White LED Applications Research Articles

Reductant-optimized exchange strategy to construct the water-resistant shell of Mn4+-doped phosphors

Solving the problem of poor moisture resistance of Mn4+-doped fluoride red light-emitting phosphors is the key to promoting their application in white light-emitting diodes (WLEDs). In this paper, a reductant-optimized exchange strategy is proposed, that is, treating phosphors in NH4F (40 %) solution with FeSO4 to form a Mn4+-free shell on its surface to improve the moisture resistance as well as to block energy transfer to surface defects. The thickness of the Mn4+-free shell was about 900 nm as characterized by FIB-SEM. The integrated fluorescence intensity of the treated sample (R-KTF:0.05Mn4+) was 1.07 times that of the untreated sample. The internal quantum yield (QYi) was 98 %. After testing in extreme hydrolysis environments (high temperature, high pressure, high humidity), it decreased to 93 %, which is significantly higher than the results of the in-situ passivation strategy (QYi = 28 %) and the reverse cation-exchange strategy (QYi = 37 %). Finally, aging results at 85 °C and 85 % relative humidity further confirmed that the application of this strategy resulted in a significant improvement in the operational stability of the WLEDs.

Synthesis and Luminescence Properties of Eu2+-Doped Sr3MgSi2O8 Blue Light-Emitting Phosphor for Application in Near-Ultraviolet Excitable White Light-Emitting Diodes.

In this study, [Sr0.99Eu0.01]3MgSi2O8 phosphors were sintered at 1200–1400 °C for 1–5 h by using the solid-state reaction method. The crystallinity and morphology of these phosphors were characterized through X-ray diffraction analysis and field-emission scanning electron microscopy, respectively, to determine their luminescence. The photoluminescence properties, including the excitation and emission properties, of the prepared phosphors were investigated through fluorescence spectrophotometry. The α-Sr2SiO4, Sr2MgSi2O7, and Sr3MgSi2O8 phases coexisted in the [Sr0.99Eu0.01]3MgSi2O8 phosphors, which were synthesized at low temperatures. The particles of these phosphors had many fine hairs on their surface and resembled Clavularia viridis, which is a coral species. Transmission electron microscopy and energy dispersive X-ray spectroscopy indicated that the fine hairs contained the Sr2SiO4 and Sr2MgSi2O7 phases. However, when the [Sr0.99Eu0.01]3MgSi2O8 phosphors were sintered at 1400 °C, the Sr3MgSi2O8 phase was observed, and the Eu2+-doped Sr3MgSi2O8 phase dominated the only broad emission band, which had a central wavelength of 457 nm (blue light). The emission peaks at this wavelength were attributed to the 4f65d1–4f7 transition at the Sr2+(I) site, where Sr2+ was substituted by Eu2+. The average decay time of the synthesized phosphors was calculated to be 1.197 ms. The aforementioned results indicate that [Sr0.99Eu0.01]3MgSi2O8 can be used as a blue-emitting phosphor in ultraviolet-excited white light-emitting diodes.

Original KGd2F7 nanocrystals in fluoro-oxide glass ceramics by Dy3+/Sm3+ co-doped for white light emission

