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Herein, a dual mode luminescence behavior of rare earth doped/codoped CaMoO4:(Eu3+, Eu3+/Yb3+) phosphors synthesized by hydrothermal method are presented. The structural analysis and surface morphology were investigated by X-ray diffraction, field emission scanning electron microscopy and Fourier transform infrared spectroscopy techniques. The optical properties were studied through UV–vis diffuse reflectance spectroscopy, photoluminescence (PL) and lifetime measurements. The PL excitation spectra of Eu3+ doped CaMoO4 phosphors were recorded at different excitation wavelengths such as 250, 270, 300, 394 nm wavelengths. The down-shifting PL emission spectra of phosphors were recorded at optimized 250 nm excitation wavelength. In addition, emission was also recorded for Eu3+/Yb3+ codoped CaMoO4 phosphor after an excitation wavelength 980 nm through up-conversion process. The phosphors show hypersensitive red emission (5D0 → 7F2) through down-shifting as well as up-conversion processes. The red color was visualized by using commission international de L’Eclairage (CIE) chromaticity diagram. Thus, the obtained results show that dual-mode red emitting phosphors may be used as spectral converter in solar cells.

In this study, white light is generated from the combination of BaMgAl10O17:Mn2+ (BAM) green phosphor and colloidal red CdSe/ZnS quantum dots (QDs) via two different solid and hybrid type geometries. Problem of aggregation in solid type device is discussed in details and motivates us to move towards the fabrication of hybrid type device structure. The photoluminescence (PL) characterization was used to record the excitation and emission spectra of BAM and QDs materials. The size of CdSe/ZnS QDs was confirmed by transmission electron microscopy technique. The CdSe/ZnS QDs owned high quantum yield (> 50%) and contributed to fabrication of high luminous efficiency of white light emitting diodes (WLEDs). The hybrid-type WLED showed 98% lm/W with outstanding color gamut values with a National Television System Committee (NTSC) value of 138% and Rec.2020 value of 105%. Moreover, the hybrid type device structure shows only 5% attenuation in luminous efficiency after 500 h of storage which maintains a great optical property.

The present paper focuses on near infrared (NIR) down-conversion photoluminescence (PL) properties by studying the energy transfer mechanism between Er 3+ and Yb 3+ in CaMoO 4 :Er 3+ , Yb 3+ phosphors. We have successfully synthesized a series of Er 3+ doped and Yb 3+ codoped CaMoO 4 phosphors by hydrothermal method. The down-conversion of Er 3+ -Yb 3+ combination with CaMoO 4 phosphor is designed to overcome the energy losses due to spectral mismatch when a high energy photon is incident on the Si-solar cell. The XRD, FESEM, EDX, PL, UV–Vis, Lifetime measurements were carried out to characterize the prepared down-converting phosphors. The crystallinity and surface morphology were studied by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) techniques. The down-conversion PL spectra have been studied using 380 nm excitation wavelength. The Er 3+ doped phosphors exhibit hypersensitive emission at 555 nm in the visible region due to 4 S 3/2 → 4 I 15/2 transition. The addition of Yb 3+ into Er 3+ doped CaMoO 4 attribute an emission at 980 nm due to 2 F 5/2 → 2 F 7/2 transition. The decrease in emission intensity in visible region and increase in NIR region reveals the energy transfer from Er 3+ to Yb 3+ through cross relaxation. The UV–Vis–NIR spectra shows the strong absorption peak around 1000 nm due to Yb 3+ ion. The lifetime measurement also reveals the energy transfer from Er 3+ to Yb 3+ ions. The maximum value of energy transfer efficiency (ETE) and corresponding theoretical internal quantum efficiency are estimated as 74% and 174% respectively.

