosphors were analysed for UV and 137 Cs γ-ray source irradiation. TL glow curves for UV-irradiated SrAl 2 O 4 :Eu 2+ , Dy 3+ phosphors were analysed.

Wet Chemical synthesis method was employed to prepare K 2 LaCl 5 :A (A = Ce 3+ , Eu 3+ , Eu 2+ , Dy 3+ , Cu + ) phosphors. The prepared phosphors were studied for their photoluminescence (PL) properties. Judd-Ofelt parameters of K 2 LaCl 5 : Eu 3+ phosphor were determined and discussed. The electron-vibrational interaction parameters of K 2 LaCl 5 : Eu 2+ and K 2 LaCl 5 : Ce 3+ phosphors were calculated by spectrum fitting method.

In the present paper, we discuss the synthesis route dependence of luminescence in Li6M(BO3)3:Eu3+ (M = Y, Gd) phosphors. The current phosphors were prepared by two distinct methods of synthesis, viz., combustion and wet chemical methods for varying concentration of Eu3+ activator and the prepared phosphors were compared with those prepared by solid state reaction method. The phosphors were effectively synthesized by combustion and wet chemical methods in an open atmosphere. Each phosphor, thus, derived was further characterized for phase purity, morphology, and luminescent properties at room temperature. The emission and excitation spectra were pursued to discover the luminescence traits. The excitation spectra indicate that the prepared phosphors can be efficiently excited at 395 nm, 467 and 540 nm/550 nm light to give emission at 595 and 614 nm due to 5D0 → 7Fj transition of Eu3+ ions. A strong and dominant red emission is achieved at 614 nm achieved from the 5D0 → 7F2 transition of Eu3+ ions. Li6M1-x(BO3)3:Eux may be a suitable red-emitting component for solid state lighting.

The electron–vibrational interaction (EVI) in 4f ↔ 5d optical transitions of Ce3 + ions in YAG, TAG and LuAG garnet phosphors have been analysed in this work. The main EVI parameters that have been estimated and reported here are Huang-Rhys factor, effective phonon energy, Stokes shift, red shift and Zero-phonon line position. The EVI parameters were estimated from the room temperature photoluminescence results that were recently reported. The spectrum fitting method was employed to determine the EVI parameters. An emission band was modelled with the aid of the calculated EVI parameters. The agreement between the modelled emission bands with the experimentally obtained ones validated the estimated values of EVI parameters.

Dy

Replacing the tricolor blend of phosphors by a single-phase white-emitting phosphor has emerged as a new technology for devising white-light-emitting diodes (WLEDs). Modification of the local structure in the crystal plays the key role in obtaining a single-phased, high CRI white-emitting phosphor. This process can also be employed to tune the color emission of the phosphor, especially those doped with Eu2+ ions. In this context, the selection of an appropriate host and the substituting chemical unit plays a vital role, as the crystal environment of the host greatly influences the photoluminescence (PL) emission of the Eu2+ ions. Herein, the color tuning of a new single-phase solid-solution Ba1.96Mg(PO4)2−x(BO3)x:0.04Eu2+ (x = 0.2, 0.5, 0.7, 1, 1.2 and 1.5) phosphor synthesized by the sol-gel/Pechini method is demonstrated. The structural variation induced by the varying composition of the borate (BO3)3− unit was analyzed by X-ray diffraction and Rietveld refinement studies. Fourier transform infrared spectroscopy revealed the presence of the vibrations corresponding to both the BO3 and PO4 chemical groups in the Ba1.96Mg(PO4)2−x(BO3)x:0.04Eu2+ phosphor. Morphological variations were also observed with the chemical co-unit substitution, which was analyzed with Scanning Electron Microscopy (SEM). PL studies indicated that the color tuning from blue-white-orange light, under near UV excitation, was achieved by varying the composition of the (BO3)3− group. The co-existence of the PO4 and BO3 groups gave rise to a higher-energy emission (420 nm) and a lower-energy emission (585 nm), respectively. The PL decay curves were analyzed to estimate the energy transfer efficiency between the higher-energy and lower-energy emission sites of the phosphor. This work presents a new strategy to tune the color emission of a singly-doped phosphor by modifying the structure of the host lattice.