Serial fluoro-oxide glass ceramics (GCs) containing 0.6 mol% Dy 3+ and various Sm 3+ from 0 mol% to 1.5 mol% co-doped novel KGd 2 F 7 nanocrystals were firstly fabricated through high temperature melt-quenching method. Then the microscopic structure of the GCs was revealed by transmission electron microscopy (TEM). And the rare-earth ions (RE 3+ ) of Dy 3+ and Sm 3+ were successfully doped in monoclinic-phase KGd 2 F 7 nanocrystals, which can be verified by energy-dispersive X-ray spectroscopy (EDX) mappings. The photoluminescence spectra of the GCs were probed systematically utilizing 365 nm excitation light. The yellow (573 nm), green (486 nm), and red (648 nm) multiple emissions were observed in the co-doped GCs, and the intensity of red became stronger because of the higher Sm 3+ doping concentrations. This contribution of multiple emissions is due to the co-absorption of both Dy 3+ and Sm 3+ for 365 nm and the presence of energy transfer (ET). Moreover, the ET between Dy 3+ and Sm 3+ was confirmed from the variations of emission spectra and measured decay curves of emissions. Furthermore, the maximum energy transfer efficiency (ETE) from Dy 3+ to Sm 3+ can reach ~60.34% and the internal quantum yield (QY) is computed to be around 31.82% upon excitation of 365 nm. The chromaticity coordinates (CIE (Commission Internationale de L′Eclairage)− 1931) of the GCs can be tuned effectively through changing activator concentrations. Ideal white light emission is at the CIE (0.3357, 0.3342), which was achieved for 0.6 mol% Dy 3+ /0.9 mol% Sm 3+ doped GCs sample. The results indicated that Dy 3+ /Sm 3+ co-doped GCs with both high thermal and chemical-physical stabilities have strong potential application in white light-emitting diodes and fluorescent display devices. • The Dy 3+ /Sm 3+ co-doped fluoro-oxide glass ceramics containing novel KGd 2 F 7 nanocrystals were firstly fabricated. • The Dy 3+ and Sm 3+ ions were successfully doped in monoclinic-phase KGd 2 F 7 nanocrystals. • The standard white light emission was obtained by changing the concentration of Sm 3+ . • The energy transfer process from the Dy 3+ to Sm 3+ has been verified to dipole-dipole interaction mechanism. • The fluoro-oxide glass ceramics containing KGd 2 F 7 nanocrystals exhibit high thermal stability.

Ba3(ZnB5O10)PO4:Tb3+ green phosphor: Microwave-assisted sintering synthesis and thermally stable photoluminescence

Green phosphor has become increasingly an attractive focus owing to its multifunctional applications in illumination, display, anti-counterfeiting, and even bio-labeling. In this paper, trivalent terbium (Tb3+)-activated Ba3(ZnB5O10)PO4 (BZBP) green phosphors were synthesized at 1050 K for 1 h via a microwave-assisted sintering route. The structural study, influence of dopant Tb3+ content and working temperature on photoluminescence behavior, and colorimetric properties were performed comprehensively. Tb3+ successfully substitutes Ba2+ in the BZBP lattice. Under 378 nm near-ultraviolet (NUV) excitation, the emission bands peak at 488, 542, 585, and 623 nm, corresponding to the 5D4→7F6, 5D4→7F5, 5D4→7F4, and 5D4→7F3 transitions of Tb3+, respectively. Despite the working temperature increases, the title phosphor maintains the high emission intensity and low chromaticity shifting, exhibiting robust thermostability and color stability. This work provides a simple and rapid synthesis method for borophosphate-based phosphor. The application of NUV-excited white light-emitting diodes fabricated with the title product and commercial phosphors (red, blue) indicates that the developed green phosphor BZBP:Tb3+ is a promising candidate material in illumination and display applications.

Tunable rare-earth-free white light emission in zinc phosphate glasses activated with [formula omitted] clusters and Mn2+ ions

ZnO–P2O5 glasses activated with Agmn+ clusters and Mn2+ ions were successfully synthetized by the melt-quenching method. X-ray diffraction patterns confirmed the glassy nature for doping concentrations up to 3.0 and 5.0 mol% of Ag+ and Mn2+ ions, respectively, whereas the Raman spectra in all cases displayed δ(P–O–P), νs(P–O–P), νs(PO2) and νas(PO2) vibrational modes, typical of a phosphate glass network. The emission spectra under 345 nm (Agmn+: S0 → S1 and Mn2+: 6A1(S) → 4T1(P) + 4E(D)), 385 nm (Agmn+: S0 → S1) and 407 nm (Mn2+: 6A1(S) → 4A1(G) + 4E(G) and Agmn+: S0 → S1) excitations, showed the broad band related to the superimposed Agmn+ cluster: S1 → S0, T2 → S0 and T1 → S0 radiative transitions along with the Mn2+: 4T1(G) → 6A1(S) one. Under 385 nm excitation, the Mn2+ emission transition is attained by energy transfer from Agmn+ clusters. Such excitations lead to emission tonalities in the bluish white to cold white (345 and 385 nm) and cold white to reddish orange (407 nm) ranges, with correlated color temperature (CCT) values in the 10,095-5371 K (345 nm), 14,768-6862 K (385 nm) and 8592-1633 K (407 nm) ranges. Purplish pink emissions upon 345 nm excitation were obtained as well. The white color tonalities together with the color rendering index (CRI) and absolute quantum yield (QY, external) values up to 95 Ra and 35%, respectively, revealed promissory features for rare-earth-free white light emitting diode applications. The Agmn+ cluster: S1 → S0 emission fitting by the Burstein model suggested that the non-radiative energy transfer is mainly mediated by an electric dipole-dipole interaction.

