Cold White Light Research Articles

Investigation on luminescent characteristics of Tb3+/Dy3+co-doped boro-phosphate glass for cool white LED and radiation shielding applications

The Tb3+/Dy3+ co-doped Boro-Phosphate Glass (BPANZDyTb) was produced (40 B2O3 + 39P2O5 + 5 Al2O3 + 5 NaF + 10 ZnO + 0.5 Tb2O3 + 0.5 Dy2O3) using melt-quenching technique. X-ray diffraction measurements, Raman, and Fourier Transform Infrared were used to evaluate the structural behavior of the prepared glass. Powder-XRD spectra, in the 10–90° range showed that the prepared glass was amorphous. FTIR analysis reveals that the network contains a variety of structural groups, including B-O-B, BO4, BO, P-O, PO2, P-O-B, and PO4 units. The UV–visible diffuse reflectance spectroscopy was used to record and study the optical linear properties of Tb3+/Dy3+ co-doped Boro-Phosphate Glass (BPANZDyTb). The photoluminescence excitation peak was obtained at 348 nm. The emission peaks were located at 484 nm (4F9/2 → 6H15/2 → blue), 576 nm (4F9/2 → 6H13/2 → yellow), and 662 nm (4F9/2 → 6H11/2 → red). Tb3+ ions are located at 412 nm (5D3 → 7F5), 441 nm (5D3 → 7F4), 546 nm (5D4 → 7F5), and 625 nm (5D4 → 7F3). The result of CIE 1931 chromaticity coordinates indicate that the prepared glass is suitable material for cold white light emitting diode applications due to its color coordinates x = 0.3106 and y = 0.3240 and correlated color temperature (CCT) values about 6768 K. The gamma-ray parameters such as half-value layer (HVL), mass attenuation coefficient (μ/ρ), mean free path (MFP), and effective atomic number (Zeff) of the BPANZDyTb glass were studied using Phy-X software. The results of the gamma-ray parameter show that the Dy3+ ions and Tb3+ ions co-doped BoroPhosphate glass is an appropriate material for radiation shielding applications.

Blue and white light emissions and energy transfer in Tm3+ and Dy3+/Tm3+ doped lithium-aluminum-zinc phosphate glasses

Lithium-aluminum-zinc phosphate glasses doped with thulium and dysprosium ions are characterized by using spectroscopy techniques. The Judd-Ofelt parameters were evaluated to calculate the radiative parameters of thulium 1D23F4 and 1G43H6 visible transitions and 3H43F4 near infrared transition, which shows the highest optical amplification parameters. Upon 356 nm excitation, the Tm3+ doped phosphate glass emits blue light with CIE1931 chromaticity coordinates x = 0.1540 and y = 0.0283 and color purity around 96.8%. With excitations at 347 and 350 nm, the Dy3+/Tm3+ doped phosphate glass emits neutral and cold white light with correlated color temperature values of 4716 and 6628 K, respectively. The dysprosium emission decay time in the codoped glass is shorter than that in the Dy3+ single-doped glass, indicating a non-radiative energy transfer from Dy3+ to Tm3+. The dominant electrical interaction involved in the energy transfer, following the model Inokuti-Hirayama, is of dipole-dipole type. The energy transfer probability and efficiency are 769.0 s-1 and 0.53, respectively. Tm3+ doped and Dy3+/Tm3+co-doped lithium-aluminum-zinc phosphate glasses could be appropriate for blue and neutral/cold white light-emitting device applications.

Electronic defect engineering of double-doped β-KYF4:Eu3+,Bi3+ red phosphors: Negative thermal quenching and applications for high-efficiency white light-emitting diodes

Commercial WLEDs in a cold white light with a lower color rendering index(Ra) and higher correlated color temperature due to the lack of a red component. Therefore, we propose to develop a non-oxide rare-earth-based red phosphor with excellent luminescence performance and thermal stability. The crystal phases, particle morphology, elemental states, photoluminescence(PL) behavior, and electronic structure were characterized. The Density Functional Theory (DFT) calculation was carried out to reveal the mechanisms of the crystal and electronic structures on the photoluminescent properties and the associated energy-transfer mechanisms. Furthermore, the optimal double-doped KYF4 phosphor with negative thermal quenching and the yellow phosphor YAG:Ce3+ were co-assembled into LEDs, which exhibited a warm white light with a color rendering index of 93.9 and a correlated color temperature of 4275 K under a driving current of 9 mA. These results indicate that the optimized phosphor has considerable potential for application in red light supplements for WLEDs.

