Enhanced Efficiency, Broadened Excitation, and Tailored Er3+ Luminescence Triggered by Te4+ Codoping in Cs2NaYbCl6 Crystals for Multifunctional Applications.

The quest for efficient and tunable luminescent materials has been at the forefront of research in the fields of chemistry and materials science. This work delves into the investigation of the luminescence properties of Er3+ ions triggered by 1% Te4+ in the environmentally benign perovskite Cs2NaYbCl6 (CNYC) crystals, aiming to enhance their efficiency and tune the luminescence color. The ratio of the green (2H11/2, 4S3/2-4I15/2) to red (4F9/2-4I15/2) emissions of Er3+ can be freely tunable by varying the concentration of Er3+ and producing the defects induced by codoping Te4+. The calculations reveal that the multiexcitonic excitations of Er3+ stem from f-f (4I15/2-4G11/2, 2H9/2) rather than d-f transitions. The broadened excitation, tuning of color, and enhancement of efficiency achieved in the luminescence perovskite crystals Cs2NaYbCl6:Te4+, Er3+ (CNYC:Te4+,Er3+) presents promising opportunities for the development of advanced optoelectronic devices with superior performance. Moreover, our investigation demonstrates the tunable luminescence response of CNYC:Er3+ to temperature variations, offering potential applications in temperature sensing.

Enhancing Luminescence in Hue-Tunable White-Light Emitting K4CdCl6:Sb3+,Mn2+ All-Inorganic Halide Perovskites: Insights from Defect Engineering and Energy Transfer.

All-inorganic halide perovskites (AIHPs) have emerged as highly promising optoelectronic materials owing to their remarkable properties, such as high-optical absorption coefficients, photoluminescence efficiencies, and dopant tolerance. Here, we investigate the AIHPs K4CdCl6:Sb3+,Mn2+ that demonstrate hue-tunable white-light emission with an exceptional photoluminescence quantum yield of up to 97%. Through a detailed investigation, we reveal that efficient energy transfer from Sb3+ to Mn2+ plays a dominant role in the photoluminescence of Mn2+, instead of the conventional 4T1g → 6A1g transition of Mn2+. Thermodynamic analysis highlights the crucial role of a Cl-rich environment in obtaining the K4CdCl6 phase, while transformation from K4CdCl6 to KCdCl3 can be achieved under Cl-poor and K-poor conditions. The theoretical analysis reveals that defect Cli is more readily formed compared to defect VK, corroborating experimental findings that the K4CdCl6:Sb3+ phase is exclusively obtained when the solution contains HCl concentrations higher than 4 mol L-1. Our work provides valuable insights into the photoluminescence mechanism of Sb3+, defect engineering through heterovalent doping, and efficient energy transfer between Sb3+ and Mn2+ in K-Cd-Cl-based perovskites, which offers a new perspective for the design and development of novel AIHPs with superior optoelectronic performance.

Spectral Tunability, Luminescence Enhancement, and Temperature Sensitivity of Sb3+-Doped Bismuth-Based Halide Emission Crystals for Anti-Counterfeiting Applications.

The synthesis of sustainable luminescent materials with simplicity, low energy consumption, and nontoxicity is of great importance in the field of chemistry and materials science. In this study, a room temperature evaporation method was employed to synthesize Sb3+-doped bismuth-based halide emission crystals, allowing for investigation of spectral tuning, luminescence enhancement, and temperature sensitivity. By substitution of Rb+ with varying concentrations of Cs+ in Rb3BiCl6 (RBC), the luminescent color of the crystals can be tuned from orange to yellow. The resulting alloyed yellow-emitting crystals were identified as Rb2CsBiCl6 (RCBC). Remarkably, when one-third of the Rb+ ions were replaced by Cs+ in the RBC, the crystals exhibited improved thermal stability and a 20-fold increase in luminescence intensity. The temperature-sensitive behavior was observed for RBC:Sb, with emission shifting from 590 to 574 nm upon heating while the yellow emission of RCBC:Sb exhibited no significant peak shift with temperature. Notably, the yellow emission of RBC:Sb could be reversibly converted back to orange light upon cooling to room temperature. In contrast, RCBC:Sb exhibited no significant peak shift with temperature. The differential temperature sensitivity between RBC:Sb and RCBC:Sb offers potential applications in anti-counterfeiting measures.

Precise Hue Control in a Single-Component White-Light Emitting Perovskite Cs2 SnCl6 through Defect Engineering Based on La3+ Doping.

