Tunable upconversion in ZnAl_2−xGa_xO₄:Er,Yb phosphors by modulating the Al/Ga ratio and application in optical thermometry

Abstract

Non-contact optical thermometer based on upconversion luminescence (UCL) with high efficiency is in high demand for application in the area of biomedical, space technology, detectors and other several applications. It...

Color tunable luminescence in ThO2:Er3+,Yb3+ nanocrystals: a promising new platform for upconversion

“…For studying the UC mechanism involved in the materials, the pump power dependence on two of the representative samples ThO 2 :1%Er 3+ ,1%Yb 3+ and ThO 2 :1%Er 3+ ,15%Yb 3+ has been carried out. The number of photons involved in the UC emission was obtained from the following relation: 6 I UC ∝ P n Ex where I UC represents the intensity of UCL, P Ex is the excitation power and n is the number of photons involved in the UC process. Fig.…”

“…Upconversion nanophosphors (UCNPs) are regularly studied in the scientific community owing to their application in many areas encompassing health, energy and the environment. 1–7 Their applicability has been attributed to the conversion of low energy photons to high energy photons exhibiting anti Stoke’s shifts and displaying bright emission, lower autofluorescence, deeper penetration, negligible photobleaching, higher photo stability, etc. 5,8 The three basic requirements to achieve efficient upconversion luminescent materials are dopant, sensitizer and host matrix.…”

ZnAl2O4:Er3+ Upconversion Nanophosphor for SPECT Imaging and Luminescence Modulation via Defect Engineering

“…Recently, lanthanide ion (Ln 3+ )-doped upconversion (UC) materials have become hot materials for high-resolution bioimaging due to their attractive property of converting near-infrared (NIR) light to visible region. − Other promising applications include temperature sensing, optical anticounterfeiting, theranostics, and photovoltaic cells. − Conventional ultraviolet (UV) excitable photoluminescence (PL) contrast agents display Stokes-shifted emission and have major limitations such as low penetration depth, high autofluorescence background from the tissues, toxicity, and DNA damage. ,, Here, UC phosphors empower the conventional contrast agents with their absorbance in the NIR region (∼700–1000 nm) lying in the “optical transparency window” of biological tissues. Hence, the use of NIR excitable UC nanomaterials as contrast agents for bioimaging offers higher spatial resolution with a low autofluorescence background, a large anti-Stokes shift, less photodamage, and deep tissue penetration. ,, …”

“…These ions emit visible light due to their unique energy levels and 4f → 4f electronic transitions . Er 3+ is the most commonly used activator ion, and the Er 3+ /Yb 3+ pair is prevalent for UCNPs, where antiStokes shifted visible emissions are obtained from ( 2 H 11/2 and 4 S 3/2 ) excited states. − ,− In the past, various reports demonstrated the potential of Er 3+ -based UCNPs for optical bioimaging, PTT, PDT, drug delivery, and in vivo tumor theranostic applications. ,,− However, most of these studies are focused on imaging-guided PDT/PTT theranostic applications. The integration of SPECT imaging with current biomedical research will be beneficial for the development of an “all-in-one” system for high-spatial contrast imaging and therapeutics.…”