Plasmonic Photocatalysis: Principles and Application

The efficient narrow band emission of Eu2+ in Cs2MP2O7 (M = Ca2+, Sr2+) is characterized by a large Stokes shift and a high quenching temperature which makes the material promising for application in warm white LEDs. The unusual Eu2+ luminescence properties were reported recently but an explanation for the peculiar behavior is lacking. In this paper we aim at providing new insights in the luminescence of the Eu2+ emission in Cs2MP2O7 through measurements at cryogenic temperatures (down to 4 K) and by comparison with the d–f luminescence of Ce3+ and Yb2+ in the same host. The results reveal a sharp onset of the Eu2+ emission and excitation bands at 4 K. Usually the sharp onset for narrow excitation and emission bands coincide at an energy corresponding to the zero-phonon (purely electronic) transition, but for Eu2+ in Cs2MP2O7 there is a large shift of 3500 cm−1 between the onsets, consistent with the large Stokes shift observed. The onset shift can be explained by emission from a lower energy distorted excited 4f65d1 state. For Ce3+, the f–d absorption bands are at energies expected based on the relation between the absorption energies for Eu2+ and Ce3+ reported by Dorenbos. Contrary to Eu2+, the emission for Ce3+ shows a normal Stokes shift and therefore the emission bands are at much higher energies than predicted from the energy of the Eu2+ emission and the Dorenbos relations. Based on the present results the unusually large Stokes shift for the Eu2+ emission in Cs2MP2O7 is assigned to a Jahn–Teller like deformation in the excited 4f65d1 state of Eu2+ that is not present in the 5d state of Ce3+.

Low-concentration Ce3+-activated ScCaO(BO3) blue-cyan phosphor with high efficiency toward full-spectrum white LED applications

Near-ultraviolet-pumped white light-emitting diodes (LEDs) based on the combination strategy of traditional RGB phosphors (blue/green/red) or blue/yellow phosphors have the drawback of inadequate color rendering index due to the cyan-gap (480–500 nm) in the emission spectrum. It is quite promising to find efficient cyan-emitting phosphors that can offset the cyan-gap to produce white LEDs with full-spectrum emission. In our work, we synthesized a Ce3+-activated ScCaO(BO3) (SCB:Ce3+) phosphor with a broadband blue-cyan emission. Under near-ultraviolet 396 nm excitation, the optimum SCB:0.005Ce3+ sample shows a blue-cyan emission band with a peak of 473 nm, which is competent for filling the cyan-gap. Meanwhile, the SCB:0.005Ce3+ blue-cyan phosphor possesses a high quantum efficiency (internal quantum efficiency = 66.5%, external quantum efficiency = 38.5%) and weak chromaticity shift (ΔEs = 1.29 × 10−2). We produce white LED devices based on 395 nm LED chips and RGB or blue/yellow/red phosphors strategies. By comparing the performance parameters of white LED devices with or without blue-cyan SCB:0.005Ce3+ phosphor, it is proved that SCB phosphor can offset the cyan gap of commercial RGB phosphors and the cyan emission lack of commercial Y3Al5O12:Ce3+ phosphor. Furthermore, SCB:0.005Ce3+ phosphor can substitute for commercial BaMgAl10O17:Eu2+ phosphor in RGB or blue/yellow/red phosphors combinations. The prepared white LEDs based on SCB:0.005Ce3+ blue-cyan phosphor, green/red or yellow/red phosphors show a lower proportion of high-energy blue light and are suitable for healthy lighting applications.

