Importantly, under the influence of the mentioned laser irradiation, the as-prepared samples exhibited bright green up-conversion luminescence that was visible to the naked eye. Up-conversion emission spectra of the nanomaterials were measured using laser light sources with λex = 785 and 975 nm. The synthesized vanadate nanomaterials had a tetragonal structure and crystallized in the form of nearly spherical nanoparticles. The up-converting inorganic nanoluminophores YVO4: Er3+ and YVO4: Yb3+ and Er3+ were obtained using a hydrothermal method and subsequent calcination. This work shows the possibility of generating pure, green up-conversion luminescence upon the excitation of Er3+-doped nanomaterials with a 785 nm NIR laser. Materials that generate pure, single-color emission are desirable in the development and manufacturing of modern optoelectronic devices. Here, synthesis, characterization, optical properties, and mechanism of upconverting nanoparticles and their applications are provided. This extends the utility of core active to multi‐ways because of multi‐functional properties, stability, easy surface functionalization, easy processing, etc. There are many ways of models such as active shell, active shell, active shell, etc. The luminescence intensity can be improved by formation. There are many reports on the decrease of luminescence intensity when the size of the particle decreases to nanosize because of the association of surface defects, surface ligand, and solvent/medium, which act as the quencher. Can upconverted luminescence reach a very high intensity in high concentration of activators as well as by absorption at non‐resonance frequency ( f nonres )? It is possible to get when laser power is more than the critical value. The highly activator‐doped samples show concentration quenching in luminescence, and absorption takes place at resonance frequency ( f res ). The maximum efficiency can be obtained from the sequential energy transfer process. In case of downconversion, the frequency of emitted light is less than that of absorbed light, whereas in the case of upconversion, the frequency of emitted light is more than that of absorbed light. There are two types of photoluminescence – downconversion and upconversion. Photoluminescence is a process of emission by absorption of light. Using UC nanoparticles, detection of uranyl down to 20 ppm has been achieved. The particles are invisible in normal light but visible upon 980 nm excitation and are useful in display devices, advanced anticounterfeiting purposes, and therapy of cancer via hyperthermia and bioimaging (since it shows red emission at ∼650 nm). Both UC and hybrid nanoparticles show interesting security ink properties upon excitation by a 980 nm laser. A hyperthermia temperature is achieved from this hybrid. In addition, the polyethylene glycol-coated UC nanoparticles are highly water-dispersible and their hybrid with Fe3O4 nanoparticles shows magnetic-luminescence properties. Upon 300 nm excitation, the downconversion emission spectrum shows a broad peak in the 400–500 nm range (related to the charge transfer band of V–O) along with Ho³⁺ peaks. Upon 980 nm laser excitation, the UC emission spectrum shows a sharp bright peak at ∼650 nm of Ho³⁺ ion and the luminescence intensity increases twofold upon K⁺ codoping. In this work, we report a polyol route for easy synthesis of upconversion (UC) phosphor nanoparticles, YVO4:Ho³⁺-Yb³⁺-K⁺, which enables large-scale production and enhancement of luminescence.
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