Adding Phyto-LED Spectrum to White-LED Light Increases the Productivity of Lettuce Plants

The effect of light of various spectral compositions on the complex morphophysiological parameters of lettuce plants in hydroponic was studied. The light sources had the following light spectra: warm white light—2700 K, cold white light—6500 K, and Phyto-LED light, as well as 2700 K + Phyto-LED and 6500 K + Phyto-LED. The dry and fresh biomass, leaf area, stem length, photosynthetic pigment content, photosynthesis and transpiration rates, chlorophyll fluorescence parameters, and percentage of plants that passed into the generative stage of development were studied. The results showed that partial and complete replacement of white LEDs by Phyto-LEDs with lower green light content and greater amounts of far-red light in the radiation spectrum caused an increase in plant productivity of 37%, average leaf area, and transpiration rate in the treatments but also promoted an earlier transition of plants to flowering under light treatment, Phyto-LEDs, and Phyto-LEDs + white LEDs. The 2700 K + Phyto-LED treatment had one of the highest productivities, as did the Phyto-LED and 6500 K + Phyto-LED treatments, but this lighting treatment provoked less flowering on the 60th day of the growing period.

Structural and Optical Characterization of a New Tetra- and Hexa-Coordinated Cd-Based Hybrid Compound with White Light Emission

The present paper deals with a new two-in-one zero-dimensional (0D) organic–inorganic hybrid compound namely (C6H10N2)4[CdBr6][CdBr4]2. This molecular crystal structure contains isolated CdBr4 tetrahedra and CdBr6 octahedra. The optical characterization by UV–Vis–NIR spectroscopy shows that the (C6H10N2)4[CdBr6][CdBr4]2 exhibits a large gap energy of 4.97 eV. Under UV excitation, this hybrid material shows a bright cold white light emission (WLE) at room temperature. The photoluminescence (PL) analysis suggests that the WLE originates from the organic molecules. Density of states (DOS) analysis using the density functional theory (DFT) demonstrates that the calculated HOMO(Br)→LUMO(organic) absorption transition (4.1 eV) does not have significant intensity, while, the transition involving the valence band (VB) and the second and third conduction bands (CB) around 5 eV are allowed, which is in good agreement with the experimental gap value. The interesting theoretical result is that the LUMO(organic)→HOMO(Br) emission is allowed, which confirms the important role of the organic molecule in the emission mechanism, in good agreement with the experimental PL analysis.

Enhancing luminescence performance via adjusting the doping concentration and boron aluminum ratio in Dy3+ -activated barium-boroaluminosilicate glasses for laser and W-LED applications

A series of barium-boroaluminosilicate [30SiO2-11Al2O3-44B2O3-5BaO-(10-x)K2O-xDy2O3 (with x = 0.25, 0.5, 0.75, 1.0, 1.25, 1.5 mol%)] glasses doped with Dy3+ ions were prepared by the high temperature (melt quenching) method. In the glass matrix, the relationship among structure, luminescence properties, and B/Al ratio was analyzed; also studied are the physical properties of glass and influence of Dy3+ concentration on the luminescence properties. Differential Scanning Calorimeter (DSC) results have shown the glass matrix exhibiting good thermal stability and high resistance to crystallization. FTIR and Raman spectra have confirmed the presence of stretching and bending vibrations of [BO3], [AlO4] and [SiO4] structural units in the prepared glass. The observed UV–Vis–NIR spectra have indicated that the existence of thirteen bands corresponding to the transition Dy3+ ions from 6H15/2 level to different excited levels; the transmittance curves obtained have shown the transmittance up to 91 %. Increase in Dy3+ concentration is found to decrease the optical band gap; the calculated Judd-Oflet parameter is found to follow the trend Ω2＞Ω4＞Ω6. Photoluminescence studies have shown three emission peaks which could be associated to the transitions: 4F9/2 → 6H15/2 (blue light), 4F9/2 → 6H13/2 (yellow light), and 4F9/2 → 6H11/2 (red light); the maximum intensity obtained for the glass with x = 0.75 mol%, with spacing between Dy3+ ions being 1.9137 Å; and the decay curve could be fitted with double exponential function. The CIE results have revealed that the chromaticity coordinates are closer to that of standard white light, and the color temperature located in the region of cold white light.