Designing tunable luminescence in Ce3+/Eu2+-codoped Ca8Zn(SiO4)4Cl2 phosphors for white light-emitting diode and optical anti-counterfeiting applications

Developing highly-efficient phosphors with tunable emissions is important since they can realize multiple applications in one compound. Herein, Ce3+/Eu2+-codoped Ca8Zn(SiO4)4Cl2 phosphors with multicolor emissions are developed to meet this requirement. The phase composition, microstructure, luminescence properties and thermal stability of the synthesized phosphors are investigated. Excited by 360 nm, Ce3+-doped Ca8Zn(SiO4)4Cl2 phosphors can emit dazzling blue light, where its intensity is impacted by Ce3+ content and the involved concentration quenching mechanism is contributed by electric dipole-dipole interaction. Moreover, with Eu2+ codoping, tunable luminescence (i.e., from blue to cyan and finally to green), which is caused by the energy transfer from Ce3+ to Eu2+, is realized in the resultant compounds excited at 360 nm. Through theoretical analysis based on emission spectrum and decay time, it is found that the energy transfer between Ce3+ and Eu2+ in the selected host lattices is efficient and its corresponding mechanism is decided by electric dipole-dipole interaction. Furthermore, the synthesized phosphors not only have splendid thermal stability but also show appropriate internal and extra quantum efficiencies of 37.6% and 15.6%, respectively. Using the designed phosphors as a cyan emitting component, a warm white light-emitting diode (i.e., white-LED) was packaged, where its correlated color temperature and color rendering index values are 4964 K and 92.4, respectively, when the driven current is 100 mA. Additionally, the feasibility of the obtained samples for optical anti-counterfeiting application is also explored. These achievements suggest that Ce3+/Eu2+-codoped Ca8Zn(SiO4)4Cl2 phosphors are promising candidates for both white-LED and optical anti-counterfeiting applications.

A novel blue excited white light emitting SrWO4: Pr3+ phosphor for single phase white-LED applications

A series of white light emitting Pr3+ activated SrWO4 phosphors are synthesized by most facile solid state reaction routes. The structural properties are investigated by X-ray diffraction (XRD) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy dispersive X-ray (EDX) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X-ray photoemission spectroscopy (XPS). The optical properties are elaborated in detail using UV–visible–NIR spectroscopy and Photoluminescence (PL) spectroscopy. Rietveld refinement of obtained XRD data is performed to investigate the crystal structure and crystallographic parameters. The photoluminescence measurements ensure that the developed phosphors emit bright white light under UV excitation of 242 nm and blue excitation of 448 nm. The maximum emission intensity is achieved at 3 mol% doping of Pr3+, followed by concentration quenching due to dipole-dipole interactions. The decay of electrons from the most populated 3P0 state in all the samples follows the single exponential nature. The average decay time varies in the same manner as the emission intensity with Pr3+ concentration. The color purities of the lights emitted from all the materials under 242 nm and 448 nm excitations are low (close to 10%) and hence suitable for white light. A bright white LED is successfully fabricated by coating the optimised phosphor SrWO4: 3 mol% Pr3+ on a 460 nm blue LED chip. The interesting results recommend that the proposed material can be used in developing single phase white-LED.

Ultra-stable Eu3+/Dy3+ co-doped CsPbBr3 quantum dot glass nanocomposites with tunable luminescence properties for phosphor-free WLED applications

Colloidal CsPbBr3 perovskite quantum dots (PQDs) have substantially improved modern optoelectronic applications, including solid-state lighting, thanks to their highly pure and intense green light emission. However, some drawbacks including lead toxicity, poor stability, and difficulties in emission color tuning hinder their practical applications. Herein, ultra-stable Eu3+/Dy3+ co-doped CsPbBr3 PQD glass nanocomposites (GNCs) with tunable color emissions from green to red and then white are synthesized via melt-quenching followed by heat-treatment method to be used in white light-emitting diodes (WLEDs). Eu3+ and Dy3+ ions are selected to overcome the color tunability obstacle of PQDs and to obtain phosphor-free white light emission with enhanced CRI values. The photoluminescent performance of GNCs is shown to be reversible at elevated temperatures and remains stable even in water. Ultimately, a prototype WLED is constructed by coupling a selected Eu3+/Dy3+ co-doped CsPbBr3 PQD GNC on top of a 400 nm-emitting LED chip to demonstrate its superior optical performance with a color rendering index of 78 and correlated color temperature of 5436 K. The developed GNCs with long-term stability, and excellent tunable luminescent properties may overcome the commercialization barriers of CsPbBr3 PQDs for WLED applications.