A blue-emitting Eu2+-doped Ca3Mg3(PO4)4 phosphor was prepared by the polyethylene glycol assisted sol-gel synthesis method. The prepared phosphor was analyzed by using X-ray diffraction and scanning electron microscopy for the investigation of its structural and morphological features. From the photoluminescence (PL) excitation and emission spectra, it was found that the prepared phosphor emits blue light under ultraviolet and near-ultraviolet excitation. Temperature-dependent PL spectra and PL lifetime decay measurements were also executed for determining the detailed features of the Eu2+ emission in this phosphor. Under 325 nm excitation, the phosphor demonstrated excellent thermal stability with the activation energy for thermal quenching of 0.291 eV. The electron-vibrational interaction in the 5d states of the optimum Eu2+-concentration present in the blue-emitting Ca3Mg3(PO4)4:Eu2+ phosphor was evaluated and discussed by using the spectrum-fitting method.

This paper reports a study of the electron-phonon interaction (EVI) for the 3d states of the Cu+ doped in MgS phosphor. Its spectroscopic results were utilized for determining the strength of the electron-phonon coupling in this sulphide-based phosphor. In Cu+ metal ion, 3d10→3d94 s1 transition is responsible for obtaining the photoluminescence (PL) spectra. Using the values of the stokes shift and the full-width at half maxima (FWHM) of the PL emission and the excitation spectra from the experimental results, the Huang-Rhys factor (S), Phonon energy (ħω) and Zero-phonon line (ZPL) position were determined. The obtained values of the Huang-Rhys factor (S) and the Phonon energy (ħω) were validated by modeling the emission spectra.

A series of MZr4(PO4)6:Dy3+ (M = Ca, Sr, Ba) phosphors were prepared by the solid state diffusion method. Confirmation of the phase formation and morphological studies were performed by X-ray powder diffraction (XRD) measurements and scanning electron microscopy, respectively. Photoluminescence (PL) properties of these phosphors were thoroughly analyzed and the characteristic emissions of Dy3+ ions were found to arise from them at an excitation wavelength of 351 nm. The PL emission spectra of the three phosphors were analyzed and compared. The CIE chromaticity coordinates assured that the phosphors produced cool white-light emission and hence, they are potential candidates for UV excited white-LEDs (WLEDs).

This work reports the photoluminescence properties of Ca3 Mg3 (PO4 )4 :Sm3+ phosphors that were synthesized by the combustion method. The phase formation and morphology of the prepared phosphors were analysed by X-ray diffraction studies and scanning electron microscopy. Ca3 Mg3 (PO4 )4 :Sm3+ phosphors give orange light emission when excited by near-ultraviolet (NUV) and blue light. The photoluminescence characteristics of the as-prepared phosphors were investigated and their emission spectra showed three peaks due to 4 G5/2 → 6 H5/2 , 4 G5/2 → 6 H7/2 and 4 G5/2 → 6 H9/2 transitions. The mechanism responsible for the concentration quenching of luminescence was found to be an electric dipole-dipole interaction. The CIE chromaticity coordinates suggested that the prepared phosphors are potential candidates for orange light-emitting diodes (LEDs).

This work reports the theoretical analysis of the electron-vibrational interaction (EVI) in 4f-5d optical transitions of Eu2+ ions in ABaPO4 (A = Li, Na, K and Rb) systems. The EVI parameters were estimated from the recently reported room temperature photoluminescence results, by employing the spectrum-fitting method. Parameters such as the Huang-Rhys factor, effective phonon energy, Stokes shift and zero-phonon line position were estimated and are reported here. The estimated EVI parameters were validated by modeling the emission band and establishing the agreement between the experimental and modeled emission bands. Copyright © 2016 John Wiley & Sons, Ltd.