Intriguing Role of Weak Electron Donor in Dictating the Luminescent Characteristics of DS‐A‐DW Materials

AbstractThe short wavelength (SW) emission region of the materials employing strong donor (DS) phenothiazine (PTZ) is generally correlated to its quasi‐axial (QAPTZ) conformer arrangement. This propels to investigate the specific role of weak donors (DW) such as carbazole (CZ) in determining the emission characteristics of molecular heredity (MH) type structural design encompassing dual donors of varying strength. For this purpose, a common DS(PTZ)–Acceptor unit is linked to the DW(CZ) unit via different linkage positions to form M1, M2, and M3, which not only alters the absorption and dual emission characteristics but also influences the delayed fluorescence phenomenon. The SW emission originates by minimizing the aggregation factor rather than by literature envisaged QAPTZ conformer. Incorporating M1 as a single molecular white light emitter (SMWLE) in near UV light emitting diode (LED) devices results in cold white light emission with CRI of 68 and CIE of (0.24, 0.33), while its corresponding solution‐processed organic light‐emitting diode devices delivers warm white electroluminescence with an EQE of 5.8%. Overall, this work demonstrates the significant contribution of the DW in attaining the white light emission characteristics of MH molecular design not only at the molecular level but also in practical light‐emitting devices.

A novel halide hybrid white light emitter with remarkable structural and emission stability

Addressing the issues of self-absorption effect among different components in traditional white light-emitting diodes (WLEDs) and the high cost associated with rare earth elements, we propose the potential utility of zero-dimensional organic–inorganic metal halide hybrids (0D OIMHs) in white WLEDs fabrication. In this study, we synthesized a novel 0D OIMH, (C5N2H14)ZnCl4, characterized by broadband white light emission. The (C5N2H14)ZnCl4 crystal features a short ultraviolet cutoff situated at 190 nm and emits cold white light with a Color Rendering Index (CRI) of 73 under an excitation wavelength of 260 nm. Furthermore, (C5N2H14)ZnCl4 demonstrates exceptional structural and emission stability in an air atmosphere over a span of three months.

Enhanced thermal stability and luminous properties of Dy3+/Tm3+/Eu3+ doped glass ceramics containing Sr4Bi(PO4)3O crystalline phases based on back energy transfer

White light emitting and optical temperature sensing materials with high thermal stability have broad market development prospects. The use of substrates with excellent thermal stability is a common idea to improve thermal stability, while the modulation of dopants to enhance thermal stability has been less studied. Therefore, in this work, Tm3+/Dy3+/Eu3+ doped transparent glass ceramics containing Sr4Bi(PO4)3O crystalline-phase were prepared by melt-crystallization method to achieve warm white light emission and optical temperature sensing with good thermal stability. Since the Tm3+-Dy3+ doped samples can only achieve cold white light emission, warm white light emission is obtained by adding Eu3+, which can emit red light. The application scenario of the material is expanded. The luminous intensities of Tm3+, Dy3+, and Eu3+ were 109.4 %, 89.1 %, and 70.7 % of those at room temperature, at 473 K. The increase in the emission intensity of Tm3+ was explained by the presence of back energy transfer (BET) from Dy3+ and Eu3+ to Tm3+. The chromaticity shift (Δε) of the samples was 2.43 × 10−4 and the luminescent colour was stable. The absolute sensitivity of the material can reach 0.69 K−1 at 473 K, and the relative sensitivity of the material can reach 1.60 % K−1 at 293 K. This work provides new ideas for the study of improving the thermal stability of materials.

