There three excelent books on OLED (PhOLED). Perhaps yoy can find an answer to your problem:

1.Highly Efficient OLEDs with phosphorescent materials, edited by Hartmuth Yersin, Wiley, 2007.

2.Organic Light Emitting Devices, edited by K.Mullen, U.Scherf, Wiley, 2006.

3. Organic Light Emitting Materials and Devices, editef by Z.Li, H.Meng, Taylor and Francis, 2007.

The problem of dopants and hosts materials for blue, green or red OLED are discussed there.

There three excelent books on OLED (PhOLED). Perhaps yoy can find an answer to your problem:

1.Highly Efficient OLEDs with phosphorescent materials, edited by Hartmuth Yersin, Wiley, 2007.

2.Organic Light Emitting Devices, edited by K.Mullen, U.Scherf, Wiley, 2006.

3. Organic Light Emitting Materials and Devices, editef by Z.Li, H.Meng, Taylor and Francis, 2007.

The problem of dopants and hosts materials for blue, green or red OLED are discussed there.

@Andrzej Danel. Thanks for the suggestions.

Try to insert the dopants such as cerium (III) and europium (II). Try as CeCl 3 or Eu (NO3) 2. Compounds need to be Ultrapure at least 99.99%. Probably you will try reactions wet with ITO. Try to see the literature ITO doping with europium or cerium by reaction in the solid state (sol-gel method or microwave assisted). Cheaper materials with titanium, zirconium, both trivalent ions can make the shift blue but introduce very broad bands in the visible spectral region. It's good to get a read on energy transfer of transition metals ions.

@Edson Abreu. Thanks for the suggestions. I want to dope my active material which is organic. I am using commercially available ITO substrates.

Emission takes place from the lowest energy state. So, if your material is intrinsically a green emitter you can easily red-shift its electroluminescence, but blue shifting is not possible. To obtain a withe OLED, you have to start with a UV/Blue material (PVK, as instance), and then to dope it with green and red emitters.