• Applied Chemistry for Engineering
• /
• v.29 no.2
• /
• pp.138-146
• /
• 2018

Photodynamic therapy (PDT) is a great potential approach for the localized tumor removal with fewer metastatic potentials and side effects in treating the disease. In the treatment process, a photosensitizer (PS) that absorbs a light energy to generate reactive oxygen is essential. In general, a visible light is used as a light source of PDT, so that side effects from the light source are inevitable. For this reason, upconversion nanoparticles (UCNPs) using near-infrared (NIR) as an excitation source are attracting attention in the field of disease diagnosis and treatment. UCNPs have the low cytotoxicity and phototoxicity, and also advantages such as deep tissue penetration and low background autofluorescence. For PDT, UCNPs should be combined with a PS which absorbs the light energy from UCNPs and transfers it to the surrounding oxygen to produce reactive oxygen. In addition, the therapeutic efficacy can be improved by modifying nanoparticle surfaces, adding anti-cancer drugs, or combining with photothermal therapy (PTT). In this review, we summarize the recent research to improve the efficiency of PDT using UCNPs.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.26 no.4
• /
• pp.159-163
• /
• 2016

Up-conversion (UC) luminescence properties of polycrystalline $Er^{3+}/Yb^{3+}$ doped $NaGd(MoO_4)_2$ phosphors synthesized by a simple solid-state reaction method were investigated in detail. Used to 980 nm excitation (InfraRed area), $Er^{3+}/Yb^{3+}$ co-doped $NaGd(MoO_4)_2$ exhibited very weak red emissions near 650 and 670 nm, and very strong green UC emissions at 540 and 550 nm corresponding to the infra 4f transitions of $Er^{3+}(^4F_{9/2},\;^2H_{11/2},\;^4S_{3/2}){\rightarrow}Er^{3+}(^4I_{15/2})$. The optimum doping concentration of $Er^{3+}$, $Yb^{3+}$ for highest emission intensity was determined by XRD and PL analysis. The $Er^{3+}/Yb^{3+}$ (10.0/10.0 mol%) co-doped $NaGd(MoO_4)_2$ phosphor sample exhibited very strong shiny green emission. A possible UC mechanism for $Er^{3+}/Yb^{3+}$ co-doped $NaGd(MoO_4)_2$ depending on the pump power dependence was discussed.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.20 no.4
• /
• pp.173-177
• /
• 2010

Thermal stabilizing effect of $Yb^{3+},\;Er^{3+}$ codoping into $TiO_2$ powder prepared by sol-gel method and its upconversion characteristics were analyzed. The effect of $TiO_2:Yb^{3+},\;Er^{3+}$ ions on crystallinity and phase transition was studied by X-ray diffraction (XRD). The change of band-gap energy induced from Yb and Er codoping was analyzed by UV-Vis. The band-gap energy of $TiO_2$ have been slightly narrowed by $Yb^{3+},\;Er^{3+}$ codoping, which indicated that the $Yb^{3+},\;Er^{3+}$ ions can enhance the photo-catalytic property of $TiO_2$. green and red up-conversions of $Yb^{3+}$ and $Er^{3+}$ co-doped $Y_2O_3:Yb^{3+},\;Er^{3+}$ phosphor were analyzed by PL equipped with 980 nm laser.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2011.11a
• /
• pp.55-57
• /
• 2011

본 논문에서는 텍스쳐 최적화 기법을 사용하는 동영상 프레임 비율 상향 변환 방법을 제안한다. 제안하는 기법은 입력 영상의 텍스쳐 특성을 분석하여 블록 매칭에 의해 예측된 움직임 벡터의 정확도를 향상시킨다. 또한 패치 단위의 영상 합성을 통해 블록 경계에서 발생하는 화질 열화 현상을 최소화한다. 실험 결과를 통하여 제안하는 기법은 자연스러운 중간 시점 영상을 생성함을 확인한다.

• Korean Journal of Materials Research
• /
• v.30 no.1
• /
• pp.50-50
• /
• 2020

• Korean Journal of Materials Research
• /
• v.25 no.9
• /
• pp.480-486
• /
• 2015

$Pb_{1-x}MoO_4:Er^{3+}/Yb^{3+}$ phosphors with various doping concentrations of $Er^{3+}$ and $Yb^{3+}$ ($x=Er^{3+}+Yb^{3+}$, $Er^{3+}=0.05$, 0.1, 0.2, and $Yb^{3+}=0.2$, 0.45) are successfully synthesized using a microwave sol-gel method, and the up-conversion photoluminescence properties are investigated. Well-crystallized particles, which are formed after heat treatment at $900^{\circ}C$ for 16 h, exhibit a fine and homogeneous morphology with particle sizes of $2-5{\mu}m$. Under excitation at 980 nm, the $Pb_{0.7}MoO_4:Er_{0.1}Yb_{0.2}$ and $Pb_{0.5}MoO_4:Er_{0.05}Yb_{0.45}$ particles exhibit a strong 525 nm emission band, a weak 550 nm emission band in the green region, and a very weak 655 nm emission band in the red region. The Raman spectra of the doped particles indicate the presence of strong peaks at higher and lower frequencies induced by the disordered structures of $Pb_{1-x}MoO_4$ through the incorporation of the $Er^{3+}$ and $Yb^{3+}$ ions into the crystal lattice, which results in the unit cell shrinkage accompanying the new phase formation of the $MoO_{4-x}$ group.