Optical and luminescent properties of Dy3+/Sm3+ doped and codoped Zinc Borophosphate glasses for W-LED application

In this work, a series of zinc borophosphate glasses (ZnPBAl), doped and codoped with Dy3+ and Sm3+, was studied for potential application in W-LEDs. The samples were prepared by the melt-quenching method and their luminescent and optical properties were investigated. The optical absorption spectra presented all Dy3+ and Sm3+ peaks corresponding to the transitions from the 6H15/2 and 6H5/2 states, respectively, to the excited energy levels. The 350 nm excitation source was chosen, considering photoluminescence excitation (PLE) results, to investigate the energy transfer from Dy3+ to Sm3+ ions. The energy transfer was indicated by photoluminescence (PL) spectra of Dy:Sm-codoped glasses and investigated by the energy transfer efficiency (η) using the lifetime data of both doped and codoped samples. The PL as a function of temperature was also studied. The CIE diagram of Dy-doped glasses showed their color emission close to the white region and the simulation of a combined Blue LED created an illumination route from warm to cold white light.

White light emission in 0D halide perovskite [(CH3)3S]2SnCl6·H2O crystals through variation of doping ns2 ions

With the rapid development of white LEDs, the research of new and efficient white light emitting materials has attracted increasing attention. Zero dimensional (0D) organic–inorganic hybrid metal halide perovskites with superior luminescent property are promising candidates for LED application, due to their abundant and tailorable structure. Herein, [(CH3)3S]2SnCl6·H2O is synthesized as a host for dopant ions Bi3+ and Sb3+. The Sb3+ doped, or Bi3+/Sb3+ co-doped, [(CH3)3S]2SnCl6·H2O has a tunable optical emission spectrum by means of varying dopant ratio and excitation wavelength. As a result, we can achieve single-phase materials suitable for emission ranging from cold white light to warm white light. The intrinsic mechanism is examined in this work, to clarify the dopant effect on the optical properties. The high stability of title crystalline material, against water, oxygen and heat, makes it promising for further application.Graphical

Efficient White Light‐Emitting Diodes Based on Cu(I) Activated Single‐Phase Halide Single Crystals

Single‐phase white light emitters have become a potential substitute for tricolor phosphor mixtures for the white light‐emitting diodes (WLEDs) application to simplify device structure and eliminate self‐absorption. Newly developed low‐dimensional halides, noted for their highly efficient luminescent characteristics, have seen increasing interest in recent years. Herein, highly efficient white‐light emission is demonstrated in single‐phase zero‐dimensional halide single crystal, namely monovalent Cu‐doped Cs2HfCl6. Cs2HfCl6:Cu single crystals have three luminescent centers. Two emission peaks at 365 nm and 380 nm correspond to the intrinsic self‐trapped excitons emission and a defect‐related trapped exciton emission, respectively. Cu doping introduces an intense Cu‐bound exciton emission peaking at 540 nm with a large Stokes shift of 250 nm and a high photoluminescence quantum yield of 68%. With different excitation wavelengths and Cu‐doping concentrations, Cs2HfCl6:Cu single crystals show tunable emissions. Under 254 nm ultraviolet light excitation, Cs2HfCl6:0.5%Cu yields cold white light with a high color rendering index (Ra = 87.3). These findings demonstrate the potential of Cs2HfCl6:Cu as a promising phosphor for cold WLEDs.

Tunable warm white light emission and energy transfer of Dy3+ co-doped Sr2 LaZrO5.5 :Eu3+ phosphors.