Single-component white light emitters based on the all-inorganic perovskites will act as outstanding candidates for applications in solid-state lighting thanks to their abundant energy states for self-trapped excitons (STE) with ultra-high photoluminescence (PL) efficiency. Here, a complementary white light is realized by dual STEs emissions with blue and yellow colors in a single-component perovskite Cs2 SnCl6 :La3+ microcrystal (MC). The dual emission bands centered at 450 and 560 nm are attributed to the intrinsic STE1 emission in host lattice Cs2 SnCl6 and the STE2 emission induced by the heterovalent La3+ doping, respectively. The hue of the white light can be tunable through energy transfer between the two STEs, the variation of excitation wavelength, and the Sn4+ /Cs+ ratios in starting materials. The effects of the doping heterovalent La3+ ions on the electronic structure and photophysical properties of the Cs2 SnCl6 crystals and the created impurity point defect states are investigated by the chemical potentials calculated using density functional theory (DFT) and confirmed by the experimental results. These results provide a facile approach to gaining novel single-component white light emitter and offer fundamental insights into the defect chemistry in the heterovalent ions doped perovskite luminescent crystals.

Bright tunable luminescence of Sb3+ doping in zero-dimensional lead-free halide Cs3ZnCl5 perovskite crystals.

Lead-free zero-dimensional (0D) perovskite nanocrystals (NCs) with isolated octahedral structures have attracted considerable attention due to their unique photoelectric properties, such as highly efficient emissions with broadband features. A series of phosphors composed of Sb3+-doped 0D perovskite crystals Cs3ZnCl5 with wavelength-tunable emission spectra have been obtained using a facile recrystallization method at room temperature in air. By controlling the doping concentration of Sb3+ in Cs3ZnCl5 lattice, bright emissions from red to orange have been achieved under excitation at 320 nm due to the expansion of the crystal lattice, and the emission excited at 275 nm is bluish-white, spanning the full visible region. Inductively coupled plasma emission spectrometry (ICP) demonstrates the Sb3+ substitutes for Zn2+ rather than Cs+ due to the similar charges and ionic radii. The luminescence performance of phosphor Cs3ZnCl5:Sb3+ can be improved obviously by replacing 3 mol% of Cs+ with Rb+ or K+ due to the further distortion of the crystal lattice. The present approach allows the synthesis of large-scale emissive lead-free 0D perovskites activated by Sb3+ with tunable luminescence color.

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.

4-Bromo-Butyric Acid-Assisted In Situ Passivation Strategy for Superstable All-Inorganic Halide Perovskite CsPbX3 Quantum Dots in Polar Media.

A crucial challenge is to develop an in situ passivation treatment strategy for CsPbX3 (CPX, X=Cl, Br, and I) quantum dots (QDs) and simultaneously retain their luminous efficiency and wavelength. Here, a facile method to significantly improve the stability of the CPX QDs via in situ crystallization with the synergistic effect of 4-bromo-butyric acid (BBA) and oleylamine (OLA) in polar solvents including aqueous solution and a possible fundamental mechanism are proposed. Monodispersed CsPbBr3 (CPB) QDs obtained in water show high photoluminescence quantum yields (PLQYs) of 86.4 % and their PL features of CPB QDs have no significant change after being dispersed in aqueous solution for 96 h, which implies the structure of CPB QDs is unchanged. The results provide a viable design strategy to synthesize all-inorganic perovskite CPX QDs with strong stability against the attack of polar solvents and shed more light on their surface chemistry.

Improved Moisture-Resistant and Luminescence Properties of a Red Phosphor Based on Dodec-fluoride K3RbGe2F12:Mn4+ through Surface Modification.

Mn4+-activated red-emitting fluoride phosphors are essential for white light-emitting diodes (WLEDs) with desirable color rendition index (CRI) because of their unique and efficient luminescence characteristics. Herein, we synthesized a novel Mn4+-activated dodec-fluoride phosphor K3RbGe2F12:Mn4+ (KRGF:Mn) through a facile ionic exchange method at room temperature. A surface-modified strategy using weak reducing agents such as oxalic acid and citric acid is proposed to improve the moisture-resistance ability of KRGF:Mn phosphor dramatically, and the possible mechanism of surface modification has been investigated. A shell formed on the surface of the KRGF:Mn phosphor reduces the concentration of Mn4+ on the surface, which can prevent the internal KRGF:Mn group hydrolysis by the external moisture and effectively decreased the probability of energy migration to surface defects, thereby increasing both the emission efficiency and the moisture-resistance ability of KRGF:Mn. More interestingly, the KRGF:Mn phosphor is quenched after soaking in water for 72 h but recovered to the initial brightness after soaking in the modifier solutions for 2 min. This work fabricates a new efficient red phosphor KRGF:Mn for application in warm WLEDs and provides insight into the mechanism of the strategy to improve the moisture resistance of the stability of Mn4+ through surface modification.