Photoluminescence Properties of (Mg\(^{2+}\)) Divalent and (Al\(^{3+}\)) Trivalent Metal Coumarinolates Doped with Quinoline for PCLED Application

Several Mg-Coumarinolates and Al-Coumarinolates doped with different concentrations of Quinoline were synthesized by simple chemical synthesis method and their PL spectra were studied. Usually, pure coumarin along with the chelates show weak luminescence and the emission is witnessed around 450 nm with excitation around 350 nm. Hence, such chelates do not find any practical applications. Addition of quinoline in lesser amount affects the emission and excitation of Mg-Coumarin and Al-Coumarin considerably. Intense photoluminescence is observed in these Mg based mixed chelates. In all samples, a well-defined emission band at 490 nm is observed with broad excitation in 350 nm to 470 nm range. Hence good overlap of excitation with 420 nm and 440 nm LED emission makes these materials suitable for white LED applications.

Evaluation of the novel Blue Emitting Phosphor with High Thermal Stability and High Color Purity for Solid State Lighting Applications - Ca2MgSi2O7: Eu2 +

This study deals with the new blue release LED phosphor activated by Eu2+. The luminescence properties of blue-emitting phosphor di-Calcium magnesium di-Silicate (Ca2MgSi2O7) doped with europium Eu2+are extensively investigated. This phosphor is produced by the high-temperature solid-state reaction method. The phase structure and crystalline size, surface morphology and elemental analysis were investigated by X-ray diffraction technique (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). The optical properties are investigated by photoluminescence (PL) properties. Phase structure of Ca2MgSi2O7: Eu2 + is a carbonite-type structure belonging to tetragonal crystallography with the space group P4̅21m; this structure forms a member and layered compound in the Myelite group. The surface of the prepared phosphors is not detected uniformly and the particle distribution is within the nanometer range. EDX ensures components of Eu2 + doped Ca2MgSi2O7 phosphor. Under UV induction, the main emission peak appeared at 470 nm. This emission peak is attributed to the typical emission of Eu2+ due to the 4F9/2 → 6H15/2 transition. The blue light-emitting properties and excellent light response of these silicate phosphors make them suitable for photonic applications and open new avenues for solid-state lighting, cathode ray tubes, fluorescent lamps and scintillators etc. The phosphor system has been researched as a new candidate for phosphor-converted white light-emitting diode (LED) applications.

Solution route to process BaZnO2:Eu3+ nano-phosphor for White-LED applications

We report a novel approach for the synthesis of single-phase BaZnO2:Eu3+nano-phosphor, using a hot-injection technique without a vacuum system. This synthesis method is rapid (∼90 min) and cost-effective compared to synthesizing the bulk phosphor. The X-ray diffraction (XRD) pattern indicates the trigonal crystal structure with space group P3121 (No.152). Transmission Electron Microscopy (TEM) images discovered the oval-shaped morphology in the nanosize region with an average particle size of ∼20 nm. The elemental composition analysis of the phosphor was done using energy dispersive X-ray analysis (EDAX). Furthermore, good thermal stability has been revealed via luminescence spectrum under the excitation of 467 nm and a retained 67% of the initial at 150 °C. Commission Internationale de l’Eclairage (CIE) color-coordinates (0.65,0.34) are in the range of orange-red region (595 nm and 610 nm) with 96.35% color purity for BaZnO2:Eu3+ nano-phosphor. The activation energy was calculated and found to be 0.25eV. Results perfectly recognized the suitability of these phosphors for the generation of white light-emitting diodes, which are otherwise difficult to synthesize at such a low temperature (300 °C). To the best of the author's knowledge, this is the first-hand report on the synthesis of europium doped BaZnO2nano-phosphor via hot injection technique.

Luminescence study of Sm3+ ,Eu3+ -doped Y2 Zr2 O7 host: optical investigation of greenish yellow to red colour tunable pyrochlore phosphor.