Eu3+ ,Dy3+ co-doped Sr2 LaZrO5.5 -based phosphors were prepared through a sol-gel method. Through characterization, it was found that the Sr2 LaZrO5.5 -based fluorescent powder co-doped with Eu3+ and Dy3+ had a cubic structure. At an excitation wavelength of 290 nm, the substrate Sr2 LaZrO5.5 exhibited strong blue emission at 468 nm, and the Sr2 LaZrO5.5 :18%Eu3+ phosphor exhibited a strong red emission peak at 612 nm. When the doping amount of Dy3+ was 5, 8, 12, 15, or 18%, the Sr2 LaZrO5.5 :18%Eu3+ phosphor changed from an orange-red light, to a warm white light, and to a cold white light. According to the emission spectra, the emission intensities of the substrates Sr2 LaZrO5.5 and Sr2 LaZrO5.5 :Eu3+ decreased with increasing Dy3+ concentration, confirming the energy transfer between the host Sr2 LaZrO5.5 -Eu3+ ,Dy3+ , and resulting in a lower CCT value, with significantly improved white light emission.

Spectral tunability of K2Lu(WO4)(PO4): Dy3+, Eu3+ phosphors and remote luminescent layers for high-quality white light

Dy3+ and Eu3+ co-doped phosphors have been emerged as potential candidate to generate high-quality white light under the ultraviolet (UV) or near ultraviolet (NUV) excitation for health and comfort lighting. Herein, K2Lu(WO4)(PO4) crystal has been newly developed to accommodate rare earth ions, such as Dy3+ and Eu3+ ions, to achieve spectral tunability of high-quality white light. Under NUV excitation, Dy3+ singly-doped K2Lu(WO4)(PO4) phosphors exhibit the desired blue emission at 486 nm and yellow emission at 575 nm, attributed to the electric dipole transition 4F9/2 → 6H15/2 and the magnetic dipole transition 4F9/2 → 6H13/2 transitions of Dy3+ ions, respectively. Interestingly, the emission color can be facilely adjusted from cold white light to pink light under 365 nm NUV excitation due to the co-doping of Eu3+ ions in K2Lu(WO4)(PO4): 0.05Dy3+ sample. Further, the remote luminescent layers containing K2Lu(WO4)(PO4): 0.05Dy3+, 0.20Eu3+ phosphor can be printed on glass substrate by screen printing technique to generate high-quality white light with the correlated color temperature (CCT) of 5433 K and color rendering index (CRI) of 87. Moreover, the remote luminescent layers exhibit better heat dissipation performance compared to conventional encapsulated LEDs and can be used as a multicolor emitting candidate for high-power white LEDs.

Synthesis, optical characteristics and thermal stability of Mn4+-doped Na3GaF6 red-emitting phosphor for high-performance warm WLED

Nowadays, Mn4+-activated fluoride red phosphors with high color purity, strong zero phonon line emission and relatively short decay time are crucial for improving the optical performance of WLED and emerging applications. In this work, a series of red-emitting Mn4+-activated fluoride phosphors in consideration of the non-equivalent substitution of Mn4+ for Ga3+ in the Na3GaF6 host are synthesized via the coprecipitation method at room temperature. The use of different reaction solvents successfully regulates the morphology, size and luminescence intensity of the phosphor. Under blue light excitation, Na3GaF6:Mn4+ sample shows a bright narrow-band red emission with exceptional correlated color temperature (4029 K). Moreover, the emission of strong zero phonon line induces the outstanding color purity of red light (93%). In addition, the critical concentration of Mn4+ is determined to be 0.04 and the concentration quenching mechanism is also systematically discussed. Noticeably, when Na3GaF6:Mn4+ phosphor achieves maximum fluorescence emission, its fluorescence lifetime value is only 3.48 ms. Additionally, the theoretical calculated results demonstrate that Na3GaF6 host can provide strong crystal field strength for Mn4+, and the Racah parameters (B and C) and nephelauxetic ratio (β1) are used to evaluate the nephelauxetic effect of Mn4+, which is compared with other types of Mn4+-activated phosphors. The activation energy, chromaticity shift and chromaticity coordinate variation are systematically calculated to analyze the thermal stability of Na3GaF6:Mn4+ red phosphor. Meanwhile, by employing the as-prepared phosphor Na3GaF6:Mn4+ as a red component, a high-performance warm WLED shows a full spectrum emission, and the corresponding cold white light emission is also transformed into the warm white light emission (CCT = 4224 K, Ra = 89.1 and LE = 111.72 lm/W). Moreover, under high driving current, such WLED exhibits stable output light efficiency. These results suggest that Na3GaF6:Mn4+ as red phosphor has a stupendous potential for warm WLED in indoor lighting.