In situ organic solvent-free synthesis of a novel red emitting Mn4+ doped KRbGeF6 phosphor at the room temperature.

Red emitting phosphors of Mn4+ doped fluorides are in high demand because the high color purities of phosphors make them potentially useful white light-emitting diodes (WLEDs) as backlights of electronic devices. We herein report an efficient red emitting phosphor KRbGeF6 : Mn4+ (KRGF : Mn) that was prepared by an in situ one-pot ion-exchange method at room temperature without organic solvents or HF. Homogenous mixtures of the starting materials with a stoichiometric KRGF : Mn ratio were partly dissolved in various acid solutions, and [MnF6]2- and [GeF6]2- successively underwent ion exchange under stirring. More importantly, in situ recrystallization of KRGF : Mn occurred simultaneously in solution with water as a solvent. Evidently, the formation of stable KRGF : Mn crystals propels the processes of dissolution and ion exchange. We also investigated the effect of inorganic acids on the resultant phases and photoluminescence properties of KRGF : Mn. The red phosphor KRGF : Mn prepared in HCl solution shows the highest luminescence intensity with an yield of 80%.

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.

Synthesis and improved photoluminescence of hexagonal crystals of Li2ZrF6:Mn4+ for warm WLED application.

A series of red-emitting phosphors composed of Li2ZrF6:Mn4+ (LZF:Mn) have been synthesized via an ionic-exchange reaction route at room temperature. The microstructure and optical characterizations have been investigated according to the detailed experiments. The morphology of the phosphor LZF:Mn changes with the concentration of HF, the reaction time and temperature. The uniform crystals of LZF:Mn with regular hexagonal tablets have been obtained in 30-40 wt% HF solutions by conducting the reaction at room temperature for about 8 h. The influences of reaction parameters on the morphology and photoluminescence properties of LZF:Mn have been systematically investigated. The luminescence intensity of LZF:Mn has been optimized by controlling the synthesis procedure and parameters. The white light-emitting diode (WLED) fabricated with LZF:Mn and Y3Al5O12:Ce3+ (YAG:Ce) on InGaN LED chip displays a warm white light with correlated color temperature (CCT) at 3789.4 K and color rendering index (CRI) of 91.

Synthesis and improved photoluminescence of a novel red phosphor LiSrGaF6:Mn4+ for applications in warm WLEDs.

Red phosphors composed of Mn4+-activated complex fluorides have attracted considerable attention for applications in warm white light-emitting diodes (WLEDs). In the present study, we report a facile strategy to synthesize a novel red phosphor LiSrGaF6:Mn4+ (LSGF:Mn) at room temperature, and we also discuss its formation mechanism. Mn4+ ions occupy Ga3+ sites located at the centers of distorted [GaF6]3- octahedrons and emit intense red luminescence when excited by UV or blue light. The effects of synthesis conditions such as the type of strontium salts, the concentrations of K2MnF6 and NH3·H2O, and the reaction temperature have been investigated. The luminescence intensity of the phosphor LSGF:Mn has been improved by optimizing the synthetic parameters. The as-prepared phosphor LSGF:Mn exhibits broad and intense absorption in the blue region and bright luminescence in the red region, which indicate that it is promising for applications in warm WLEDs.

A novel red phosphor of seven-coordinated Mn4+ ion-doped tridecafluorodizirconate Na5Zr2F13 for warm WLEDs.

Herein, a novel red phosphor based on seven-coordinated Mn4+ ion-doped tridecafluorodizirconate, Na5Zr2F13 (NZF), has been synthesized by stirring a mixture of K2MnF6, NaF, and H2ZrF6 at room temperature. The crystal structure and morphology of the as-obtained phosphor NZF:Mn have been determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The composition and distribution of Mn4+ ions in NZF have been confirmed by energy-dispersive spectroscopy (EDS) and element mapping via transmission electron microscopy (TEM). The phosphor NZF:Mn exhibits a strong zero phonon line (ZPL) at 616 nm under excitation of blue light from a GaN light-emitting diode (LED) chip; this is attributed to the low symmetry of Mn4+ ions occupied in a seven-coordinated environment. The luminescence intensity of NZF:Mn has been optimized by controlling the synthesis procedure and synthetic parameters. The luminescence mechanism of the red phosphor NZF:Mn has been investigated according to the detailed experimental results. A warm white light has been produced by a WLED fabricated with the red phosphor NZF:Mn and the commercial yellow phosphor Y3Al5O12:Ce3+ (YAG:Ce) on a GaN LED chip.

