Enhancement of luminescence emission from GdVO4:Er3+/Yb3+ phosphor by Li+ co-doping

Morphology of the GdVO4 crystal: first-principles studies

The present paper reports a theoretical investigation based on first-principles density functional theory calculations to predict the external morphology of the tetragonal GdVO₄ crystal from its internal structure. The Bravais-Friedel-Donnay-Harker (BFDH) method, attachment energy (AE) method and surface energy (SE) method were used in this study. Slice energies (cohesive, attachment and specific surface) of the three main crystal faces having (110), (101) and (200) orientation and their d_hkl thicknesses were computed using CRYSTAL17 code, in the frame of a 2D periodic slab model. The relative growth rate (R_hkl) and the morphological importance (MI_hkl) for each unrelaxed and relaxed (hkl) face of interest were determined. Consequently, the crystal shapes predicted based upon BFDH, AE and SE methods were represented by the Wulff construction. The results of the morphology crystal predictions, based on the above methods, were compared both against each other and against the experimentally observed morphologies. A quite satisfactory agreement between the predicted and observed crystal morphologies is noticed.

Application of rare earth-doped nanoparticles in biological imaging and tumor treatment

Rare earth-doped nanoparticles have been widely used in disease diagnosis, drug delivery, tumor therapy, and bioimaging. Among various bioimaging methods, the fluorescence imaging technology based on the rare earth-doped nanoparticles can visually display the cell activity and lesion evolution in living animals, which is a powerful tool in biological technology and has being widely applied in medical and biological fields. Especially in the band of near infrared (700–1700 nm), the emissions show the characteristics of deep penetration due to low absorption, low photon scattering, and low autofluorescence interference. Furthermore, the rare earth-doped nanoparticles can be endowed with the water solubility, biocompatibility, drug-loading ability, and the targeting ability for different tumors by surface functionalization. This confirms its potential in the cancer diagnosis and treatment. In this review, we summarized the recent progress in the application of rare earth-doped nanoparticles in the field of bioimaging and tumor treatment. The luminescent mechanism, properties, and structure design were also discussed.

Enhanced upconversion luminescence of GdVO4:Er3+/Yb3+ prepared by spray pyrolysis using organic additives

Spray pyrolysis was applied to prepare Er³⁺/Yb³⁺-doped GdVO₄ particles, and their emission properties were investigated by varying the Er³⁺/Yb³⁺ content and the calcination temperature from 900 to 1400 °C. Ethylene glycol (EG), citric acid (CA) and N,N-dimethylformamide (DMF) were used as organic additives in order to improve the upconversion of GdVO₄:Er³⁺/Yb³⁺. The resulting GdVO₄:Er³⁺/Yb³⁺ particles show strong green emission due to ²H_11/2/⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ and weak red peak due to the ⁴F_9/2 → ⁴I_15/2 transition of Er³⁺. From the result observed by changing the pumping power of the near-infrared (NIR, 980 nm) laser, the observed green emission is caused by a typical two-photon process. In terms of achieving the highest upconversion luminescence, the optimal Er³⁺ and Yb³⁺ contents are 1.5% and 20% with respect to Gd, respectively. The luminescence intensity steadily increased as the calcination temperature was elevated up to 1200 °C due to the increment of crystallinity. The upconversion intensity showed a linear relationship with the crystallite size in all the calcination temperature range. Using the EG/CA/DMF mixture as organic additives improves the upconversion emission about 4.3 times higher than when no organic additives are used, due to the enhancement of crystallinity as well as the enlargement of primary particle size.

GdVO₄:Er/Yb fine particles with good upconversion luminescence was prepared by spray pyrolysis using organic additives.

The role of Li+ in the upconversion emission enhancement of (YYbEr)2O3 nanoparticles