Preparation, optical properties and energy transfer of SrLaAlO4: Dy3+, Eu3+

A series of Dy3+/Eu3+ single doped and co-doped SrLaAlO4 phosphors was synthesized by the traditional high-temperature solid-state method, and their structure, morphology and optical properties were characterized. The X-ray diffraction (XRD) shows a small amount of doping with Dy3+ and Eu3+ does not change the crystal structure of the matrix SrLaAlO4 and the best synthesis temperature is 1450 °C. The scanning electron microscopy (SEM) indicates the particle size directly ranges from 1 to 5 μm roughly and the energy dispersive spectroscopy (EDS) patterns show that SrLaAlO4: Dy3+ phosphor and SrLaAlO4: Dy3+, Eu3+ phosphor were successfully synthesized. SrLaAlO4: Dy3+ phosphor can be effectively excited by near-ultraviolet light, producing two strong emission lights at 483 nm (blue light) and 579 nm (yellow light), presenting a cold white light; SrLaAlO4: Eu3+ phosphor can be effectively excited by near-ultraviolet light, producing red lights at 622 nm; the characteristic emission peaks of Dy3+ and Eu3+ can be shown simultaneously under the same excitation wavelength in SrLaAlO4: Dy3+, Eu3+ phosphor. By changing the relative doping concentration ratio of Dy3+ and Eu3+, the modulation of SrLaAlO4: Dy3+, Eu3+ phosphor from cold white to warm white light can be achieved. In addition, the study of the luminescent mechanism and lifetime shows that there is energy transfer between Dy3+ and Eu3+ in SrLaAlO4: Dy3+, Eu3+ phosphor.

Vacancy-ordered Te4+-doped Rb2ZrCl6 double perovskite microcrystals for solid-state lighting and non-contact optical thermometry

In this work, we prepared the highly efficient yellow light-emitting vacancy-ordered Te4+-doped Rb2ZrCl6 microcrystals (RZCTs) through a hydrothermal method. RZCT with a photoluminescence quantum yield of 34.6% was prepared at Te4+ feeding ratio of 5%. RZCT is used to fabricate high-efficiency white light-emitting diodes, and adjusting the current can realize the transition of cold and warm white light with CIE color coordinates of (0.31, 0.28) and (0.36, 0.37), respectively. It is also applied to non-contact thermometry using photoluminescence lifetime, of which maximum relative and absolute sensitivities were obtained as 0.89% and 4.76 × 10−3 K−1, respectively. The study shows that the lead-free Te4+-doped perovskite microcrystals exist great potential in next-generation solid-state lighting and non-contact optical thermometry.

In situ and General Multidentate Ligand Passivation Achieves Efficient and Ultra-Stable CsPbX3 Perovskite Quantum Dots for White Light-Emitting Diodes.

Inorganic CsPbX3 perovskite quantum dots (PeQDs) show great potential in white light-emitting diodes (WLEDs) due to excellent optoelectronic properties, but their practical application is hampered by low photoluminescence quantum yield (PLQY) and especially poor stability. Herein, we developed an in-situ and general multidentate ligand passivation strategy that allows for CsPbX3 PeQDs not only near-unit PLQY, but significantly improved stability against storage, heat, and polar solvent. The enhanced optical property arises from high effectiveness of the multidentate ligand, diethylenetriaminepentaacetic acid (DTPA) with five carboxyl groups, in passivating uncoordinated Pb2+ defects and suppressing nonradiative recombination. First-principles calculations reveal that the excellent stability is attributed to tridentate binding mode of DTPA that remarkably boosts the adsorption capacity to PeQD core. Finally, combining the green and red PeQDs with blue chip, we demonstrated highly luminous WLEDs with distinctly enhanced operation stability, a wide color gamut of 121.3% of national television system committee, standard white light of (0.33,0.33) in CIE 1931, and tunable color temperatures from warm to cold white light readily by emitters' ratio. This study provides an operando yet general approach to achieve efficient and stable PeQDs for WLEDs and accelerates their progress to commercialization.

