Highly efficient NIR–NIR upconversion in potassium substituted CaMoO4:Tm3+, Yb3+ phosphor for potential biomedical applications

Hom Nath Luitel; Rumi Chand; Toshio Torikai; Mitsunori Yada; Takanori Watari

doi:10.1039/C4RA12436G

Highly efficient NIR–NIR upconversion in potassium substituted CaMoO₄:Tm³⁺, Yb³⁺ phosphor for potential biomedical applications†

Hom Nath Luitel,*^ab Rumi Chand,^a Toshio Torikai,^a Mitsunori Yada^a and Takanori Watari*^a

* Corresponding authors

^a Department of Advanced Technology Fusion, Saga University, Honjo-1, Saga, Japan
E-mail: mehomnath@yahoo.com, watarit@cc.saga-u.ac.jp
Fax: +81 952 28 8548
Tel: +81 952 28 8683

^b Shinwa-Biso Co., Ltd., 1-15-22, Moriguchi, Osaka, Japan

Abstract

We obtained highly efficient NIR to NIR (excitation by 980 nm, emission at 800 nm) upconversion in CaMoO₄:Tm³⁺, Yb³⁺, M⁺ (M = Li, Na, K, Rb) nanocrystals synthesized by a hydrothermal method. The XRD patterns show that they are all of tetragonal structure despite a small amount of RE³⁺ and M⁺ ion doping. The solid solubility of lithium, sodium, potassium and rubidium ions in the CaMoO₄ were found to be 30 mol%, 20 mol%, 10 mol% and 5 mol%, respectively. The doped M⁺ ions affect the crystal field symmetry around Tm³⁺ ions in the CaMoO₄ host, which results in the change of the irradiation transition probabilities between their transition levels and intensifies the UC intensities. Compared with CaMoO₄:Tm³⁺, Yb³⁺, the NIR to NIR upconversion emission intensity of CaMoO₄:Tm³⁺, Yb³⁺, 0.10M⁺ nanocrystals increases 2.2, 3.3, 47 and 10 fold for Li, Na, K and Rb, respectively. The K substituted CaMoO₄:Tm³⁺, Yb³⁺ phosphor exhibited intense UC emission pumped by less than 1 mW laser power and can have potential application in NIR to NIR photodynamic diagnosis.

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Article information

DOI: https://doi.org/10.1039/C4RA12436G
Article type: Paper
Submitted: 20 Oct 2014
Accepted: 27 Jan 2015
First published: 27 Jan 2015

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RSC Adv., 2015,5, 17034-17040

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Highly efficient NIR–NIR upconversion in potassium substituted CaMoO₄:Tm³⁺, Yb³⁺ phosphor for potential biomedical applications

H. N. Luitel, R. Chand, T. Torikai, M. Yada and T. Watari, RSC Adv., 2015, 5, 17034 DOI: 10.1039/C4RA12436G

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