Pyrochlore phosphors have shown their worth in modern day lighting in the last few years. Colour tunability of the phosphor is one of the modern techniques used to obtain white light-emitting diodes (WLEDs). In the proposed work, Y2 Zr2 O7 :Sm3+ ,Eu3+ phosphors were investigated for WLED applications as well as display devices. A convectional solid-state diffusion method was used to synthesize the proposed phosphors. X-ray diffraction of the proposed phosphors was performed and compared with the standard Inorganic Crystal Structure Database. The crystal structure of the sample was cubic in nature, obtained from Rietveld refinement. Vibrational and morphological studies on the samples were carried out using Fourier transform infrared spectroscopy and scanning electron microscopy analysis. The photoluminescence study of the colour tunable phosphor showed the characteristic peak of Sm3+ together with the two sharp peaks of Eu3+ ions. Greenish yellow to red colour tunability was observed in the proposed phosphor with enhancement of Eu3+ ions. All these results showed the worth of this sample for WLEDs applications as well as in display devices.

Luminescence studies of a Li2 Ca1-x SiO4 :xSm3+ phosphor for the generation of white light under NUV-excited phosphor converting LEDs.

In this paper, we present new aspects of Sm3+ -doped pure Li2 CaSiO4 as a suitable candidate for white light emitting diode (WLED) applications. The samples were mainly prepared using a conventional modified solid-state synthesis technique. The structural studies were done using X-ray diffraction and Rietveld refinement. Instruments such as a scanning electron microscope (SEM) were used to obtain information about the morphology of the as-prepared samples. Photoluminescence (PL) analysis of phosphor samples for variable concentrations of doping ions with variable excitations were presented. When doped with Sm3+ in host Li2 CaSiO4 it emitted intense blue, green and red emissions and a more intense red emission peak (605 nm) under 408 nm excitation (near-UV-blue). Our study shows that the as-prepared phosphor may be useful for optical devices and mainly for WLEDs. The corresponding transitions of doping ions and concentration quenching effect were studied in detail. The 1931 Commission Internationale de l'Eclairage (x, y) chromaticity coordinates showed the distribution of spectral regions calculated from PL emission spectra and this was found (0.63, 0.36) in the red region, so the phosphor may be useful for near-UV-blue excited WLED applications.

Introducing cation disorder to enhance thermal stability in LuY3(BO3)4: Eu3+ phosphors for pc-WLEDs

Thermal quenching is a serious drawback that limits the application of phosphor-converted white light-emitting diodes (pc-WLEDs), because the operating temperature of phosphors tends to increase, resulting in emission loss due to non-radiative transitions. Herein,by introducing Lu3+ ions and Eu3+ ions into YBO3 to create lattice distortion and cation disorder, a series of Lu1-xY3(BO3)4: xEu3+ red phosphors have been designed to obtain novel phosphors with excellent thermal stability. The phosphors were synthesized by the traditional high-temperature solid-phase method. XRD results and EDS energy spectrum access the phase composite and crystal structure. Under 393 nm excitation, Lu1-xY3(BO3)4: xEu3+ phosphors emit red light peaking at 594 nm, 613 nm, and 651 nm Lu0.6Y3(BO3)4:0.4Eu3+ and Lu0.2Y3(BO3)4:0.8Eu3+ can maintain 93% and 86% emission intensity respectively at 150 °C, and they can still maintain 90.2% and 78% respectively at 200 °C. Thermoluminescence spectroscopy proves that the Lu0.2Y3(BO3)4:0.8Eu3+ phosphor has deep defects at 145 °C and 400 °C, which can release electrons to compensate for the emission intensity at high temperatures, thereby improving thermal stability.The prepared phosphor has extremely high thermal stability and particularly high color rendering purity (99.8%). Under the driving current of 120 mA, the color rendering index of the pc-WLED packaged with Lu0.2Y3(BO3)4:0.8Eu3+ phosphor powder is 89.4, and the correlated color temperature is 4681K.All these results indicate that LuY3(BO3)4:Eu3+ phosphors are promising for pc-WLED applications, especially for applications requiring high temperature operating conditions.

Enhanced red emitting of LiY(MoO4)2: Sm3+ phosphors by Pr3+ for white LED application

Enhanced red emitting of LiY(MoO4)2: Sm3+ phosphors by Pr3+ for white LED application

Large Spectral Shift of Mn2+ Emission Due to the Shrinkage of the Crystalline Host Lattice of the Hexagonal CsCdCl3 Crystals and Phase Transition.