• Korean Chemical Engineering Research
• /
• v.53 no.5
• /
• pp.620-626
• /
• 2015

$Ho^{3+}$ doped $SrAl_2O_4$ upconversion phosphor powders were synthesized by spray pyrolysis, and the crystallographic properties and luminescence characteristics were examined by varying activator concentrations and heattreatment temperatures. The effect of organic additives on the crystal structure and luminescent properties was also investigated. $SrAl_2O_4:Ho^{3+}$ powders showed intensive green emission due to the $^5F_4/^5S_2{\rightarrow}^5I_8$ transition of $Ho^{3+}$. The optimal $Ho^{3+}$ concentration in order to achieve the highest luminescence was 0.1%. Over this concentration, emission intensities were largely diminished via a concentration quenching due to dipole-dipole interaction between activator ions. According to the dependence of emission intensity on the pumping power of a laser diode, it was clear that the upconversion of $SrAl_2O_4:Ho^{3+}$ occurred via the ground state absorption-excited state absorption processes involving two near-IR photons. Synthesized powders were monoclinic as a major phase, having some hexagonal phase. The increase of heat-treatment temperatures from $1000^{\circ}C$ to $1350^{\circ}C$ led to crystallinity enhancement of monoclinic phase, reducing hexagonal phase. The hexagonal phase, however, did not disappear even at $1350^{\circ}C$. When both citric acid (CA) and ethylene glycol (EG) were added to the spray solution, the resulting powders had pure monoclinic phase without forming hexagonal phase, and led to largely enhancement of crystallinity. Also, N,N-Dimethylformamide (DMF) addition to the spray solution containing both CA and EG made it possible to effectively reduce the surface area of $SrAl_2O_4:Ho^{3+}$ powders. Consequently, the $SrAl_2O_4:Ho^{3+}$ powders prepared by using the spray solution containing CA/EG/DMF mixture as the organic additives showed about 168% improved luminescence compared to the phosphor prepared without organic additives. It was concluded that both the increased crystallinity of high-purity monoclinic phase and the decrease of surface area were attributed to the large enhancement of upconversion luminescence.

• Proceedings of the Optical Society of Korea Conference
• /
• 2000.02a
• /
• pp.18-19
• /
• 2000

Recently, coherent control of exciton populations has been demonstrated through terahertz, reflection, and four-wave-mixing experiments. However, the most direct probe of exciton population control is the absorption, which has been lacking in previous studies. In this report, we probe the time evolution of exciton population directly through a transmission experiment. In particular, using upconversion technique with both narrow (spectrally broad) and long (spectrally narrow) pulses, we can obtain both the temporal and the spectral information. The main thrust of our report is that when phase controlled, the second pulse can be either greatly enhanced or completely destroyed by gaining energy from exciton (thus destroying the exciton population) or giving all of its energy to the system (thus greatly increasing the exciton population), respectively. (omitted)

• Journal of Powder Materials
• /
• v.25 no.2
• /
• pp.170-177
• /
• 2018

Colloidally synthesized luminescent nanocrystals (NCs) have attracted tremendous attention due to their unique nanoscale optical and electronic properties. The emission properties of these NCs can be precisely tuned by controlling their size, shape, and composition as well as by introducing appropriate dopant impurities. Nowadays, these NCs are actively utilized for various applications such as optoelectronic devices including light emitting diodes (LEDs), lasers, and solar cells, and bio-medical applications such as imaging agents and bio-sensors. In this review, we classify luminescent nanomaterials into quantum dots (QDs), upconversion nanoparticles (UCNPs), and perovskite NCs and present their intrinsic emission mechanism. Furthermore, the recently emerging issues of efficiency, toxicity, and durability in these materials are discussed for better understanding of industry demands. As well, the future outlook will be offered for researchers to guide the direction of future research.

• Journal of the Optical Society of Korea
• /
• v.1 no.1
• /
• pp.10-14
• /
• 1997

Single pulse laser excitation at 656 nm and successive pulse excitation at 635.2 and 648.4 nm produced blue emission at 480 nm by two-step upconversion process in Tm/sup 3+/:LaF/sub 3/. The excited-state absorption cross-section of the /sup 3/F/sub 4/ to /sup 1/G/sub 4/ transition was estimated by a looping mechanism with cross-relaxation processes. The dynamics of up-conversion andthe possibility of the photon avalanche by a pulse laser excitation were studied by numerical simulation with the rate equation model.