Abnormal site occupancy and high performance in warm WLEDs of a novel red phosphor, NaHF2:Mn4+, synthesized at room temperature.

A novel red phosphor, NaHF2:Mn4+ (NHF:Mn), was obtained via substituting Na+ located at the center of the octahedron coordinated with six F- ions with Mn4+ in the host lattice of NHF. The phase purity and the exact composition of the obtained NHF:Mn were confirmed by X-ray powder diffraction (XRD), Rietveld refinement, energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and infrared (IR) spectroscopy, respectively. The luminescence intensity of NHF:Mn was enhanced by optimizing the synthetic conditions. A series of warm white light-emitting diodes (WLEDs) with a color rendering index (CRI) higher than 88.0 and correlated color temperatures (CCT) between 3146 and 5172 K were obtained by encapsulating the as-prepared red phosphor NHF:Mn with the yellow one Y3Al5O12:Ce3+ (YAG:Ce) on blue chips. The advantage of the synthetic strategy to obtain NHF:Mn can be extended to develop novel Mn4+ doped red phosphors via substituting for central ions with unequal electric charge in the centers of octahedra.

Tunable Yellow-Red Photoluminescence and Persistent Afterglow in Phosphors Ca4LaO(BO3)3:Eu3+ and Ca4EuO(BO3)3.

In most Eu3+ activated phosphors, only red luminescence from the 5D0 is obtainable, and efficiency is limited by concentration quenching. Herein we report a new phosphor of Ca4LaO(BO3)3:Eu3+ (CLBO:Eu) with advanced photoluminescence properties. The yellow luminescence emitted from the 5D1,2 states is not thermally quenched at room temperature. The relative intensities of the yellow and red emission bands depend strongly on the Eu3+ doping concentration. More importantly, concentration quenching of Eu3+ photoluminescence is absent in this phosphor, and the stoichiometric compound of Ca4EuO(BO3)3 emits stronger luminescence than the Eu3+ doped compounds of CLBO:Eu; it is three times stronger than that of a commercial red phosphor of Y2O3:Eu3+. Another beneficial phenomenon is that ligand-to-metal charge transfer (CT) transitions occur in the long UV region with the lowest charge transfer band (CTB) stretched down to about 3.67 eV (∼330 nm). The CT transitions significantly enhance Eu3+ excitation, and thus result in stronger photoluminescence and promote trapping of excitons for persistent afterglow emission. Along with structure characterization, optical spectra and luminescence dynamics measured under various conditions as a function of Eu3+ doping, temperature, and excitation wavelength are analyzed for a fundamental understanding of electronic interactions and for potential applications.

Enhanced photoluminescence and phosphorescence properties of green phosphor Zn2GeO4:Mn(2+)via composition modification with GeO2 and MgF2.

A green long-lasting phosphorescence (LLP) phosphor Zn2GeO4:Mn(2+) (ZGOM) has been synthesized by a solid-state method at 1100 °C in air. The luminescence intensity has been improved up to 9 and 6 times through mixing GeO2 and MgF2 into the composition, respectively. The phosphorescence duration of the sample has been prolonged to 5 h. The phosphor, composed of a mixture of Zn2GeO4 (ZGO), GeO2, and MgGeO3 phases, emits enhanced green luminescence with a broad excitation band between 250 nm to 400 nm. Under identical measurement conditions, the optimized phosphor ZGOM has a higher emission intensity and shows longer wavelength emission than those of the commercial green LLP phosphor SrAl2O4:Eu,Dy (SAOED) under an excitation at 336 nm. The quantum yield of the sample modified by GeO2 and MgF2 is as high as 95.0%. Understanding of the formation mechanism for enhancement of emission intensity and prolonging of phosphorescence duration of ZGOM is fundamentally important, which might be extended to other identified solid-state inorganic phosphor materials for advanced properties.

A red phosphor BaTiF(6):Mn(4+): reaction mechanism, microstructures, optical properties, and applications for white LEDs.

Red phosphors BaTiF6:Mn(4+) with microrod and polyhedron morphologies have been prepared respectively by etching TiO2 and Ti(OC4H9)4 in a HF solution with an optimized concentration of KMnO4 at 1.5 mmol L(-1) in hydrothermal conditions. The red phosphor BaTiF6:Mn(4+) exhibits a broad excitation band in the blue region and sharp emission peaks in the red region. A white LED (WLED) fabricated with the red phosphor BaTiF6:Mn(4+) shows "warm" white light that possesses a color rendering index of 93.13 at a color temperature of 4073.1 K.