All-inorganic halide perovskite crystals are considered excellent optical host lattices for various dopants to obtain wavelength-tunable emissions with ultra-broad bands even over a wide spectral range. Here, a series of Mn2+-doped bulk ligand-free CsCdCl3 (CCC) perovskite crystals with a hexagonal shape and size of about 1 millimeter (mm) have been prepared by a facile hydrothermal method. These CCC:Mn2+ (CCC:Mn) crystals emit the representative orange-red photoluminescence (PL) of Mn2+ (4T1(G)-6A1(S)) in the centers of hexagonal octahedrons coordinated with six Cl- ions. A fine-tuning of the Mn2+ concentration from 1 to 50 mol % Cd2+ induces a substantial red shift of emission spectra from 570 to 630 nm due to the shrinkage of the crystalline host lattice, and the maximum intensity of emission is achieved at 20 mol % Mn2+ doping. A further increase in the Mn2+ concentration causes a decrease of the PL intensity due to the phase transition from CCC to CsMnCl3·2H2O (CMCH). The strong excitation bands at 360, 370, 420, and 440 nm can make the excitation of the emissive CCC:Mn crystals possible with ultraviolet (UV) and blue chips for application in white light-emitting diodes (WLEDs). The similarity of the Mn2+-concentration-dependent emission spectra excited by various wavelengths indicates that there is only one type of site for Mn2+ occupation in CCC.

Enhancement of dysprosium oxide doped zinc alumino borosilicate glasses in thermal, optical and luminescence domain for solid state lighting application

Zinc alumino borosilicate (ZABS) glasses incorporated with Dy3+ ions are prepared through melt-quenching technique. Non-crystallinity behaviour of the glasses are confirmed through XRD studies. The presence of functional and vibrational groups in the glass network are witnessed through FTIR studies. From the differential thermal analysis (DTA), the thermal stability of the glasses are found to be greater than 90 °C. UV–Visible–NIR spectra of glasses showed strong absorptions of Dy3+ ions in the NIR region (∼1267 nm). The highest bandgap value is obtained for ZABSDy0.5 (4.27 eV) glass that has the lowest amount of non-bridging oxygens. The ionic nature of dysprosium ions in the glass vicinity is thereby known through bonding parameter calculation. Judd-Ofelt (J-O) intensity parameters showed the trend Ω2 > Ω6 > Ω4, maintained same for all synthesized glasses. The luminescence spectra showed three emission peaks of Dy3+ ions at 482 (6H15/2), 575 (6H13/2) and 663 (6H11/2) nm. The hypersensitive transition observed at 4F9/2 → 6H13/2 exhibits a greater emission cross-section and radiative transition for all the glasses. Through the decay measurements, the lifetime of the Dy3+ ions are calculated. The estimated CIE coordinates for the glasses showed their location in white light region. The correlated colour temperature (CCT) values are obtained between 4200 and 4500 K suggesting the importance of glasses to use for white-LEDs application.

Recent Progress and Prospects on Metal Halide Perovskite Nanocrystals as Color Converters in the Fabrication of White Light-Emitting Diodes

Recently, metal-halide perovskite nanocrystals (NCs) have shown major development and have attracted substantial interest in a wide range of applications, such as light-emitting diodes (LEDs), solar cells, lasers, and photodetectors due to their attractive properties, such as superior PL emission, a wider range of color tunability, narrow emission spectra, better color purity, low cost, easy solution-processability, and so on. In the past, many color-converting materials, such as III-nitrides, organics, polymers, metal chalcogenides, were investigated for solid-state lighting (SSL) white light-emitting diodes (WLEDs). Still, they suffer from issues such as low stability, low color rendering index (CRI), high correlated color temperature (CCT), low luminous efficiency (LE), and high cost. In this sense, metal-halide perovskite NCs exhibit a better color gamut compared with conventional lighting sources, and production costs are comparatively cheaper. Such materials may offer an upcoming substitute for future color-converting WLEDs. In this review, we discuss the metal halide perovskite NCs and their synthesis protocols. Then we elaborate on the recent progress of halide perovskite NCs as a conversion layer in the application of WLEDs.