Abhishek Kumar Soni

Stark sublevels in Tm3+–Yb3+ codoped Na2Y2B2O7 nanophosphor for multifunctional applications

The phase and crystal structure of the Na2Y2B2O7:Tm3+–Yb3+ inorganic phosphor prepared by solution combustion method have been identified by powder X-ray diffraction technique. Surface morphology and particle size have been examined using field emission scanning electron microscopy and high resolution transmission electron microscopy characterizations of the prepared materials. No absorption band around 980 nm has been observed in the Tm3+ doped phosphors, whereas a broad band around 980 nm in the Tm3+–Yb3+ codoped phosphors corresponding to the 2F7/2 ← 2F5/2 absorption transition of Yb3+ ion has been detected. Upconversion emission bands have been observed in the UV, visible and NIR regions upon excitation with a 980 nm laser diode. The temperature sensing behaviour and the concept of a nanoheater of the developed nanophosphor have been demonstrated by using the stark sublevels of the 1G4 level of the Tm3+ ion, which are responsible for the blue upconversion emission. A maximum sensor sensitivity of about 4.54 × 10−3 K−1 at 300 K for the developed multifunctional nanophosphor has been determined. A temperature gain of about ∼435 K has been observed at a laser power density of 66.88 W cm−2 and the colour coordinates do not change with the variation of the pump power density. For localizing and heating hyperthermia based cancer cells using NIR radiation, a very low pump power density of about ∼7.0 W cm−2 has been established. The experimental observations prove that the developed material can be used as a multifunctional nanomaterial in optical devices and biological applications.

Frequency upconversion and fluorescence intensity ratio method in Yb3+-ion-sensitized Gd2O3:Er3+-Eu3+ phosphors for display and temperature sensing

Near infrared (NIR) to visible frequency upconversion emission studies in Er3+-Eu3+/Er3+-Eu3+-Yb3+ co-doped/tri-doped Gd2O3 phosphors prepared by the co-precipitation technique have been explored under 980 nm laser diode radiation. The developed phosphors were characterized with the help of XRD, FE-SEM and FTIR analysis. No upconversion (UC) emission was found in the Eu3+-doped Gd2O3 phosphor. UC emission from Eu3+ ions along with Er3+ ions was observed in Er3+-Eu3+ and Er3+-Eu3+-Yb3+ co-doped/tri-doped phosphors. The UC emission arising from the Er3+ and Eu3+ ions was enhanced several times due to the incorporation of Yb3+ ions. The processes involved in the UC emission were obtained on the basis of the effect of energy transfer/sensitization through the Yb3+ → Er3+ → Eu3+ process. The red/green intensity ratio was improved from 0.16 to 1.50 and 1.01 to 1.50 for Er3+-Eu3+-Yb3+ tri-doped phosphors as compared to the Er3+-doped and Er3+-Yb3+ co-doped phosphors, respectively, at a fixed pump power density. A UC fluorescence intensity ratio (FIR)-based temperature sensing study was performed in the prepared Er3+-Eu3+-Yb3+ tri-doped Gd2O3 phosphors for green upconversion emission bands in the 300 K-443 K temperature range. A maximum sensor sensitivity of about ∼0.0043 K-1 at 300 K was achieved for the synthesized tri-doped phosphors upon excitation with a 980 nm laser diode. The colour coordinates lying in the green-yellow region are invariant, with variation in pump power density and temperature. The observed results support the utility of the prepared tri-doped phosphors in optical temperature sensing, display devices and NIR to visible upconverters.

Upconversion emission study in Tm3+ and Ho3+ doped Gd2(MoO4)3 phosphor

Upconversion luminescence properties in Tm3+ and Ho3+ ions doped Gd2(MoO4)3 phosphors have been studied by using 980 nm laser diode radiation. Tm3+ and Ho3+ ions doped Gd2(MoO4)3 phosphors have been prepared by chemical co-precipitation technique. The crystal structure identification of the doped phosphors has been confirmed via X-ray diffraction analysis. Intense blue upconversion emission peak at 478 nm corresponding to the 1G4→3H6 transition has been obtained in the Tm3+ doped phosphor. Whereas, in the Ho3+ doped phosphor blue upconversion emission peak at 490 nm corresponding to the 5F3→5I8 transition has been obtained. The colour co-ordinate analysis confirmed that the prepared both (Tm3+ and Ho3+) doped phosphors can be used in making blue colour emitting devices.

Optical studies in Er3+ doped BaMoO4 downconverting phosphor for blue LEDs

Erbium ion (Er3+) doped BaMoO4 phosphor has been synthesized via co-precipitation technique. Phase formation of the prepared phosphor has been recognized by powder X-ray diffraction analysis. The photoluminescence emission spectrum has been recorded in 400-800nm wavelength range under 380nm excitation. The observed photoluminescence peaks are explained with the help of energy level structure. The prepared phosphor seems capable to produce efficient blue colour emission which can be useful for making blue light emitting diodes (LEDs).

NIR to visible upconversion emission in Tm3+ doped Na2Y2B2O7 powder phosphor

Tm3+ ions doped Na2Y2B2O7 powder phosphor has been synthesized through combustion method. Crystal structure and phase of the prepared sample have been investigated by powder X-ray diffraction (XRD) analysis. Upconversion emission bands in the 400-900 nm range under the excitation of 980nm diode laser have been acquired, and involved upconversion mechanism has been discussed with the help of a suitable energy level diagram. The colour coordinate of developed phosphor has been calculated by CIE chromaticity diagram. Present phosphor can be used in fabrication of upconverting LEDs.

Upconversion luminescence in BaMoO4:Pr3+ phosphor for display devices

The frequency upconversion is an important nonlinear optical property by which near infrared light is converted into the visible light. The BaMoO4:Pr3+ powder phosphor has been synthesized by solid state reaction method. The upconversion emission bands are recorded under the excitation of 808 nm diode laser. The phase formation of the prepared phosphor has been identified by powder X-ray diffraction (XRD) technique. The upconversion emission mechanism and colour coordinate have been explained by using energy level and CIE (International Commission on Illumination) chromaticity diagram study, respectively.