The mechanism of upconversion enhancement for Li+-doped materials is still contentious. Attempting to settle the debate, here the upconversion emission enhancement of (Y0.97-xYb0.02Er0.01Lix)2O3, x = 0.000-0.123, nanoparticles is studied. Li+ incorporation in the Y2O3 host lattice is achieved via co-precipitation and solid-state reaction routes. In contrast to numerous reports, elemental analysis reveals that the former method does not afford Li+-bearing nanoparticles. The solid-state reaction route accomplishes an effective Li+ doping, as witnessed by inductively coupled plasma atomic emission spectroscopy and X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy and powder X-ray diffraction showed an increase in nanoparticle size with increasing Li+ concentration. Rietveld refinement of powder X-ray diffraction data shows that the cubic lattice parameter decreases with increasing Li+ content. The emission quantum yield increases tenfold with increasing Li+ content up to x = 0.123, reaching a maximal value of 0.04% at x = 0.031. XPS and infrared spectroscopy show that the carbonate groups increase with increasing Li+ content, thus not supporting the prevailing view that the upconversion luminescence enhancement observed upon Li+ nanoparticle's doping is due to the decrease of the number of quenching carbonate groups present. Rather, the particle size increment and the decrease in the lattice parameter of the host crystals are shown to be the prime sources of quantum yield enhancement.

MgTiO3:Mn4+ a multi-reading temperature nanoprobe

MgTiO₃ nanoparticles doped with Mn⁴⁺, with homogeneous size ranging about 63.1 ± 9.8 nm, were synthesized by a molten salt assisted sol gel method. These nanoparticles have been investigated as optical thermal sensors. The luminescence of tetravalent manganese ion in octahedral environment within the perovskite host presents drastic variations with temperature. Three different thermometry approaches have been proposed and characterized. Two luminescence intensity ratios are studied. Firstly between the two R-lines of Mn⁴⁺ emission at low temperature (−250 °C and −90 °C) with a maximal sensitivity of 0.9% °C⁻¹, but also secondly between ²E → ⁴A₂ (R-line) and the ⁴T₂ → ⁴A₂ transitions. This allows studying the temperature variation within a larger temperature range (−200 °C to 50 °C) with a sensitivity between 0.6% °C⁻¹ and 1.2% °C⁻¹ over this range. The last proposed method is the study of the lifetime variation versus temperature. The effective lifetime value corresponds to a combination of transitions from two excited energy levels of the tetravalent manganese (²E and ⁴T₂) in thermal equilibrium toward the fundamental ⁴A₂ state. Since the more energetic transition (⁴T₂ → ⁴A₂) is spin-allowed, contrary to the ²E → ⁴A₂ one, the lifetime drastically decreases with the increase in temperature leading to an impressive high sensitivity value of 4.1% °C⁻¹ at 4 °C and an exceptional temperature resolution of 0.025 °C. According to their optical features, MgTiO₃:Mn⁴⁺ nanoparticles are indeed suitable candidates for the luminescence temperature probes at the nanoscale over several temperature ranges.

Luminescence properties of MgTiO₃ nanoparticles doped with Mn⁴⁺ ions are investigated for precise temperature determination.

Tunable emission from LiBaBO3 :Eu3+ ;Bi3+ phosphor for solid-state lighting

Europium (Eu³⁺ ) and bismuth (Bi³⁺ ) co-activated LiBaBO₃ powder phosphors were synthesized by a solid-state reaction and the structure, particle morphology, optical and photoluminescent properties were investigated. X-Ray diffraction patterns of the LiBaBO₃ phosphors crystallized in a pure monoclinic phase, i.e. there were no secondary phases due to either incidental impurities or undecomposed starting materials. Scanning electron microscopy images showed that the powders were made up of fluffy needle-like particles that were randomly aligned. The band-gap of the LiBaBO₃ host was estimated to be 3.33 eV from the UV/vis absorption data. Blue emission was observed from the LiBaBO₃ host, which is ascribed to self-activation of the host matrix. In addition, greenish-blue (493 nm) and red (613 nm) emissions were observed from europium-doped samples and were attributed to the emissions of Eu²⁺ and Eu³⁺ , respectively. Furthermore, after codoping with Bi³⁺ , the emission intensity of Eu³⁺ located at 613 nm was significantly enhanced. From the Commission Internationale de I'Eclairage (CIE) color coordinates, white emission was observed from LiBa_1-x BO₃ :xEu³⁺ (x = 0.020 and 0.025) phosphor powders with color coordinates of x = 0.368, y = 0.378 and x = 0.376, y = 0.366, respectively.

Luminescence and electrochemical properties of rare earth (Gd, Nd) doped V2O5 nanostructures synthesized by a non-aqueous sol–gel route

Vanadium pentoxide nanostructures have been obtained from an alkoxide sol–gel, prepared by a simple and inexpensive facile non-aqueous method.