The insufficient utilization of incident solar radiation in UV and IR region by existing single-junction photovoltaic devices restrict their efficiency. The triple molybdate NaCaLa(MoO4)3:Tb3+/Yb3+ phosphor was synthesized by solid state method in order to harness the unutilized part of solar spectrum. The structural and optical studies such as X-Ray diffraction (XRD), Photoluminescence (PL), Up-conversion (UC) and UV-Vis diffuse reflectance characterizations were carried out to examine the prepared sample. The structural refinement of XRD powder data of prepared phosphor was also performed with space group I41a(88). The sample was characterized by dual excitation i.e. UV and IR radiation that shows green emission corresponds to 5D4-7F5 transition of Tb3+ ions. The obtained results indicate that synthesized material can be used as spectral converter to convert unutilized incident solar photons into the energies that are more effectively absorbed by the solar cell, hence efficiency can be improved.

High-brightness white-light-emitting diodes (w-LEDs) with excellent color quality is demonstrated by using nontoxic nanomaterials. Previously, we have reported the high color quality w-LEDs with heavy-metal phosphor and quantum dots (QDs), which may cause environmental hazards. In the present work, liquid-type white LEDs composed of nontoxic materials, named as graphene and porous silicon quantum dots are fabricated with a high color rendering index (CRI) value gain up to 95. The liquid-typed device structure possesses minimized surface temperature and 25% higher value of luminous efficiency as compare to dispensing-typed structure. Further, the as-prepared device is environment friendly and attributed to low toxicity. The low toxicity and high R9 (87) component values were conjectured to produce new or improve current methods toward bioimaging application.

In the present work, we have synthesized a CaMoO4:(1%)Er3+,(1%)Yb3+ down-converting phosphor by hydrothermal method. The primary goal of studying down-conversion is to enhance the conversion efficiency of Si-solar cell by converting one high energy (UV) photon into two low energy (NIR) photons. The various characterization such as XRD, FESEM and Photoluminescence (PL) were carried out. The X-ray diffraction (XRD) pattern exhibit tetragonal crystal structure and has a space group of I41a (88). The FESEM microphotograph shows surface morphology having a abundance of particles in spherical shape. The PL emission spectra were recorded both in Visible and NIR regions. There is hypertensive emission peak at 555 nm in the visible region due to 4S3/2 → 4I15/2 transition of Er3+ ions and an emission at 980 nm (2F5/2 → 2F7/2) due to Yb3+ ions. The result shows a demand of this down-converting material in the field of solar energy to improve the efficiency of Si-solar-cell.

We have successfully developed rare-earth doped/codoped calcium molybdate phosphors; CaMoO4:Re3+ (Re3+=Tb3+/Sm3+/Tm3+,Er3+,Yb3+) as a spectral converter for solar cell application by using hydrothermal method. The X-ray diffraction (XRD), Field emission scanning microscopy (FE-SEM), Fourier transformation infrared spectroscopy (FTIR), UV–Vis diffuse reflectance spectroscopy, photoluminescence (PL), up-conversion (UC), lifetime measurements were used to characterize the prepared phosphors. In combination with Rietveld refinement, crystal structure was confirmed to be tetragonal with space group I41a (88). The as synthesized CaMoO4:Tb3+, Sm3+, Tm3+ downshifting (DS) phosphors exhibit hypersensitive green, red and blue emission (547 nm, 600 nm and 453 nm) corresponding to 5D4→7F5, 4G5/2 → 6H7/2, 1D2→3F4 transitions, respectively. Moreover, up-conversion (UC) studies of CaMoO4: Er3+/Yb3+ codoped phosphors exhibit strong green and weak red emission (525 nm, 553 nm and 657 nm) corresponding to 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively. Further, DS/UC and the lifetime measurements were play a profound role to explain the energy transfer mechanism. The obtained results depict that these phosphors can efficiently convert UV and IR photons into visible leading to overcome spectral losses arises due to spectral mismatch.

We demonstrate inorganic halide perovskite quantum-dots-based white light-emitting diodes via three different geometries, including liquid, solid, and hybrid types. Problems of fast anion exchange and aggregation in the cases of liquid- and solid-type devices are discussed in detail and push us to move towards the fabrication of a hybrid-type device structure. The experiment results illustrate that a hybrid-type device has the highest luminance efficiency (51 lm/W) and a wide color gamut (122% of NTSC and 91% of Rec. 2020). Therefore, we conclude that a hybrid-type device can provide an outstanding color gamut for high color gamut display applications.