Dy3+/Eu3+/Nb5+ doped NaGdSb2O7 phosphors greatly enhance white light emission

In this paper, a new phosphor NaGdSb2O7 (NGSO) was synthesized by high-temperature solid-phase method, and the transition from cold white light to warm white fluorescence emission was realized by studying the luminous intensity of Dy and Eu under different doping and adjusting the doping ratio of Dy and Eu. In addition, when Nb partially replaces Sb, the band gap of the sample changes, the band structure is changed, and the light intensity is enhanced. The symmetry of the crystal lattice is changed, and the crystal structure is gradually asymmetrical, which promotes the gradual enhancement of fluorescence intensity. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy, absorption spectroscopy and fluorescence lifetime were used to measure the parameters of phase purity, valence state, photoluminescence, absorption emission cross-section and fluorescence decay time. All experimental results show that NGSO: Dy, Eu, Nb phosphors have potential application value in the field of white light-emitting diodes (LEDs).

Novel strategies for the enhancement of the NIR emission in the Ca doped ZnO system: Doping with Cr or adding Sb2S3

We report two novel strategies to enhance the NIR emission in the ZnO:Ca system. In the first strategy, we synthesized ZnO:Ca nanoparticles using a wet chemical method and doped them with various concentration of Cr. SEM images showed that the ZnO:Ca,Cr nanoparticles had a grain-like morphology and their sizes increased from 33 to 110 nm after incrementing the Cr concentration from 4 to 17 mol%. The analysis by X-ray diffraction (XRD) revealed that he ZnO:Ca,Cr sample made with 4 mol% of Cr had a pure hexagonal phase but the other samples synthesized with Cr concentration above 11 mol% presented the hexagonal phase and a small content of Cr2O3 (<3%). Moreover, the photoluminescence (PL) spectra of these samples showed two main emission peaks in the blue and NIR regions (λexc = 265 and 365 nm). In particular, the ZnO:Ca,Cr sample made with 17 mol% of Cr had the strongest NIR emission in the 700–850 nm region and only this sample showed a prominent NIR emission peak at 805 nm. Moreover, the CIE maps showed that the emissions of the ZnO:Ca,Cr samples are located in the blue region under excitation at 265 nm, but it was tuned to the orange region under excitation at 365 nm. In the second strategy, different amounts of Sb2S3 was added during the synthesis of ZnO:Ca to form ZnO:Ca/Sb2S3 composites. In this case, we obtained different morphologies of grains, rod-like and sheet-like for Sb2S3 contents of 10, 28 and 34 wt%, respectively. In addition, the composites presented a mixture of hexagonal and orthorhombic phases, which corresponded to the ZnO and Sb2S3, respectively. The ZnO:Ca/Sb2S3 composites had NIR emissions peaks in the 650–800 nm region and their intensity increased with the content of Sb2S3. Furthermore, their visible emission was tuned from blue to orange-red or to cold white light according to the CIE maps. Overall, the best ZnO:Ca,Cr sample had 312% and 37% higher emission than the ZnO:Ca reference sample and the best ZnO:Ca/Sb2S3 composite (under 265 nm excitation), respectively. In general, XPS studies showed the existence of oxygen vacancy defects, which produced the visible-NIR emissions in all the samples. The strategies presented here for NIR emission enhancement are feasible at low cost and the NIR emissions produced here occur within the first biological window (700–1000 nm), which is of interest for biomedical applications.